Hyperparathyrodism
Hyperparathyroidism is a condition characterized by excessive secretion of parathyroid hormone, leading to hypercalcemia, bone resorption, and disturbances in calcium-phosphorus metabolism.
Hyperparathyroidism
Hyperparathyroidism (HPT) refers to a state of excessive parathyroid hormone (PTH) secretion, resulting in disordered calcium-phosphate homeostasis. Let's break down the word:
- "Hyper" = excessive
- "Para" = beside (the parathyroid glands sit beside the thyroid)
- "Thyroid" = shield-shaped (Greek thyreos) — refers to the thyroid gland adjacent to which the parathyroids sit
- "ism" = a condition or state
So the name literally tells you: a condition of excessive activity of the glands beside the thyroid.
There are three distinct types, each with a fundamentally different mechanism:
| Type | Mechanism | PTH Level | Calcium Level |
|---|---|---|---|
| Primary (1° HPT) | Autonomous, unregulated PTH overproduction from intrinsic parathyroid pathology | ↑ or inappropriately normal | ↑ (hypercalcemia) |
| Secondary (2° HPT) | Physiological, compensatory PTH hypersecretion in response to chronic hypocalcemia (e.g. CKD, vitamin D deficiency) | ↑ | ↓ or normal |
| Tertiary (3° HPT) | Autonomous PTH secretion that has become independent of the original stimulus, after prolonged secondary HPT (the glands become hyperplastic/autonomous) | ↑ | ↑ (hypercalcemia) |
Conceptual Key: Primary vs Secondary vs Tertiary
Think of it this way:
- Primary = the parathyroid itself is broken (intrinsic disease, usually an adenoma).
- Secondary = the parathyroid is doing its job correctly — responding to low calcium — but the underlying problem (CKD, vitamin D deficiency) keeps calcium low, so it keeps working overtime.
- Tertiary = the parathyroid has been working overtime for so long (years of secondary HPT, typically in CKD patients on dialysis) that it has undergone irreversible hyperplasia and now functions autonomously — even if you fix the underlying calcium, it won't stop.
2. Epidemiology
- Most common cause of hypercalcemia in the outpatient/ambulatory setting [1][2]
- Prevalence: ~1–2 per 1,000 in the general population [3]
- Demographics: peaks in the 6th–7th decade, average age ~59 years [3]
- Sex: M:F ≈ 1:2–3 — significantly more common in postmenopausal women [3]
- Why? Estrogen has a protective role in calcium homeostasis; after menopause, the loss of estrogen unmasks subtle parathyroid pathology and increases bone turnover, making the disease manifest
- Incidence: approximately 25–30 per 100,000 person-years in Western populations; increasingly recognized in Asian populations including Hong Kong with wider use of routine biochemistry panels
- The vast majority of cases are now detected incidentally through routine blood tests showing asymptomatic hypercalcemia — the "asymptomatic" form is by far the most common presentation in developed countries
- Extremely common in CKD patients, especially those on dialysis
- Prevalence increases with advancing CKD stage: nearly universal in CKD Stage 5 (ESKD)
- In Hong Kong, with a large dialysis population, secondary HPT is a very significant clinical problem
- Occurs in a subset of long-standing secondary HPT patients, particularly those with CKD who have received a renal transplant — the transplanted kidney corrects the renal failure, but the parathyroids remain autonomous
- Less common overall
High Yield: Primary HPT is the #1 cause of hypercalcemia in the outpatient setting. Malignancy is the #1 cause of hypercalcemia in the inpatient setting. [2]
3. Risk Factors
| Category | Risk Factor | Explanation |
|---|---|---|
| Demographics | Female sex (postmenopausal) | Estrogen withdrawal unmasks parathyroid disease |
| Age > 50 years | Accumulating somatic mutations in parathyroid tissue | |
| Radiation | Previous head and neck irradiation | Ionizing radiation damages parathyroid cell DNA, promoting adenoma formation (similar mechanism to thyroid cancer post-radiation) [1][4] |
| Brain irradiation for childhood leukemia | ||
| Total body irradiation for bone marrow transplant | ||
| Environmental radiation exposure | ||
| Familial/Genetic | MEN1 (menin gene on chromosome 11q13) | Causes 4-gland parathyroid hyperplasia [1][2] |
| MEN2A (RET proto-oncogene) | Causes parathyroid hyperplasia/adenoma [1][2] | |
| Familial isolated hyperparathyroidism | ||
| Hyperparathyroidism-jaw tumour (HPT-JT) syndrome (CDC73/HRPT2 gene) | Associated with parathyroid carcinoma | |
| Drugs | Lithium | Shifts the calcium-PTH set point to the right (higher calcium needed to suppress PTH) |
| Thiazide diuretics (unmasking) | Thiazides reduce urinary calcium excretion → can unmask underlying HPT |
- CKD (most important and common)
- Vitamin D deficiency (very common in Hong Kong — indoor lifestyle, limited sun exposure, elderly)
- Malabsorption syndromes (celiac disease, inflammatory bowel disease, bariatric surgery)
- Chronic dietary calcium deficiency
- Prolonged secondary HPT (especially CKD patients on dialysis for years)
- Post-renal transplant (the stimulus is removed but glands remain autonomous)
4. Anatomy and Function of the Parathyroid Glands
4.1 Gross Anatomy
- Typically 4 parathyroid glands (superior pair + inferior pair), though ~13% of people have supernumerary glands (5 or more)
- Each gland is tiny: ~5 × 3 × 1 mm, weighing 30–50 mg (the size of a grain of rice)
- Located on the posterior surface of the thyroid gland, within or just outside the thyroid capsule
- Colour: yellow-brown (due to fat content), which helps surgeons identify them
| Gland | Embryological Origin | Clinical Significance |
|---|---|---|
| Superior parathyroids | 4th pharyngeal pouch | Relatively constant position (posterolateral to upper thyroid poles) — less likely to be ectopic |
| Inferior parathyroids | 3rd pharyngeal pouch (with the thymus) | Migrate further during development → more variable position → may be found anywhere from the angle of the mandible down to the anterior mediastinum (within the thymus) |
Why does ectopic location matter?
If a patient has biochemically confirmed primary HPT but imaging cannot localize the adenoma in the usual position, think about ectopic locations — especially intrathymic (anterior mediastinum), retroesophageal, carotid sheath, or intrathyroidal. The inferior glands are far more commonly ectopic because they have a longer embryological migration path (from the 3rd pharyngeal pouch, traveling with the thymus).
- Supplied by the inferior thyroid artery (branch of the thyrocervical trunk from the subclavian artery)
- Superior glands may also receive supply from the superior thyroid artery or anastomoses
- This is why surgeons must be extremely careful during thyroidectomy to preserve parathyroid blood supply — devascularization leads to hypoparathyroidism
- The recurrent laryngeal nerve (RLN) runs in close proximity to the parathyroid glands (between the trachea and esophagus, posterior to the thyroid lobe)
- Surgeons identify the RLN as a landmark during parathyroidectomy
The parathyroid gland contains two main cell types:
| Cell Type | Function | Appearance |
|---|---|---|
| Chief cells | Produce and secrete PTH | Small, pale, principal cell type |
| Oxyphil cells | Function less well understood; rich in mitochondria | Larger, eosinophilic cytoplasm; important for Sestamibi scanning because the tracer accumulates in mitochondria [1] |
- With age, the glands accumulate more fat and oxyphil cells
- In parathyroid adenomas, there is a predominance of chief cells (often with a rim of normal compressed parathyroid tissue)
- Parathyroid adenomas are rich in oxyphilic cells (which have abundant mitochondria) — this is the basis for Sestamibi scanning [1]
4.3 Parathyroid Hormone (PTH) Physiology
PTH is an 84-amino acid polypeptide hormone. Its primary role is to raise serum calcium and lower serum phosphate. Understanding PTH physiology is essential to understanding every aspect of hyperparathyroidism.
Detailed PTH actions:
-
Bone (most rapid effect for acute calcium correction):
- Stimulates osteoclast-mediated bone resorption → releases calcium and phosphate into blood
- In chronic excess: causes osteitis fibrosa cystica (brown tumours, subperiosteal resorption, salt-and-pepper skull)
-
Kidney (dual action):
- ↑ Calcium reabsorption in the distal convoluted tubule (DCT)
- ↓ Phosphate reabsorption in the proximal convoluted tubule (PCT) → phosphaturia → this is why primary HPT causes low phosphate (hypophosphatemia)
- ↑ 1α-hydroxylase activity in the PCT → converts 25(OH)D₃ to 1,25(OH)₂D₃ (calcitriol) → the active form of vitamin D
-
Gut (indirect, via vitamin D):
- Calcitriol increases intestinal calcium and phosphate absorption
- The calcium-sensing receptor (CaSR) on parathyroid chief cells is the master regulator
- When serum ionized calcium rises → CaSR is activated → suppresses PTH secretion
- When serum ionized calcium falls → CaSR is less active → stimulates PTH secretion
- This is a classic negative feedback loop
CaSR and Familial Hypocalciuric Hypercalcemia (FHH)
FHH results from an inactivating mutation in the CaSR [2]. This means the parathyroid glands cannot "sense" the high calcium → PTH remains inappropriately normal or mildly elevated despite hypercalcemia. Crucially, the renal CaSR is also affected → the kidney reabsorbs too much calcium → low urinary calcium excretion (Ca:Cr clearance ratio < 0.01). FHH is a benign condition that does NOT require surgery — it is the most important mimic of primary HPT that you must exclude with a 24-hour urine calcium [1].
| Hormone | Source | Effect on Ca²⁺ | Effect on PO₄ |
|---|---|---|---|
| PTH | Parathyroid chief cells | ↑↑ | ↓ |
| Calcitriol (1,25(OH)₂D₃) | Kidney (1α-hydroxylase) | ↑ | ↑ |
| Calcitonin | Thyroid C cells (parafollicular) | ↓ (inhibits osteoclasts) | ↓ |
| FGF-23 | Osteocytes | — | ↓↓ (phosphaturic) |
5. Etiology and Pathophysiology
5.1 Primary Hyperparathyroidism
| Cause | Frequency | Key Features |
|---|---|---|
| Solitary parathyroid adenoma | ~80–85% | Benign, clonal neoplasm of one gland; remaining glands are suppressed/atrophic [1][3] |
| Multi-gland hyperplasia | ~10–15% | All four glands enlarged; associated with MEN1, MEN2A [1][2] |
| Double adenomas | ~1–2% (some series up to 5–10%) | Two separate adenomas; important to consider during surgical planning [1] |
| Parathyroid carcinoma | *** < 1%*** | Very rare; often presents with very high calcium ( > 3.5 mmol/L) and a palpable neck mass; associated with HRPT2/CDC73 gene mutation and HPT-JT syndrome [1][2] |
The fundamental problem is autonomous, unregulated PTH secretion that is not appropriately suppressed by high serum calcium:
- Adenoma/hyperplasia → autonomous PTH secretion → the normal negative feedback via CaSR is lost or the "set point" is shifted upward
- Excess PTH actions:
- Bone: ↑ osteoclast activity → bone resorption → hypercalcemia + bone disease (osteoporosis, osteitis fibrosa cystica)
- Kidney: ↑ Ca reabsorption + ↓ PO₄ reabsorption → hypercalcemia + hypophosphatemia
- ↑ 1α-hydroxylase → ↑ calcitriol → ↑ gut Ca absorption → further hypercalcemia
- Despite ↑ renal Ca reabsorption, the filtered load of calcium is so high that hypercalciuria still occurs → renal stones (calcium oxalate and calcium phosphate)
- Biochemical signature: Hypercalcemia + elevated (or inappropriately normal) PTH + low phosphate + high/normal ALP [2]
Why is PTH 'inappropriately normal' still abnormal?
Even if the PTH level falls within the laboratory reference range, it should be SUPPRESSED in the presence of hypercalcemia (because high calcium should turn off the parathyroids via CaSR). A "normal" PTH in the setting of hypercalcemia is therefore inappropriately unsuppressed and highly suggestive of primary HPT. [2]
| Syndrome | Gene | Parathyroid Pathology | Other Features |
|---|---|---|---|
| MEN1 | MEN1 (encoding MENIN) on 11q13 | Parathyroid hyperplasia (most common manifestation, ~95%) | Pancreatic endocrine tumours (gastrinoma, insulinoma); Pituitary tumours (prolactinoma) [1][4] |
| MEN2A | RET proto-oncogene | Parathyroid hyperplasia (~20–30%) | Medullary thyroid carcinoma; Phaeochromocytoma [1][4] |
| MEN2B | RET proto-oncogene | NOT typically associated with HPT | Medullary thyroid carcinoma; Phaeochromocytoma; Mucosal neuromas / intestinal ganglioneuromatosis [4] |
| HPT-JT syndrome | CDC73 (HRPT2) | Parathyroid carcinoma risk ↑↑ | Ossifying fibromas of jaw, renal cysts/tumours |
| Familial isolated HPT | Various (MEN1, CDC73, CaSR, GCM2) | Adenoma or hyperplasia | No other syndromic features |
Exam High Yield: MEN1 = 3 P's: Parathyroid, Pancreas, Pituitary [1][4]. MEN2A = Medullary thyroid carcinoma + Phaeochromocytoma + Parathyroid hyperplasia [1][4]. MEN2B does NOT include parathyroid disease — instead has mucosal neuromas.
5.2 Secondary Hyperparathyroidism
The common denominator is chronic hypocalcemia or hyperphosphatemia driving compensatory PTH hypersecretion:
| Cause | Mechanism |
|---|---|
| CKD (most important) | (1) ↓ 1α-hydroxylase → ↓ calcitriol → ↓ gut Ca absorption → hypocalcemia; (2) ↓ renal PO₄ excretion → hyperphosphatemia → complexes with Ca → ↓ ionized Ca; (3) hyperphosphatemia directly stimulates PTH; (4) ↑ FGF-23 in CKD also suppresses 1α-hydroxylase |
| Vitamin D deficiency | ↓ calcitriol → ↓ gut Ca absorption → hypocalcemia |
| Malabsorption (celiac, IBD, bariatric surgery) | ↓ Ca and vitamin D absorption → hypocalcemia |
| Chronic dietary Ca deficiency | Inadequate Ca intake → hypocalcemia |
This is a stepwise cascade — understanding the sequence is crucial:
- Declining GFR → ↓ renal phosphate excretion → hyperphosphatemia
- Hyperphosphatemia → directly stimulates PTH secretion AND complexes with calcium → ↓ ionized calcium
- Declining GFR → ↓ functioning renal mass → ↓ 1α-hydroxylase activity → ↓ calcitriol production
- ↓ Calcitriol → ↓ intestinal Ca absorption → hypocalcemia
- ↓ Calcitriol also normally suppresses PTH gene transcription → loss of this suppression → further ↑ PTH
- Hypocalcemia + hyperphosphatemia + ↓ calcitriol → compensatory parathyroid hyperplasia and ↑ PTH secretion
- Over time → all four glands become hyperplastic (diffuse hyperplasia initially, then may become nodular)
- Consequences of chronic 2° HPT:
- Renal osteodystrophy (high-turnover bone disease / osteitis fibrosa cystica)
- Vascular calcification (Ca × PO₄ product elevation → metastatic calcification in vessels and soft tissues)
- Calciphylaxis (rare but devastating — calcification of small dermal vessels → skin necrosis)
5.3.1 Pathophysiology
- After years of secondary HPT stimulation (usually in CKD patients on long-term dialysis), the parathyroid glands undergo monoclonal transformation
- The glands become autonomously functioning — they secrete PTH independently of serum calcium
- Even if the underlying cause is corrected (e.g. successful renal transplant restoring normal GFR and vitamin D metabolism), PTH remains elevated → persistent hypercalcemia
- Biochemical signature: ↑ PTH + ↑ calcium (similar to primary HPT but in the context of known CKD/prior secondary HPT)
- The glands are typically nodular hyperplastic with reduced expression of CaSR and vitamin D receptors, making them resistant to normal feedback
6. Classification
| Primary | Secondary | Tertiary | |
|---|---|---|---|
| Pathology | Intrinsic parathyroid disease | Compensatory response to hypocalcemia | Autonomous after prolonged 2° HPT |
| PTH | ↑ or inappropriately normal | ↑↑ | ↑↑ |
| Calcium | ↑ | ↓ or normal | ↑ |
| Phosphate | ↓ (phosphaturia from PTH) | ↑ (in CKD) | Variable |
| Common cause | Adenoma (85%) | CKD, Vit D deficiency | Long-standing CKD on dialysis |
Modern classification recognizes several phenotypes:
| Phenotype | Description |
|---|---|
| Symptomatic | Classic "stones, bones, moans, thrones, psychic overtones" |
| Asymptomatic | The majority of primary HPT cases today — detected incidentally on routine bloodwork showing hypercalcemia |
| Normocalcemic primary HPT | Persistently elevated PTH with consistently normal serum calcium (after excluding all causes of secondary HPT) — a relatively new entity; may represent the earliest form of primary HPT |
Normocalcemic Primary HPT
This is a recently recognized entity. The patient has elevated PTH but normal calcium on repeated testing. You MUST first exclude all secondary causes (vitamin D deficiency, CKD, malabsorption, medications). If PTH remains elevated after correction of these factors, and calcium is normal, the diagnosis is normocalcemic primary HPT. These patients may still develop complications (osteoporosis, kidney stones) and require monitoring.
7. Clinical Features
7.1 Clinical Features of Primary Hyperparathyroidism
The classic teaching mnemonic for hypercalcemia symptoms is "Stones, Bones, Moans, Thrones, and Psychic Overtones" [2]. However, the majority of primary HPT patients today are asymptomatic and detected incidentally.
| System | Symptom | Pathophysiological Basis |
|---|---|---|
| General | Fatigue, malaise, weakness | Hypercalcemia depresses neuromuscular excitability (Ca²⁺ raises the threshold potential of nerves and muscles, making them harder to depolarize) |
| Depression, anxiety | Direct CNS effects of hypercalcemia on neuronal function | |
| Renal ("Stones" + "Thrones") | Renal colic / flank pain (nephrolithiasis) | Hypercalciuria (despite ↑ tubular reabsorption, the filtered load is so high that net urinary calcium is elevated) → calcium oxalate and calcium phosphate stone formation |
| Polyuria | Hypercalcemia inhibits aquaporin-2 expression in the collecting duct by inhibiting adenylyl cyclase → ↓ cAMP → nephrogenic diabetes insipidus → inability to concentrate urine [2] | |
| Polydipsia | Secondary to polyuria → dehydration → thirst | |
| Nocturia | Consequence of polyuria | |
| GI ("Moans") | Constipation | Hypercalcemia decreases smooth muscle contractility (similar mechanism — raised depolarization threshold in smooth muscle cells) |
| Anorexia, nausea, vomiting | Hypercalcemia stimulates gastrin secretion → ↑ gastric acid; also direct effects on GI smooth muscle and the chemoreceptor trigger zone | |
| Abdominal pain | May be from constipation, peptic ulcer disease (↑ gastrin), or pancreatitis | |
| Peptic ulcer disease | PTH and hypercalcemia stimulate gastrin release → ↑ HCl secretion | |
| Acute pancreatitis | Mechanism debated but likely: (1) calcium deposits in pancreatic duct → obstruction; (2) intracellular calcium activation of trypsinogen → autodigestion | |
| Skeletal ("Bones") | Bone pain | Excessive osteoclast-mediated bone resorption → microfractures, periosteal stretching |
| Pathological fractures | Severe bone resorption → osteoporosis and cortical bone loss, especially at sites rich in cortical bone (distal 1/3 radius) | |
| Joint pain / arthralgia | CPPD crystal deposition (pseudogout) — hyperPTH is a recognized metabolic cause of CPPD disease [5] | |
| Neuropsychiatric ("Psychic Overtones") | Confusion, cognitive impairment | Hypercalcemia impairs synaptic transmission and neuronal excitability |
| Depression, anxiety, psychosis | Altered CNS calcium signalling | |
| Drowsiness → coma (severe hypercalcemia) | Progressive CNS depression | |
| Cardiovascular | Hypertension | Hypercalcemia increases vascular smooth muscle tone (↑ intracellular Ca²⁺ in vascular smooth muscle → vasoconstriction) [6] |
| Shortened QT interval (on ECG) | Ca²⁺ accelerates phase 2 (plateau) repolarization of cardiac myocytes | |
| Arrhythmias | At very high calcium levels, cardiac conduction abnormalities occur | |
| Muscular | Proximal muscle weakness | Hypercalcemia impairs neuromuscular junction transmission and muscle contractility |
| Sign | Pathophysiological Basis |
|---|---|
| Usually no specific signs (most patients are asymptomatic) | Modern detection is biochemical, not clinical |
| Dehydration (dry mucous membranes, reduced skin turgor, tachycardia) | Polyuria from nephrogenic DI → volume depletion; also anorexia/vomiting contribute. Hypercalcemia is often clinically associated with dehydration [3] |
| Band keratopathy | Calcium deposition in the cornea (at the medial and lateral limbus in the interpalpebral fissure) — visible on slit lamp. Occurs in chronic hypercalcemia. |
| Palpable neck mass (rare) | Suggests parathyroid carcinoma (adenomas are far too small to palpate) |
| Proximal myopathy (difficulty rising from chair) | Hypercalcemia impairs muscle function |
| Hypertension | Present in up to 40–60% of primary HPT patients [6] |
| Shortened QT interval on ECG | Accelerated cardiac repolarization due to hypercalcemia |
| Chondrocalcinosis / pseudogout | CPPD crystal deposition secondary to hyperPTH — may see acute joint swelling [5] |
The 'Classic' vs 'Modern' Presentation
The full-blown "stones, bones, moans" presentation is now the exception, not the rule, in developed countries. Most primary HPT is discovered as asymptomatic hypercalcemia on routine blood tests. Don't be fooled into thinking every patient will present dramatically. However, in exam scenarios, they love to test the classic features!
These patients typically present with features of the underlying disease (e.g. CKD) rather than hypercalcemia (calcium is usually low or normal):
| Feature | Pathophysiological Basis |
|---|---|
| Bone pain / fractures | Renal osteodystrophy — high-turnover bone disease (osteitis fibrosa cystica) from chronic PTH excess |
| Muscle weakness | Hypocalcemia → neuromuscular irritability paradoxically combined with myopathy from vitamin D deficiency and uraemia |
| Pruritus (especially in CKD) | Elevated Ca × PO₄ product → metastatic calcification in skin; also uraemic pruritus |
| Vascular calcification | Chronic hyperphosphatemia + elevated Ca × PO₄ product → calcification of blood vessel walls → ↑ cardiovascular risk |
| Calciphylaxis (calcific uraemic arteriolopathy) | Small vessel calcification → skin ischemia → painful necrotic ulcers (livedo reticularis → violaceous plaques → black eschar). Very high mortality. |
| Soft tissue calcification | Periarticular deposits, conjunctival calcium, visceral calcification |
| Growth retardation (children) | Disturbed bone metabolism in growing skeleton |
| Symptoms of hypocalcemia (if present) | Perioral/acral paraesthesia, Trousseau's sign, Chvostek's sign, tetany, seizures |
- Features of hypercalcemia (similar to primary HPT) in a patient with a history of longstanding CKD/dialysis
- Persistent hypercalcemia after renal transplant is a classic scenario
- Bone disease may be severe (long-standing renal osteodystrophy)
This is the classic skeletal manifestation of severe, prolonged hyperparathyroidism (now rare in developed countries due to early detection):
| Feature | Description | Mechanism |
|---|---|---|
| Subperiosteal bone resorption | Best seen on X-ray of hands (radial aspect of middle phalanges) | Osteoclast activity beneath the periosteum — PTH-driven |
| Brown tumours (osteoclastomas) | Lytic bone lesions filled with fibrous tissue, hemosiderin-laden macrophages (giving brown colour), and giant cells | Localized areas of intense osteoclast activity → bone destruction → hemorrhage → fibrosis |
| Salt-and-pepper skull | Diffuse mottled appearance on skull X-ray | Multiple tiny lytic and sclerotic areas from alternating resorption and repair |
| Bone cysts | Radiolucent areas in long bones | Advanced resorption → cystic degeneration |
| Osteoporosis | Generalized bone loss, especially cortical bone (distal 1/3 radius) | Chronic PTH preferentially resorbs cortical bone |
| Pathological fractures | Fractures through weakened bone | Severely compromised bone integrity |
Key Point: In primary HPT, bone loss preferentially affects cortical bone (e.g. distal 1/3 radius on DEXA) rather than trabecular bone. In contrast, postmenopausal osteoporosis preferentially affects trabecular bone (e.g. vertebral bodies). This is because PTH has a catabolic effect on cortical bone but a relatively anabolic effect on trabecular bone (via intermittent PTH stimulation of osteoblasts — the same principle behind teriparatide therapy).
| Feature | Frequency | Mechanism |
|---|---|---|
| Nephrolithiasis | ~15–20% of primary HPT patients | Hypercalciuria → calcium stone formation (calcium oxalate > calcium phosphate) |
| Nephrocalcinosis | Less common than stones | Diffuse calcium deposition within the renal parenchyma (medullary > cortical) |
| Renal impairment | Variable | Chronic hypercalcemia → renal vasoconstriction + tubular damage + nephrocalcinosis |
| Nephrogenic diabetes insipidus | Common subclinical | As described above — hypercalcemia inhibits aquaporin-2 expression |
8. Associations and Complications as Presenting Features
- Hyperparathyroidism is a recognized secondary cause of hypertension [6]
- Mechanism: hypercalcemia → ↑ vascular smooth muscle tone, ↑ RAAS activity, vascular remodelling
- Should be considered in the workup of secondary hypertension
- Primary hyperparathyroidism is a medical cause of recurrent calcium stones [7]
- Leads to hypercalciuria → should be screened for in all recurrent stone formers
- Risk factors for stones in HPT: hypercalciuria, hyperphosphaturia, and possibly low urine citrate
- HyperPTH is a metabolic cause of CPPD deposition (3.35× risk) [5]
- Should be considered in younger patients presenting with pseudogout or chondrocalcinosis
| Parameter | Primary HPT | Secondary HPT | Tertiary HPT | FHH | Malignancy (PTHrP) |
|---|---|---|---|---|---|
| Serum Ca | ↑ | ↓ or N | ↑ | ↑ (mild) | ↑↑ |
| PTH | ↑ or inappropriately N | ↑↑ | ↑↑ | N or mildly ↑ | ↓ (suppressed) |
| Phosphate | ↓ | ↑ (CKD) | Variable | N | ↓ (PTHrP mimics PTH) |
| ALP | N or ↑ | ↑ | ↑ | N | ↑ (bone mets) or N |
| 24h urine Ca | ↑ (> 200 mg/d) | Variable | Variable | ↓↓ (Ca:Cr ratio < 0.01) | Variable |
| Vitamin D | N or ↑ (1,25) | ↓ | ↓ | N | N |
| Creatinine | N (unless renal complication) | ↑ (CKD) | ↑ (CKD) | N | Variable |
High Yield Summary
Definition: Hyperparathyroidism = excessive PTH. Primary (intrinsic parathyroid disease → hypercalcemia), Secondary (compensatory to hypocalcemia, usually CKD), Tertiary (autonomous after prolonged secondary).
Epidemiology: Primary HPT is the most common cause of outpatient hypercalcemia. Prevalence 1–2/1000. Peak 6th–7th decade. F:M = 2–3:1.
Risk Factors: Female sex, postmenopausal, head/neck irradiation, MEN1 (parathyroid + pancreas + pituitary), MEN2A (MTC + pheo + parathyroid), lithium use.
Causes of Primary HPT: Solitary adenoma (~85%) > Hyperplasia (~10–15%, think MEN) > Double adenoma (1–2%) > Carcinoma ( < 1%).
Biochemistry: Primary HPT = ↑Ca + ↑/inappropriately normal PTH + ↓PO₄. Must do 24h urine Ca to exclude FHH.
Clinical Features: Most are asymptomatic. Classic = "Stones, Bones, Moans, Thrones, Psychic Overtones." Hypercalcemia causes: nephrolithiasis, osteoporosis/osteitis fibrosa cystica, constipation, polyuria, depression/confusion, hypertension.
Key Differentiator from FHH: 24h urine calcium — HIGH in primary HPT, LOW in FHH (Ca:Cr clearance ratio < 0.01).
Secondary HPT in CKD: ↓GFR → ↑PO₄ + ↓calcitriol → ↓Ca → ↑PTH → renal osteodystrophy, vascular calcification, calciphylaxis.
Localization (NOT diagnosis): USG + Sestamibi scan — Sestamibi accumulates in mitochondria of oxyphil-cell-rich adenomas with slow washout compared to thyroid tissue.
Active Recall - Hyperparathyroidism (Definition, Epidemiology, Etiology, Pathophysiology, Clinical Features)
[1] Senior notes: maxim.md (Primary hyperparathyroidism section) [2] Senior notes: Ryan Ho Chemical Path.pdf (p23, Hypercalcemia section) [3] Senior notes: Ryan Ho Endocrine.pdf (p41, Primary Hyperparathyroidism section) [4] Senior notes: felixlai.md (Etiology — MEN table, Head and neck irradiation section) [5] Senior notes: Ryan Ho Rheumatology.pdf (p41, CPPD Disease section) [6] Senior notes: Ryan Ho Cardiology.pdf (p177, Secondary Hypertension workup) [7] Senior notes: felixlai.md (Urinary stones — Risk factors section) [8] Lecture slides: GC 218. I have a swelling in the neck Neck mass (Notes).pdf [9] Senior notes: Ryan Ho Diagnostic Radiology.pdf (p60, Parathyroid Scintigraphy) [10] Senior notes: Ryan Ho Fundamentals.pdf (p430, Hypercalcemia section)
Differential Diagnosis of Hyperparathyroidism
The differential diagnosis of hyperparathyroidism is really two overlapping clinical problems that the examiner can frame in different ways:
- "The patient has hypercalcemia — what is the cause?" (i.e., DDx of hypercalcemia, where primary HPT is one possibility)
- "The patient has elevated PTH — what is the cause?" (i.e., DDx of elevated PTH, distinguishing primary from secondary from tertiary HPT and other PTH-dependent causes)
Both approaches converge on the same diagnostic logic: measure PTH, and then bifurcate into PTH-dependent vs PTH-independent causes. Let me walk you through this systematically.
When a patient is found to have confirmed hypercalcemia (corrected calcium > 2.6 mmol/L or ionized calcium elevated), the single most important next step is to measure the intact PTH level. This splits the differential cleanly into two camps [2][10]:
The PTH Pivot Point
This is the single most important branch point. A "normal" PTH in the setting of hypercalcemia is NOT normal — it is inappropriately unsuppressed. If calcium is genuinely high, PTH should be suppressed via the CaSR negative feedback loop. A PTH that is even within the reference range with concurrent hypercalcemia should be treated as "PTH-dependent" and investigated as probable primary HPT. [2]
These are conditions where the parathyroid gland itself is driving the hypercalcemia:
| Condition | Frequency | Key Differentiating Features | Pathophysiology |
|---|---|---|---|
| Primary HPT | Most common cause of outpatient hypercalcemia [2][3] | ↑ PTH, ↑ Ca, ↓ PO₄, ↑ 24h urine Ca (> 200 mg/d, Ca:Cr clearance ratio > 0.02); often asymptomatic; usually solitary adenoma | Autonomous PTH secretion from adenoma/hyperplasia → unregulated bone resorption, renal Ca retention, and calcitriol synthesis |
| Tertiary HPT | Uncommon; CKD context | ↑ PTH, ↑ Ca; history of long-standing CKD/dialysis or recent renal transplant with persistent hypercalcemia | Prolonged secondary HPT → monoclonal transformation → autonomous parathyroid function that persists even after correction of renal failure |
| Familial Hypocalciuric Hypercalcemia (FHH) | Uncommon but critical DDx | ↑ Ca (usually mild, < 3.0 mmol/L), PTH normal or mildly ↑, ↓↓ 24h urine Ca (Ca:Cr clearance ratio < 0.01), often family history of "hypercalcemia" investigated but never treated | Inactivating mutation in CaSR → parathyroid glands and kidneys cannot sense high calcium → PTH remains unsuppressed + kidneys reabsorb too much calcium. Benign condition — does NOT require surgery [1][2] |
| Lithium-induced HPT | Uncommon | History of lithium use (usually bipolar disorder); ↑ PTH, ↑ Ca | Lithium shifts the CaSR set point to the right → higher calcium concentration required to suppress PTH → functional hyperparathyroidism. May also cause true parathyroid adenoma formation with long-term use |
FHH: The Must-Not-Miss Mimic
FHH is the most important differential to exclude before sending a patient with primary HPT to surgery. Why? Because FHH is benign and surgery will not cure it (the kidneys also have defective CaSR). The test is simple: 24-hour urine calcium is mandatory in every case of suspected primary HPT [1]. A Ca:Cr clearance ratio < 0.01 strongly suggests FHH. If in doubt, genetic testing for CaSR mutations is available.
How to differentiate Primary HPT from FHH:
| Feature | Primary HPT | FHH |
|---|---|---|
| Inheritance | Sporadic (mostly) or MEN | Autosomal dominant |
| Family history | Usually negative (unless MEN) | Often positive for mild hypercalcemia in multiple family members |
| Calcium level | Variable (can be very high in carcinoma) | Usually mildly elevated ( < 3.0 mmol/L) |
| PTH | ↑ or inappropriately normal | Normal or mildly ↑ |
| 24h urine calcium | ↑ (hypercalciuric) | ↓↓ (hypocalciuric) |
| Ca:Cr clearance ratio | > 0.02 | *** < 0.01*** |
| Management | Surgery (parathyroidectomy) | No treatment needed |
| Genetic test | MEN1/RET if familial | CaSR mutation |
The Ca:Cr clearance ratio is calculated as: (24h urine Ca × Plasma Cr) / (Plasma Ca × 24h urine Cr). A ratio < 0.01 = FHH; > 0.02 = primary HPT; 0.01–0.02 is a grey zone requiring further workup including genetic testing.
These are conditions where the hypercalcemia is driven by something other than the parathyroid glands, and PTH is appropriately suppressed by negative feedback:
| Condition | Frequency | Key Differentiating Features | Pathophysiology |
|---|---|---|---|
| Malignancy | Most common cause of inpatient hypercalcemia [2] | PTH ↓ (suppressed); often very high Ca ( > 3.0 mmol/L); usually clinically apparent cancer; check PTHrP, imaging | Multiple mechanisms — see below |
| Vitamin D intoxication | Uncommon | History of excessive vitamin D supplementation; ↑ 25(OH)D; PTH suppressed | Exogenous excess → ↑ gut Ca absorption + ↑ bone resorption |
| Granulomatous disease (sarcoidosis, TB) | Uncommon; important in HK (TB endemic) | ↑ 1,25(OH)₂D₃ (calcitriol) with normal/low 25(OH)D; PTH suppressed; clinical/radiological features of granulomatous disease | Activated macrophages in granulomas express 1α-hydroxylase autonomously → unregulated conversion of 25(OH)D to active 1,25(OH)₂D₃ → ↑ gut Ca absorption [2][10] |
| Milk-alkali syndrome | Uncommon | History of excessive calcium + alkali intake (e.g. calcium carbonate for GERD, tums); metabolic alkalosis; renal impairment | ↑ oral Ca → hypercalcemia → renal vasoconstriction → ↓ GFR → ↓ Ca excretion → worsening hypercalcemia. Alkalosis ↑ renal Ca reabsorption → vicious cycle [10] |
| Thyrotoxicosis | Uncommon cause | Clinical features of thyrotoxicosis; ↑ T4, ↓ TSH | Thyroid hormones directly stimulate osteoclastic bone resorption → release of calcium |
| Immobilization | In context of prolonged bed rest | History of prolonged immobilization (e.g. spinal cord injury, prolonged ICU stay); young patients and Paget's disease particularly susceptible | Loss of mechanical loading → uncoupled bone remodelling with ↑ osteoclast and ↓ osteoblast activity → net calcium release |
| Paget's disease of bone | Uncommon; usually normocalcemic | ↑↑ ALP; characteristic X-ray changes; calcium usually only elevated if immobilized or coincident hyperPTH | Highly increased bone turnover with ↑ osteoclast activity; normally compensated, but immobilization removes osteoblast stimulus → hypercalcemia [3b] |
| Adrenal insufficiency | Rare cause | Features of Addison's disease; ↑ K, ↓ Na, ↓ cortisol | Cortisol normally opposes vitamin D action on gut Ca absorption and promotes renal Ca excretion; deficiency → ↑ Ca reabsorption + ↑ gut absorption; also haemoconcentration → apparent ↑ total Ca [10] |
| Thiazide diuretics | Common medication; usually mild | History of thiazide use; mild hypercalcemia | Thiazides ↑ Ca reabsorption in the DCT (by enhancing Na/Ca exchange) → ↓ urinary Ca → ↑ serum Ca. Important: thiazides can unmask underlying primary HPT |
| Paraproteinemia (e.g. MGUS, myeloma) | Check if ↑ globulin gap | Factitious hypercalcemia: ↑ total Ca but normal ionized Ca; ↑ total protein with normal albumin → ↑ globulin | Immunoglobulins bind calcium → ↑ total calcium measurement. Always check ionized calcium to distinguish true from factitious hypercalcemia [2] |
Malignancy-Related Hypercalcemia — Sub-mechanisms:
This deserves special attention because it is the most common cause of inpatient hypercalcemia [2] and has multiple distinct mechanisms:
| Mechanism | Frequency | Cancer Types | Biochemistry | How It Works |
|---|---|---|---|---|
| Humoral hypercalcemia of malignancy (HHM) — PTHrP | ~80% of malignancy-related hypercalcemia | SCC lung, HCC, breast CA, renal cell CA, small cell CA ovary [2] | ↑ PTHrP, ↓ PTH, ↓ PO₄ (PTHrP mimics PTH at kidney → phosphaturia), ↑ ALP (variable) | Tumour secretes PTHrP (parathyroid hormone-related peptide) which binds the same receptor as PTH → mimics PTH actions on bone and kidney. But note: PTHrP does NOT upregulate 1α-hydroxylase as effectively as PTH → calcitriol usually normal/low |
| Local osteolytic hypercalcemia (LOH) | ~20% | Breast CA (bone mets), multiple myeloma [2] | ↓ PTH, ↑ ALP, ↑ PO₄ (released from destroyed bone) | Tumour cells in bone secrete local cytokines (IL-6, TNF-β, RANKL) → activate osteoclasts → focal bone destruction → calcium release. In myeloma, this is a key feature (CRAB: Calcium, Renal, Anaemia, Bone lytic lesions) |
| Calcitriol-mediated | Rare | Lymphoma (Hodgkin's and non-Hodgkin's) | ↑ 1,25(OH)₂D₃ | Similar to granulomatous disease — lymphoma cells express 1α-hydroxylase → autonomous calcitriol production |
| Ectopic PTH secretion | Very rare | Various | ↑ PTH (true PTH, not PTHrP) | Extremely rare — tumour actually produces intact PTH |
PTHrP vs PTH: Why the distinction matters
PTHrP is structurally similar to PTH at the N-terminal (first 13 amino acids are highly homologous) → it activates the same PTH/PTHrP receptor (PTH1R) on bone and kidney. This is why it mimics PTH effects: ↑ bone resorption, ↑ renal Ca reabsorption, ↓ PO₄ reabsorption. However, PTHrP does NOT effectively stimulate 1α-hydroxylase → 1,25(OH)₂D₃ is usually normal/low (unlike primary HPT where calcitriol may be elevated). Also, PTHrP is a different molecule from PTH — it does NOT cross-react with intact PTH assays. So the intact PTH will be suppressed (appropriately) by the hypercalcemia while PTHrP is doing the damage. [2]
Sometimes the clinical question is framed differently: "PTH is elevated — what is the cause?" This is particularly relevant when a patient has elevated PTH but calcium may be high, normal, or low:
| PTH Status | Calcium | Condition | Key Clue |
|---|---|---|---|
| ↑ PTH | ↑ Ca | Primary HPT | Most common outpatient hypercalcemia; check 24h urine Ca to exclude FHH |
| ↑ PTH | ↑ Ca | Tertiary HPT | History of CKD/dialysis; persistent hypercalcemia post-transplant |
| ↑ PTH | ↑ Ca (mild) | FHH | Low urine Ca, Ca:Cr ratio < 0.01, family history |
| ↑ PTH | ↑ Ca | Lithium-induced | Lithium use history |
| ↑↑ PTH | ↓ or N Ca | Secondary HPT | CKD (check creatinine), Vitamin D deficiency (check 25-OH-D), malabsorption |
| ↑ PTH | N Ca | Normocalcemic primary HPT | Persistently elevated PTH with consistently normal calcium AFTER excluding all secondary causes |
| ↑ PTH | ↓ Ca | Secondary HPT (severe) | Actively hypocalcemic patient — the PTH is compensatory |
5. Differential Diagnosis by Clinical Presentation
Since hyperparathyroidism presents through its complications, it is also important to consider where HPT sits in the differential for each of these presenting complaints:
Primary HPT should be considered in any patient with recurrent calcium stones, especially if:
- Stones are calcium phosphate (more suggestive of HPT than calcium oxalate)
- Hypercalcemia or hypercalciuria is documented
- Bilateral or recurrent stones in a young patient
Other DDx for recurrent calcium stones [7]:
- Idiopathic hypercalciuria (most common)
- Hyperoxaluria (dietary, enteric post-bariatric surgery, primary)
- Hypocitraturia (renal tubular acidosis type 1, chronic diarrhea)
- Hyperuricosuria
- Medullary sponge kidney
- Primary hyperparathyroidism (must check calcium and PTH in all recurrent stone formers) [7]
Primary HPT should be considered in:
- Premenopausal women or men with unexplained osteoporosis
- Osteoporosis predominantly at the distal 1/3 radius (cortical bone site)
- Any patient with osteoporosis + hypercalcemia
Other DDx: postmenopausal osteoporosis, glucocorticoid-induced, vitamin D deficiency, hypogonadism, myeloma, metastatic bone disease.
Hyperparathyroidism is a recognized metabolic cause of CPPD deposition (3.35× risk) [5]. In any patient presenting with chondrocalcinosis or pseudogout, especially if younger than expected (< 55 years), screen for:
- Hyperparathyroidism (check calcium and PTH)
- Haemochromatosis (check ferritin, transferrin saturation)
- Hypomagnesemia (check magnesium)
- Hypophosphatasia (check ALP — paradoxically low)
- Wilson's disease (if young; check ceruloplasmin)
Hyperparathyroidism is listed as an endocrine cause of secondary hypertension [6]:
The endocrine causes to consider (from the "DANCER" mnemonic for secondary HTN) [6]:
- Thyroid: hyperthyroidism, hypothyroidism
- Adrenals: Cushing's, Conn's (primary aldosteronism), phaeochromocytoma
- Parathyroid: hyperparathyroidism [6]
- Others: pre-eclampsia, acromegaly
Parathyroid disease is listed as a medical cause of secondary mood disorders [11]. Hypercalcemia from primary HPT can cause depression, anxiety, cognitive impairment, and even psychosis. Always check calcium in patients with new-onset psychiatric symptoms, especially if:
- Older patient with new depression + fatigue + constipation
- Psychiatric symptoms refractory to standard treatment
Hypercalcemia from primary HPT is a recognized but uncommon cause of acute pancreatitis. The mnemonic for causes of pancreatitis includes "Hyperparathyroidism/Hypercalcemia" under metabolic causes (the "GET SMASHED" mnemonic: Gallstones, Ethanol, Trauma, Steroids, Mumps/Malignancy, Autoimmune, Scorpion stings, Hyperlipidemia/Hypercalcemia/Hypothermia, ERCP, Drugs).
Secondary HPT is listed among non-haematological causes of myelofibrosis — though this is rare, it demonstrates the systemic effects of chronic PTH excess on the marrow microenvironment [12].
| Investigation | Purpose | Interpretation |
|---|---|---|
| Corrected calcium / ionized Ca | Confirm true hypercalcemia | Rule out factitious hypercalcemia from ↑ albumin or paraprotein [2] |
| Intact PTH | Most important branch point | PTH-dependent vs PTH-independent [2][10] |
| 24h urine calcium | Distinguish primary HPT from FHH | ↑ in primary HPT, ↓↓ in FHH (Ca:Cr ratio < 0.01) [1] |
| Phosphate | Supports diagnosis | ↓ in primary HPT (PTH causes phosphaturia); ↑ in CKD-related secondary HPT; ↓ in PTHrP-mediated malignancy [2][10] |
| 25(OH)D | Rule out vitamin D deficiency/excess | ↓ in secondary HPT; ↑↑ in vitamin D intoxication |
| 1,25(OH)₂D₃ | Granulomatous disease/lymphoma | ↑ in sarcoidosis, TB, lymphoma (autonomous 1α-hydroxylase) |
| PTHrP | Malignancy workup | ↑ in humoral hypercalcemia of malignancy |
| ALP | Bone turnover marker | ↑ in HPT with bone disease, Paget's, bone metastases. ↑ ALP predicts risk of hungry bone syndrome post-op [1] |
| RFT (creatinine, eGFR) | Rule out CKD | Elevated creatinine points toward secondary or tertiary HPT |
| Serum protein electrophoresis | Exclude myeloma/paraproteinemia | If ↑ globulin gap or factitious hypercalcemia suspected [2] |
| Vitamin D, ferritin, Mg | Screen for secondary causes of CPPD/secondary HPT | Comprehensive metabolic workup |
| Feature | Primary HPT | FHH | Malignancy (PTHrP) | Malignancy (LOH) | Granulomatous | Vitamin D excess |
|---|---|---|---|---|---|---|
| PTH | ↑ or inappropriately N | N or mildly ↑ | ↓ | ↓ | ↓ | ↓ |
| Ca | ↑ | ↑ (mild) | ↑↑ | ↑↑ | ↑ | ↑ |
| PO₄ | ↓ | N | ↓ | ↑ | N or ↓ | N or ↑ |
| ALP | N or ↑ | N | Variable | ↑ | N | N |
| 24h urine Ca | ↑ | ↓↓ | ↑ | Variable | ↑ | ↑ |
| PTHrP | N | N | ↑↑ | N | N | N |
| 25(OH)D | N | N | N | N | N | ↑↑ |
| 1,25(OH)₂D₃ | N or ↑ | N | N or ↓ | N | ↑↑ | Variable |
| Clinical context | Asymptomatic, postmenopausal | Family history, young, benign | Known cancer, acute | Bone pain, known mets | Sarcoid, TB, CXR findings | Supplement Hx |
High Yield Summary — Differential Diagnosis
-
The PTH level is the single most important differentiating test in the workup of hypercalcemia. PTH-dependent (↑/inappropriately normal PTH) vs PTH-independent (↓ PTH).
-
Primary HPT is the most common cause of outpatient hypercalcemia. Malignancy is the most common cause of inpatient hypercalcemia.
-
24h urine calcium must always be checked to exclude FHH before proceeding to surgery for primary HPT. FHH = Ca:Cr clearance ratio < 0.01; primary HPT = ratio > 0.02.
-
Malignancy-related hypercalcemia has multiple mechanisms: PTHrP (80%, humoral; SCC lung, HCC, breast), local osteolysis (20%; breast mets, myeloma — CRAB), calcitriol (lymphoma), ectopic PTH (very rare).
-
Granulomatous diseases (sarcoidosis, TB — important in Hong Kong) cause hypercalcemia via autonomous 1α-hydroxylase in macrophages → ↑ 1,25(OH)₂D₃.
-
Secondary HPT: think CKD, vitamin D deficiency. PTH is elevated but calcium is low/normal. This is a compensatory response.
-
Tertiary HPT: autonomous PTH after prolonged secondary HPT. Classic scenario: persistent hypercalcemia after renal transplant.
-
Hyperparathyroidism should be considered in the DDx of: recurrent renal stones, unexplained osteoporosis, pseudogout/CPPD, secondary hypertension, depression, and acute pancreatitis.
Active Recall - Differential Diagnosis of Hyperparathyroidism
References
[1] Senior notes: maxim.md (Primary hyperparathyroidism section) [2] Senior notes: Ryan Ho Chemical Path.pdf (p23, Hypercalcemia section) [3] Senior notes: Ryan Ho Endocrine.pdf (p41, Primary Hyperparathyroidism section) [5] Senior notes: Ryan Ho Rheumatology.pdf (p41-42, CPPD Disease section) [6] Senior notes: Ryan Ho Cardiology.pdf (p177, Secondary Hypertension workup) [7] Senior notes: felixlai.md (Urinary stones — Risk factors section) [10] Senior notes: Ryan Ho Fundamentals.pdf (p430, Hypercalcemia section) [11] Senior notes: Ryan Ho Psychiatry.pdf (p140, Mood Disorders — secondary to medical condition) [12] Senior notes: Ryan Ho Haemtology.pdf (p77, Myelofibrosis — non-haematological causes) [13] Senior notes: felixlai.md (Localization studies section) [14] Senior notes: Ryan Ho Diagnostic Radiology.pdf (p60, Parathyroid Scintigraphy)
Diagnostic Criteria, Algorithm, and Investigation Modalities
1. Diagnostic Criteria
There is no single "diagnostic criteria checklist" like the Jones criteria or SLICC criteria for lupus. Instead, the diagnosis of primary HPT is fundamentally biochemical — it rests on demonstrating the characteristic hormone-calcium pattern and systematically excluding mimics.
Diagnosis: ↑ serum calcium + inappropriately ↑ PTH (need not be above the reference range) in the setting of normal renal function [3]
Let me break this down from first principles:
| Criterion | Explanation | Why This Makes Sense |
|---|---|---|
| Hypercalcemia (corrected Ca > 2.6 mmol/L or ↑ ionized Ca) | Confirmed on at least 2 occasions to exclude transient or laboratory artefact | A single elevated value could be spurious — dehydration, tourniquet artifact, postprandial variation |
| Elevated or inappropriately normal PTH | Even a PTH within the reference range is "inappropriate" if calcium is high — because CaSR should have suppressed it | This is the key conceptual point: the normal feedback loop (high Ca²⁺ → CaSR activation → PTH suppression) is broken. A "normal" PTH with high calcium = the parathyroid is not responding to feedback = autonomous secretion [2][3] |
| Normal renal function (eGFR) | Must exclude CKD to differentiate from tertiary HPT | In CKD, PTH elevation could represent secondary or tertiary HPT rather than primary |
| Exclusion of FHH (24h urine calcium mandatory) | Ca:Cr clearance ratio > 0.02 supports primary HPT; < 0.01 suggests FHH | FHH is benign and does not require surgery — failing to exclude it leads to unnecessary parathyroidectomy [1][3] |
| Exclusion of other causes of elevated PTH | Vitamin D deficiency, medications (lithium, thiazides) | These cause secondary elevations of PTH that can mimic primary HPT |
The 'inappropriately normal' PTH
This is a classic exam pitfall. Students see a PTH of 5.5 pmol/L (reference 1.5–6.9) and say "PTH is normal — it can't be primary HPT." But if the calcium is 2.95 mmol/L, that PTH should be suppressed to near zero. A "normal" PTH with hypercalcemia is functionally the same as an elevated PTH — the gland is not responding to feedback. Always interpret PTH in the context of the calcium level. [2][3]
This is a more recently recognized entity. The criteria are:
- Persistently elevated PTH on at least 2 occasions separated by ≥ 3 months
- Consistently normal albumin-corrected total calcium AND normal ionized calcium
- Systematic exclusion of ALL secondary causes of elevated PTH:
- Vitamin D deficiency (25-OH-D must be > 50 nmol/L / 20 ng/mL)
- CKD (eGFR must be > 60 mL/min)
- Medications (thiazides, lithium, denosumab)
- Malabsorption syndromes
- Hypercalciuria (idiopathic)
This is essentially a diagnosis of exclusion: "I've corrected everything that could secondarily elevate PTH, and it's still high, but calcium is stubbornly normal."
No formal "criteria" — the diagnosis is clinical and biochemical:
| Feature | Expected Finding |
|---|---|
| PTH | ↑↑ (often markedly elevated, can be > 10× normal in advanced CKD) |
| Calcium | ↓ or normal (NOT elevated) |
| Phosphate | ↑ (in CKD); ↓ or N (in vitamin D deficiency/malabsorption) |
| 25-OH-D | ↓ if vitamin D deficiency is the cause |
| eGFR | ↓ if CKD is the cause |
| Context | Known CKD, vitamin D deficiency, or malabsorption |
| Feature | Expected Finding |
|---|---|
| PTH | ↑↑ (persistently) |
| Calcium | ↑ (this is what distinguishes it from secondary HPT) |
| Context | Long-standing CKD/dialysis history OR persistent hypercalcemia after renal transplant |
| Parathyroid glands | Typically nodular hyperplasia (may be very large) |
The key distinguishing feature from secondary HPT: calcium is elevated (the glands have become autonomous and are now overproducing PTH irrespective of calcium feedback).
The diagnostic approach follows a stepwise, logical sequence. I'll walk through the thinking, then present it as a mermaid diagram.
Step 1: Confirm true hypercalcemia
- Repeat calcium measurement
- Calculate albumin-corrected calcium OR measure ionized calcium
- Rule out factitious hypercalcemia (paraproteinemia → check ionized Ca) [2]
Step 2: Measure intact PTH — the pivot point
- This splits the differential into PTH-dependent vs PTH-independent
Step 3: If PTH-dependent — work up for primary HPT
- Check 24h urine calcium to exclude FHH
- Check vitamin D to exclude secondary HPT (vitamin D deficiency with compensatory PTH rise that has "escaped" into hypercalcemia is possible but unusual)
- Check renal function to exclude tertiary HPT
- Review medications (lithium, thiazides)
Step 4: Screen for complications of hypercalcemia/HPT
- Renal: imaging for stones, renal function
- Bone: DEXA scan (3 sites)
- Other: ECG, ALP
Step 5: If surgery is planned — localization studies
- Localization studies are NOT for diagnosis and do NOT determine the need for surgery [1][13]
- They are performed ONLY after the biochemical diagnosis is confirmed and the decision to operate is made
- Purpose: guide the surgical approach (focused/minimally invasive vs bilateral exploration)
Step 6: If PTH-independent — work up for malignancy and other causes
3. Investigation Modalities — Detailed Breakdown
I will organize investigations into three categories:
- Biochemical investigations (for diagnosis)
- Complication screening (for staging severity)
- Localization studies (for surgical planning)
3.1 Biochemical Investigations (Diagnostic)
| Aspect | Detail |
|---|---|
| What to order | Total serum calcium + serum albumin (to calculate corrected calcium) OR ionized calcium directly |
| Corrected calcium formula | Corrected Ca (mmol/L) = Total Ca + 0.02 × (40 − [Albumin in g/L]) [10] |
| Why correct for albumin | ~40% of total serum calcium is bound to albumin. If albumin is low (e.g., liver disease, nephrotic syndrome), total Ca will be falsely low even though the physiologically active ionized fraction is normal. Conversely, if albumin is high, total Ca may be falsely elevated |
| When to use ionized Ca | Acid-base disturbances (acidosis ↑ ionized Ca by displacing Ca from albumin; alkalosis ↓ ionized Ca), suspected paraproteinemia, critical illness |
| Key interpretation | Corrected Ca > 2.6 mmol/L = hypercalcemia. Repeat at least once to confirm |
Factitious Hypercalcemia
Paraproteinemia (e.g. MGUS, myeloma) can cause factitious hypercalcemia [2]. The immunoglobulin molecules bind calcium, raising the TOTAL calcium measurement, but ionized calcium is normal. Clue: ↑ total protein with normal albumin → ↑ globulin gap. Always check ionized calcium if the clinical picture doesn't match. Also, phosphate may appear abnormal because immunoglobulin can precipitate with phosphate, interfering with the assay [2].
| Aspect | Detail |
|---|---|
| Assay | "Intact PTH" (also called "whole PTH" or "2nd generation PTH") measures the full 84-amino-acid molecule. Older "mid-molecule" assays are obsolete |
| Reference range | Typically 1.5–6.9 pmol/L (varies by lab) |
| Key interpretation | ↑ PTH with ↑ Ca = primary HPT (or tertiary, or FHH). An inappropriately "normal" PTH with hypercalcemia is still diagnostic [2][3]. ↓ PTH with ↑ Ca = PTH-independent cause (malignancy, vitamin D, etc.) |
| Pitfalls | PTH has a short half-life (~4 minutes) → blood sample must be handled properly (transport on ice, avoid hemolysis). Also, renal failure → accumulation of PTH fragments → can interfere with some assays |
| Finding | Interpretation | Mechanism |
|---|---|---|
| ↓ PO₄ | Supports primary HPT or PTHrP-mediated malignancy | PTH (and PTHrP) ↓ phosphate reabsorption in the PCT → phosphaturia → hypophosphatemia [15] |
| ↑ PO₄ | Suggests CKD (secondary/tertiary HPT) or local osteolysis from bone metastases | CKD → ↓ renal PO₄ excretion; bone destruction releases stored PO₄ |
| Normal PO₄ | Does not exclude HPT but less supportive | Early disease or dietary influences |
| Aspect | Detail |
|---|---|
| Source | Bone-specific isoenzyme reflects osteoblast activity (bone formation/turnover) |
| In primary HPT | Normal or ↑. Elevated ALP indicates significant bone disease (osteitis fibrosa cystica, active bone remodelling) |
| Clinical significance | ↑ ALP predicts risk of hungry bone syndrome post-operatively [1]. Why? High ALP = high bone turnover = lots of osteoblasts actively laying down bone. After parathyroidectomy, PTH suddenly drops → osteoclasts stop resorbing → but osteoblasts continue forming bone → they "suck up" calcium, phosphate, and magnesium from the blood → profound hypocalcemia, hypophosphatemia, hypomagnesemia |
| Also useful for | DDx: markedly ↑ ALP with normal Ca/PO₄ → think Paget's disease rather than HPT |
| Aspect | Detail |
|---|---|
| Mandatory investigation | Must check in every case of suspected primary HPT [1][3] |
| Purpose | Distinguish primary HPT (↑ urine Ca) from FHH (↓ urine Ca) |
| Calculation | Ca:Cr clearance ratio = (24h urine Ca × Plasma Cr) / (Plasma Ca × 24h urine Cr) |
| Interpretation | > 0.02 → primary HPT; < 0.01 → FHH; 0.01–0.02 → indeterminate (consider genetic testing for CaSR mutation) |
| Also documents | Degree of hypercalciuria — important for assessing renal stone risk and is one of the criteria for surgical intervention in asymptomatic primary HPT [13] |
| Aspect | Detail |
|---|---|
| Purpose | Rule out vitamin D deficiency as a cause of secondary HPT; rule out vitamin D excess as a cause of PTH-independent hypercalcemia |
| In primary HPT | 25-OH-D may be normal or low. Vitamin D deficiency is extremely common in the general population (including HK) and can coexist with primary HPT — this is important because: (a) Vitamin D deficiency can mask hypercalcemia (the Ca may be "normal" when it should be high); (b) It worsens bone disease; (c) It should be cautiously repleted before/after surgery |
| Interpretation | Low 25-OH-D with ↑ PTH and low/normal Ca → secondary HPT. Low 25-OH-D with ↑ PTH and ↑ Ca → primary HPT with concurrent vitamin D deficiency |
| Aspect | Detail |
|---|---|
| Purpose | Rule out CKD (which would point to secondary or tertiary HPT); establish baseline renal function; assess for renal complications of HPT |
| In primary HPT | Should be normal unless chronic hypercalcemia has caused renal damage (nephrocalcinosis, renal stones, tubular dysfunction) |
| Interpretation | ↓ eGFR + ↑ PTH + ↑ Ca + history of CKD/dialysis → tertiary HPT. ↓ eGFR + ↑ PTH + ↓/N Ca → secondary HPT |
| Test | Purpose | Interpretation |
|---|---|---|
| 1,25(OH)₂D₃ (calcitriol) | Not routinely measured in primary HPT workup but useful if suspecting granulomatous disease or lymphoma | ↑ in sarcoidosis, TB, lymphoma (autonomous 1α-hydroxylase) [10] |
| PTHrP | If PTH is suppressed (PTH-independent hypercalcemia) | ↑ in humoral hypercalcemia of malignancy |
| ECG | Screen for cardiac effects of hypercalcemia | Shortened QT interval (accelerated repolarization), arrhythmias at very high Ca |
| Serum magnesium | Baseline; important perioperatively | Severe hypoMg can impair PTH secretion; also drops in hungry bone syndrome |
| FBC, ESR, LDH | If malignancy suspected | Anaemia, ↑ ESR, ↑ LDH suggest haematological malignancy |
| Serum protein electrophoresis (SPEP) | If paraproteinemia/myeloma suspected | Monoclonal band = myeloma/MGUS [2] |
Once primary HPT is diagnosed biochemically, you need to assess for end-organ damage. This determines both the severity of disease and whether the patient meets criteria for surgery (even if "asymptomatic"):
Investigations are targeted at defining possible complications due to increased PTH levels and hypercalcemia [13]
| Investigation | What It Assesses | Key Findings in HPT |
|---|---|---|
| DEXA bone densitometry (3 sites) | Bone mineral density at lumbar spine (L1–L4, trabecular bone), hip (femoral neck, mixed), and distal 1/3 radius (cortical bone) [3][13] | Osteopenia/osteoporosis preferentially at cortical sites (distal 1/3 radius > hip > spine). T-score ≤ −2.5 at any site = surgical indication. Remember: PTH preferentially resorbs cortical bone |
| Vertebral fracture assessment (VFA or lateral spine X-ray) | Subclinical vertebral fractures | Vertebral compression fractures may be present even without symptoms; if found, constitutes a surgical indication |
| USG kidneys / KUB X-ray | Detect stones in the urinary tract [1][13] | Nephrolithiasis (surgical indication even if asymptomatic on imaging), nephrocalcinosis (medullary calcification) |
| RFT | Renal function | eGFR < 60 mL/min = surgical indication (even if asymptomatic) |
| 24h urine calcium | Document degree of hypercalciuria [13] | > 10 mmol/day (or > 400 mg/day) = surgical indication. Also risk factor for stone formation |
| ALP | Bone turnover | ↑ ALP predicts risk of hungry bone syndrome post-op [1] |
| ECG | Cardiac effects of hypercalcemia | Shortened QT interval |
Why DEXA Must Include the Distal 1/3 Radius
In standard osteoporosis screening (e.g., postmenopausal women), DEXA typically measures the lumbar spine and hip. But in primary HPT, the characteristic bone loss is at cortical sites due to PTH's preferential resorption of cortical bone. The distal 1/3 of the radius is the most cortical site routinely measured by DEXA, and it is the most sensitive site for detecting HPT-related bone loss. If you only measure spine and hip, you may miss significant cortical bone loss. [3]
3.3 Localization Studies (Pre-operative, NOT Diagnostic)
This is one of the most frequently tested and most misunderstood concepts:
Localization studies are NOT used in the diagnosis of primary hyperparathyroidism NOR to determine the need for surgery. They are indicated ONLY when primary HPT is confirmed with biochemical tests and the decision for surgery has been made. [1][13][14]
The purpose of localization studies is to:
- Guide the surgical approach: Can the surgeon do a focused/minimally invasive parathyroidectomy (if a single adenoma is clearly localized)? Or is bilateral neck exploration needed?
- Identify ectopic glands: Intrathymic, retroesophageal, carotid sheath, mediastinal
- 5% of patients present with double adenomas — localization helps identify these [1]
a) Ultrasound (USG) Neck
| Aspect | Detail |
|---|---|
| Advantages | Non-invasive, no radiation, inexpensive, widely available, can be done at bedside, can assess concurrent thyroid pathology |
| Sonographic features | Homogeneous hypoechoic nodule posterior to the thyroid lobe, often with an extra-thyroidal feeding vessel with peripheral vascularity on Doppler imaging [13] |
| Limitations | Operator-dependent; poor sensitivity for ectopic glands (cannot see mediastinal/retroesophageal locations); may miss small or multigland disease; affected by concurrent thyroid nodules |
| Sensitivity | ~75–80% for single adenoma; much lower for multigland disease |
b) ⁹⁹ᵐTc-Sestamibi Scintigraphy (Parathyroid Scan)
This is the workhorse nuclear medicine study for parathyroid localization. Understanding the mechanism from first principles is key:
| Aspect | Detail |
|---|---|
| Radiopharmaceutical | ⁹⁹ᵐTc-sestamibi [1][14] |
| Mechanism | Sestamibi accumulates in mitochondria. The washout rate depends on the number of mitochondria in the tissue. Parathyroid adenomas are rich in oxyphilic cells which have abundant mitochondria → slow washout compared to the thyroid gland, which has fewer mitochondria [1][14] |
| Technique: dual-phase | Early image (10–20 min): tracer uptake in BOTH thyroid and parathyroid glands (both take it up initially). Delayed image (2h): faster tracer washout from thyroid tissue → the parathyroid adenoma persists as a focus of retained activity [1][14] |
| Protocols | Single isotope dual-phase scan: as described above — most commonly used. Dual isotope subtraction imaging (⁹⁹Tc-sestamibi + ⁹⁹Tc-pertechnetate): subtract the thyroid signal (pertechnetate is thyroid-specific) to isolate parathyroid uptake [1] |
| SPECT/CT | Single-photon emission CT (SPECT): 3D reconstruction with higher anatomical resolution; can be fused with CT images (SPECT/CT) for precise anatomical localization [1][14] |
| False positive | Hurthle cell adenoma of the thyroid — also rich in mitochondria/oxyphil cells → slow washout mimics parathyroid adenoma [1] |
| False negative | Parathyroid hyperplasia (all 4 glands mildly enlarged — less dramatic uptake), multiple adenomas, small adenomas, concurrent thyroid disease. A negative Sestamibi scan does NOT preclude the diagnosis of primary HPT [13] |
| Sensitivity | ~80–90% for single adenoma; ~30–45% for multigland disease |
Clinical Pearl: Sestamibi and Surgery
The combination of concordant USG + Sestamibi findings pointing to a single adenoma allows the surgeon to proceed with a focused (minimally invasive) parathyroidectomy — a smaller incision, less dissection, shorter operating time, and lower complication risk. If the two imaging modalities are discordant or suggest multigland disease, the surgeon should plan for bilateral neck exploration. [1]
| Modality | Indication | Details |
|---|---|---|
| 4D CT scan | When USG + Sestamibi are negative/discordant; re-operative cases | Multiphase CT with pre-contrast, arterial, venous, and delayed phases. Parathyroid adenomas show characteristic early arterial enhancement and rapid washout (the "4th dimension" is time/contrast dynamics). Advantage: excellent anatomical detail. Disadvantage: high radiation dose [1] |
| MRI | Mediastinal ectopic glands, pregnant patients (no radiation) | Parathyroid adenomas show low intensity on T1, high intensity on T2 [13]. Good for identifying ectopic mediastinal or retroesophageal glands |
| PET scan | Refractory cases | ¹¹C-methionine or ¹⁸F-fluorocholine PET/CT — used when conventional imaging fails. Methionine is taken up by metabolically active parathyroid tissue [13] |
| Selective venous sampling | Invasive — reserved for re-operative cases or unrevealing non-invasive tests [1][13] | Catheterization of cervical veins (superior/middle/inferior thyroid, thymic, vertebral veins) with measurement of PTH levels. A 1.5–2× increase in PTH from a representative cervical vein compared to a peripheral site is considered abnormal [13]. Most common invasive modality for parathyroid localization |
| Selective arteriography | Invasive — reserved for re-operative/difficult cases [13] | Performed by combining selective transarterial hypocalcemic stimulation (injection of sodium citrate to induce hypocalcemia) with non-selective venous sampling. The induced hypocalcemia stimulates PTH release from the abnormal gland, which is then detected in the venous samples [13] |
| Modality | Purpose | How It Works |
|---|---|---|
| Intraoperative PTH monitoring | Confirm successful removal of hyperfunctioning tissue | Miami criteria: PTH drops to normal range AND falls > 50% from the highest pre-excision value at 10 minutes post-resection [1]. If criteria NOT met → suspect multigland disease → convert to bilateral exploration |
| Intraoperative ultrasound | Real-time identification of adenoma during surgery | Handheld probe placed directly on surgical field |
| Frozen section | Confirm excised tissue is parathyroid | Rapid histological examination during surgery. Especially important in subtotal parathyroidectomy ("3.5 resection") to confirm the remnant tissue contains parathyroid tissue [1] |
| Gamma probe | Used with Sestamibi injection pre-op | Handheld probe detects radioactivity to guide surgeon to the "hot" adenoma |
Standard investigations for primary HPT (JCEM 2014, updated 5th International Workshop 2022) [3]:
A. Confirm the diagnosis:
- PTH, serum calcium (corrected), phosphate, ALP
- 24h urine calcium + Ca:Cr clearance ratio (exclude FHH)
- 25-OH-D (exclude vitamin D deficiency)
- Creatinine, eGFR (exclude CKD/tertiary HPT)
- Review medications (thiazides → stop and recheck; lithium → stop if safe and recheck)
B. Screen for MEN syndromes (if clinical suspicion or young age, family history, multigland disease):
- Genetic testing for MEN1, RET
- Screen for pituitary tumours (prolactin, IGF-1), pancreatic endocrine tumours, phaeochromocytoma (urinary catecholamines/metanephrines)
C. Screen for complications:
- DEXA at 3 sites: lumbar spine, hip, distal 1/3 radius [3][13]
- Vertebral fracture assessment (lateral spine X-ray or VFA)
- USG kidneys / KUB for nephrolithiasis/nephrocalcinosis [1][13]
- RFT
- ECG
D. If surgery decided → Localization:
- USG neck + Sestamibi scan (first-line) [1][14]
- ± 4D CT, SPECT/CT, MRI if needed
- ± Invasive studies (selective venous sampling, arteriography) for re-operative/difficult cases
5. Investigations for Secondary and Tertiary HPT
| Investigation | Purpose | Key Findings |
|---|---|---|
| Intact PTH | Confirm elevated PTH | Markedly elevated (often > 3–9× ULN in CKD Stage 5) |
| Calcium and phosphate | Assess Ca-PO₄ balance | Ca low/normal; PO₄ elevated |
| 25-OH-D | Assess vitamin D status | Often low in CKD |
| Ca × PO₄ product | Assess metastatic calcification risk | > 4.4 mmol²/L² (or > 55 mg²/dL²) = high risk |
| ALP / Bone-specific ALP | Assess bone turnover | ↑ in high-turnover renal osteodystrophy |
| Hand X-ray | Subperiosteal resorption | Radial aspect of middle phalanges — classic finding |
| Lateral spine X-ray | "Rugger jersey spine" | Alternating sclerotic and lucent bands in vertebral bodies |
| Skull X-ray | "Salt-and-pepper skull" | Diffuse mottled lucencies |
| Bone biopsy (rarely done) | Gold standard for renal osteodystrophy classification | Distinguishes high-turnover (osteitis fibrosa) from low-turnover (adynamic bone) disease |
- Same investigations as secondary HPT PLUS:
- Confirm hypercalcemia (this is what distinguishes it from secondary)
- If post-transplant: confirm the transplant has restored renal function (the persistence of ↑ PTH + ↑ Ca despite normal renal function = tertiary)
- Localization studies (USG + Sestamibi) if parathyroidectomy is planned
| Finding | Where to Look | Significance |
|---|---|---|
| Subperiosteal bone resorption | Hand X-ray — radial aspect of middle phalanges | Pathognomonic of hyperparathyroidism; also distal phalangeal tufts, medial aspect of proximal tibiae, distal clavicles |
| "Salt-and-pepper" skull | Skull X-ray / CT | Diffuse mottled tiny lucencies from trabecular bone resorption |
| "Rugger jersey" spine | Lateral thoracolumbar spine X-ray | Alternating bands of sclerosis (endplates) and lucency (central body) — characteristic of secondary HPT / renal osteodystrophy |
| Brown tumours | Long bones, jaw, pelvis, ribs | Lytic lesions with well-defined margins; can mimic metastases |
| Tapering of distal clavicles | Shoulder X-ray | Resorption of the distal acromial end |
| Bone cysts | Central medullary portions of MCP, ribs, pelvis | Advanced disease [3] |
| Nephrolithiasis / nephrocalcinosis | KUB / USG kidneys | Calcium stones; medullary calcification |
| Chondrocalcinosis | Knee X-ray (most commonly menisci), wrist (triangular fibrocartilage) | Linear calcification in cartilage — think CPPD / pseudogout secondary to HPT |
| Parathyroid adenoma on USG | Posterior to thyroid lobe | Hypoechoic nodule with peripheral vascularity on Doppler [13] |
| Sestamibi: persistent focal uptake | Delayed 2h image | Persistent activity after thyroid washout = hyperfunctioning parathyroid tissue [1][14] |
High Yield Summary — Diagnosis
-
Diagnosis of primary HPT is BIOCHEMICAL: ↑ Ca + ↑/inappropriately normal PTH + normal RFT. PTH must always be interpreted in context of calcium.
-
24h urine calcium is MANDATORY to exclude FHH. Ca:Cr clearance ratio < 0.01 = FHH; > 0.02 = primary HPT.
-
Standard workup: PTH, Ca, PO₄, ALP, 25-OH-D, RFT, 24h urine Ca. Screen complications: DEXA (3 sites including distal 1/3 radius), USG kidneys, ECG.
-
Localization studies (USG + Sestamibi) are NOT diagnostic and do NOT determine the need for surgery. They are performed ONLY after biochemical diagnosis is confirmed and surgery is decided → guide surgical approach.
-
Sestamibi mechanism: accumulates in mitochondria; parathyroid adenomas rich in oxyphilic cells (abundant mitochondria) → slow washout at 2h vs thyroid. False positive: Hurthle cell adenoma. False negative: hyperplasia, small adenomas.
-
Intraoperative PTH (Miami criteria): PTH drops to normal + falls > 50% at 10 min post-excision → confirms successful removal. If NOT met → convert to bilateral exploration.
-
↑ ALP predicts hungry bone syndrome post-parathyroidectomy — high bone turnover means osteoblasts will rapidly sequester calcium after PTH drops.
-
Normocalcemic primary HPT: persistently ↑ PTH with normal Ca after excluding ALL secondary causes (Vit D deficiency, CKD, medications, malabsorption).
Active Recall - Diagnosis of Hyperparathyroidism
References
[1] Senior notes: maxim.md (Primary hyperparathyroidism section) [2] Senior notes: Ryan Ho Chemical Path.pdf (p23, Hypercalcemia section; p25-26, Hypocalcemia and Vitamin D sections) [3] Senior notes: Ryan Ho Endocrine.pdf (p42, Primary Hyperparathyroidism — Dx and Standard Ix) [10] Senior notes: Ryan Ho Fundamentals.pdf (p430-432, Hypercalcemia and Hypocalcemia sections) [13] Senior notes: felixlai.md (Localization studies section, p1016-1025) [14] Senior notes: Ryan Ho Diagnostic Radiology.pdf (p60, Parathyroid Scintigraphy) [15] Senior notes: Ryan Ho Urogenital.pdf (p33, Phosphate homeostasis)
Management of Hyperparathyroidism
The management of hyperparathyroidism depends fundamentally on which type you are dealing with (primary, secondary, or tertiary), whether the patient is symptomatic, and whether they meet criteria for surgical intervention. Surgery is the only curative option for primary HPT, but the decision of when to operate — especially in asymptomatic patients — is one of the most commonly tested topics.
2. Indications for Surgery — Primary HPT
This is one of the highest-yield topics. Surgery (parathyroidectomy) is the only curative treatment for primary HPT with a cure rate of ~95–98% [3].
ALL symptomatic patients should be offered surgery [1][3][13]:
- Symptomatic renal stones / nephrocalcinosis
- Bone disease (pathological fractures, osteitis fibrosa cystica)
- Severe hypercalcemia symptoms (psychic overtones, recurrent pancreatitis, etc.)
- Parathyroid crisis (severe, life-threatening hypercalcemia)
- Parathyroid carcinoma (suspected or confirmed)
The guidelines for operating on asymptomatic patients have been refined through several International Workshops. The most current criteria (5th International Workshop 2022, building on JCEM 2014) [3][13]:
Surgery is indicated if ANY ONE of the following is present:
| Criterion | Threshold | Rationale (Why this criterion) |
|---|---|---|
| Age | *** < 50 years*** | Younger patients have longer lifetime exposure to PTH excess → cumulative bone loss, renal damage, and cardiovascular risk. Also, monitoring compliance over decades is difficult [1][3] |
| Serum calcium | Corrected Ca > 0.25 mmol/L (1 mg/dL) above ULN (i.e., > 2.85 mmol/L if ULN is 2.60) | Higher calcium = higher complication risk. The degree of hypercalcemia correlates with symptom severity and end-organ damage [3][13] |
| Skeletal | DEXA T-score ≤ −2.5 at lumbar spine, total hip, femoral neck, OR distal 1/3 radius; OR vertebral fracture on imaging (XR, CT, MRI, VFA) | Significant bone disease indicates PTH is causing material harm even if the patient feels fine [1][3] |
| Renal | eGFR < 60 mL/min; OR 24h urine Ca > 400 mg/d (10 mmol/d) + ↑ biochemical stone risk; OR nephrolithiasis/nephrocalcinosis on imaging (XR, USG, CT) | Renal complications indicate end-organ damage that will worsen without intervention [1][3][13] |
Mnemonic: CASR for Surgical Criteria in Asymptomatic PHPT
CASR (like the calcium-sensing receptor!) [1]:
- Calcium ≥ 2.8 mmol/L (or > 0.25 above ULN)
- Age < 50
- Skeletal (T-score ≤ −2.5 or vertebral fracture)
- Renal (eGFR < 60 / urine Ca > 10 mmol/d / stones on imaging)
| Indication | Rationale |
|---|---|
| Persistent or recurrent primary HPT | Failed prior surgery → re-exploration needed [13] |
| Familial primary HPT (MEN1, MEN2A) | Multigland disease → surgery planned differently (bilateral exploration, cervical thymectomy) |
| Suspected parathyroid carcinoma | Must perform en-bloc resection (not simple adenoma excision) |
| Parathyroid crisis | Severe hypercalcemia (typically Ca > 3.5 mmol/L) with acute deterioration → medical stabilization then urgent surgery |
| Patient preference | Some informed patients with asymptomatic PHPT who do not meet criteria may still opt for surgery rather than lifelong monitoring |
| Contraindication | Explanation |
|---|---|
| Known contralateral recurrent laryngeal nerve (RLN) injury | If the patient already has a unilateral RLN palsy (e.g., from prior thyroid surgery), operating on the other side risks bilateral RLN injury → bilateral vocal cord paralysis → airway compromise requiring emergent tracheostomy. This is a life-threatening complication [13] |
| Severe comorbidities making patient unfit for GA/surgery | e.g., severe heart failure, advanced malignancy, severe COPD — risks of surgery outweigh benefits |
| Symptomatic cervical disc disease | Relative contraindication — neck extension required during surgery may be poorly tolerated [13] |
| Familial hypocalciuric hypercalcemia (FHH) | Surgical intervention does NOT result in cure because the defect is in the CaSR, not the parathyroid glands. The patient does not have primary HPT [13] |
3. Surgical Treatment Options
This is the preferred approach when localization studies identify a single adenoma:
| Aspect | Detail |
|---|---|
| Indication | Adenoma identified on pre-operative localization studies (concordant USG + Sestamibi) [1] |
| Premise | Based on the fact that ~80–85% of primary HPT is caused by a solitary adenoma [1] |
| Approach | Open with < 3 cm incision, video-assisted, or imaging-guided (gamma probe if Sestamibi given pre-op) [1] |
| Anaesthesia | Can be performed under local/regional anaesthesia (cervical block) or GA |
| Intraoperative PTH monitoring | REQUIRED — takes advantage of PTH's short half-life (~3–5 minutes) [13] |
| Miami criteria | PTH drops > 50% from the highest pre-excision value AND returns to normal range at 10 minutes post-resection [1][3] |
| If Miami criteria NOT met | Suspect multigland disease → convert to bilateral neck exploration [1] |
| Benefits | ↓ operative time, ↓ dissection, ↓ cost, smaller incision, ↓ post-operative hypocalcemia, equal success rate compared with bilateral exploration [13] |
| Cure rate | ~98% [3] |
| Nerve injury rate | *** < 1%*** [3] |
| Aspect | Detail |
|---|---|
| Indications | Conversion from focused parathyroidectomy (Miami criteria not met); MEN1/MEN2A (known multigland disease); uncertain or discordant imaging (e.g., USG not consistent with Sestamibi findings); negative localization studies; suspected double adenomas [1] |
| Approach | Kocher's incision (transverse collar incision in a skin crease ~2 cm above the sternal notch) — the same incision used for thyroidectomy |
| Procedure | All four parathyroid glands are identified and assessed. The strategy depends on the pathology found: |
3.2.1 Options During Bilateral Exploration
a) Subtotal Parathyroidectomy ("3.5 gland resection")
This is the standard approach for multigland hyperplasia (e.g., MEN1, MEN2A, 4-gland hyperplasia):
- 3 glands are completely resected
- Fourth gland: half is excised and sent for frozen section (to confirm it is parathyroid tissue) [1]
- The remaining half-gland is left in situ, with its blood supply preserved
- Marked with non-absorbable sutures to aid identification if re-operation is needed in the future [1]
- Goal: preserve ~50–80 mg of vascularized parathyroid tissue to maintain calcium homeostasis while removing most of the hyperfunctioning tissue
b) Total Parathyroidectomy with Autotransplantation
| Aspect | Detail |
|---|---|
| When used | Rare; primarily in tertiary HPT or severe multigland disease where subtotal resection is insufficient; when renal transplant is highly unlikely |
| Procedure | All 4 glands are removed entirely. Small fragments of parathyroid tissue (~60 mg) are immediately autotransplanted into a muscle pocket |
| Transplant sites | Forearm (brachioradialis muscle) — preferred because it provides easy access for future excision if the graft becomes hyperplastic. Alternatively, neck (sternocleidomastoid muscle) [1] |
| Cryopreservation | Additional parathyroid tissue may be cryopreserved for delayed autotransplantation if the initial graft fails [3] |
| Verification of graft function | After ~6 weeks, a PTH gradient between the transplant arm and the contralateral arm can confirm graft function |
c) Cervical Thymectomy
- Indicated if MEN1 — to resect supernumerary parathyroid glands that may be located within the thymus [1]
- The inferior parathyroid glands embryologically develop from the 3rd pharyngeal pouch along with the thymus → ectopic supernumerary glands are commonly intrathymic
- A transcervical thymectomy (removing the cervical horns of the thymus through the neck incision) is performed at the time of parathyroidectomy
| Aspect | Detail |
|---|---|
| Suspicion clues | Very high Ca ( > 3.5 mmol/L), palpable neck mass, very high PTH ( > 5–10× ULN), hoarseness (RLN invasion) |
| Surgical approach | En-bloc resection: removal of the parathyroid tumour with the ipsilateral thyroid lobe, surrounding soft tissue, and any involved structures. Simple enucleation must be avoided (→ tumour spillage → recurrence) |
| Adjuvant | No proven effective adjuvant therapy (neither RT nor chemo is highly effective). Cinacalcet and denosumab may help control hypercalcemia |
| Prognosis | Variable; 5-year survival ~85% if R0 resection; recurrence is common |
4. Medical Management — Primary HPT
Medical therapy is NOT curative but is used when surgery is contraindicated or declined:
- Surgically unfit patients (severe comorbidities, high anaesthetic risk)
- Patient declines surgery
- Asymptomatic primary HPT not meeting surgical criteria
| Agent | Mechanism | Effect | Indication |
|---|---|---|---|
| Cinacalcet ("calci-mimetic" = "calcium-mimic") | Allosteric agonist of the CaSR → mimics the action of calcium on the receptor → ↓ PTH secretion from parathyroid cells [3][13] | Effective in ↓/normalizing serum Ca; less consistent effect on PTH levels; no proven benefit on BMD [3] | Patients in whom parathyroidectomy is indicated but surgery is contraindicated [3][13] |
| Bisphosphonates (e.g., alendronate) | Inhibit osteoclast-mediated bone resorption by binding to hydroxyapatite in bone → taken up by osteoclasts → induce apoptosis | ↑ BMD (especially at spine and hip); minimal effect on serum Ca | Patients with osteoporosis who cannot undergo surgery |
| Denosumab (RANKL inhibitor) | Monoclonal antibody against RANKL → prevents RANK-RANKL interaction → ↓ osteoclast formation and activity | ↑ BMD; ↓ serum Ca | Alternative to bisphosphonates; useful in renal impairment (bisphosphonates are contraindicated in severe CKD) |
| SERMs (e.g., raloxifene) | Selective estrogen receptor modulators → estrogen-like effects on bone → ↓ bone resorption | ↑ BMD at some sites | Postmenopausal women with primary HPT and osteoporosis |
| HRT (hormone replacement therapy) | Estrogen replacement → ↓ bone resorption | ↑ BMD; modest ↓ serum Ca | Postmenopausal women (limited use due to risk profile) |
Cinacalcet: Important Limitations
Cinacalcet is very effective at lowering calcium, but it does NOT address the underlying bone disease — BMD does not consistently improve. It also does not reduce stone risk or reverse other complications. Therefore, it is a temporizing measure, not a cure. Surgery remains the definitive treatment whenever possible. [3]
Regular monitoring is essential because disease can progress [3]:
| Parameter | Frequency | Purpose |
|---|---|---|
| Serum calcium | Annually | Detect worsening hypercalcemia |
| DEXA at 3 sites | Every 1–2 years (lumbar spine, hip, distal 1/3 radius) | Detect progressive bone loss |
| Vertebral imaging (XR/VFA) | If clinically indicated (height loss, back pain) | Detect subclinical vertebral fractures |
| eGFR/Creatinine | Annually | Detect renal deterioration |
| Renal imaging (USG/XR/CT) | If stones suspected (new flank pain, haematuria) | Detect new nephrolithiasis/nephrocalcinosis |
| 24h urine biochemical stone profile | If stone risk assessment needed | Document hypercalciuria / stone risk |
General advice for conservatively managed patients:
- Adequate hydration (≥ 1.5–2 L/day) — to reduce stone risk and prevent dehydration-related worsening of hypercalcemia
- Avoid dehydration triggers (excess diuretics, hot weather without fluid replacement)
- Moderate calcium intake (~1000 mg/day) — do NOT restrict calcium excessively (paradoxically worsens PTH secretion)
- Correct vitamin D deficiency cautiously (maintain 25-OH-D > 50 nmol/L) — low vitamin D worsens PTH elevation and bone disease
- Avoid thiazides (reduce renal calcium excretion → worsen hypercalcemia)
- Avoid lithium if possible (shifts CaSR set point)
When a patient presents with severe hypercalcemia (typically Ca > 3.5 mmol/L) — often called hypercalcemic crisis — this is a medical emergency requiring rapid treatment before definitive surgery [3b]:
Aims: (1) rapid control of severe hypercalcemia, (2) early diagnosis of cause [3b]
Step-by-Step Emergency Management:
| Step | Treatment | Mechanism | Details |
|---|---|---|---|
| 1. Remove precipitants | Stop offending drugs | Remove exacerbating factors | Calcium supplements, vitamin D, thiazides, lithium, ranitidine [3b] |
| 2. Volume resuscitation | Normal saline (NS) rehydration at 100–500 mL/h | Restores intravascular volume → ↑ GFR → ↑ renal calcium excretion. In the PCT and loop of Henle, Na and Ca reabsorption are coupled — rehydration ↓ Na reabsorption → ↓ Ca reabsorption [3b] | Target euvolemia (estimated 3–4 L/day). Guided by urine output and CVP. Most hypercalcemic patients are severely dehydrated from polyuria + poor oral intake |
| 3. Loop diuretic | Furosemide 20–40 mg IV Q4–12h | ↑ urinary calcium excretion by blocking the Na-K-2Cl cotransporter in the loop of Henle → ↓ lumen-positive voltage → ↓ paracellular Ca reabsorption | ONLY after adequate rehydration — giving loop diuretics to a dehydrated patient worsens volume depletion and can precipitate renal failure [3b]. Monitor UO (~200 mL/h target), Na, K, Ca, Mg |
| 4. Bisphosphonate | IV pamidronate 30–90 mg in 250–500 mL NS over 4–6h; OR IV zoledronate 4 mg over 15 min | ↓ osteoclast-mediated bone resorption → ↓ calcium release from bone | Pamidronate: max effect in several days; do NOT repeat before 7 days. Zoledronate: max effect at 72h [3b]. Caution in renal impairment: pamidronate C/I if eGFR < 30, renal dose adjustment if eGFR < 60 |
| 5. Calcitonin | Salmon calcitonin 4 U/kg IM/SC Q12h | ↓ osteoclast activity + ↑ renal Ca excretion → ↓ serum Ca | Rapid onset (2–3 hours) — bridges the gap while waiting for bisphosphonate to take effect. BUT tachyphylaxis develops within 2–3 days → effect wanes [3b]. Given together with bisphosphonate initially |
| 6. Other agents | Denosumab (if renal impairment precludes bisphosphonates); Cinacalcet (calcimimetic); Corticosteroids (hydrocortisone 50 mg IV Q8h) for granulomatous disease / lymphoma / vitamin D intoxication; Haemodialysis with zero/low-Ca dialysate as last resort [3b] | Various mechanisms | Denosumab especially useful in CKD (does not require renal clearance). Corticosteroids: onset 3–5 days, reduce 1α-hydroxylase activity in granulomas |
| Pamidronate | Calcitonin | |
|---|---|---|
| Action | More potent, commonly used. Slow onset (days). Do NOT repeat before 7 days. Long-lasting effect (~2–4 weeks [3b] | Rapid onset (2–3h). Tachyphylaxis in 2–3 days → given together with bisphosphonate initially [3b] |
| Precaution | ↓ eGFR: C/I if < 30, renal dosing if < 60 [3b] | Minimal renal concerns |
The goal is to treat the underlying cause and suppress PTH to an appropriate range while avoiding complications of over-treatment (adynamic bone disease):
6.1 Stepwise Approach (KDIGO Guidelines)
| Step | Intervention | Mechanism | Target |
|---|---|---|---|
| 1. Phosphate control | Low phosphate diet (800–1000 mg/day); Phosphate binders with meals (e.g., calcium carbonate/acetate, sevelamer, lanthanum) | ↓ gut PO₄ absorption → ↓ serum PO₄ → removes stimulus for PTH secretion + ↓ Ca×PO₄ product → ↓ metastatic calcification | Serum PO₄ toward normal range |
| 2. Vitamin D supplementation | Nutritional vitamin D (cholecalciferol/ergocalciferol) if 25-OH-D < 30 ng/mL; Active vitamin D (calcitriol or alfacalcidol) in advanced CKD | Nutritional vit D: replenish substrate. Active vit D: bypasses impaired 1α-hydroxylase → ↑ Ca absorption, direct suppression of PTH gene transcription | 25-OH-D > 30 ng/mL; PTH in target range for CKD stage |
| 3. Calcimimetics | Cinacalcet | Allosteric CaSR agonist → ↓ PTH secretion | CKD 3–5D with PTH above target despite phosphate control and vitamin D |
| 4. Dialysis optimization | Appropriate dialysate Ca concentration | Adjust Ca influx/efflux during dialysis | Avoid hypercalcemia and hypocalcemia |
| 5. Surgery (if refractory) | Subtotal parathyroidectomy or total parathyroidectomy with autotransplantation | Remove autonomously hyperplastic glands | Indicated when medical therapy fails (severe, refractory HPT with progressive bone disease, calciphylaxis, or intractable symptoms) |
7. Management of Tertiary Hyperparathyroidism
Definition: persistent autonomous hypercalcemic hyperparathyroidism after renal replacement therapy [1]
- Persistent severe hypercalcemia
- Impaired graft function (in post-transplant patients — hypercalcemia can damage the transplanted kidney)
- Progressive symptoms (e.g., osteoporotic fractures, nephrolithiasis in transplanted kidney, calciphylaxis)
| Procedure | When to Use | Details |
|---|---|---|
| Total parathyroidectomy | Only when renal transplant is highly unlikely (i.e., patient will remain on dialysis indefinitely) | Removes all glands → patient becomes permanently hypoparathyroid → requires lifelong calcium and vitamin D |
| Total parathyroidectomy with autotransplantation | Standard approach | All glands removed; parathyroid fragments transplanted to forearm (brachioradialis) or neck (SCM) for easy access if future regrowth [1] |
| Subtotal parathyroidectomy ("3.5 resection") | Alternative approach | Same as for primary HPT multigland disease — 3 glands removed, half of 4th preserved in situ |
- Cinacalcet: can reduce calcium while awaiting surgery or in non-surgical candidates
- Bisphosphonates: if significant bone disease (but caution with renal function)
8. Post-operative Management and Monitoring
| Action | Timing | Rationale |
|---|---|---|
| Check serum calcium | Post-op Day 1 (and serially Q6–12h if high-risk for hungry bone syndrome) [1] | Detect post-op hypocalcemia — the most common early complication |
| Monitor for hypocalcemia symptoms | Continuous for 24–48h | Perioral tingling, paraesthesia, Trousseau/Chvostek signs, tetany |
| Check Mg and PO₄ | Post-op Day 1 | May also drop in hungry bone syndrome |
| Voice assessment | Post-op and before discharge | Screen for RLN injury → hoarseness |
| Neck observation | First 6–12h | Reactionary haemorrhage → neck haematoma → airway compromise |
| Severity | Treatment |
|---|---|
| Mild / asymptomatic | Oral calcium carbonate (1–3 g/day in divided doses) ± oral calcitriol (0.25–0.5 μg BD) |
| Symptomatic (tetany, prolonged QTc) | IV calcium gluconate 10–20 mL of 10% solution over 10 minutes (slow bolus) [13b], followed by continuous infusion if needed. Switch to oral when stable |
| Hungry bone syndrome | Severe and prolonged hypocalcemia despite normal/elevated PTH → aggressive IV and oral calcium + calcitriol + magnesium. May require high-dose calcium for weeks. Predicted by pre-op ↑ ALP [1] |
Hungry Bone Syndrome — Understanding the Mechanism
Hungry bone syndrome = severe and prolonged hypocalcemia despite normal or even elevated levels of PTH [13b]. It is exacerbated by suppressed remaining PTH levels and associated with hypophosphatemia and hypomagnesemia [13b].
Pathogenesis: After parathyroidectomy, the sudden removal of high circulating PTH causes the previously over-stimulated osteoclasts to cease resorbing bone. However, osteoblasts — which had been activated by chronic PTH — continue to form bone avidly. This creates a massive net influx of calcium, phosphate, and magnesium into the "hungry" skeleton. The result is profound, prolonged hypocalcemia that can be life-threatening.
Risk factors: Pre-op ↑ ALP (indicates high bone turnover), large adenoma, severe/prolonged hyperparathyroidism, older age, vitamin D deficiency. [1][13b]
| Complication / Outcome | Definition | Management |
|---|---|---|
| Cure | Normocalcemia for > 6 months post-op | Routine follow-up; may discharge if stable |
| Persistent hyperparathyroidism | Hypercalcemia < 6 months post-op | Due to missed pathology at initial surgery → re-localization studies → bilateral neck exploration [1] |
| Recurrent hyperparathyroidism | Hypercalcemia > 6 months post-op (after initial normocalcemia) | Due to missed pathology, regrowth of remnant, or parathyromatosis (disseminated parathyroid tissue in the neck/mediastinum soft tissues from rupture of parathyroid gland during the initial operation) → Sestamibi scan → bilateral exploration [1] |
| Permanent hypoparathyroidism | Requiring calcium/vitamin D supplementation ≥ 1 year post-op [1] | Lifelong oral calcium + calcitriol. Monitor for complications (nephrocalcinosis from calcitriol, cataracts, basal ganglia calcification) |
9. Special Situations
- Primary HPT in pregnancy can cause neonatal hypocalcemia (maternal hypercalcemia suppresses fetal parathyroids) and other complications (miscarriage, pre-eclampsia)
- Mild: conservative management with hydration and monitoring
- Severe or symptomatic: surgery in the 2nd trimester (safest period for anaesthesia)
- Bisphosphonates, cinacalcet, and calcitonin are generally avoided or used with extreme caution
- Lithium causes hyperparathyroidism and hypercalcemia by shifting the CaSR set point [16]
- First step: if clinically safe, stop lithium and re-evaluate calcium/PTH after washout
- If hypercalcemia persists after lithium cessation → true primary HPT has developed (lithium may have triggered adenoma formation)
- If lithium cannot be discontinued → manage as primary HPT; cinacalcet can be used as a bridge; surgery if criteria met
- Correction of underlying hyperparathyroidism is part of the management of CPPD disease [5]
- However, existing chondrocalcinosis may not resolve after parathyroidectomy
- Acute pseudogout attacks: manage as per standard CPPD guidelines (joint aspiration, intra-articular steroids, NSAIDs, colchicine)
| Primary HPT | Secondary HPT | Tertiary HPT | |
|---|---|---|---|
| Definitive Rx | Parathyroidectomy | Treat underlying cause (CKD management, vitamin D) | Parathyroidectomy |
| Surgical approach | Focused PTx (single adenoma) or BCE (multigland) | Surgery only if refractory | Subtotal PTx or Total PTx + autotransplant |
| Medical Rx | Cinacalcet, bisphosphonates (if unfit for surgery) | Phosphate binders, vitamin D, cinacalcet, dialysis | Cinacalcet (temporizing) |
| Monitoring (if conservative) | Annual Ca, DEXA Q1–2y, annual eGFR, renal imaging PRN | Per KDIGO guidelines (frequent PTH, Ca, PO₄, vitamin D) | Usually proceed to surgery |
High Yield Summary — Management
-
Surgery is the ONLY cure for primary HPT. Cure rate ~95–98%.
-
All symptomatic patients should undergo parathyroidectomy.
-
Asymptomatic PHPT surgical criteria (CASR mnemonic): Ca ≥ 2.85 (> 0.25 above ULN); Age < 50; Skeletal (T-score ≤ −2.5 or vertebral fracture); Renal (eGFR < 60, urine Ca > 400 mg/d, or stones/nephrocalcinosis on imaging). Any ONE criterion met = operate.
-
Focused parathyroidectomy: for localized single adenoma. Requires pre-op localization (USG + Sestamibi) + intraoperative PTH (Miami criteria: > 50% drop + normalize at 10 min). If criteria not met → convert to bilateral exploration.
-
Bilateral exploration: for MEN syndromes, discordant imaging, multigland disease. Subtotal (3.5 gland) or total parathyroidectomy ± autotransplantation.
-
Cervical thymectomy: add for MEN1 (supernumerary intrathymic glands).
-
Medical options (if surgery C/I): cinacalcet (↓ Ca but no BMD benefit), bisphosphonates/denosumab (↑ BMD), SERMs.
-
Contraindications to surgery: contralateral RLN injury, FHH, surgically unfit.
-
Post-op: Check Ca on Day 1. Watch for hungry bone syndrome (predicted by ↑ pre-op ALP) — treat with aggressive Ca + calcitriol + Mg. Permanent hypoparathyroidism = needing supplements ≥ 1 year.
-
Severe hypercalcemia emergency: Rehydrate (NS) → loop diuretic (AFTER rehydration) → calcitonin (rapid, tachyphylaxis in 2–3d) + bisphosphonate (slow onset, lasts weeks) → cinacalcet/denosumab/steroids/dialysis for refractory cases.
Active Recall - Management of Hyperparathyroidism
References
[1] Senior notes: maxim.md (Primary hyperparathyroidism — Management section; Tertiary hyperparathyroidism section) [3] Senior notes: Ryan Ho Endocrine.pdf (p42-43, Primary Hyperparathyroidism — Surgical treatment, Conservative Tx) [3b] Senior notes: Ryan Ho Endocrine.pdf (p41, Management of Severe Hypercalcemia) [5] Senior notes: Ryan Ho Rheumatology.pdf (p42, CPPD Disease — Management) [13] Senior notes: felixlai.md (Treatment section, p1021-1025; Localization studies, p1016-1020) [13b] Senior notes: felixlai.md (Hungry bone syndrome, p1011) [16] Senior notes: Ryan Ho Psychiatry.pdf (p53, Lithium — Unwanted effects, Hyperparathyroidism)
Complications of Hyperparathyroidism
Complications of hyperparathyroidism fall into two broad categories that you must understand:
- Complications of the disease itself (from chronic hypercalcemia and excess PTH) — these are the reasons we treat hyperparathyroidism in the first place
- Complications of the treatment (surgical complications of parathyroidectomy) — these are what we discuss in informed consent and monitor for post-operatively
I'll cover both systematically, explaining the mechanism from first principles for each.
1. Complications of the Disease — Primary Hyperparathyroidism
These are the end-organ consequences of chronic hypercalcemia and PTH excess. They map onto the classic "stones, bones, moans, thrones, psychic overtones" mnemonic but go deeper.
| Complication | Prevalence | Pathophysiology | Clinical Significance |
|---|---|---|---|
| Nephrolithiasis | ~15–20% of primary HPT patients | Despite PTH increasing tubular Ca reabsorption, the filtered load of calcium is so high (from hypercalcemia) that net urinary calcium excretion is elevated (hypercalciuria). This supersaturates the urine with calcium → calcium oxalate and calcium phosphate stone crystallization. The alkaline urine pH from bicarbonate retention in the PCT also favours calcium phosphate precipitation | Renal stones are the most common symptomatic complication of primary HPT. Recurrent calcium stones, especially calcium phosphate stones, should prompt screening for HPT [3][13] |
| Nephrocalcinosis | Less common than stones | Diffuse deposition of calcium salts within the renal parenchyma (medullary > cortical). The renal medulla has a concentrated, alkaline environment that favours calcium precipitation. Chronic hypercalciuria → gradual interstitial calcium deposition | Visible on USG/CT as medullary calcification. Progressive → renal damage |
| Chronic kidney disease | Variable | Multiple mechanisms: (1) Chronic hypercalcemia → renal vasoconstriction (Ca²⁺ contracts afferent arteriolar smooth muscle → ↓ GFR); (2) nephrocalcinosis → interstitial nephritis and tubular damage; (3) obstructive uropathy from stones; (4) direct tubulotoxicity of calcium | eGFR < 60 is a surgical indication even in asymptomatic patients [3] |
| Nephrogenic diabetes insipidus | Very common (subclinical) | Hypercalcemia inhibits adenylyl cyclase in the collecting duct → ↓ cAMP → ↓ aquaporin-2 insertion → inability to concentrate urine | Presents as polyuria and polydipsia. Contributes to dehydration, which worsens hypercalcemia (a vicious cycle) |
| Renal tubular dysfunction | Variable | Direct tubulotoxic effects of hypercalcemia and PTH on renal tubular cells | May manifest as Type 1 (distal) RTA → metabolic acidosis → further stone risk [3] |
The Hypercalcemia-Dehydration Vicious Cycle
Hypercalcemia → nephrogenic DI → polyuria → dehydration → haemoconcentration → worsening hypercalcemia → more polyuria. This is why patients with primary HPT often present with dehydration, and why aggressive IV hydration is the first-line emergency treatment for severe hypercalcemia. Breaking this cycle is essential.
| Complication | Pathophysiology | Key Features |
|---|---|---|
| Osteoporosis / Osteopenia | Continuously ↑ PTH → cortical > trabecular bone resorption [3]. Chronic PTH stimulates osteoclasts → sustained net bone resorption → demineralization | ↓ BMD more pronounced at cortical sites (forearm, hip) than trabecular sites (spine) [3]. 2–3× increased risk of vertebral, distal forearm, and pelvic fractures [3] |
| Osteitis fibrosa cystica | The classical bone lesion of primary HPT (now uncommon in developed countries due to early detection) [3]. Intense focal osteoclast activity → bone resorption → replacement by fibrous tissue and hemosiderin-laden macrophages | Components: Brown tumours (in jaw, long bones, ribs — osteoclastic aggregations with fibrous tissue, brown because of hemosiderin [3]); Subperiosteal bone resorption (radial aspect of middle phalanges); Bone cysts (medullary MCP, ribs, pelvis); Salt-and-pepper skull; Tapering of distal clavicles [3][13] |
| Pathological fractures | Severely weakened bone from demineralization → fracture with minimal or no trauma | 2–3× risk particularly vertebral compression fractures, distal forearm (Colles'), and pelvic fractures [3] |
| Bone pain and deformity | Microfractures, periosteal stretching from resorption, and deformity from weakened bone architecture | More prominent in severe/longstanding disease; bowing of long bones possible in extreme cases |
Bone involvement is detected by DEXA (bone densitometry) at the forearm, hip, and spine [13]. Osteoporosis (T-score ≤ −2.5) is an indication for surgery even in asymptomatic patients.
| Complication | Pathophysiology | Notes |
|---|---|---|
| Constipation | Hypercalcemia raises the threshold for smooth muscle depolarization → decreased GI motility → slowed transit time | Very common; often the symptom that prompts investigation |
| Anorexia, nausea, vomiting | (1) Hypercalcemia stimulates the chemoreceptor trigger zone in the area postrema; (2) Direct smooth muscle depression → gastric atony; (3) ↑ gastrin secretion → ↑ HCl → gastric irritation | Can contribute to dehydration and weight loss |
| Peptic ulcer disease / Dyspepsia | Hypercalcemia stimulates gastrin release from G-cells → ↑ gastric acid secretion → mucosal damage. Additionally, in MEN1, a concurrent gastrinoma (Zollinger-Ellison syndrome) may be present | Part of MEN1 screen: multiple/refractory peptic ulcers + HPT → think gastrinoma [3] |
| Acute pancreatitis | Mechanism debated but includes: (1) Intrapancreatic calcium deposition in ducts → obstruction; (2) Premature intracellular activation of trypsinogen by excess calcium → autodigestion; (3) Direct calcium toxicity to acinar cells | Uncommon but serious. Hypercalcemia is a recognized metabolic cause of pancreatitis (think "GET SMASHED" mnemonic — the "H" includes Hypercalcemia/Hyperparathyroidism) |
| Abdominal pain | Combination of constipation, PUD, pancreatitis, and direct smooth muscle effects | Generalized or epigastric |
| Complication | Pathophysiology | Clinical Features |
|---|---|---|
| Fatigue and weakness | Hypercalcemia depresses neuromuscular excitability (raises the threshold potential for neuronal and muscle cell depolarization) | Often the earliest symptom; may be dismissed as "getting old" |
| Depression and anxiety | Direct CNS effects of calcium on neuronal signalling — calcium is a key intracellular second messenger; excess extracellular Ca²⁺ disrupts synaptic transmission and neurotransmitter release | May be the presenting complaint; can improve after parathyroidectomy |
| Cognitive impairment | Impaired hippocampal and cortical neuronal function from chronic hypercalcemia | Memory loss, difficulty concentrating, "brain fog" |
| Confusion → drowsiness → coma | Progressive CNS depression with worsening hypercalcemia | Severe hypercalcemia ( > 3.5 mmol/L) = medical emergency |
| Psychosis | Rarely, severe hypercalcemia causes frank psychotic symptoms | Important differential in new-onset psychosis — always check calcium |
| Complication | Pathophysiology | Clinical Significance |
|---|---|---|
| Hypertension | Multiple mechanisms: (1) ↑ intracellular Ca²⁺ in vascular smooth muscle → vasoconstriction; (2) ↑ RAAS activity; (3) Vascular remodelling and stiffening | Present in 40–60% of primary HPT patients. HPT is a recognized secondary cause of hypertension [6]. May not fully reverse after surgery |
| LVH (left ventricular hypertrophy) | Consequence of chronic hypertension + direct trophic effect of PTH and calcium on cardiomyocytes | ↑ cardiovascular mortality risk [3] |
| Arrhythmias | Hypercalcemia shortens the cardiac action potential (accelerates phase 2 repolarization) → shortened QT interval. At very high levels, conduction abnormalities and fatal arrhythmias can occur | ECG: shortened QT interval. Severe hypercalcemia → bradycardia, heart block, cardiac arrest |
| Intimal/vascular calcification | Chronic elevated Ca × PO₄ product → ectopic calcium deposition in vessel walls | ↑ arterial stiffness → further hypertension; ↑ cardiovascular event risk [3] |
| Complication | Pathophysiology | Notes |
|---|---|---|
| Chondrocalcinosis / CPPD disease / Pseudogout | Hyperparathyroidism is a metabolic cause of CPPD crystal deposition. PTH excess → abnormal pyrophosphate metabolism; elevated calcium + pyrophosphate → calcium pyrophosphate dihydrate crystal formation in cartilage | HPT carries 3.35× risk of CPPD [5]. Joint pain from pseudogout and secondary arthritis [3]. Screen for HPT in younger patients with chondrocalcinosis |
| Gout | Some association, possibly through altered renal urate handling in the setting of HPT-related renal dysfunction | Less well-established than CPPD association |
| Proximal myopathy | Hypercalcemia impairs neuromuscular junction function and muscle contractility | Difficulty rising from chairs, climbing stairs |
This is the most acute and life-threatening complication of primary HPT:
| Feature | Detail |
|---|---|
| Definition | Acute, severe hypercalcemia (typically Ca > 3.5 mmol/L) with multi-organ dysfunction |
| Triggers | Dehydration (intercurrent illness, vomiting, reduced fluid intake), thiazide diuretics, immobilization, concurrent illness |
| Presentation | Profound dehydration, confusion → stupor → coma, severe abdominal pain (pancreatitis, ileus), cardiac arrhythmias, oliguria/anuria |
| Mortality | Can be fatal if untreated |
| Management | Emergency medical treatment (NS rehydration → loop diuretic → calcitonin + bisphosphonate → cinacalcet/denosumab/dialysis) followed by urgent parathyroidectomy once stabilized |
These are additional complications specific to the CKD context:
| Complication | Pathophysiology | Clinical Features |
|---|---|---|
| Renal osteodystrophy | Spectrum of bone disease in CKD: high-turnover (osteitis fibrosa from ↑ PTH), low-turnover (adynamic bone from over-suppression of PTH), mixed, and osteomalacia (from vitamin D deficiency) | Bone pain, fractures, deformity. "Rugger-jersey spine" on X-ray (alternating sclerotic/lucent bands in vertebral bodies) [13] |
| Vascular calcification | Chronic hyperphosphatemia + elevated Ca × PO₄ product → hydroxyapatite deposition in vessel walls (medial calcification) and cardiac valves | ↑↑ cardiovascular mortality in CKD patients. Coronary artery calcification, peripheral arterial calcification, valvular calcification |
| Calciphylaxis (calcific uraemic arteriolopathy) | Calcification of small dermal and subcutaneous arterioles → thrombotic occlusion → ischaemic skin necrosis | Extremely painful violaceous patches → livedo reticularis → black necrotic eschar. Very high mortality (~60–80%). Risk factors: obesity, diabetes, warfarin use, high Ca × PO₄ product |
| Soft tissue / metastatic calcification | Ca × PO₄ product supersaturation → calcium deposition in periarticular tissues, conjunctiva, cornea (band keratopathy), lungs, myocardium | Pruritus (skin calcification), red eyes (conjunctival calcification), tumoral calcinosis (periarticular deposits) |
| Growth retardation (in children) | Disrupted skeletal metabolism from renal osteodystrophy + metabolic acidosis + nutritional deficiencies | Important in paediatric CKD patients |
3. Complications of Treatment — Surgical Complications of Parathyroidectomy
Parathyroidectomy shares many complications with thyroidectomy because of the anatomical proximity. The complications can be organized by timing:
| Complication | Mechanism | Management |
|---|---|---|
| Intraoperative bleeding | Injury to thyroid vessels (superior/inferior thyroid arteries), parathyroid feeding vessels, or adjacent cervical veins | Direct haemostasis; usually controlled intraoperatively |
| Reactionary haemorrhage → Neck haematoma | Post-operative bleeding (usually from a ligated vessel) → haematoma in the paratracheal space → venous obstruction → acute laryngeal oedema → airway compromise [1][3c] | Emergency bedside management: cut subcuticular stitches and stitches holding strap muscles to evacuate blood → call seniors for intubation [3c]. This is a surgical airway emergency — if not decompressed urgently, the patient can asphyxiate |
| Oesophageal injury | Rare; from overly aggressive dissection posteriorly | Repair if identified; can cause mediastinitis if missed |
| Tracheal injury | Very rare | Repair |
Neck Haematoma: A Life-Threatening Emergency
A tense, firm, immobile neck swelling with progressive dyspnoea after parathyroidectomy = haematoma compressing the airway. The first action is NOT to call for intubation — it is to OPEN THE WOUND at the bedside by cutting the skin sutures and strap muscle stitches to evacuate the blood and decompress the airway. Only then attempt definitive airway management. Every surgical ward should have a stitch cutter/clip remover at the bedside of post-thyroid/parathyroid surgery patients. [3c]
| Complication | Incidence | Mechanism | Details |
|---|---|---|---|
| Recurrent laryngeal nerve (RLN) injury | *** < 1% in experienced hands*** [3] | The RLN runs in close proximity to the parathyroid glands (between the trachea and oesophagus, often within the tracheo-oesophageal groove). It can be injured by traction, cautery, or transection during dissection | Unilateral RLN injury: ipsilateral vocal cord paralysis → hoarseness, ineffective cough, breathy voice, ↑ risk of aspiration pneumonia [13b][1b]. Bilateral RLN injury: bilateral vocal cord paralysis → stridor, dyspnoea, airway obstruction (the cords remain in the midline/adducted position) → may require emergency re-intubation ± tracheostomy [1b]. Can be transient (traction neuropraxia) or permanent (transection) |
| External branch of the superior laryngeal nerve (EBSLN) injury | Uncommon in parathyroidectomy (more relevant in thyroidectomy) | EBSLN supplies the cricothyroid muscle which tenses the vocal cord for high-pitched sounds | Loss of high pitch, vocal fatigue, poor volume [1b]. Important to ask pre-operatively if the patient is a professional singer or voice user |
| Hypocalcemia (most common complication overall) | Transient: 10–20%; Permanent: 1–4% | Multiple mechanisms depending on the surgical context — see below | Routinely check serum calcium on post-op Day 1 [1] |
| Wound infection | Very rare (clean surgical field) | Standard surgical wound infection | Not considered a significant complication of clean neck surgery [1b] |
Mechanisms of Post-operative Hypocalcemia:
This is the MOST common complication of parathyroidectomy and deserves detailed understanding [1b][13b]:
| Mechanism | Context | Duration | Explanation |
|---|---|---|---|
| Transient suppression of remaining normal glands | After focused parathyroidectomy for a single adenoma | Transient (days to weeks) | The autonomous adenoma was suppressing the remaining normal glands via negative feedback (high calcium from the adenoma → the other 3 glands atrophy/become quiescent). After adenoma removal, PTH drops, and the remaining glands take time to "wake up" and resume normal function [1] |
| Hungry bone syndrome | After removal of large adenoma or longstanding/severe HPT | Prolonged (weeks to months) | Sudden removal of high circulating PTH → osteoclasts cease resorbing, but osteoblasts (previously stimulated by chronic PTH) continue avidly forming bone → massive net calcium, phosphate, and magnesium influx into the "hungry" skeleton [1][13b]. Defined as severe and prolonged hypocalcemia despite normal or elevated PTH + hypophosphatemia + hypomagnesemia [13b] |
| Devascularization of remaining glands | After bilateral exploration / subtotal PTx | Can be transient or permanent | Inadvertent damage to the blood supply (inferior thyroid artery branches) of the remaining parathyroid tissue → ischaemic injury → temporary or permanent hypofunction |
| Permanent hypoparathyroidism | After extensive surgery (total PTx, cancer surgery) | Permanent: defined as requiring calcium/vitamin D supplementation ≥ 1 year post-op [1] | Complete loss of functional parathyroid tissue → lifelong dependence on calcium and calcitriol replacement |
Clinical features of post-operative hypocalcemia:
- Perioral numbness (earliest symptom — the circumoral region is the most sensitive to hypocalcemia) [1b]
- Acral paraesthesia (tingling in fingers and toes)
- Carpopedal spasm (painful flexion of wrists and feet)
- Chvostek's sign: tapping over the facial nerve (anterior to the ear) → ipsilateral facial muscle twitching
- Trousseau's sign: inflating a BP cuff above systolic for 3 minutes → carpal spasm (more specific than Chvostek's)
- Severe: laryngospasm → can require emergency intubation / surgical airway [1b] — this is the most dangerous manifestation
- Seizures (in extreme cases)
Management of post-operative hypocalcemia [13b]:
- Acute/severe (symptomatic, laryngospasm): IV 10–20 mL of 10% calcium gluconate over 10 minutes (slow bolus) [13b]
- Replacement: Oral calcium carbonate + calcitriol (1,25-(OH)₂D₃) [13b]
- For hungry bone syndrome: aggressive high-dose oral/IV calcium + calcitriol + magnesium replacement; may require weeks of supplementation
Risk factor for hungry bone syndrome: Pre-operative ↑ ALP predicts risk of hungry bone syndrome [1] — because high ALP = high bone turnover = lots of active osteoblasts ready to sequester calcium once PTH drops.
| Complication | Definition / Timing | Mechanism | Management |
|---|---|---|---|
| Persistent hyperparathyroidism | Hypercalcemia persisting < 6 months post-op [1] | Due to missed pathology at the initial surgery — unidentified second adenoma, unrecognized multigland disease, ectopic gland not found | Re-localization studies (Sestamibi, 4D CT) → bilateral neck exploration (BCE) [1] |
| Recurrent hyperparathyroidism | Hypercalcemia recurring > 6 months post-op (after a period of initial normocalcemia) [1] | Several mechanisms: (1) Missed pathology (as above); (2) Parathyromatosis — disseminated parathyroid tissue within the soft tissue of the neck and mediastinum due to rupture of a parathyroid gland during the initial operation → these tissue fragments become hyperfunctioning [1]; (3) Regrowth of a parathyroid remnant (in subtotal PTx) | Re-localization (Sestamibi scan) → BCE [1]. Parathyromatosis is very difficult to cure because the tissue is widely scattered |
| Permanent hypoparathyroidism | Requiring calcium/vitamin D supplementation ≥ 1 year post-op [1] | Insufficient remaining parathyroid tissue (removed, devascularized, or autograft failure) | Lifelong oral calcium + calcitriol. Long-term monitoring for complications: nephrocalcinosis (from calcitriol therapy → hypercalciuria without PTH to reabsorb calcium), cataracts, basal ganglia calcification. Recombinant PTH (teriparatide) or PTH(1-84) may be considered in refractory cases |
| Hypertrophic scar / Keloid | Months post-op | Abnormal wound healing, especially in predisposed individuals (younger patients, darker skin types) | Prevention: meticulous wound closure in skin crease (Kocher's incision). Treatment: silicone sheets, steroid injections, laser therapy |
Persistent vs Recurrent HPT: The 6-Month Rule
This distinction matters because the cause and approach differ:
- Persistent ( < 6 months): the operation didn't work → something was missed → usually need bilateral exploration.
- Recurrent ( > 6 months): the operation initially worked (normocalcemia achieved) but the disease came back → could be regrowth of remnant, or parathyromatosis from gland rupture during the initial surgery. Both require careful re-localization before re-operation. [1]
In addition to the general surgical complications above, tertiary HPT surgery has specific considerations:
| Complication | Detail |
|---|---|
| Profound post-operative hypocalcemia | Even more severe and prolonged than in primary HPT surgery because the bone disease is more advanced (years of secondary/tertiary HPT → severe osteopenia → extreme hungry bone syndrome). May require prolonged IV calcium infusion |
| Autograft failure | After total parathyroidectomy with autotransplantation, the transplanted parathyroid tissue in the forearm may fail to engraft → permanent hypoparathyroidism. Cryopreserved tissue can be used for delayed autotransplantation |
| Graft-dependent recurrence | The autograft in the forearm can undergo hyperplasia and become autonomously hyperfunctioning → recurrent HPT. Advantage of forearm transplantation: easy surgical access for partial graft excision under local anaesthesia [1] |
| Impact on renal transplant | In post-transplant patients, persistent severe hypercalcemia can damage the transplanted kidney → graft dysfunction. This is a key indication for parathyroidectomy in tertiary HPT |
This is a classic exam scenario: a patient becomes acutely dyspnoeic after parathyroidectomy (or thyroidectomy). The differential is crucial [1b]:
| Cause | Mechanism | Key Features | Immediate Action |
|---|---|---|---|
| Haemorrhage / Neck haematoma | Bleeding → paratracheal haematoma → venous obstruction → laryngeal oedema | Tense, firm, immobile neck swelling; hypovolaemic shock | Open wound at bedside (cut stitches) → evacuate blood → call for intubation |
| Bilateral RLN injury | Both recurrent laryngeal nerves damaged → bilateral vocal cord paralysis (cords in midline/adducted position) → airway obstruction | Stridor, inability to phonate, onset immediately upon extubation | Re-intubation → tracheostomy if persistent |
| Laryngospasm from hypocalcemia | Severe post-op hypocalcemia → neuromuscular hyperexcitability → spasm of laryngeal muscles | Usually occurs 12–72h post-op; associated with perioral/acral paraesthesia, Trousseau/Chvostek signs | IV calcium gluconate STAT → resolve spasm → intubation if refractory |
| Tracheal injury / Pneumothorax | Intraoperative tracheal or pleural injury (rare) | Subcutaneous emphysema, tracheal air leak, respiratory distress | Chest drain if pneumothorax; tracheal repair |
| Tracheomalacia | Degeneration of tracheal cartilage from chronic compression by a large goitre (more relevant to thyroidectomy for massive goitres) → floppy tracheal wall → collapse after external support removed | Stridor worsening with inspiration | Positive pressure ventilation → tracheostomy if severe |
| System | Complication | Consequence |
|---|---|---|
| Cardiovascular | Accelerated atherosclerosis, vascular calcification, LVH | ↑ cardiovascular mortality (particularly in secondary/tertiary HPT in CKD) |
| Renal | Progressive CKD from nephrocalcinosis and recurrent stones | May eventually require dialysis |
| Skeletal | Progressive osteoporosis → fragility fractures → disability | Loss of independence, chronic pain |
| Quality of life | Chronic fatigue, depression, cognitive impairment | Often underappreciated; can significantly improve after surgery |
| Malignancy risk | Some studies suggest a modestly ↑ risk of certain cancers (breast, colon, kidney) in primary HPT, though causality is not established | Under investigation; not currently a surgical indication |
| Category | Complication | Mechanism | Key Management Point |
|---|---|---|---|
| Disease — Renal | Nephrolithiasis, nephrocalcinosis, CKD, nephrogenic DI | Hypercalciuria, renal vasoconstriction, tubulotoxicity | Surgical indication if stones/eGFR < 60 |
| Disease — Bone | Osteoporosis, osteitis fibrosa cystica, fractures | ↑ PTH → cortical bone resorption | Surgical indication if T-score ≤ −2.5 |
| Disease — GI | Constipation, PUD, pancreatitis | Smooth muscle depression, ↑ gastrin, Ca-mediated trypsinogen activation | Treat HPT; PPI for PUD |
| Disease — Neuro | Depression, confusion, coma | Neuronal dysfunction from hypercalcemia | May improve post-parathyroidectomy |
| Disease — CVS | HTN, LVH, arrhythmia, vascular calcification | Vasoconstriction, cardiac Ca effects | May not fully reverse post-op |
| Disease — MSK | CPPD/pseudogout | Abnormal pyrophosphate metabolism | Treat HPT; CPPD may persist |
| Surgery — Early | Neck haematoma | Bleeding → airway compromise | Open wound at bedside |
| Surgery — Early | RLN injury | Nerve traction/transection | Medialization (unilateral); tracheostomy (bilateral) |
| Surgery — Early | Hypocalcemia (most common) | Gland suppression, hungry bone syndrome, devascularization | IV Ca gluconate → oral Ca + calcitriol |
| Surgery — Late | Persistent HPT ( < 6 mo) | Missed pathology | Re-localization → BCE |
| Surgery — Late | Recurrent HPT ( > 6 mo) | Missed pathology, parathyromatosis, remnant regrowth | Re-localization → BCE |
| Surgery — Late | Permanent hypoparathyroidism | Insufficient remaining tissue | Lifelong Ca + calcitriol |
High Yield Summary — Complications
-
Disease complications map onto "Stones, Bones, Moans, Thrones, Psychic Overtones" + CVS (HTN, LVH, arrhythmias) + MSK (CPPD/pseudogout).
-
Renal stones are the most common symptomatic complication of primary HPT. Always screen for HPT in recurrent stone formers.
-
Bone loss is preferentially cortical (distal 1/3 radius > hip > spine). Osteitis fibrosa cystica is the classic but now uncommon bone lesion.
-
Hypocalcemia is the MOST common complication of parathyroidectomy. Check Ca on post-op Day 1. Symptoms: perioral numbness → carpopedal spasm → Trousseau/Chvostek → laryngospasm. Treat with IV calcium gluconate (acute) and oral Ca + calcitriol (maintenance).
-
Hungry bone syndrome: severe prolonged hypocalcemia + hypophosphatemia + hypomagnesemia despite normal/elevated PTH. Predicted by pre-op ↑ ALP. Caused by osteoblasts continuing bone formation after PTH drops.
-
Neck haematoma: tense neck swelling + dyspnoea post-op = open wound at bedside FIRST, then manage airway.
-
RLN injury: unilateral = hoarseness; bilateral = stridor + airway obstruction → re-intubation/tracheostomy. Rate < 1% in experienced hands.
-
Persistent HPT ( < 6 months) = missed pathology. Recurrent HPT ( > 6 months) = missed pathology, remnant regrowth, or parathyromatosis (from gland rupture during surgery).
-
Permanent hypoparathyroidism = requiring Ca/vitamin D supplementation ≥ 1 year post-op.
-
Secondary HPT in CKD: additional complications include vascular calcification, calciphylaxis (high mortality), renal osteodystrophy ("rugger-jersey spine"), and soft tissue calcification.
Active Recall - Complications of Hyperparathyroidism
References
[1] Senior notes: maxim.md (Primary hyperparathyroidism — Specific complications section; Thyroidectomy complications; Parathyroid anatomy) [1b] Senior notes: maxim.md (Thyroidectomy complications — RLN injury, parathyroid injury, post-op dyspnoea DDx) [3] Senior notes: Ryan Ho Endocrine.pdf (p42, Primary Hyperparathyroidism — S/S, Hyperparathyroid bone disease, Cardiovascular complications) [3c] Senior notes: Ryan Ho Endocrine.pdf (p22, Thyroidectomy complications — haematoma, RLN injury, hypocalcemia, hungry bone syndrome) [5] Senior notes: Ryan Ho Rheumatology.pdf (p41-42, CPPD Disease) [6] Senior notes: Ryan Ho Cardiology.pdf (p177, Secondary Hypertension — Hyperparathyroidism) [13] Senior notes: felixlai.md (Bone involvement in HPT, p1024-1025; Complications screening) [13b] Senior notes: felixlai.md (Complications of thyroidectomy/parathyroidectomy — hypocalcemia, hungry bone syndrome, RLN injury, p1010-1011)
High Yield Summary
Definition: Hyperparathyroidism = excessive PTH. Primary (intrinsic parathyroid disease → hypercalcemia), Secondary (compensatory to hypocalcemia, usually CKD), Tertiary (autonomous after prolonged secondary).
Epidemiology: Primary HPT is the most common cause of outpatient hypercalcemia. Prevalence 1–2/1000. Peak 6th–7th decade. F:M = 2–3:1.
Risk Factors: Female sex, postmenopausal, head/neck irradiation, MEN1 (parathyroid + pancreas + pituitary), MEN2A (MTC + pheo + parathyroid), lithium use.
Causes of Primary HPT: Solitary adenoma (~85%) > Hyperplasia (~10–15%, think MEN) > Double adenoma (1–2%) > Carcinoma ( < 1%).
Biochemistry: Primary HPT = ↑Ca + ↑/inappropriately normal PTH + ↓PO₄. Must do 24h urine Ca to exclude FHH.
Clinical Features: Most are asymptomatic. Classic = "Stones, Bones, Moans, Thrones, Psychic Overtones." Hypercalcemia causes: nephrolithiasis, osteoporosis/osteitis fibrosa cystica, constipation, polyuria, depression/confusion, hypertension.
Key Differentiator from FHH: 24h urine calcium — HIGH in primary HPT, LOW in FHH (Ca:Cr clearance ratio < 0.01).
Secondary HPT in CKD: ↓GFR → ↑PO₄ + ↓calcitriol → ↓Ca → ↑PTH → renal osteodystrophy, vascular calcification, calciphylaxis.
Localization (NOT diagnosis): USG + Sestamibi scan — Sestamibi accumulates in mitochondria of oxyphil-cell-rich adenomas with slow washout compared to thyroid tissue.
High Yield Summary — Differential Diagnosis
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The PTH level is the single most important differentiating test in the workup of hypercalcemia. PTH-dependent (↑/inappropriately normal PTH) vs PTH-independent (↓ PTH).
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Primary HPT is the most common cause of outpatient hypercalcemia. Malignancy is the most common cause of inpatient hypercalcemia.
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24h urine calcium must always be checked to exclude FHH before proceeding to surgery for primary HPT. FHH = Ca:Cr clearance ratio < 0.01; primary HPT = ratio > 0.02.
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Malignancy-related hypercalcemia has multiple mechanisms: PTHrP (80%, humoral; SCC lung, HCC, breast), local osteolysis (20%; breast mets, myeloma — CRAB), calcitriol (lymphoma), ectopic PTH (very rare).
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Granulomatous diseases (sarcoidosis, TB — important in Hong Kong) cause hypercalcemia via autonomous 1α-hydroxylase in macrophages → ↑ 1,25(OH)₂D₃.
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Secondary HPT: think CKD, vitamin D deficiency. PTH is elevated but calcium is low/normal. This is a compensatory response.
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Tertiary HPT: autonomous PTH after prolonged secondary HPT. Classic scenario: persistent hypercalcemia after renal transplant.
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Hyperparathyroidism should be considered in the DDx of: recurrent renal stones, unexplained osteoporosis, pseudogout/CPPD, secondary hypertension, depression, and acute pancreatitis.
High Yield Summary — Diagnosis
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Diagnosis of primary HPT is BIOCHEMICAL: ↑ Ca + ↑/inappropriately normal PTH + normal RFT. PTH must always be interpreted in context of calcium.
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24h urine calcium is MANDATORY to exclude FHH. Ca:Cr clearance ratio < 0.01 = FHH; > 0.02 = primary HPT.
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Standard workup: PTH, Ca, PO₄, ALP, 25-OH-D, RFT, 24h urine Ca. Screen complications: DEXA (3 sites including distal 1/3 radius), USG kidneys, ECG.
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Localization studies (USG + Sestamibi) are NOT diagnostic and do NOT determine the need for surgery. They are performed ONLY after biochemical diagnosis is confirmed and surgery is decided → guide surgical approach.
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Sestamibi mechanism: accumulates in mitochondria; parathyroid adenomas rich in oxyphilic cells (abundant mitochondria) → slow washout at 2h vs thyroid. False positive: Hurthle cell adenoma. False negative: hyperplasia, small adenomas.
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Intraoperative PTH (Miami criteria): PTH drops to normal + falls > 50% at 10 min post-excision → confirms successful removal. If NOT met → convert to bilateral exploration.
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↑ ALP predicts hungry bone syndrome post-parathyroidectomy — high bone turnover means osteoblasts will rapidly sequester calcium after PTH drops.
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Normocalcemic primary HPT: persistently ↑ PTH with normal Ca after excluding ALL secondary causes (Vit D deficiency, CKD, medications, malabsorption).
High Yield Summary — Management
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Surgery is the ONLY cure for primary HPT. Cure rate ~95–98%.
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All symptomatic patients should undergo parathyroidectomy.
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Asymptomatic PHPT surgical criteria (CASR mnemonic): Ca ≥ 2.85 (> 0.25 above ULN); Age < 50; Skeletal (T-score ≤ −2.5 or vertebral fracture); Renal (eGFR < 60, urine Ca > 400 mg/d, or stones/nephrocalcinosis on imaging). Any ONE criterion met = operate.
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Focused parathyroidectomy: for localized single adenoma. Requires pre-op localization (USG + Sestamibi) + intraoperative PTH (Miami criteria: > 50% drop + normalize at 10 min). If criteria not met → convert to bilateral exploration.
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Bilateral exploration: for MEN syndromes, discordant imaging, multigland disease. Subtotal (3.5 gland) or total parathyroidectomy ± autotransplantation.
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Cervical thymectomy: add for MEN1 (supernumerary intrathymic glands).
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Medical options (if surgery C/I): cinacalcet (↓ Ca but no BMD benefit), bisphosphonates/denosumab (↑ BMD), SERMs.
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Contraindications to surgery: contralateral RLN injury, FHH, surgically unfit.
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Post-op: Check Ca on Day 1. Watch for hungry bone syndrome (predicted by ↑ pre-op ALP) — treat with aggressive Ca + calcitriol + Mg. Permanent hypoparathyroidism = needing supplements ≥ 1 year.
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Severe hypercalcemia emergency: Rehydrate (NS) → loop diuretic (AFTER rehydration) → calcitonin (rapid, tachyphylaxis in 2–3d) + bisphosphonate (slow onset, lasts weeks) → cinacalcet/denosumab/steroids/dialysis for refractory cases.
High Yield Summary — Complications
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Disease complications map onto "Stones, Bones, Moans, Thrones, Psychic Overtones" + CVS (HTN, LVH, arrhythmias) + MSK (CPPD/pseudogout).
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Renal stones are the most common symptomatic complication of primary HPT. Always screen for HPT in recurrent stone formers.
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Bone loss is preferentially cortical (distal 1/3 radius > hip > spine). Osteitis fibrosa cystica is the classic but now uncommon bone lesion.
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Hypocalcemia is the MOST common complication of parathyroidectomy. Check Ca on post-op Day 1. Symptoms: perioral numbness → carpopedal spasm → Trousseau/Chvostek → laryngospasm. Treat with IV calcium gluconate (acute) and oral Ca + calcitriol (maintenance).
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Hungry bone syndrome: severe prolonged hypocalcemia + hypophosphatemia + hypomagnesemia despite normal/elevated PTH. Predicted by pre-op ↑ ALP. Caused by osteoblasts continuing bone formation after PTH drops.
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Neck haematoma: tense neck swelling + dyspnoea post-op = open wound at bedside FIRST, then manage airway.
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RLN injury: unilateral = hoarseness; bilateral = stridor + airway obstruction → re-intubation/tracheostomy. Rate < 1% in experienced hands.
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Persistent HPT ( < 6 months) = missed pathology. Recurrent HPT ( > 6 months) = missed pathology, remnant regrowth, or parathyromatosis (from gland rupture during surgery).
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Permanent hypoparathyroidism = requiring Ca/vitamin D supplementation ≥ 1 year post-op.
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Secondary HPT in CKD: additional complications include vascular calcification, calciphylaxis (high mortality), renal osteodystrophy ("rugger-jersey spine"), and soft tissue calcification.
Hashimoto's Thyroiditis
Hashimoto's thyroiditis is a chronic autoimmune disorder in which antibodies target the thyroid gland, leading to lymphocytic infiltration, progressive destruction of thyroid tissue, and eventual hypothyroidism.
Hyperthyroidism
Hyperthyroidism is a condition of excessive thyroid hormone production resulting in a hypermetabolic state characterized by weight loss, tachycardia, tremor, and heat intolerance.