Pseudogout is a crystal arthropathy caused by the deposition of calcium pyrophosphate dihydrate crystals in joints, resulting in acute or chronic inflammatory arthritis.

Pseudogout (Calcium Pyrophosphate Dihydrate Crystal Deposition Disease)

2. Epidemiology

3. Anatomy and Function

Joint	Why?
Knee (> 50%)	Largest synovial joint with thick meniscal fibrocartilage — the meniscus is a major site of CPPD deposition ^[2]
Wrist	Triangular fibrocartilage complex (TFCC) — fibrocartilage-rich
Shoulder	Glenoid labrum (fibrocartilage)
Ankle, feet, elbow	Less common but still recognized

This is a key distinguishing feature from gout: pseudogout affects more proximal/large joints (especially knees and shoulders) while gout classically affects the 1st MTP joint ^[1]^[3].

4. Etiology and Pathophysiology

4A. Etiology (Causes)

The majority of CPPD disease is idiopathic, occurring in elderly individuals with degenerative joint disease. However, there are important secondary and familial causes to consider ^[1]^[2]:

High Yield: Secondary Causes of CPPD — The 5 H's Mnemonic

When a patient under 55 presents with CPPD, screen for secondary causes. Think of the 5 H's:

Hyperparathyroidism (primary) — 3.35× risk ^[2]
Haemochromatosis
Hypophosphatasia (low ALP)
Hypomagnesaemia
Hypothyroidism ^[1]

(Some sources also include Wilson's disease — copper overload)

Secondary Cause	Mechanism of CPPD Promotion
Hyperparathyroidism ^[1]^[2]	PTH → ↑serum calcium → ↑Ca²⁺ available for complexing with pyrophosphate → CPPD crystal formation. Also PTH directly stimulates chondrocyte metabolism. 3.35× risk ^[2]
Haemochromatosis ^[2]	Iron deposits in cartilage → oxidative damage to chondrocytes → increased PPi release; iron also inhibits pyrophosphatase → reduced PPi breakdown. "Arthropathy of iron overload" with squared-off bone ends and hook-like osteophytes at MCPJs ^[4]
Hypophosphatasia ^[1]^[2]	Alkaline phosphatase (ALP) normally hydrolyzes PPi → inorganic phosphate. Low ALP → PPi accumulates → CPPD crystal formation.
Hypomagnesaemia ^[1]^[2]	Mg²⁺ is a cofactor for pyrophosphatases. Low Mg → impaired PPi breakdown → PPi accumulates. Mg²⁺ also increases CPP crystal solubility, so low Mg → crystals precipitate more readily.
Hypothyroidism ^[1]	Mechanism unclear — possibly altered proteoglycan metabolism in cartilage, changing the matrix environment to favour crystal nucleation.
Wilson's disease ^[2]	Copper accumulation → chondrocyte damage, similar mechanism to iron in haemochromatosis.

This is the critical chain of events you must understand from first principles:

Step-by-Step:

Excessive Pyrophosphate (PPi) Production ^[2]:
- Chondrocytes produce PPi as a normal byproduct of ATP hydrolysis and nucleotide triphosphate pyrophosphohydrolase (NTPPPH/ENPP1) activity.
- In ageing, OA, or familial CPPD, there is increased ATP breakdown by chondrocytes → increased PPi formation ^[2].
- The ANKH transmembrane protein transports intracellular PPi to the extracellular space. Gain-of-function mutations (familial cases) → excessive extracellular PPi.
Impaired PPi Clearance:
- PPi is normally converted by alkaline phosphatase (ALP) to inorganic phosphate (Pi) ^[2].
- In conditions with low ALP (hypophosphatasia), low Mg²⁺ (cofactor for pyrophosphatases), or altered cartilage matrix, this clearance is impaired.
CPPD Crystal Formation:
- Under the influence of growth-promoting factors, PPi complexes with calcium to form CPPD crystals ^[2].
- Proteoglycan depletion in OA cartilage removes a natural inhibitor of mineralization → crystal nucleation is facilitated ^[2].
- Cell damage from OA/ageing → release of cellular ATP → further PPi production ^[2].
Crystal Shedding ("Crystal Stripping"):
- Crystals initially form within the cartilage matrix (this can be asymptomatic for years, showing only as chondrocalcinosis on X-ray).
- A triggering event (trauma, surgery, acute illness, bisphosphonate treatment, parathyroidectomy) causes crystals to be shed from cartilage into the synovial fluid.
- Why surgery/illness triggers attacks: rapid shifts in serum calcium, changes in joint use/loading, and inflammatory milieu all promote crystal release.
Innate Immune Activation (same mechanism as gout):
- Shed CPPD crystals are phagocytosed by resident synovial macrophages and recruited neutrophils.
- Crystal phagocytosis activates the NLRP3 inflammasome → caspase-1 activation → cleavage of pro-IL-1β to active IL-1β.
- IL-1β drives intense neutrophilic inflammation: vasodilation, increased vascular permeability, neutrophil chemotaxis.
- This produces the clinical picture of an acute "hot joint" — red, swollen, warm, exquisitely tender.
Chronic Effects ^[2]:
- CPPD crystals may amplify the destructive effect of OA ^[2]
- Gout-like induction of neutrophilic inflammation causes chronic synovitis in some patients ^[2]
- In severe cases, progressive joint destruction can mimic neuropathic (Charcot) arthropathy

Why Does Pseudogout Attack After Surgery?

Post-operative pseudogout is a well-known phenomenon (classically post-parathyroidectomy). After surgery:

Rapid drop in serum calcium (especially after parathyroidectomy — "hungry bone syndrome") alters crystal solubility
Systemic stress response, dehydration, immobilization
Shift in local joint milieu → crystal shedding from cartilage into synovial space

Triggers include: trauma, surgery (especially parathyroidectomy), severe medical illness, and bisphosphonate treatment ^[2].

EULAR Classification of CPPD Disease Clinical Phenotypes [2]

Clinical Phenotype	Also Known As	Key Features
Asymptomatic CPPD	Lanthanic ("hidden") CPPD	Majority of cases. Incidental chondrocalcinosis on X-ray. No symptoms.
Acute CPP crystal arthritis	Pseudogout	Acute, severe, gout-like monoarthritis. Most commonly knee (> 50%), wrist, shoulder, ankles, feet, elbows ^[2]. Spontaneously resolving but may persist > 1–2 weeks (longer than typical gout).
Chronic inflammatory arthritis	Pseudo-RA (< 5%)	Symmetrical or near-symmetrical polyarthritis with morning stiffness, fatigue, synovial thickening, ↓ROM ^[2]. Wrists, MCPJs, knees, elbows. Key difference from RA: independent wax-and-wane pattern in individual joints (cf. synchronous fluctuation in RA) ^[2]. Non-erosive.
OA with CPPD	Pseudo-OA (most common symptomatic form)	Typical OA presentation with progressive joint degeneration. ~50% have episodes of acute inflammatory arthritis superimposed ^[2]. Often affects joints atypical for primary OA (wrist, MCPJ, shoulder, elbow). Accelerated degeneration when involving atypical joints with early calcification ^[2].
Severe joint degeneration	Pseudo-neuropathic	Mimics neuropathic (Charcot) arthropathy — severe destructive changes
Spinal involvement	Pseudo-AS	Spinal stiffness ± bony ankylosis, can mimic ankylosing spondylitis ^[2]

The key point: CPPD disease is not just "pseudogout." It is a spectrum. The acute attack (pseudogout) is only one manifestation. The chronic forms (pseudo-OA, pseudo-RA) may be even more clinically important in elderly patients ^[2].

6. Clinical Features

Symptom	Pathophysiological Basis
Sudden onset of severe, intense joint pain (acute pseudogout)	CPPD crystal shedding → phagocytosis by macrophages/neutrophils → NLRP3 inflammasome activation → IL-1β → intense inflammatory cascade. The acute onset corresponds to the sudden release of pre-formed crystals from cartilage into the joint space.
Joint stiffness (especially morning stiffness in pseudo-RA)	Chronic low-grade synovial inflammation → synovial thickening and fluid accumulation → stiffness, particularly after prolonged immobility (overnight). Similar mechanism to RA but with crystal-driven rather than autoimmune-driven inflammation.
Pain worse on movement, reduced ROM	Joint effusion distends the capsule; crystal-induced inflammation in synovium and periarticular structures causes nociceptor activation. Localized oedema, ↓ROM (due to active inflammation or flexion contracture) ^[2].
Chronic, progressive joint pain (pseudo-OA)	CPPD crystals amplify cartilage degradation in pre-existing OA → proteoglycan loss, subchondral bone remodelling. ~50% have superimposed episodes of acute inflammatory arthritis ^[2].
Fatigue (pseudo-RA)	Chronic IL-1β and IL-6 production → systemic inflammatory response → fatigue (same mechanism as in RA).
Pain in atypical joints for OA (wrist, MCPJ, shoulder, elbow)	CPPD deposition targets fibrocartilage-rich structures — TFCC of wrist, shoulder labrum — joints not typically affected by primary OA. If a patient has "OA" in unusual joints, think CPPD.
Spinal stiffness	Crystal deposition in intervertebral disc fibrocartilage and ligamentum flavum → inflammatory reaction and bony ankylosis. Can mimic ankylosing spondylitis ^[2].
Cluster attacks (multiple adjacent joints flaring simultaneously)	"Cluster attacks refer to the occurrence of synchronous inflammation of several adjacent joints. This can be a feature of both pseudogout and gout" ^[2]. Mechanism: crystal shedding from one joint may trigger a systemic inflammatory response that lowers the threshold for crystal shedding in neighbouring joints.

Triggers for Acute Attacks

Triggers: trauma, surgery (especially parathyroidectomy), severe medical illness, bisphosphonate treatment ^[2].

Why these triggers?

Trauma/surgery: mechanical disruption of cartilage matrix → crystal release
Parathyroidectomy: sudden drop in PTH → rapid fall in serum Ca²⁺ → altered crystal solubility → shedding
Severe illness: metabolic stress, dehydration, pH changes → altered mineral solubility
Bisphosphonates: alter calcium/phosphate metabolism; also directly affect crystal turnover in cartilage

Sign	Pathophysiological Basis
Joint warmth (hot joint)	IL-1β and prostaglandins → vasodilation of synovial blood vessels → increased blood flow to the joint → surface warmth.
Joint erythema (redness)	Same vasodilatory mechanism. Histamine, bradykinin, and prostaglandins from inflammatory cells increase capillary permeability and dilation → redness of overlying skin.
Joint swelling / effusion	Inflammatory exudate (protein-rich fluid + neutrophils) accumulates in the joint space. Vascular permeability is increased by IL-1β, TNF-α. The joint capsule distends.
Tenderness on palpation	Sensitization of nociceptors by prostaglandins (PGE₂) and bradykinin. The pressure of palpation on an inflamed, distended capsule activates these sensitized nerve endings → pain.
Reduced range of motion	Pain-limited active ROM (guarding) + physical obstruction by effusion + synovial thickening. In chronic cases, flexion contractures may develop ^[2].
Synovial thickening (chronic pseudo-RA)	Chronic crystal-driven inflammation → synovial hyperplasia (similar to pannus in RA but less destructive). Synovial thickening is a sign of chronic inflammatory arthritis (pseudo-RA) ^[2].
Low-grade fever (occasionally)	IL-1β and IL-6 are endogenous pyrogens → act on the hypothalamic thermoregulatory centre → reset thermostat upward. Not always present — and importantly, fever does not reliably distinguish pseudogout from septic arthritis (you must aspirate!).
Chondrocalcinosis (radiological sign)	CPPD crystal deposition within cartilage → radiodensities visible on plain X-ray. Irregular faint punctate/linear radiodensities in articular cartilage (± ligaments, tendons, synovium, bursa, joint capsules) ^[2]. Classic sites: knee menisci, TFCC of wrist, pubic symphysis.

Feature	Gout	Pseudogout	Septic Arthritis
Most common joint	1st MTP ^[1]	Knee (> 50%), then wrist, shoulder ^[1]^[2]	Knee, hip (large joints)
Age/Sex	M > > F, 4th–5th decade	M:F ≈ 1:1, > 60 years old ^[1]^[2]	Any age
Crystal	MSU: needle-shaped, negatively birefringent ^[1]	CPPD: rhomboid-shaped, positively birefringent ^[1]^[2]	No crystals
Duration of attack	7–10 days	May persist > 1–2 weeks (longer than gout) ^[2]	Doesn't self-resolve
X-ray	Punched-out erosions, preserved joint space	Chondrocalcinosis ^[1]^[2]	Soft tissue swelling, late joint destruction
Synovial WCC	10–50k	15–30k, 90% neutrophils ^[2]	> 50–100k

Exam Trap: Crystal Birefringence

A very common exam question:

MSU crystals (gout): needle-shaped, NEGATIVELY birefringent (yellow when parallel to the compensator axis) ^[1]
CPPD crystals (pseudogout): rhomboid-shaped, POSITIVELY birefringent (blue when parallel to the compensator axis) ^[1]^[2]

Memory trick: Think of the "P" rule:

Pseudogout → Positively birefringent → Calcium Pyrophosphate
Gout → Negatively birefringent → Monosodium urate (Not positive)

When you suspect CPPD, particularly in younger patients (< 55), you should actively screen for secondary causes by asking about and examining for:

Associated Condition	What to Ask/Look For
Hyperparathyroidism	Symptoms of hypercalcaemia ("bones, stones, abdominal moans, psychic groans") — bone pain, renal stones, constipation, confusion, polyuria. Previous neck surgery.
Haemochromatosis	Family history, skin pigmentation (bronze/slate grey), hepatomegaly, diabetes, erectile dysfunction, arthropathy of MCPJs.
Hypothyroidism	Fatigue, cold intolerance, weight gain, constipation, dry skin, bradycardia.
Hypomagnesaemia	Often iatrogenic (PPIs, diuretics), chronic alcoholism. Muscle cramps, tremor, arrhythmia.
Hypophosphatasia	Rare — history of recurrent fractures, dental abnormalities, low ALP on blood tests.
Wilson's disease	Young patient, neuropsychiatric symptoms, Kayser-Fleischer rings, liver disease.
Familial	Family history of chondrocalcinosis — onset < 55 years, AD inheritance ^[2].

Feature	Gout	Pseudogout
Crystal composition	Monosodium urate (MSU)	Calcium pyrophosphate dihydrate (CPPD) ^[1]
Crystal shape	Needle-shaped ^[1]	Rhomboid-shaped ^[1]^[2]
Birefringence	Negatively birefringent ^[1]	Positively birefringent ^[1]^[2]
Most common joint	1st MTP (podagra) ^[1]	Knee > wrist > shoulder ^[1]^[2]
Age of onset	4th–5th decade (M)	> 60 years (rare < 55) ^[1]^[2]
Sex ratio	M:F ≈ 9:1	M:F ≈ 1:1 ^[2]
Risk factors	Purines, alcohol, diuretics, CKD	HyperPTH, haemochromatosis, hypoMg, hypophosphatasia, hypothyroidism ^[1]^[2]
X-ray	Punched-out erosions, overhanging edge	Chondrocalcinosis ^[1]^[2]
Serum marker	Uric acid (not useful acutely)	Ca, PO₄, Mg, ALP, ferritin (screen post-diagnosis)
Long-term prophylaxis	Allopurinol / febuxostat (ULT)	No specific disease-modifying therapy exists for CPPD — treat underlying cause

OA is usually present prior to CPPD disease ^[2]. The relationship is bidirectional and synergistic:

OA → promotes CPPD formation:

Proteoglycan loss → ↓inhibition of mineralization → crystal nucleation is facilitated ^[2]
Altered growth factor milieu (TGF-β, IGF-1) → stimulates PPi production ^[2]
Chondrocyte damage → release of cellular ATP → ↑PPi production ^[2]

CPPD → amplifies OA damage:

Crystals directly damage cartilage matrix
Crystal-induced inflammation → MMP and cytokine release → cartilage degradation
Creates a vicious cycle of damage and deposition

This is why pseudo-OA is the most common symptomatic form of CPPD disease ^[2] — it represents OA accelerated and modified by crystal deposition.

High Yield Summary

CPPD disease is a spectrum: asymptomatic chondrocalcinosis → acute pseudogout → pseudo-OA → pseudo-RA → severe destructive arthropathy.
Crystals: rhomboid-shaped, positively birefringent under polarized light (cf. gout: needle-shaped, negatively birefringent).
Joints: knee (> 50%), wrist, shoulder — more proximal than gout.
Demographics: elderly (> 60, rare < 55), M:F ≈ 1:1.
If age < 55, screen for secondary causes: hyperPTH, haemochromatosis, hypoMg, hypophosphatasia, hypothyroidism, Wilson's disease, familial chondrocalcinosis.
Pathophysiology: ↑PPi production by chondrocytes + ↓PPi clearance → PPi complexes with Ca²⁺ → CPPD crystals → shed into joint → NLRP3 inflammasome → IL-1β → acute inflammation.
Triggers: trauma, surgery (especially parathyroidectomy), severe illness, bisphosphonates.
X-ray: chondrocalcinosis (punctate/linear calcification in cartilage — especially knee menisci and wrist TFCC).
Acute pseudogout attacks last longer than gout (may persist > 1–2 weeks) and can present with cluster attacks.
No disease-modifying therapy for CPPD exists (unlike gout which has urate-lowering therapy) — management is symptomatic + treat underlying metabolic cause.

Active Recall - Pseudogout Definition, Epidemiology, Etiology, Pathophysiology and Clinical Features

Differential Diagnosis of Pseudogout

Because CPPD disease is a spectrum, the differential diagnosis depends on which clinical phenotype the patient presents with. Let us organize this systematically:

CPPD Phenotype	Mimics (DDx)
Acute pseudogout (acute monoarthritis)	Septic arthritis, gout, trauma/haemarthrosis, OA flare, monoarticular onset of RA/SpA
Pseudo-RA (chronic inflammatory polyarthritis)	Rheumatoid arthritis, SLE, viral polyarthritis, polymyalgia rheumatica
Pseudo-OA (chronic degenerative arthropathy)	Primary OA, haemochromatosis arthropathy
Pseudo-neuropathic (severe destructive)	Charcot (neuropathic) arthropathy
Pseudo-AS (spinal stiffness)	Ankylosing spondylitis, diffuse idiopathic skeletal hyperostosis (DISH)

This is the most important and most commonly examined scenario — the elderly patient presenting to A&E with an acutely hot, swollen joint.

Full Differential Diagnosis Table for Acute Monoarthritis

Category	Condition	Key Distinguishing Features	Why It Mimics Pseudogout
Infection	Septic arthritis (bacterial) ^[1]^[3]^[5]	Hot, swollen, tender joint is septic arthritis until proven otherwise ^[1]. Usually S. aureus in native joints, S. epidermidis in prosthetic joints ^[1]. Synovial WBC usually > 50–100k, neutrophil predominant ^[1]. Urgent Gram stain + C/ST mandatory. Risk factors: immunocompromised, IVDU, prosthetic joint, RA, DM ^[5].	Presents identically to pseudogout — fever, red swollen joint. The key difference is that septic arthritis does NOT self-resolve and causes rapid joint destruction within days if untreated.
Infection	Gonococcal arthritis ^[3]^[5]	Sexually active young patient. Purulent mono/oligoarthritis in distal joints (knees, wrists, ankles) OR asymmetric non-purulent polyarthritis with dermatitis ^[3]. Swabs of pharynx, urethra, cervix, anorectum ^[1].	Can present as acute monoarthritis but typically younger patient, different demographics from pseudogout.
Infection	Mycobacterial (TB) arthritis ^[3]	Indolent, progressive monoarthritis in immunocompromised patients or those with TB contact ^[3]. Insidious onset (cf. acute in pseudogout). AFB smear + culture of synovial fluid.	Slower onset distinguishes from pseudogout, but must be considered in HK where TB remains endemic.
Crystal	Gout (MSU crystal) ^[1]^[3]^[6]	1st MTP most common (podagra) ^[1]^[6]. M:F ≈ 9:1 ^[1]. Commonest age: 30–60 years ^[6]. Needle-shaped, negatively birefringent crystals ^[1]. Serum urate often elevated (but NOT diagnostic acutely — serum UA level useful but not diagnostic ^[6]). Spontaneous resolution over 5–14 days ^[5].	Both are crystal-induced acute monoarthritis. However, gout favours younger men with 1st MTP involvement; pseudogout favours older patients with knee/wrist involvement. Co-existence possible (CPPD crystals in ~5% of gout fluids ^[2]).
Crystal	Hydroxyapatite deposition ^[3]	Basic calcium phosphate crystals. Causes calcific periarthritis (especially shoulder — supraspinatus tendon). Often peri-articular rather than intra-articular. Crystals not visible on standard polarized microscopy (too small) — requires alizarin red S staining.	Can cause acute shoulder pain mimicking pseudogout of the shoulder. However, hydroxyapatite is typically periarticular (tendon/bursa) while CPPD is intra-articular.
Crystal	Calcium oxalate deposition ^[3]	Acute arthritis in dialysis patients ^[5]. Bipyramidal (envelope-shaped) crystals, positively birefringent.	Rare. Only consider in patients on chronic dialysis.
Trauma	Fracture / haemarthrosis ^[3]	History of trauma. Onset seconds to minutes after injury ^[3]. May be associated with coagulopathy (warfarin, haemophilia) or intra-articular tumour ^[3]. Aspirate may be bloodstained (haemarthrosis).	Acute onset like pseudogout but trauma history is key. Note: trauma can also TRIGGER a pseudogout attack by shedding crystals — so both can coexist.
Degenerative	OA flare ^[3]	Weight-bearing joint, history of overuse/pre-existing OA ^[3]. Can present with acutely painful synovitis mimicking other differentials ^[3]. However, lower WBC count in synovial fluid (< 2000, non-inflammatory range).	OA commonly coexists with CPPD (pseudo-OA is the most common symptomatic CPPD phenotype ^[2]), making differentiation challenging.
Inflammatory	Monoarticular onset of RA ^[3]	May initially present as monoarthritis before evolving into symmetrical polyarthritis. Check RF, anti-CCP.	Consider if patient goes on to develop symmetrical small joint involvement.
Inflammatory	Spondyloarthritis (SpA) ^[3]	Classically asymmetrical oligoarthritis, usually in men < 45y ^[3]. Associated with enthesitis, dactylitis, anterior uveitis, HLA-B27 positivity.	Different demographics (younger men) and pattern (oligoarthritis, lower limb predominance, axial involvement).
Uncommon	Avascular necrosis (AVN) ^[3]	Hip or knee. Risk factors: corticosteroids, alcohol, SLE, sickle cell. Insidious onset. MRI diagnostic.	Presentation is more gradual than acute pseudogout.
Uncommon	Pigmented villonodular synovitis (PVNS) ^[3]	Chronic, recurrent haemorrhagic joint effusion, usually monoarticular (knee). MRI: characteristic low-signal "blooming" artefact.	Rare — chronic rather than acute.

High Yield GC Lecture Point: Gout vs Pseudogout Clinical Features

From GC lecture slides ^[6]:

Gout: M:F = 8:1, commonest age 30–60 years, initial presentation monoarticular, first MTP joint affected first in 20%
Systemic upset is common during acute stage
Pruritus and desquamation of overlying skin
Diagnosis by demonstration of UA crystals in joint
Serum UA level useful but not diagnostic

These contrast with pseudogout where:

M:F ≈ 1:1, age > 60, rare < 55 ^[2]
Knee > 50%, wrist, shoulder ^[1]^[2]
Both may have systemic upset, but desquamation of skin is more classically described with gout

B. Differential Diagnosis of Chronic CPPD Phenotypes

Feature	Pseudo-RA (chronic CPPD) ^[2]	True RA
Age	> 60 years	Any age (peak 30–50)
Sex	M:F ≈ 1:1	F > > M
Pattern	Symmetrical or near-symmetrical polyarthritis ^[2]	Symmetrical polyarthritis
Joints	Wrist, MCPJ, knee, elbow	MCP, PIP, wrist, MTP (spares DIP)
Erosions	Non-erosive ^[2]	Erosive (marginal erosions)
RF / anti-CCP	Negative	Positive (70–80%)
Fluctuation pattern	Independent wax-and-wane in individual joints (cf. synchronous in RA) ^[2]	Synchronous fluctuation across joints
X-ray	Chondrocalcinosis + degenerative changes	Periarticular osteopenia, marginal erosions
Morning stiffness	Present (significant)	Present (> 1 hour)

The most clinically useful distinguishing feature: In pseudo-RA, individual joints flare and settle independently of each other, whereas in true RA, disease activity tends to fluctuate synchronously across all affected joints ^[2]. Also, pseudo-RA is non-erosive — if you see marginal erosions on X-ray, think true RA.

Feature	Pseudo-OA (CPPD + OA) ^[2]	Primary OA
Joints	Atypical for OA: wrist, MCPJ, shoulder, elbow ^[2]	Typical: DIP, PIP, 1st CMCJ, knee, hip
Inflammatory episodes	~50% have acute inflammatory flares superimposed ^[2]	Occasional mild synovitis
Course	Accelerated joint degeneration when involving atypical joints ^[2]	Gradual, slowly progressive
X-ray	Chondrocalcinosis + OA changes	OA changes without chondrocalcinosis
Clue	OA in joints where OA "shouldn't be" = think CPPD	OA in expected weight-bearing joints

Clinical Pearl — OA in Unusual Joints

If you see osteoarthritis in the wrist, MCPJ, shoulder, or elbow — joints where primary OA is uncommon — always consider CPPD disease (pseudo-OA) and look for chondrocalcinosis on X-ray. The presence of OA in these atypical sites should prompt joint aspiration looking for CPPD crystals and a metabolic screen (Ca, PO₄, Mg, ALP, ferritin) ^[2].

This is the most dangerous diagnostic mistake to make. The table below summarizes the key differences, but remember: clinical features alone cannot reliably distinguish them — you must aspirate.

Feature	Pseudogout	Septic Arthritis
Onset	Acute (hours to 1–2 days)	Acute (hours to days)
Fever	May be present (low-grade)	Usually present (high-grade), may be absent in elderly ^[5]
Joint	Knee, wrist, shoulder	Knee (> 90%), wrist, ankle, hip ^[5]
Synovial WCC	15,000–30,000/mm³, 90% neutrophils ^[2]	> 50,000–100,000/mm³, > 90% neutrophils ^[1]
Crystals on polarized LM	Rhomboid, positively birefringent ^[1]^[2]	Absent
Gram stain	Negative	May be positive — sensitivity ~50–75%
Culture	Negative	Positive (gold standard)
Course if untreated	Self-resolving (1–2+ weeks)	Progressive joint destruction within DAYS
Can coexist?	YES — crystal arthropathy and infection can coexist ^[1]	YES

Exam Trap: Co-existence of Crystals and Infection

Crystals and infection can coexist in the same joint ^[1]. Finding CPPD (or MSU) crystals on polarized microscopy does NOT rule out septic arthritis. You must always send Gram stain and culture. Conversely, a patient with known CPPD disease who develops a "flare" may actually have septic arthritis — never assume.

Polarising microscopy (may co-exist with crystal arthropathy) — this is explicitly stated in the context of septic arthritis workup ^[1].

If you see linear/punctate calcification in cartilage on X-ray, don't automatically call it CPPD disease. The differential for radiographic chondrocalcinosis includes:

Cause	Notes
CPPD deposition	Most common cause. Look for meniscal calcification (knee), TFCC calcification (wrist).
Normal ageing	Prevalence of chondrocalcinosis increases with age — up to 30–60% in > 85 years ^[2]. Not all chondrocalcinosis = symptomatic CPPD disease.
Osteoarthritis	Chondrocalcinosis is commonly seen in OA joints and is not specific for CPPD disease ^[2].
Hyperparathyroidism	Screen with Ca, PTH.
Haemochromatosis	Distinctive pattern: squared-off bone ends and hook-like osteophytes at MCPJs ^[4].
Hypophosphatasia	Low ALP.
Hypomagnesaemia	Check serum Mg.
Gout	CPPD crystals present in ~5% of gout joint fluids ^[2].

Feature	Pseudogout	Gout	Septic Arthritis	RA	OA
Age	> 60	30–60	Any	30–50	> 50
Sex	M:F ≈ 1:1	M > > F	Any	F > M	F > M
Joint	Knee, wrist, shoulder	1st MTP	Knee, hip	MCP, PIP, wrist	DIP, PIP, knee, hip
Onset	Acute	Acute	Acute	Insidious (or acute)	Gradual
Crystal	CPPD (rhomboid, +ve biref.)	MSU (needle, −ve biref.)	None	None	None
Synovial WCC	15–30k	10–50k	> 50–100k	2–50k	< 2k
X-ray	Chondrocalcinosis	Punched-out erosions	Soft tissue swelling	Marginal erosions	Osteophytes, joint space loss
Serology	—	Urate (not acute)	Blood/SF culture	RF, anti-CCP	—
Self-resolving?	Yes (1–2+ wk)	Yes (5–14d)	NO	No	N/A

Several systemic diseases are associated with CPPD and may present with joint symptoms of their own, making the differential more complex:

Condition	Joint Manifestation Beyond CPPD	How to Distinguish
Haemochromatosis ^[4]	Iron-overload arthropathy: squared-off bone ends, hook-like osteophytes at 2nd/3rd MCPJs	Ferritin, transferrin saturation. Arthropathy usually does not respond to iron removal ^[4].
Hyperparathyroidism ^[1]^[2]	Osteitis fibrosa cystica, subperiosteal bone resorption, brown tumours	Serum Ca, PTH. CPPD risk 3.35× ^[2]. Post-parathyroidectomy flare is classic.
Acromegaly ^[7]	Hypertrophic arthropathy due to enlargement of synovial tissue and cartilage and pseudogout ^[7]	Look for acral enlargement, coarse facies, raised IGF-1.
Hypothyroidism ^[1]	Myxoedematous arthropathy, carpal tunnel syndrome	TSH, fT4.
Wilson's disease ^[2]	Premature OA, especially in knees and wrists	Ceruloplasmin, 24h urine copper, Kayser-Fleischer rings.

High Yield GC Lecture Point: Approach to the Pain Red Joint

From the GC lecture "Pain red joint" ^[6]:

The approach to a painful red joint requires urgent joint aspiration to distinguish crystal arthritis from septic arthritis
Diagnosis of gout is by demonstration of UA crystals in joint ^[6] — by analogy, diagnosis of pseudogout requires demonstration of CPPD crystals
Serum UA level is useful but not diagnostic ^[6] — similarly, serum calcium/phosphate levels do not diagnose CPPD, only suggest secondary causes

The lecture emphasizes that crystal identification on polarized microscopy is the cornerstone investigation for both gout and pseudogout.

High Yield Summary — Differential Diagnosis of Pseudogout

The #1 differential for acute pseudogout is septic arthritis — must be excluded by joint aspiration (Gram stain, C/ST) in EVERY case. Crystals and infection can coexist.
Gout vs pseudogout: different crystals (MSU needle/−ve biref. vs CPPD rhomboid/+ve biref.), different joints (1st MTP vs knee/wrist), different demographics (younger men vs elderly M=F).
Pseudo-RA vs true RA: pseudo-RA is non-erosive, RF/anti-CCP negative, with independent wax-and-wane pattern in individual joints (not synchronous like RA).
Pseudo-OA clue: OA in atypical joints (wrist, MCPJ, shoulder, elbow) → suspect CPPD and look for chondrocalcinosis.
Chondrocalcinosis on X-ray is not specific for CPPD — also seen in normal ageing and OA.
Age < 55 with CPPD: screen for secondary causes (hyperPTH, haemochromatosis, hypoMg, hypophosphatasia, hypothyroidism, Wilson's).
Acromegaly is associated with both hypertrophic arthropathy and pseudogout.
Trauma can both mimic AND trigger pseudogout — trauma causes crystal shedding from cartilage.

Active Recall - Differential Diagnosis of Pseudogout

References

^[1] Senior notes: Maksim Medicine Notes.pdf (Rheumatology, pp. 327–331) ^[2] Senior notes: Ryan Ho Rheumatology.pdf (Sections 2.1, 2.4.2, pp. 28–42) ^[3] Senior notes: Ryan Ho Fundamentals.pdf (Section 3.7.1–3.7.2, pp. 406–408) ^[4] Senior notes: Ryan Ho GI.pdf (p. 294 — Haemochromatosis arthropathy) ^[5] Senior notes: Maksim Surgery Notes.pdf (p. 274–275 — Septic arthritis) ^[6] Lecture slides: GC 075. Pain red joint.pdf (p. 27) ^[7] Senior notes: Ryan Ho Endocrine.pdf (p. 111 — Acromegaly)

Diagnostic Criteria, Algorithm, and Investigations for Pseudogout (CPPD Disease)

There are no universally adopted "classification criteria" for CPPD disease analogous to the 2015 ACR/EULAR gout criteria. However, the widely used McCarty diagnostic criteria (modified) stratify diagnosis into definite, probable, and possible ^[2]:

McCarty Criteria for CPPD Disease

Category	Criteria
Definite CPPD disease	(a) Positively birefringent crystals on polarized light microscopy + cartilage/joint capsule calcification on X-ray; OR (b) CPP crystals demonstrated in tissue or synovial fluid by definitive means (e.g., X-ray diffraction, electron microscopy — rarely done in practice) ^[2]
Probable CPPD disease	(a) Positively birefringent crystals on polarized light microscopy (without radiographic chondrocalcinosis); OR (b) Cartilage/joint capsule calcification on X-ray (without crystal identification on aspirate) ^[2]
Possible CPPD disease	Clinical presentation consistent with CPPD (acute pseudogout in knee/wrist in elderly patient) but neither crystals demonstrated nor chondrocalcinosis seen — essentially a clinical suspicion only

Why is this two-pronged (crystals + imaging)?

Crystals on aspirate = proves the crystal is present in the joint space
Chondrocalcinosis on X-ray = proves calcium-containing crystal deposition in cartilage
Having both makes the diagnosis definite because you have confirmed: (a) the nature of the crystal (CPPD by polarized microscopy), and (b) the site of deposition (cartilage by imaging).
Either one alone is only probable because: crystals without X-ray changes could theoretically be artefact or other crystals; chondrocalcinosis without crystal ID could be from other calcium salts (e.g., hydroxyapatite).

Exam Trap: Chondrocalcinosis ≠ CPPD Disease

Chondrocalcinosis is a radiological finding, not a diagnosis ^[2]. It is commonly present in the elderly population (30–60% of those > 85 years) and in OA. Not all chondrocalcinosis is symptomatic CPPD disease. Conversely, not all CPPD disease has visible chondrocalcinosis on plain X-ray — early disease or small deposits may be missed. Therefore:

Chondrocalcinosis alone = probable CPPD disease
Chondrocalcinosis + CPPD crystals in aspirate = definite CPPD disease

3. Investigation Modalities — Detailed Breakdown

Test	What You're Looking For	Why
Macroscopic appearance	Colour, clarity, viscosity	Normal = transparent, straw-coloured. Inflammatory = translucent, yellow. Septic = opaque, purulent. Haemarthrosis = blood-stained ^[1]^[3].
Polarized light microscopy	CPPD: rhomboid/pleomorphic, weakly positively birefringent ^[1]^[2]^[3]	Definitively identifies the crystal type. Weakly positive birefringent = blue when the long axis is parallel to the compensator axis (red plate).
WCC + differential	Inflammatory range vs septic range	See table below
Gram stain (URGENT) ^[1]^[6]	Bacteria on smear	Rapid preliminary result (sensitivity ~50–75%). Must be done urgently if septic arthritis suspected.
Culture + sensitivity ^[1]^[6]	Definitive microbiological diagnosis	Gold standard for septic arthritis. Takes 24–72h.
AFB smear + culture	Mycobacteria (TB)	Consider in HK (endemic TB), immunocompromised patients, indolent monoarthritis ^[1]

Category	Clarity	WCC/mL	% Neutrophils	Interpretation
Normal	Transparent	< 200	< 25%	Normal joint
Non-inflammatory	Transparent	< 2,000	< 25%	OA, mechanical derangement, early AVN
Inflammatory	Translucent	2,000–100,000	25–75%	Crystal arthritis (gout, pseudogout), RA, SpA ^[1]^[3]
Septic	Opaque	50,000–300,000	> 90%	Bacterial infection — treat urgently ^[1]^[3]

For pseudogout specifically ^[2]:

WBC: 15,000–30,000/mm³ during acute attacks (firmly in the "inflammatory" range)
90% neutrophils during acute attacks
Lower WCC in chronically symptomatic joints (pseudo-RA, pseudo-OA)

Crystal Identification Under Polarized Light Microscopy

How polarized microscopy works (from first principles):

Polarized light passes through the specimen. Crystals refract (bend) light differently depending on their molecular structure.
A first-order red compensator (a quartz plate that shifts light wavelength) is placed in the optical path.
Birefringence = the crystal splits incoming light into two rays travelling at different speeds through the crystal.
- Negatively birefringent (gout/MSU): the fast ray is parallel to the long axis of the crystal → crystal appears yellow when parallel to the compensator
- Positively birefringent (pseudogout/CPPD): the slow ray is parallel to the long axis → crystal appears blue when parallel to the compensator

Memory aid:

"Pseudogout = Positive = Pyrophosphate = Blue when Parallel"
"Gout = Negative = Yellow when parallel" (think: Negative = opposite colour to what you'd expect)

Practical caveat: CPPD crystals are weakly positively birefringent and smaller than MSU crystals, so they can be harder to identify under the microscope. A skilled microscopist is essential.

XR: chondrocalcinosis (opacities in fibrocartilage, e.g. knee menisci) ^[1]

What is chondrocalcinosis?

Irregular faint punctate/linear radiodensities in articular cartilage (± ligaments, tendons, synovium, bursa, joint capsules) ^[2]
It represents calcium-containing crystal deposits within cartilage that are dense enough to be radio-opaque

Classic Sites of Chondrocalcinosis on X-ray:

Site	What You See	Why This Location
Knee menisci	Linear calcification within the meniscal fibrocartilage, seen on AP view between the femoral condyle and tibial plateau	Menisci are fibrocartilage — rich in type I collagen with lower proteoglycan content, predisposing to crystal deposition
Wrist TFCC	Triangular calcification between ulna and carpal bones on PA view	Triangular fibrocartilage complex — another fibrocartilage-rich site
Pubic symphysis	Calcification of the fibrocartilaginous disc	Fibrocartilaginous joint
Shoulder labrum	Fine calcification around the glenoid	Labrum is fibrocartilage
Hyaline cartilage	Thin line of calcification paralleling the articular surface (distinct from the bone cortex)	CPPD can deposit in hyaline cartilage too, though fibrocartilage is more common

Additional XR findings in CPPD disease ^[2]:

Finding	Description	Phenotype
Degenerative changes	Subchondral cysts, osteophytes, decreased joint space ^[2]	Pseudo-OA
MCPJ: squared-off bone ends and hook-like osteophytes ^[2]	Characteristic pattern — also seen in haemochromatosis	Pseudo-OA / haemochromatosis-associated CPPD
Wrist: isolated/unusually extensive radiocarpal joint narrowing ^[2]	OA changes in a joint where primary OA is uncommon	Pseudo-OA
PFJ: severe patellofemoral joint space degeneration ^[2]	Severe degeneration out of proportion to the rest of the knee	Pseudo-OA
Absence of erosions	Unlike gout (punched-out erosions) or RA (marginal erosions)	All CPPD phenotypes

Key GC lecture point: "Plain x-ray" is listed as a standard investigation for the approach to a painful joint ^[6]. "Chondrocalcinosis: sign of pseudogout" ^[8].

How to Differentiate CPPD Chondrocalcinosis from Gout on X-ray

Feature	Pseudogout X-ray	Gout X-ray
Calcification	Chondrocalcinosis (linear/punctate in cartilage)	No cartilage calcification
Erosions	No "punched-out" erosions	"Punched out" erosion with overhanging sclerotic margin ^[1]
Joint space	Narrowed (degenerative)	Preserved until advanced disease ^[1]
Soft tissue	No tophi	Soft tissue tophi

Musculoskeletal ultrasound is increasingly used as a bedside investigation for crystal arthropathies.

Key USG finding in CPPD ^[2]:

Thin hyperechoic band paralleling the bone cortex and separated from it by hypoechoic cartilage — this is the "double line sign" or "pseudodouble contour"

Why this appearance?

CPPD crystals deposit within the middle of the cartilage (within the substance of hyaline cartilage), creating a bright (hyperechoic) line. Below it is the hypoechoic normal cartilage, and above it is also cartilage → the crystal line appears to "float" within the cartilage, parallel to the bone surface.
This is different from the gout "double contour sign" where MSU crystals deposit on the surface of articular cartilage (like sugar coating on a donut), creating a hyperechoic line directly on top of the cartilage surface.

USG Finding	Crystal	Location of Deposition
Double contour sign	MSU (gout)	On cartilage surface
Double line / hyperechoic band within cartilage	CPPD (pseudogout)	Within cartilage substance

USG can also detect:

Joint effusion (anechoic fluid within joint space)
Synovial hypertrophy (thickened, hypoechoic synovium — suggests chronic inflammation)
Meniscal/fibrocartilage calcification in the knee

After diagnosis of CPPD, should screen Ca, P, Mg, ALP, ferritin ^[2]

Blood Test	What You're Screening For	Why
Calcium + PTH	Hyperparathyroidism ^[1]^[2]^[6]	PTH → ↑Ca → promotes CPPD crystal formation. PTH directly stimulates chondrocyte metabolism. 3.35× risk ^[2].
Phosphate	Hypophosphatasia ^[1]^[2]^[6]	Low phosphate in context of low ALP suggests hypophosphatasia
Magnesium	Hypomagnesaemia ^[1]^[2]^[6]	Mg is a cofactor for pyrophosphatases (enzymes that break down PPi). Low Mg → PPi accumulation.
ALP	Hypophosphatasia ^[1]^[2]^[6]	ALP converts PPi → Pi. Low ALP → PPi accumulates → CPPD formation.
Ferritin (± transferrin saturation)	Haemochromatosis ^[2]^[6]	Iron damages chondrocytes and inhibits pyrophosphatases
TSH	Hypothyroidism ^[1]^[6]	Mechanism unclear but well-established association
Ceruloplasmin (if young patient)	Wilson's disease ^[2]	Copper-mediated chondrocyte damage

When to screen more aggressively for secondary causes:

Age < 55 — CPPD is rare below 55 and a secondary cause should be actively sought ^[2]
Florid/polyarticular chondrocalcinosis
Recurrent attacks in young patient
Family history of chondrocalcinosis

GC High Yield: Causes of Pseudogout

From GC lecture slides ^[6]:

"Causes of Pseudogout:

Hereditary
Idiopathic – Aging ( > 65 y.o)
Probable metabolic disease associations:
- Hyperparathyroidism
- Haemochromatosis
- Hypothyroidism
- Gout
- Hypomagnesemia
- Hypophosphatasia"

These are the conditions you need to know and screen for with appropriate blood tests.

Test	Purpose	Expected in Pseudogout
CBC d/c ^[1]^[6]	Assess for leukocytosis (infection?), anaemia (chronic disease?)	May show mild leukocytosis with neutrophilia during acute attack (inflammatory response). Marked leukocytosis raises suspicion for septic arthritis.
ESR / CRP ^[3]^[6]	Inflammatory markers	Elevated during acute attack. Useful if joint fluid examination equivocal ^[3]. However, also elevated in septic arthritis and other inflammatory conditions — not specific.
RFT / LFT ^[1]^[6]	"Electrolytes and renal and liver function to detect end-organ damage and guide antibiotic choice" ^[6]	Important for guiding NSAID/colchicine dosing (renal impairment) and if septic arthritis is in the differential (antibiotic choice).
Blood culture ^[1]^[6]	"Blood cultures should always be taken" ^[6] when septic arthritis is considered	Should be sent if any suspicion of infection — cannot rely on joint fluid alone (sensitivity ~50–75% for Gram stain).
RF / anti-CCP	Rule out RA if pseudo-RA phenotype	Expected to be negative in CPPD. If positive, consider true RA (or note that RF can be false-positive in elderly).
Serum urate	Rule out coexisting gout	May be elevated (gout and CPPD can coexist in ~5% of cases ^[2]). Not useful for CPPD diagnosis per se.

These are not first-line investigations but have specific roles:

Modality	Role in CPPD	When to Use
MRI	"Most appropriate imaging where required" ^[6]. Can detect synovitis, effusion, cartilage damage, crystal deposits (appear as low-signal areas in cartilage). Most sensitive for detecting osteomyelitis if coexisting infection suspected ^[6].	Diagnostic uncertainty, suspected deep joint infection (hip), assessing chronic structural damage
CT	Can detect chondrocalcinosis with higher sensitivity than plain X-ray (especially in spine and small joints). Dual-energy CT (DECT) is used for gout (urate identification) but is NOT specific for CPPD.	Equivocal plain X-ray, spinal CPPD ("crowned dens syndrome" — calcification around odontoid process)

4. Special Diagnostic Scenarios

Investigation	Key Finding in CPPD	Sensitivity	Notes
Joint aspiration — Polarized microscopy	Rhomboid-shaped, weakly positively birefringent crystals ^[1]^[2]^[3]	Gold standard	Also send Gram stain/culture to exclude infection
Joint aspiration — WCC	15,000–30,000/mm³, 90% neutrophils ^[2]	—	Inflammatory range; septic if > 50–100k
Plain X-ray	Chondrocalcinosis (punctate/linear calcification in cartilage) ^[1]^[2]^[8]	Moderate (misses early/small deposits)	Also look for degenerative changes
USG	Hyperechoic band within cartilage, parallel to bone cortex ^[2]	Good for cartilage and meniscal calcification	Operator-dependent; increasingly used at bedside
Serum Ca, P, Mg, ALP, ferritin	Screen for secondary causes	N/A	Should screen after diagnosis ^[2]
CBC, ESR/CRP, RFT/LFT	Inflammatory markers, guide drug dosing	N/A	Non-specific
Blood culture	Exclude bacteraemia/septic arthritis	N/A	"Blood cultures should always be taken" ^[6]
CT	Higher sensitivity for chondrocalcinosis (spine, small joints)	High	Crowned dens syndrome
MRI	Synovitis, effusion, structural damage, r/o osteomyelitis	High	"Most appropriate imaging where required" ^[6]

High Yield Summary — Diagnosis of Pseudogout

Diagnosis is NOT based on clinical features alone — requires arthrocentesis and/or X-ray ^[2].
Definite CPPD disease = positively birefringent crystals on polarized LM + chondrocalcinosis on X-ray ^[2].
Probable CPPD disease = either crystals on aspirate OR chondrocalcinosis on X-ray (but not both) ^[2].
Synovial fluid aspiration is key — send for polarized microscopy, WCC + differential, Gram stain, C/ST ^[6].
CPPD crystals: rhomboid, weakly positively birefringent (blue when parallel to compensator). Smaller and harder to see than MSU crystals.
Synovial WCC: 15,000–30,000 with 90% neutrophils ^[2] — inflammatory but lower than septic arthritis ( > 50k).
X-ray: chondrocalcinosis = punctate/linear calcification in fibrocartilage (knee menisci, wrist TFCC, pubic symphysis) ^[1]^[2].
After diagnosis, screen metabolic causes: Ca, P, Mg, ALP, ferritin ^[2]. Add TSH, PTH, ceruloplasmin if age < 55 ^[6].
Warfarin does not contraindicate needle aspiration ^[6].
Blood cultures should always be taken when septic arthritis is considered ^[6].
USG: hyperechoic band within cartilage (cf. gout double contour sign on surface of cartilage) ^[2].

Active Recall - Diagnostic Criteria, Algorithm and Investigations for Pseudogout

References

^[1] Senior notes: Maksim Medicine Notes.pdf (Rheumatology, pp. 309, 327–331) ^[2] Senior notes: Ryan Ho Rheumatology.pdf (Sections 2.1, 2.4.2, pp. 28–42) ^[3] Senior notes: Ryan Ho Fundamentals.pdf (Section 3.7.1–3.7.2, pp. 406–410) ^[6] Lecture slides: GC 075. Pain red joint.pdf (pp. 5, 23, 54, 57) ^[8] Senior notes: Maksim Surgery Notes.pdf (pp. 272, 275)

Management of Pseudogout (CPPD Disease)

1. Acute Pseudogout Management

Supportive measures: ice pack, immobilization, joint rest for 48–72h ^[2]

Measure	Mechanism	Practical Notes
Ice packs	Local vasoconstriction → reduced inflammatory exudate and swelling; also provides analgesic effect by reducing nerve conduction velocity	Apply 15–20 mins on, then off. Protect skin with cloth barrier.
Joint immobilization/rest	Reduces mechanical shear stress on inflamed synovium → reduces crystal shedding and nociceptor activation	48–72 hours of relative rest ^[2], then gradually mobilize to prevent stiffness/contracture
Elevation	Gravity-assisted venous and lymphatic drainage → reduces oedema	Elevate the affected limb above heart level

1C. Systemic Anti-Inflammatory Therapy (For Polyarticular or When IA Injection Not Feasible)

Management is the same as gout: NSAID, IA steroid, colchicine ^[1]

Systemic anti-inflammatory drug if > 2 joints involved ^[2]

There are three main systemic options. The choice depends on patient comorbidities:

Aspect	Details
Mechanism	NSAIDs inhibit cyclooxygenase (COX-1 and COX-2) → ↓prostaglandin synthesis (especially PGE₂) → ↓vasodilation, ↓vascular permeability, ↓pain sensitization, ↓fever
Regimen	High dose initially, tapering over 5–7 days. E.g., indomethacin 50 mg TDS × 2 days then 25 mg TDS × 3 days; or naproxen 500 mg BD × 5 days ^[1]
Why high dose then taper?	You need to overwhelm the inflammatory cascade early. Once the crystal-driven inflammation begins to subside (as neutrophils clear and IL-1β levels fall), you can reduce the dose.
PPI co-prescription	Always consider adding a PPI (e.g., omeprazole 20 mg daily) because NSAIDs inhibit COX-1 in gastric mucosa → ↓protective prostaglandins → risk of peptic ulceration
Indications	Polyarticular pseudogout, no renal impairment, no GI/cardiovascular contraindications
Contraindications	Renal impairment (NSAIDs reduce renal prostaglandin-mediated afferent arteriolar dilation → ↓GFR → AKI); active peptic ulcer disease; heart failure (fluid retention, ↑afterload); anticoagulant use (↑bleeding risk); elderly (higher risk of all the above)
Special note	Renal impairment: reduce dose ^[1]. COX-2 selective inhibitors (e.g., celecoxib) have lower GI risk but still carry renal and cardiovascular risk.

In practice, many pseudogout patients are elderly with CKD and cardiovascular disease → NSAIDs are often relatively contraindicated, making colchicine or steroids the preferred choice.

Aspect	Details
Mechanism	Colchicine ("col-chi-cine", from Colchicum autumnale — autumn crocus) binds tubulin → disrupts microtubule polymerization → inhibits neutrophil chemotaxis, adhesion, phagocytosis, and NLRP3 inflammasome assembly. Effectively "disarms" the neutrophils that drive the acute crystal-induced inflammation.
Why it works in crystal disease specifically	Crystal arthritis is uniquely dependent on neutrophil-driven inflammation via the NLRP3 inflammasome → IL-1β pathway. Colchicine directly inhibits the assembly of the inflammasome and the neutrophil functions required for crystal phagocytosis and inflammatory amplification.
Dose for acute attack	Low-dose regimen (current standard): 0.5 mg TDS or 1 mg then 0.5 mg 1 hour later (max 1.5 mg in first 24h), then 0.5 mg BD–TDS until attack resolves
Dose for prophylaxis	0.5 mg once or twice daily (long-term low-dose to prevent recurrent attacks)
Indications	NSAID contraindicated (renal impairment, GI risk, cardiovascular disease); polyarticular attacks; prophylaxis of recurrent attacks
Contraindications / Cautions	Severe renal impairment (colchicine is renally cleared — dose reduction or avoidance if eGFR < 30); hepatic impairment; concurrent use of P-glycoprotein/CYP3A4 inhibitors (e.g., clarithromycin, cyclosporine) → markedly ↑colchicine levels → toxicity risk
Side effects	GI (diarrhoea, nausea, abdominal cramps — dose-limiting); bone marrow suppression (rare at standard doses); myopathy, neuropathy (chronic use, especially with renal impairment)
Key point	Colchicine works best when given early (within 12–24h of symptom onset). Effectiveness decreases substantially if started > 36h after attack onset.

Aspect	Details
Mechanism	Broad suppression of the inflammatory cascade: inhibits NF-κB transcription factor → ↓pro-inflammatory cytokines (IL-1β, IL-6, TNF-α); inhibits phospholipase A₂ → ↓prostaglandins and leukotrienes; ↓neutrophil migration and activity
Regimen (PO)	Prednisolone 20–30 mg daily for 3–5 days, then taper over 7–10 days. Or equivalent dose of methylprednisolone.
Regimen (IM)	Single IM injection of triamcinolone 40–80 mg or methylprednisolone 80–120 mg — useful when oral intake is not possible
Indications	Both NSAIDs and colchicine contraindicated; polyarticular flare; oral intake not possible (IM/IV route); severe systemic upset
Contraindications / Cautions	Active or suspected infection (must exclude septic arthritis first); uncontrolled diabetes (hyperglycaemia); decompensated heart failure (fluid retention); active peptic ulcer. Short courses (5–7 days) generally well-tolerated even in these patients.
Pros	Effective, rapid onset, relatively safe for short course even in CKD patients (unlike NSAIDs)
Cons	Hyperglycaemia (important in elderly diabetic patients — common in pseudogout demographic); fluid retention; insomnia; immunosuppression

Choosing Between the Three Agents — Practical Decision-Making

Patient Scenario	Best Choice	Why
Young/middle-aged, no CKD, no GI history	NSAID (e.g., naproxen, indomethacin)	Most potent and rapid anti-inflammatory; well-tolerated in young
Elderly with CKD (eGFR < 60)	Colchicine (dose-adjusted) or systemic steroid	NSAIDs contraindicated (renal prostaglandin inhibition → AKI)
On anticoagulants	Colchicine or systemic steroid	NSAIDs ↑bleeding risk
Diabetic patient	Colchicine or NSAID (if renal function OK)	Steroids cause hyperglycaemia
Septic arthritis not yet excluded	None of the above until Gram stain/culture available	IA steroid and systemic immunosuppression in the face of sepsis = disaster
1–2 joints, infection excluded	IA aspiration + IA steroid	First-line, most effective, least systemic side effects

Correction of underlying cause, e.g. hyperparathyroidism ^[2]

This is the only truly "disease-modifying" intervention in CPPD:

Cause	Treatment	Impact on CPPD
Hyperparathyroidism	Parathyroidectomy (if primary hyperPTH meets surgical indications)	Normalizes Ca metabolism; may reduce frequency of acute attacks, but existing chondrocalcinosis usually does not regress. NB: Parathyroidectomy itself can trigger an acute attack post-operatively ^[2].
Haemochromatosis	Phlebotomy, iron chelation	Reduces iron load but arthropathy usually does NOT respond to iron removal ^[4] — damage is already done
Hypomagnesaemia	Magnesium supplementation (PO or IV)	Restores Mg as cofactor for pyrophosphatases; may reduce PPi accumulation. Small studies show improvement in attack frequency.
Hypophosphatasia	Enzyme replacement therapy (asfotase alfa) in severe cases	Very rare; specialist management
Hypothyroidism	Levothyroxine replacement	Treats the metabolic abnormality; may reduce but not eliminate CPPD
Wilson's disease	Penicillamine, trientine, zinc	Copper chelation; arthropathy may partially improve

Important Exam Point: Treating the Cause Does NOT Dissolve Existing Crystals

Even when you treat the underlying metabolic cause (e.g., parathyroidectomy for hyperPTH), the CPPD crystals already deposited in cartilage persist. Treating the cause prevents further crystal accumulation and may reduce attack frequency, but chondrocalcinosis typically does not regress on X-ray. This is fundamentally different from gout, where urate-lowering therapy can actually dissolve MSU crystals and shrink tophi over time.

3. Chronic/Prophylactic Management

For patients with recurrent acute attacks or chronic symptoms (pseudo-OA, pseudo-RA), ongoing management is needed:

Agent	Dose	Indication	Mechanism in Prophylaxis
Low-dose colchicine	0.5 mg once or twice daily	Recurrent acute pseudogout attacks	Continuously inhibits NLRP3 inflammasome and neutrophil function at a low level → raises the threshold for crystal-induced inflammation
Low-dose NSAID	E.g., naproxen 250 mg BD	Alternative to colchicine if tolerated	Ongoing COX inhibition → ↓baseline prostaglandin-mediated inflammatory readiness
Low-dose prednisolone	5–7.5 mg daily	Both colchicine and NSAID contraindicated	Use the minimum effective dose; monitor for steroid side effects (osteoporosis, diabetes, hypertension)
Hydroxychloroquine	200 mg daily	Pseudo-RA phenotype (chronic inflammatory CPPD)	Anti-inflammatory, modulates TLR signalling and lysosomal pH; some evidence for benefit in chronic CPPD — often trialled when other agents fail
Methotrexate	7.5–15 mg weekly	Refractory pseudo-RA (limited evidence)	Broad immunosuppression; case series and small trials show benefit in resistant chronic CPPD
IL-1 inhibitors (anakinra, canakinumab)	Specialist use	Refractory acute or chronic CPPD, all other agents failed/contraindicated	Directly blocks IL-1β — the key cytokine in the NLRP3 inflammasome–crystal inflammation pathway. Logical target but expensive; limited formal evidence in CPPD (better evidence in gout)

Why IL-1 blockade makes pathophysiological sense: The entire crystal-induced inflammatory cascade converges on IL-1β release via the NLRP3 inflammasome. Blocking IL-1β with anakinra (recombinant IL-1 receptor antagonist) or canakinumab (anti-IL-1β monoclonal antibody) "cuts off the head of the snake." Used in practice for refractory cases but not yet standard first-line.

Intervention	Purpose	Details
Physiotherapy	Maintain ROM, strengthen periarticular muscles, prevent contractures	Particularly important in pseudo-OA and pseudo-RA; start early after acute attack settles
Weight management	Reduce mechanical load on weight-bearing joints (especially knees)	Relevant since knee is the most commonly affected joint
Walking aids	Offload affected joints	Walking stick held in contralateral hand to affected knee
Joint protection education	Avoid high-impact activities, pacing activities	Especially important in severe pseudo-OA

Surgery plays a limited role and is reserved for end-stage structural damage:

Procedure	Indication	Notes
Arthroplasty (joint replacement) ^[8]	End-stage joint destruction (pseudo-OA with severe degeneration), failed conservative management, significant functional impairment	TKR for knee, THR for hip, shoulder replacement for glenohumeral involvement
Arthrodesis (joint fusion) ^[8]	Small joint disease with severe degeneration	E.g., wrist arthrodesis for severely degenerated radiocarpal joint
Arthroscopic debridement ^[3]	Remove loose bodies, debride damaged cartilage, drainage for pain relief	Diagnostic: assess degree of cartilage damage, synovial biopsy for equivocal cases. Therapeutic: debridement of damaged cartilage, removal of loose bodies, drainage for pain relief ^[3]
Spinal decompression	Pseudo-AS with spinal stenosis or neurological compromise	Rare

5. Special Scenarios

Aspect	Pseudogout (CPPD)	Gout (MSU)
Acute attack treatment	NSAID, IA steroid, colchicine ^[1] — identical	NSAID, IA steroid, colchicine — identical
Disease-modifying therapy	NONE — no crystal-dissolving agent exists	Urate-lowering therapy (allopurinol, febuxostat, probenecid)
Long-term prophylaxis	Low-dose colchicine, low-dose NSAID	Urate-lowering therapy (target serum urate < 0.36 mmol/L)
Treat underlying cause	Correct metabolic cause (hyperPTH, hypoMg, etc.) ^[2]	Lifestyle (diet, alcohol), stop offending drugs, treat CKD
Anti-IL-1 for refractory	Anakinra/canakinumab (limited evidence)	Anakinra/canakinumab (stronger evidence)

High Yield Summary — Management of Pseudogout

Management is the same as gout for acute attacks: NSAID, IA steroid, colchicine ^[1].
First-line for 1–2 joints: Thorough joint aspiration + IA glucocorticoid injection ^[2] — but must r/o septic arthritis before injection of steroid ^[2].
IA steroid regimen: Triamcinolone acetonide 40 mg + 1–2 mL 1% lidocaine for large joints; relief within 8–24h ^[2].
Systemic therapy if > 2 joints: NSAID (with PPI) vs colchicine vs systemic steroid — choice depends on renal function, GI risk, cardiovascular risk.
Supportive: ice pack, immobilization, joint rest for 48–72h ^[2].
No disease-modifying therapy exists for CPPD — unlike gout, you cannot dissolve the crystals.
Correction of underlying cause (e.g. hyperparathyroidism) ^[2] is the only way to modify disease progression, but existing crystals persist.
Chronic prophylaxis: low-dose colchicine (0.5 mg daily–BD), low-dose NSAID, or hydroxychloroquine for pseudo-RA phenotype.
IL-1 inhibitors (anakinra) are used for refractory cases — pathophysiologically rational (targets NLRP3/IL-1β pathway).
Surgery (arthroplasty, arthrodesis) reserved for end-stage structural damage.

Active Recall - Management of Pseudogout

References

^[1] Senior notes: Maksim Medicine Notes.pdf (Rheumatology, pp. 328–331) ^[2] Senior notes: Ryan Ho Rheumatology.pdf (Section 2.4.2, pp. 41–42) ^[3] Senior notes: Ryan Ho Fundamentals.pdf (Section 3.7.1, p. 407) ^[4] Senior notes: Ryan Ho GI.pdf (p. 294 — Haemochromatosis arthropathy) ^[8] Senior notes: Maksim Surgery Notes.pdf (pp. 270–272)

Complications of Pseudogout (CPPD Disease)

OA with CPPD (pseudo-OA, most common): accelerated joint degeneration especially when involving joints atypical for OA and early calcification present ^[2]

This is the most clinically significant long-term complication of CPPD disease.

Mechanism from first principles:

Vicious cycle:
OA → cartilage damage → ↑PPi release → CPPD crystal formation
CPPD crystals → amplify cartilage degradation (direct mechanical + inflammatory MMP release)
→ more OA → more crystals → accelerated destruction

CPPD crystals activate synovial macrophages → release of matrix metalloproteinases (MMP-1, MMP-3, MMP-13) and pro-inflammatory cytokines (IL-1β, TNF-α)
These MMPs directly degrade type II collagen and aggrecan in cartilage
~50% of pseudo-OA patients have superimposed episodes of acute inflammatory arthritis ^[2], each episode causing additional cartilage damage
The degeneration is disproportionately severe and occurs in joints atypical for primary OA (wrist, MCPJ, shoulder, elbow) ^[2]

X-ray features of advanced pseudo-OA ^[2]:

Subchondral cysts, osteophytes, decreased joint space ^[2]
MCPJ: squared-off bone ends and hook-like osteophytes ^[2]
Wrist: isolated/unusually extensive radiocarpal joint narrowing ^[2]
PFJ (patellofemoral joint): severe space degeneration ^[2]

Clinical consequence: Progressive pain, stiffness, and loss of function → eventual need for joint replacement (arthroplasty) ^[8].

Spinal involvement: spinal stiffness ± bony ankylosis, can mimic ankylosing spondylitis ^[2]

CPPD crystal deposition in spinal structures can cause several complications:

Spinal Complication	Mechanism	Clinical Impact
Crowned dens syndrome	CPPD deposition around odontoid process (C2)	Acute severe neck pain + fever mimicking meningitis. Can lead to C1–C2 instability if chronic.
Spinal stenosis	Crystal deposition in ligamentum flavum → hypertrophy → canal narrowing	Neurogenic claudication, myelopathy, radiculopathy
Bony ankylosis	Chronic crystal-driven inflammation → periarticular ossification	Progressive loss of spinal mobility, resembling AS clinically
Compression fracture	Weakened vertebral bodies from chronic inflammation and altered bone metabolism	Acute back pain, kyphotic deformity, height loss

2. Complications of Missed Diagnosis / Diagnostic Error

Complication	Cause	Mechanism
NSAID-induced AKI	NSAIDs in elderly patients with CKD	NSAIDs inhibit prostaglandin-mediated afferent arteriolar dilation → ↓GFR → acute kidney injury. The pseudogout demographic (elderly, often with CKD) is at the highest risk.
NSAID-induced GI bleeding	NSAIDs inhibit COX-1 → ↓protective gastric prostaglandins	Peptic ulceration, upper GI haemorrhage. Elderly patients often on concurrent anticoagulants/antiplatelets, compounding risk.
Steroid-induced hyperglycaemia	Systemic or IA corticosteroids	Glucocorticoids increase hepatic gluconeogenesis, cause peripheral insulin resistance, and reduce glucose uptake by muscle. Particularly dangerous in the diabetic elderly patient.
Colchicine toxicity	Colchicine overdose or use in renal/hepatic impairment	Colchicine has a narrow therapeutic index. Toxicity → severe GI symptoms (diarrhoea, vomiting), bone marrow suppression (pancytopaenia), multi-organ failure, death. Drug interactions with CYP3A4/P-gp inhibitors (clarithromycin, cyclosporine) dramatically increase risk.
Septic arthritis from IA injection	Introduction of skin flora during arthrocentesis	Risk ~1/15,000–1/50,000 per injection with proper aseptic technique. Must use sterile technique and prep skin adequately.
Post-injection flare	Steroid crystal-induced synovitis	Microcrystalline steroid suspension can itself provoke a transient inflammatory response (usually settles within 24–48 hours). Can be confused with failed treatment or developing infection.

3. Complications of Associated Metabolic Diseases

CPPD disease does not exist in isolation — it is frequently associated with systemic metabolic conditions that carry their own serious complications. Failure to screen for and treat these conditions is a significant source of preventable morbidity.

Joint pain: chondrocalcinosis, arthritis, pseudogout and gout ^[9]

If CPPD is the presenting feature of undiagnosed primary hyperparathyroidism, the patient is at risk of all the complications of hypercalcaemia:

System	Complication	Mechanism
Renal	Renal stone, nephrocalcinosis, CKD ^[9]	Hypercalciuria → calcium stone formation; calcium deposition in renal parenchyma → progressive nephron loss
Skeletal	Osteoporosis, pathological fractures, osteitis fibrosa cystica ^[9]	Continuous PTH excess → cortical bone resorption; 2–3× risk of vertebral, distal forearm, pelvic fractures ^[9]
Cardiovascular	HTN, LVH, arrhythmia ^[9]	Calcium effects on vascular smooth muscle tone and cardiac conduction
GI	Epigastric pain, dyspepsia ^[9]	Calcium stimulates gastrin release → ↑acid secretion
Neuropsychiatric	Depression, confusion, fatigue	Calcium effects on neuronal excitability

Key exam point: Post-parathyroidectomy pseudogout flare — surgery itself is a trigger for acute pseudogout (rapid Ca drop alters crystal solubility) ^[2]. The treating team must warn the patient and be prepared to manage acute attacks post-operatively.

These are often under-recognized but have a major impact on quality of life in the elderly:

Complication	Mechanism	Clinical Impact
Immobility / deconditioning	Recurrent attacks + chronic pain → reduced activity → muscle atrophy, cardiovascular deconditioning	Falls risk, DVT/PE, pressure ulcers, sarcopenia
Falls and fractures	Knee and hip involvement → gait instability; pain avoidance behaviour → altered biomechanics	Hip fractures in the elderly carry ~30% 1-year mortality
Loss of independence	Chronic pain + reduced ROM in hands (wrist MCPJ) and knees → inability to perform ADLs	Need for carers, social services, residential care
Depression and anxiety	Chronic pain, loss of function, social isolation	Underdiagnosed in elderly; worsens pain perception (central sensitization)
Polypharmacy complications	NSAID/colchicine/steroid added to existing medications → drug interactions	CKD progression, GI bleeding, falls (from steroid-induced proximal myopathy)

Category	Complication	Key Mechanism	Severity
Recurrent attacks	Progressively frequent, prolonged, polyarticular flares	Persistent crystal burden; ongoing cartilage damage releases more crystals	Moderate–High
Structural	Accelerated OA (pseudo-OA) ^[2]	Crystal amplification of cartilage degradation	High
Structural	Severe destructive arthropathy (pseudo-neuropathic) ^[2]	Overwhelming crystal-driven tissue destruction	Very High
Structural	Flexion contractures ^[2]	Chronic synovitis → capsular fibrosis	Moderate
Spinal	Crowned dens syndrome, spinal stenosis, ankylosis	Crystal deposition in spine	Moderate–High
Diagnostic	Missed septic arthritis ^[1]	Assumption that hot joint = crystal flare without aspirating	Life-threatening
Iatrogenic	NSAID nephrotoxicity, GI bleeding, colchicine toxicity, steroid hyperglycaemia	Drugs used to treat CPPD	Variable
Metabolic	Complications of hyperPTH, haemochromatosis, hypothyroidism, hypoMg	Underlying associated metabolic disease	Variable–High
Functional	Immobility, falls, loss of independence, depression	Chronic pain + recurrent flares in elderly population	High

High Yield Summary — Complications of Pseudogout

Recurrent acute attacks become more frequent and polyarticular over time — no crystal-dissolving therapy exists.
Accelerated joint degeneration (pseudo-OA) ^[2] is the most common and clinically significant long-term complication — CPPD amplifies OA damage, especially in atypical joints (wrist, MCPJ, shoulder).
Severe destructive arthropathy can mimic neuropathic (Charcot) arthropathy ^[2] — devastating joint destruction with preserved sensation.
Flexion contractures develop from chronic synovitis and capsular fibrosis ^[2].
The most dangerous "complication" is missed septic arthritis — crystals and infection can coexist ^[1]; always aspirate and culture.
Iatrogenic complications (NSAID AKI, GI bleeding; colchicine toxicity; steroid hyperglycaemia) are common because CPPD patients are elderly with multiple comorbidities.
Screen for and treat associated metabolic diseases — undiagnosed hyperparathyroidism, haemochromatosis, hypomagnesaemia, and hypothyroidism carry their own serious complications.
Haemochromatosis arthropathy does NOT respond to iron removal ^[4].
Post-parathyroidectomy pseudogout flare is a classic post-operative complication ^[2].
Functional impact on elderly patients is severe: immobility → falls → fractures → loss of independence → depression.

Active Recall - Complications of Pseudogout

References

^[1] Senior notes: Maksim Medicine Notes.pdf (Rheumatology, pp. 329–331) ^[2] Senior notes: Ryan Ho Rheumatology.pdf (Sections 2.4.1.2, 2.4.2, 2.8, pp. 38–42, 67) ^[4] Senior notes: Ryan Ho GI.pdf (p. 294 — Haemochromatosis arthropathy) ^[5] Senior notes: Ryan Ho Rheumatology.pdf (Section 2.8, p. 67 — Septic arthritis risk factors) ^[8] Senior notes: Maksim Surgery Notes.pdf (pp. 270–272) ^[9] Senior notes: Ryan Ho Endocrine.pdf (pp. 42, 111 — Hyperparathyroidism, Acromegaly)

High Yield Summary

CPPD disease is a spectrum: asymptomatic chondrocalcinosis → acute pseudogout → pseudo-OA → pseudo-RA → severe destructive arthropathy.
Crystals: rhomboid-shaped, positively birefringent under polarized light (cf. gout: needle-shaped, negatively birefringent).
Joints: knee (> 50%), wrist, shoulder — more proximal than gout.
Demographics: elderly (> 60, rare < 55), M:F ≈ 1:1.
If age < 55, screen for secondary causes: hyperPTH, haemochromatosis, hypoMg, hypophosphatasia, hypothyroidism, Wilson's disease, familial chondrocalcinosis.
Pathophysiology: ↑PPi production by chondrocytes + ↓PPi clearance → PPi complexes with Ca²⁺ → CPPD crystals → shed into joint → NLRP3 inflammasome → IL-1β → acute inflammation.
Triggers: trauma, surgery (especially parathyroidectomy), severe illness, bisphosphonates.
X-ray: chondrocalcinosis (punctate/linear calcification in cartilage — especially knee menisci and wrist TFCC).
Acute pseudogout attacks last longer than gout (may persist > 1–2 weeks) and can present with cluster attacks.
No disease-modifying therapy for CPPD exists (unlike gout which has urate-lowering therapy) — management is symptomatic + treat underlying metabolic cause.

High Yield Summary — Differential Diagnosis of Pseudogout

The #1 differential for acute pseudogout is septic arthritis — must be excluded by joint aspiration (Gram stain, C/ST) in EVERY case. Crystals and infection can coexist.
Gout vs pseudogout: different crystals (MSU needle/−ve biref. vs CPPD rhomboid/+ve biref.), different joints (1st MTP vs knee/wrist), different demographics (younger men vs elderly M=F).
Pseudo-RA vs true RA: pseudo-RA is non-erosive, RF/anti-CCP negative, with independent wax-and-wane pattern in individual joints (not synchronous like RA).
Pseudo-OA clue: OA in atypical joints (wrist, MCPJ, shoulder, elbow) → suspect CPPD and look for chondrocalcinosis.
Chondrocalcinosis on X-ray is not specific for CPPD — also seen in normal ageing and OA.
Age < 55 with CPPD: screen for secondary causes (hyperPTH, haemochromatosis, hypoMg, hypophosphatasia, hypothyroidism, Wilson's).
Acromegaly is associated with both hypertrophic arthropathy and pseudogout.
Trauma can both mimic AND trigger pseudogout — trauma causes crystal shedding from cartilage.

High Yield Summary — Diagnosis of Pseudogout

Diagnosis is NOT based on clinical features alone — requires arthrocentesis and/or X-ray ^[2].
Definite CPPD disease = positively birefringent crystals on polarized LM + chondrocalcinosis on X-ray ^[2].
Probable CPPD disease = either crystals on aspirate OR chondrocalcinosis on X-ray (but not both) ^[2].
Synovial fluid aspiration is key — send for polarized microscopy, WCC + differential, Gram stain, C/ST ^[6].
CPPD crystals: rhomboid, weakly positively birefringent (blue when parallel to compensator). Smaller and harder to see than MSU crystals.
Synovial WCC: 15,000–30,000 with 90% neutrophils ^[2] — inflammatory but lower than septic arthritis ( > 50k).
X-ray: chondrocalcinosis = punctate/linear calcification in fibrocartilage (knee menisci, wrist TFCC, pubic symphysis) ^[1]^[2].
After diagnosis, screen metabolic causes: Ca, P, Mg, ALP, ferritin ^[2]. Add TSH, PTH, ceruloplasmin if age < 55 ^[6].
Warfarin does not contraindicate needle aspiration ^[6].
Blood cultures should always be taken when septic arthritis is considered ^[6].
USG: hyperechoic band within cartilage (cf. gout double contour sign on surface of cartilage) ^[2].

High Yield Summary — Management of Pseudogout

Management is the same as gout for acute attacks: NSAID, IA steroid, colchicine ^[1].
First-line for 1–2 joints: Thorough joint aspiration + IA glucocorticoid injection ^[2] — but must r/o septic arthritis before injection of steroid ^[2].
IA steroid regimen: Triamcinolone acetonide 40 mg + 1–2 mL 1% lidocaine for large joints; relief within 8–24h ^[2].
Systemic therapy if > 2 joints: NSAID (with PPI) vs colchicine vs systemic steroid — choice depends on renal function, GI risk, cardiovascular risk.
Supportive: ice pack, immobilization, joint rest for 48–72h ^[2].
No disease-modifying therapy exists for CPPD — unlike gout, you cannot dissolve the crystals.
Correction of underlying cause (e.g. hyperparathyroidism) ^[2] is the only way to modify disease progression, but existing crystals persist.
Chronic prophylaxis: low-dose colchicine (0.5 mg daily–BD), low-dose NSAID, or hydroxychloroquine for pseudo-RA phenotype.
IL-1 inhibitors (anakinra) are used for refractory cases — pathophysiologically rational (targets NLRP3/IL-1β pathway).
Surgery (arthroplasty, arthrodesis) reserved for end-stage structural damage.

High Yield Summary — Complications of Pseudogout

Recurrent acute attacks become more frequent and polyarticular over time — no crystal-dissolving therapy exists.
Accelerated joint degeneration (pseudo-OA) ^[2] is the most common and clinically significant long-term complication — CPPD amplifies OA damage, especially in atypical joints (wrist, MCPJ, shoulder).
Severe destructive arthropathy can mimic neuropathic (Charcot) arthropathy ^[2] — devastating joint destruction with preserved sensation.
Flexion contractures develop from chronic synovitis and capsular fibrosis ^[2].
The most dangerous "complication" is missed septic arthritis — crystals and infection can coexist ^[1]; always aspirate and culture.
Iatrogenic complications (NSAID AKI, GI bleeding; colchicine toxicity; steroid hyperglycaemia) are common because CPPD patients are elderly with multiple comorbidities.
Screen for and treat associated metabolic diseases — undiagnosed hyperparathyroidism, haemochromatosis, hypomagnesaemia, and hypothyroidism carry their own serious complications.
Haemochromatosis arthropathy does NOT respond to iron removal ^[4].
Post-parathyroidectomy pseudogout flare is a classic post-operative complication ^[2].
Functional impact on elderly patients is severe: immobility → falls → fractures → loss of independence → depression.

Pseudogout

1. Definition

2. Epidemiology

Prevalence and Incidence

Demographics

Hong Kong Context

3. Anatomy and Function

Joint Cartilage — The Target Tissue

Joints Most Commonly Affected

4. Etiology and Pathophysiology

4A. Etiology (Causes)

i. Idiopathic (Most Common)

ii. Familial (Hereditary) Chondrocalcinosis

iii. Metabolic Diseases (Must-Know Secondary Causes)

iv. Joint-Level Factors

4B. Pathophysiology (Crystal Formation → Inflammation)

5. Classification

6. Clinical Features

6A. Symptoms

6B. Signs

Clinical Pearls — Distinguishing Pseudogout from Gout and Septic Arthritis

6C. Important Clinical Associations to Elicit on History

7. Comparison of Crystal-Induced Arthropathies (Summary Table)

8. Role of Osteoarthritis in CPPD (Important Concept)

Active Recall - Pseudogout Definition, Epidemiology, Etiology, Pathophysiology and Clinical Features

References

Why Differential Diagnosis Matters in Pseudogout

Framing the Differential: Which Clinical Phenotype Are You Dealing With?

A. Differential Diagnosis of Acute Pseudogout (Acute Monoarthritis)

B. Differential Diagnosis of Chronic CPPD Phenotypes

Pseudo-RA vs True RA

Pseudo-OA vs Primary OA

C. The Critical Distinction: Pseudogout vs Septic Arthritis

D. Approach to Differential Diagnosis — Clinical Decision Framework

E. Differential Diagnosis of Chondrocalcinosis on X-ray

F. Summary: How to Differentiate Pseudogout from Its Key Mimics

G. Conditions Associated with CPPD That May Confuse the Differential

Active Recall - Differential Diagnosis of Pseudogout

The Diagnostic Philosophy — Why You Cannot Diagnose Pseudogout Clinically

1. Diagnostic Criteria for CPPD Disease

2. Diagnostic Algorithm

3. Investigation Modalities — Detailed Breakdown

3A. Joint Aspiration (Arthrocentesis) — The Cornerstone Investigation

What to Send Synovial Fluid For

Synovial Fluid WCC Interpretation

3B. Plain X-ray — Looking for Chondrocalcinosis and Structural Changes

3C. Ultrasound (USG)

3D. Blood Tests — Screening for Secondary Causes

3E. Other Blood Tests — Acute Inflammatory Workup

3F. Advanced Imaging — MRI and CT

4. Special Diagnostic Scenarios

4A. "Crowned Dens Syndrome" (CDS)

4B. Post-Surgical / Post-Illness Pseudogout

5. Comprehensive Investigation Summary Table

Active Recall - Diagnostic Criteria, Algorithm and Investigations for Pseudogout

The Fundamental Management Challenge

Management Algorithm

1. Acute Pseudogout Management

1A. Supportive (Non-Pharmacological) Measures

1B. Joint Aspiration + Intra-Articular Glucocorticoid Injection (First-Line for 1–2 Joints)

1C. Systemic Anti-Inflammatory Therapy (For Polyarticular or When IA Injection Not Feasible)

Option 1: NSAIDs (± PPI)

Option 2: Colchicine

Option 3: Corticosteroids (Systemic — PO/IM/IV)

2. Management of Underlying/Secondary Causes

3. Chronic/Prophylactic Management

3A. Pharmacological Prophylaxis

3B. Non-Pharmacological Chronic Management

4. Surgical Management

5. Special Scenarios

5A. Hospital-Acquired / Post-Operative Pseudogout

5B. Asymptomatic Chondrocalcinosis

5C. Crowned Dens Syndrome

6. Comparison: Management of Pseudogout vs Gout

Active Recall - Management of Pseudogout

Why Understanding Complications Matters

1. Joint-Related Complications

1A. Recurrent Acute Pseudogout Attacks

1B. Accelerated Joint Degeneration (Pseudo-OA)

1C. Severe Destructive Arthropathy (Pseudo-Neuropathic Joint)