Aplastic Anaemia
Aplastic anaemia is a bone marrow failure syndrome characterized by pancytopenia and hypocellular marrow resulting from destruction or suppression of haematopoietic stem cells.
Aplastic Anaemia
Aplastic anaemia (AA) is pancytopenia resulting from bone marrow hypoplasia or aplasia [1][2]. Breaking the name down: "a-" (without) + "plastic" (formation/growth) = failure of formation; "anaemia" = low haemoglobin. So the name literally tells you: the bone marrow has failed to form blood cells.
More precisely, AA is a bone marrow failure syndrome in which all three haematopoietic lineages (erythroid, myeloid, megakaryocytic) are reduced, leaving behind a marrow that is largely replaced by fat. The key conceptual point is that the problem is NOT abnormal cells proliferating — it is the absence of normal cells [3].
This is a critical distinction: In leukaemia and MDS, the marrow is hypercellular with abnormal/malignant cells crowding out normal haematopoiesis. In aplastic anaemia, the marrow is hypocellular — it is empty. There are no abnormal cells, just a profound deficiency of normal haematopoietic stem cells (HSCs).
Key Concept — What Makes Aplastic Anaemia Unique
Aplastic anaemia = pancytopenia + hypocellular bone marrow + NO malignant infiltration + NO fibrosis. Think of it as a "factory shutdown" rather than a "factory takeover."
A related but distinct entity is pure red cell aplasia (PRA/PRCA), which affects only the erythroid lineage (isolated anaemia with absent reticulocytes, normal WBC and platelets) [1]. This is NOT aplastic anaemia proper but shares the concept of selective marrow failure.
- Rare disease: incidence approximately 4–6 per million per year in Asia — notably 2–3× higher in Asia (including Hong Kong, mainland China, Japan, Thailand) compared with the West (~2 per million/year) [2][4]. The reason for this geographic discrepancy is incompletely understood but may relate to environmental exposures (e.g. pesticides, traditional herbal medicines, benzene in industrial settings) and genetic susceptibility.
- M:F ratio ≈ 1:1 [2][4]
- 50% of cases occur in patients < 30 years old, but AA can present at any age [2][4]. There is a bimodal age distribution with peaks in:
- Adolescents/young adults (15–25 years)
- Elderly (> 60 years)
- In children, inherited bone marrow failure syndromes (e.g. Fanconi anaemia) must always be considered [4].
High Yield — Hong Kong/Asia Context
The incidence of acquired aplastic anaemia is 2–3× higher in Asia than in Western countries. This is a commonly tested epidemiological fact. When seeing a young patient in Hong Kong with pancytopenia and hypocellular marrow, AA should be high on the differential.
3. Anatomy and Function of the Bone Marrow
To understand AA, you need to understand what the bone marrow does and what goes wrong.
The bone marrow is the primary site of haematopoiesis from late fetal life onwards. In adults, active (red) marrow is concentrated in:
- Axial skeleton: vertebrae, pelvis (iliac crest — the usual biopsy site), sternum, ribs
- Proximal ends of long bones (femur, humerus)
The marrow consists of:
- Haematopoietic compartment: haematopoietic stem cells (HSCs), progenitor cells, maturing blood cell precursors
- Stromal/microenvironment compartment: fat cells (adipocytes), fibroblasts, endothelial cells, osteoblasts — these form the "niche" that supports HSCs
- Vascular sinusoids: allow mature blood cells to enter the circulation
- HSCs are pluripotent — they can self-renew and differentiate into all blood cell lineages
- They reside in specialised niches (endosteal niche near bone, perivascular niche near sinusoids)
- Normal marrow cellularity is roughly 100 minus the patient's age (e.g. a 30-year-old should have ~70% cellularity)
In AA, the HSC pool is destroyed or profoundly depleted. The marrow becomes hypocellular (often < 25% cellularity) and is replaced by fat (adipocytes) and stromal cells. Because the stem cells are gone, all downstream lineages fail:
| Lineage Affected | Result | Clinical Consequence |
|---|---|---|
| Erythroid | ↓ Red blood cells | Anaemia (fatigue, pallor, dyspnoea) |
| Myeloid (granulocytic) | ↓ Neutrophils | Recurrent/severe infections |
| Megakaryocytic | ↓ Platelets | Bleeding tendency |
Note: Lymphocytes are largely produced in lymphoid organs (thymus, lymph nodes, spleen) and are therefore relatively spared, which is why AA does NOT typically cause lymphopenia as a prominent feature.
4. Aetiology (with Focus on Hong Kong)
4.1 Acquired Causes (~95% of cases in adults)
| Drug Category | Examples | Mechanism |
|---|---|---|
| Cytotoxic drugs | Alkylating agents, antimetabolites | Anticipated, dose-dependent marrow suppression (nadir day 7–10); usually reversible [2] |
| Antibiotics | Chloramphenicol, sulphonamides | Idiosyncratic (Type B ADR), not dose-dependent; chloramphenicol is the classic example |
| NSAIDs | Phenylbutazone, indomethacin, diclofenac | Idiosyncratic |
| DMARDs | Penicillamine, gold | Idiosyncratic, immune-mediated |
| Thionamides (anti-thyroid) | Carbimazole, propylthiouracil | Idiosyncratic; can cause agranulocytosis or full AA |
| Anticonvulsants | Carbamazepine, phenytoin | Idiosyncratic |
| Alcohol | Ethanol | Direct toxic effect on HSCs |
HK-Relevant Drug Causes
In Hong Kong, the most exam-relevant drug causes are: chloramphenicol (classic, though rarely used now), carbimazole (commonly used for Graves' disease in HK), NSAIDs (very commonly prescribed), and carbamazepine/phenytoin (used in epilepsy). Also remember azathioprine — while it more commonly causes dose-dependent myelosuppression (especially with low TPMT activity), it can contribute to marrow failure [6].
- Benzene — industrial solvent; well-established cause of AA and leukaemia. Hong Kong's proximity to industrial areas in the Pearl River Delta makes this relevant.
- Toluene (glue-sniffing) [2]
- Organophosphates, DDT (pesticides) [2] — relevant in Asian agricultural communities
- Ionising radiation [2] — dose-dependent; used therapeutically (radiotherapy) or accidental exposure
This is a high-yield association:
- Non-A, non-B, non-C hepatitis (seronegative hepatitis) — the classic viral association
- AA develops 2–3 months after an episode of acute hepatitis [2]
- Especially in boys and young men [2]
- The causative virus has never been conclusively identified (hence "seronegative")
- Mechanism: the hepatitis virus (or the immune response it triggers) cross-reacts with and destroys HSCs
- "Hepatitis is well known to precede aplastic anaemia" [3]
- HIV [2]
- EBV [2]
- Parvovirus B19 — classically causes transient aplastic crisis (pure red cell aplasia) in patients with chronic haemolytic anaemia (e.g. sickle cell, hereditary spherocytosis), NOT full aplastic anaemia in immunocompetent individuals. However, in immunocompromised patients, persistent B19 infection can cause prolonged red cell aplasia.
- Paroxysmal nocturnal haemoglobinuria (PNH) — AA and PNH have a well-established overlap
- PNH is a clonal disorder caused by a somatic mutation in the PIGA gene (on X chromosome) → deficiency of GPI-anchored proteins (CD55, CD59) on blood cells → complement-mediated haemolysis, thrombosis
- Up to 40–50% of AA patients have small PNH clones detectable by flow cytometry
- AA can evolve into PNH, and vice versa
- The PNH clone may have a survival advantage in the setting of autoimmune attack on normal HSCs (because the altered surface makes them "invisible" to the immune attack)
- Myelodysplastic syndrome (MDS) — "hypoplastic MDS" can mimic AA [2]
- Rare but recognised; may resolve after delivery
- Mechanism unclear — possibly hormonal effects on HSCs or pregnancy-related immune dysregulation
These are inherited bone marrow failure syndromes (IBMFS) — important especially in paediatric patients [1][2][4]:
| Syndrome | Inheritance | Key Features | Diagnostic Test |
|---|---|---|---|
| Fanconi Anaemia (FA) | AR (most) / XR | Short stature, café-au-lait spots, thumb abnormalities (absent/hypoplastic thumbs, radial ray defects), renal malformations, microcephaly; ↑ risk of MDS/AML | Diepoxybutane (DEB) / mitomycin C chromosome breakage test [4][7] |
| Dyskeratosis Congenita (DC) | XR (most), AR, AD | Classic triad: nail dystrophy, oral leukoplakia, reticular skin pigmentation; telomere biology disorder → mutation in telomere-related genes (e.g. DKC1, TERC, TERT) | Telomere length measurement (very short telomeres) |
| Shwachman-Diamond Syndrome | AR | Exocrine pancreatic insufficiency + bone marrow failure + skeletal abnormalities | Genetic testing (SBDS gene); low trypsinogen/pancreatic isoamylase |
High Yield — Fanconi Anaemia
Fanconi anaemia is the most common inherited cause of aplastic anaemia. The DEB (diepoxybutane) instability/chromosome breakage test is the diagnostic test — it demonstrates excessive chromosomal breakage when cells are exposed to DNA crosslinking agents. This reflects the underlying defect in DNA repair mechanisms in FA. FA patients have a markedly increased risk of malignancy (MDS, AML, squamous cell carcinomas) [4][7].
5. Pathophysiology
Understanding the pathophysiology is crucial because it directly informs treatment strategy.
The pathophysiology involves T-cell–mediated destruction of the haematopoietic stem cell [3][5].
The current model:
-
Trigger/Initiating Event: An environmental insult (virus, drug, toxin) or an unknown antigen alters the immunological appearance of HSCs, or triggers an aberrant immune response.
-
Immune Activation:
- Cytotoxic CD8+ T cells (oligoclonal expansion) recognise and attack HSCs
- T-cell–mediated destruction of HSCs is postulated to be the cause of AA [3]
- Th1-type cytokine profile predominates: ↑ IFN-γ, ↑ TNF-α → these cytokines are directly toxic to HSCs and also upregulate Fas expression on HSCs, triggering Fas/FasL-mediated apoptosis
-
Genetic Susceptibility:
-
HSC Destruction:
- Direct killing by cytotoxic T cells (perforin/granzyme pathway)
- Fas/FasL-mediated apoptosis
- Cytokine-mediated suppression (IFN-γ, TNF-α)
- Result: profoundly depleted HSC pool → hypocellular marrow → pancytopenia
-
Evidence Supporting Autoimmune Mechanism:
- ~70% of patients respond to immunosuppressive therapy (ATG + Ciclosporin)
- In vitro: patient T cells suppress normal donor haematopoietic colony formation
- Clonal T-cell expansions found in AA patients
- Association with other autoimmune diseases
In some secondary cases, the mechanism is direct damage to HSCs without significant immune involvement:
- Cytotoxic drugs / radiation: directly damage DNA of rapidly dividing cells (including HSCs) → dose-dependent, usually predictable and reversible
- Benzene and other toxins: direct toxic effect on HSC DNA
- Viruses: may directly infect and lyse HSCs (in addition to triggering immune-mediated destruction)
In Fanconi anaemia, the underlying defect is in one of the Fanconi anaemia complementation group (FANC) genes — there are > 20 identified. These genes encode proteins involved in the DNA damage repair pathway, specifically the repair of interstrand crosslinks (ICLs) in DNA. When this pathway is defective:
- Accumulation of DNA damage → HSC apoptosis → progressive marrow failure
- Genomic instability → increased risk of MDS, AML, and solid tumours
In Dyskeratosis Congenita, the defect is in telomere maintenance genes. Telomeres shorten prematurely → HSCs undergo replicative senescence → progressive marrow failure.
This deserves special mention because it is frequently tested:
- In AA, the immune attack selectively destroys normal HSCs (those with intact GPI-anchored proteins)
- A pre-existing or acquired clone with a PIGA mutation (lacking GPI-anchored proteins CD55/CD59) may escape immune destruction because the T-cell attack targets antigens presented via GPI-linked molecules
- This clone has a selective survival advantage → expands → gives rise to the PNH clone
- Clinically: patients may develop features of PNH (intravascular haemolysis, thrombosis) on top of AA
- Flow cytometry for CD55/CD59 is used to screen for PNH clones in all AA patients [5]
6. Classification
As discussed above: Congenital vs Acquired (Idiopathic vs Secondary)
This classification is critical for guiding treatment decisions [5][7]:
| Severity | Criteria |
|---|---|
| Very Severe AA (vSAA) | Meets SAA criteria AND ANC < 0.2 × 10⁹/L [5] |
| Severe AA (SAA) | BM cellularity < 25% (or 25–50% if < 30% residual cells are haematopoietic) AND ≥ 2 of: (1) ANC < 0.5 × 10⁹/L (2) Platelets < 20 × 10⁹/L (3) Reticulocyte count < 20 × 10⁹/L [5][7] |
| Non-severe AA (NSAA) | BM hypocellularity consistent with AA but peripheral blood cytopenias NOT fulfilling criteria for SAA [5] |
High Yield — Severity Classification
The severity classification dictates management: Severe/Very Severe AA → urgent treatment needed (HSCT or IST). Non-severe AA may be observed initially with supportive care. The key numbers to remember: ANC < 0.5 (severe), < 0.2 (very severe); Plt < 20; Retic < 20.
| Entity | Key Distinguishing Feature |
|---|---|
| Pure Red Cell Aplasia (PRCA) | Isolated erythroid failure; WBC and platelets normal. Congenital: Diamond-Blackfan anaemia. Acquired: thymoma, lymphoproliferative diseases, parvovirus B19 [1] |
| Hypoplastic MDS | Hypocellular marrow BUT with dysplastic morphology and/or cytogenetic abnormalities (e.g. monosomy 7, trisomy 8, del(5q)) |
| Large granular lymphocyte (LGL) leukaemia | Can mimic AA; diagnosed by flow cytometry showing clonal T-LGL or NK-LGL expansion |
7. Clinical Features
The clinical features of AA are a direct consequence of pancytopenia — the failure of all three lineages [1][4][5].
7.1 Symptoms
| Symptom | Pathophysiological Basis |
|---|---|
| Fatigue / lethargy / malaise | Decreased O₂ delivery to tissues → reduced aerobic metabolism → easy fatigability |
| Dyspnoea on exertion | ↓ O₂ carrying capacity → compensatory ↑ respiratory rate, especially during increased O₂ demand (exercise) |
| Palpitations | Compensatory ↑ heart rate (↑ cardiac output to maintain tissue oxygenation despite low Hb) |
| Dizziness / lightheadedness | Reduced cerebral O₂ delivery |
| Angina (in elderly / those with IHD) | Reduced myocardial O₂ supply cannot meet demand |
| Symptoms of high-output heart failure (if chronic/severe) | Chronic ↓ Hb → compensatory ↑ cardiac output over time → volume overload → HF |
The onset of anaemic symptoms in AA is typically insidious (weeks to months) because marrow failure develops gradually. This contrasts with acute blood loss where symptoms are sudden.
| Symptom | Pathophysiological Basis |
|---|---|
| Recurrent infections | Neutrophils are the first-line innate immune defence against bacteria and fungi. ANC < 0.5 × 10⁹/L = severe neutropenia → dramatically increased infection risk |
| Fever | Infection → pyrogen release → hypothalamic set-point elevation |
| Sore throat / mouth ulcers | Oropharyngeal mucosa is a common site of infection/breakdown when neutrophil surveillance is lost |
| Skin infections / abscesses | Impaired neutrophil-mediated bacterial killing at skin barrier |
Infections are typically bacterial (sepsis, pneumonia, UTI) but invasive fungal infections are an important cause of death [5]. Why? Because profound, prolonged neutropenia allows opportunistic organisms (Aspergillus, Candida) to establish invasive infection.
| Symptom | Pathophysiological Basis |
|---|---|
| Easy bruising | ↓ platelets → impaired primary haemostasis → bleeding into subcutaneous tissues with minimal trauma |
| Petechiae | Tiny capillary bleeds that are not sealed because of insufficient platelets for platelet-plug formation |
| Epistaxis (nosebleeds) | Nasal mucosa is thin and vascular; vulnerable to bleeding with ↓ platelet count |
| Gingival (gum) bleeding | As above — mucosal surfaces are vulnerable |
| Menorrhagia (in women) | Heavy menstrual bleeding due to impaired haemostasis |
| Haematuria, melaena (if severe) | Mucosal bleeding in urinary or GI tract |
| Intracranial haemorrhage (life-threatening) | Very low platelets (< 10 × 10⁹/L) → risk of spontaneous CNS bleeding |
The bleeding pattern in thrombocytopenia is characteristically mucocutaneous (skin + mucous membranes) — this is a "primary haemostasis" defect. Compare with coagulation factor deficiency which causes deep tissue/joint bleeding (haemarthrosis).
7.2 Signs
| Sign | Pathophysiological Basis |
|---|---|
| Pallor (conjunctival, palmar crease, nail bed) | ↓ Hb → ↓ red colour of blood perfusing superficial tissues |
| Tachycardia | Compensatory ↑ HR to maintain cardiac output |
| Flow murmur (ejection systolic murmur) | ↓ blood viscosity (from ↓ Hb) + ↑ cardiac output → turbulent flow across valves |
| Bounding pulse / wide pulse pressure | Hyperdynamic circulation as a compensatory response to anaemia |
| Sign | Explanation |
|---|---|
| Petechiae | Non-blanching pinpoint red dots; indicate capillary bleeding from thrombocytopenia |
| Purpura / ecchymoses | Larger areas of subcutaneous bleeding |
| Mucosal bleeding | Gingival, nasal, conjunctival |
| Sign | Explanation |
|---|---|
| Fever | Sign of active infection in a neutropenic patient — this is a medical emergency (febrile neutropenia) |
| Oral ulcers / candidiasis | Loss of mucosal immune defence |
| Signs of pneumonia, cellulitis, perianal infection | Common sites of infection in neutropenic patients |
This is extremely high yield for distinguishing AA from other causes of pancytopenia:
Why not? Because AA is a marrow failure syndrome, not a proliferative/infiltrative disease. Lymphadenopathy and hepatosplenomegaly suggest haematological malignancy (leukaemia, lymphoma) or extramedullary haematopoiesis (myelofibrosis). In AA, there is nothing proliferating — there is simply an absence of cells.
High Yield — GC Lecture Slide
"Symptoms of pancytopenia (anaemia, neutropenia, thrombocytopenia). NO lymphadenopathy. NO hepatosplenomegaly. In young patients, watch out for the presence of congenital physical abnormalities (inherited bone marrow failure syndromes)." [1]
In children/young adults, look for physical stigmata of inherited conditions [1][4][5]:
| Feature | Associated Condition |
|---|---|
| Thumb abnormalities (absent/hypoplastic thumbs), radial ray defects | Fanconi Anaemia |
| Short stature | Fanconi Anaemia |
| Café-au-lait spots | Fanconi Anaemia |
| Microcephaly | Fanconi Anaemia |
| Renal malformations | Fanconi Anaemia |
| Skeletal deformities | Inherited BM failure syndromes [4] |
| Nail dystrophy, oral leukoplakia, reticular skin pigmentation | Dyskeratosis Congenita |
| Exocrine pancreatic insufficiency + skeletal abnormalities | Shwachman-Diamond Syndrome |
- Haemolytic anaemia features: jaundice, dark urine (haemoglobinuria — especially morning urine), splenomegaly (mild)
- Thrombosis: unusual site (e.g. hepatic vein [Budd-Chiari], cerebral, mesenteric)
- These suggest the presence of a PNH clone in a patient with AA [5]
A typical presentation of aplastic anaemia:
A young patient (teens to 30s) presenting with weeks to months of progressive fatigue, recurrent infections (fevers, sore throat), and easy bruising/bleeding. On examination: pallor, petechiae/purpura, possibly oral ulcers or signs of infection. Crucially, there is NO lymphadenopathy and NO hepatosplenomegaly. Blood tests show pancytopenia with low reticulocyte count and normocytic or macrocytic anaemia.
| History Component | Why It Matters |
|---|---|
| Drug history | NSAIDs, anticonvulsants, antibiotics, anti-thyroid drugs — potential causative agents |
| Occupational/toxin exposure | Benzene, pesticides, radiation |
| Recent viral illness (especially hepatitis) | Seronegative hepatitis preceding AA by 2–3 months |
| Family history | Inherited BM failure syndromes; consanguinity |
| Age of onset | Young → consider inherited causes |
| Travel history | Infections (malaria, leishmaniasis — these cause pancytopenia but via different mechanisms) |
| Transfusion history | Prior transfusions suggest chronic/established disease; also relevant for HLA sensitisation (affects HSCT planning) |
70% 1-year mortality if untreated; 80–90% 5-year survival if treated [5]. This underscores that AA is a life-threatening condition that requires prompt diagnosis and treatment. The two main causes of death in untreated AA are:
- Overwhelming infection (bacterial sepsis, invasive fungal infection)
- Severe haemorrhage (particularly intracranial)
High Yield Summary
Definition: Pancytopenia + hypocellular BM (replaced by fat) + NO malignant infiltration/fibrosis.
Epidemiology: 4–6/million/year in Asia (2–3× Western); M:F = 1:1; bimodal age peak (young adults, elderly).
Key Aetiologies: Idiopathic/autoimmune (70–80%); Drugs (chloramphenicol, NSAIDs, anticonvulsants, carbimazole); Seronegative hepatitis (2–3mo after episode); Toxins (benzene); Inherited (Fanconi anaemia — DEB test; Dyskeratosis congenita; Shwachman-Diamond).
Pathophysiology: T-cell–mediated destruction of HSCs (IFN-γ, TNF-α → Fas/FasL apoptosis + direct killing). HLA-DR2 overexpression. PNH clone may survive by escaping immune attack.
Severity (Modified Camitta):
- Severe: BM cellularity < 25% + ≥ 2 of: ANC < 0.5, Plt < 20, Retic < 20
- Very Severe: Severe + ANC < 0.2
- Non-severe: Doesn't meet SAA criteria
Clinical Features: Symptoms/signs of pancytopenia (anaemia + neutropenia/infection + mucocutaneous bleeding). NO lymphadenopathy, NO hepatosplenomegaly. In young patients: look for dysmorphic features (inherited BM failure). Associated PNH: haemolysis + thrombosis.
Prognosis: Fatal if untreated (70% 1y mortality); 80–90% 5y survival with treatment.
Active Recall - Aplastic Anaemia (Definition to Clinical Features)
[1] Lecture slides: GC 047. Family history of anaemia.pdf (slide on Aplastic anaemia – clinical features) [2] Senior notes: Ryan Ho Haemtology.pdf (p31 — Section 2.4.2 Aplastic Anaemia) [3] Senior notes: Block A - Hematology Data Interpretation.pdf (p1 — aplastic anaemia discussion) [4] Senior notes: Adrian Lui Pediatrics Notes.pdf (p368 — Section 10.1.3 Familial and Aplastic Anemia) [5] Senior notes: Ryan Ho Haemtology.pdf (p32 — AA pathophysiology, clinical features, diagnostic criteria) [6] Senior notes: Introduction to Clinical pharmacology (I) (Pharmaco-Genomics, Precision Medicine).pdf (p5 — azathioprine and TPMT) [7] Senior notes: Maksim Medicine Notes.pdf (p168 — Aplastic anemia) [8] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p1380-1382 — AML risk factors including AA)
Differential Diagnosis of Aplastic Anaemia
When you encounter a patient with pancytopenia — the hallmark laboratory finding that brings aplastic anaemia into consideration — you must systematically work through the differential diagnosis. The core question is: why does this patient have low red cells, white cells, AND platelets? The answer lies in understanding the two fundamental mechanisms that can produce pancytopenia, and then narrowing down within each.
There are only two broad mechanisms [9]:
- ↓ Bone marrow production — the "factory" is failing
- ↑ Peripheral destruction / consumption / sequestration — the factory is working, but the products are being destroyed faster than they're made
Within decreased production, there are further subdivisions:
- Marrow is empty (hypocellular) → aplastic anaemia, some inherited BM failure syndromes
- Marrow is full but dysfunctional (ineffective haematopoiesis) → MDS, megaloblastic anaemia
- Marrow is full but replaced/infiltrated by something abnormal → leukaemia, lymphoma, myelofibrosis, metastatic cancer, infections
Exam Approach — The Pancytopenia Differential
When presented with a patient with pancytopenia in an OSCE or written exam, your first thought should be: Is the bone marrow the problem (production failure) or is it peripheral destruction/sequestration? The reticulocyte count is your first clue: low reticulocytes = production problem; elevated reticulocytes = peripheral destruction (the marrow is trying to compensate). Then, the bone marrow biopsy tells you whether the marrow is hypocellular (AA), hypercellular with abnormal cells (leukaemia/MDS), or infiltrated (fibrosis/metastases).
2. Differential Diagnoses — Detailed Comparison
2.1 Conditions with Hypocellular Bone Marrow (Most Important Differentials for AA)
This is the single most important and difficult differential to distinguish from aplastic anaemia [5][10].
| Feature | Aplastic Anaemia | Hypoplastic MDS |
|---|---|---|
| BM cellularity | < 25%, profoundly hypocellular | Hypocellular (but typically 25–50%) |
| Morphology | Morphologically normal residual haematopoietic cells [4][5] | Dysplastic morphology in ≥ 1 lineage (e.g. hypolobated/hypogranular neutrophils, ring sideroblasts, micromegakaryocytes) [10] |
| Cytogenetics | Normal karyotype | Abnormal karyotype in many cases (e.g. monosomy 7, del(5q), trisomy 8) [10] |
| Blasts | < 5%, no excess | May have increased blasts (5–19%) |
| Age | Bimodal (young adults + elderly) | Median age ~65; increasing incidence with age [7] |
| Hepatosplenomegaly | NO [1][4] | NO (similar to AA) [7] |
| Response to IST | ~70% respond to ATG + Ciclosporin | Some respond, but less reliably |
| Malignant potential | Can evolve to MDS/AML | Pre-leukaemia: may transform to acute leukaemia [7] |
"Some MDS have hypoplastic marrow (hypoplastic MDS) especially if therapy-related, but these cases should have morphologically/karyotypically abnormal marrow cells, which are not present in AA" [10]
Why is this distinction critical? Because treatment is fundamentally different. AA is treated with immunosuppression or HSCT. Higher-risk MDS may require chemotherapy, hypomethylating agents, or HSCT with different conditioning. Misdiagnosing MDS as AA (and giving only immunosuppression) could delay appropriate treatment and allow leukaemic transformation.
How to distinguish clinically: You cannot reliably distinguish them on clinical grounds alone — both present with pancytopenia without organomegaly. The diagnosis is made on bone marrow biopsy with cytogenetics and molecular genetics [8][10].
These present in childhood/young adulthood and must be considered in any young patient with AA [1][4]:
| Syndrome | Distinguishing Clues |
|---|---|
| Fanconi Anaemia | Dysmorphic features: short stature, café-au-lait spots, thumb abnormalities, radial ray defects, renal malformations, microcephaly. Confirmed by DEB chromosome breakage test [4][5] |
| Dyskeratosis Congenita | Classic triad: nail dystrophy, oral leukoplakia, reticular skin pigmentation. Telomere length very short |
| Shwachman-Diamond Syndrome | Exocrine pancreatic insufficiency + skeletal abnormalities + BM failure |
"In young patients, watch out for the presence of congenital physical abnormalities (inherited bone marrow failure syndromes)" [1]
These are important because: (1) Management differs — Fanconi patients are exquisitely radiosensitive and require modified HSCT conditioning regimens; (2) They carry increased risk of MDS/AML and solid tumours requiring lifelong surveillance [4][7].
2.2 Conditions with Hypercellular / Normocellular Marrow but Pancytopenia
| Feature | Aplastic Anaemia | Acute Leukaemia |
|---|---|---|
| BM cellularity | Hypocellular (empty) | Hypercellular — packed with blast cells |
| Blasts | No abnormal cells on PBS [4][5] | ≥ 20% blasts in BM or peripheral blood [10][11] |
| Organomegaly | NO lymphadenopathy, NO hepatosplenomegaly [1][4] | Lymphadenopathy, hepatosplenomegaly often present (especially ALL) [11][12] |
| Extramedullary involvement | Absent | Gum hypertrophy (AML-M5), CNS involvement (ALL), mediastinal mass (T-ALL), skin infiltration [11][12] |
| DIC | Not a feature | Prominent in acute promyelocytic leukaemia (APML) [11] |
| PBS | Pancytopenia, NO blasts | Blasts often visible; may see Auer rods (AML) |
Why does acute leukaemia cause pancytopenia? Because malignant blast cells crowd out normal haematopoietic precursors in the marrow (a "factory takeover"). The mechanism is fundamentally different from AA where the factory is simply shut down [11][12].
The key clinical clue: if a pancytopenic patient has lymphadenopathy, hepatosplenomegaly, gum hypertrophy, or circulating blasts, think leukaemia, NOT aplastic anaemia. "NO lymphadenopathy, NO hepatosplenomegaly" in AA [1] — these negative findings are what push you towards AA rather than leukaemia.
| Feature | Aplastic Anaemia | Megaloblastic Anaemia |
|---|---|---|
| MCV | Normal or mildly ↑ (usually 100–110 fL) | Markedly ↑ (often > 110 fL, can be > 120 fL) [13] |
| PBS | No abnormal cells | Hypersegmented neutrophils (≥ 5 lobes) + macro-ovalocytes [13] |
| BM | Hypocellular, no megaloblastic change | Hypercellular with megaloblastic erythropoiesis (large erythroblasts with immature nuclei) |
| Reticulocytes | Low | Low (ineffective erythropoiesis) |
| B12 / Folate | Normal | Low B12 and/or low RBC folate |
| LDH / bilirubin | Normal or mildly ↑ | Markedly ↑ (intramedullary haemolysis — ineffective erythropoiesis destroys precursors within BM) [13] |
| Neurological features | Absent | Subacute combined degeneration of the cord (B12 deficiency only) — paraesthesia, ataxia, UMN + LMN signs [13] |
Why can megaloblastic anaemia cause pancytopenia? DNA synthesis is impaired in all rapidly dividing cells (not just red cells). So neutrophil and platelet precursors are also affected → pancytopenia. But the marrow is actually hypercellular (full of megaloblastic precursors that are being destroyed before they mature — "ineffective haematopoiesis").
This is a crucial differential to exclude because megaloblastic anaemia is easily treatable with B12/folate replacement. Missing it and treating as AA would be a serious error. This is why serum B12 and RBC folate are always checked in the workup of suspected AA [5][8].
MCV > 120 fL generally has only 2 differentials: (1) chemotherapy, (2) pernicious anaemia [13]
| Feature | Aplastic Anaemia | Myelofibrosis |
|---|---|---|
| BM | Hypocellular, replaced by fat | Replaced by fibrosis (reticulin/collagen) |
| PBS | No abnormal cells | Leukoerythroblastic picture: tear-drop RBCs (dacrocytes) + nucleated RBCs + immature granulocytes [9] |
| Splenomegaly | NO [1][4] | Massive splenomegaly (extramedullary haematopoiesis) |
| Constitutional symptoms | Usually not prominent | Prominent: weight loss, night sweats, fevers |
| JAK2/CALR/MPL mutations | Absent | Often present (primary myelofibrosis) |
Why does myelofibrosis cause pancytopenia? The marrow space is replaced by fibrosis → haematopoietic failure. Compensatory extramedullary haematopoiesis occurs in the spleen and liver (hence massive splenomegaly). The leukoerythroblastic blood film is the classic PBS clue.
Key distinguishing features: massive splenomegaly + tear-drop cells on PBS → myelofibrosis, NOT AA. In AA, the marrow is replaced by fat (not fibrosis) and there is no BM infiltration by fibrosis/malignancy [4][5].
| Feature | Distinguishing Clues |
|---|---|
| Metastatic carcinoma (breast, prostate, lung most common) | Known primary tumour; leukoerythroblastic PBS; BM biopsy shows nests of carcinoma cells |
| Hairy cell leukaemia | Splenomegaly (often massive); characteristic "hairy" lymphocytes on PBS; BM shows diffuse infiltration with fibrosis; tartrate-resistant acid phosphatase (TRAP) +ve; BRAF V600E mutation |
| Granulomatous infections (TB, fungal) | Fever, systemic symptoms; BM shows granulomata; culture/PCR for organisms |
| Storage diseases (Gaucher, Niemann-Pick) | Usually paediatric; hepatosplenomegaly; characteristic cells on BM (Gaucher cells) |
2.3 Conditions with Predominantly Peripheral Destruction / Sequestration
| Feature | Aplastic Anaemia | Hypersplenism |
|---|---|---|
| Splenomegaly | NO [1][4] | Yes — often with stigmata of chronic liver disease |
| BM | Hypocellular | Normocellular or hypercellular (reactive) |
| Mechanism | BM failure | Pooling and destruction of blood cells in enlarged spleen |
| Cytopenias | All lineages severely affected | Usually mild-moderate; platelets often most affected |
Why does hypersplenism cause pancytopenia? An enlarged spleen (from portal hypertension, haematological malignancy, etc.) sequesters and destroys blood cells in its red pulp. The marrow is actually reactive/hyperplastic (trying to compensate).
PNH deserves special mention because it is not just a differential — it is an overlapping condition with AA [5][8]:
| Feature | Aplastic Anaemia alone | PNH (± AA overlap) |
|---|---|---|
| Haemolysis | Absent | Intravascular haemolysis: ↑ LDH, ↑ unconjugated bilirubin, ↓ haptoglobin, haemoglobinuria (dark urine, classically morning) |
| Thrombosis | Not a feature | Thrombosis in unusual sites (hepatic veins [Budd-Chiari], cerebral, mesenteric, dermal) — leading cause of death in PNH [8] |
| Flow cytometry | Normal CD55/CD59 | ↓ CD55/CD59 (deficiency of GPI-anchored proteins) [4][5][8] |
| BM | Hypocellular | May be hypocellular (AA-PNH overlap) or normocellular |
Up to 50% of AA patients have detectable PNH clones [8]. This is why flow cytometry for CD55/CD59 (or FLAER assay) is mandatory in every AA workup.
- SLE can cause pancytopenia through multiple mechanisms: autoimmune destruction of all lineages, immune complex deposition in marrow, and sometimes a true AA-like picture
- Other autoimmune conditions (e.g. rheumatoid arthritis with Felty syndrome) can cause pancytopenia
- Distinguished by: positive autoimmune markers (ANA, anti-dsDNA), clinical features of the autoimmune disease, and usually normocellular/hypercellular BM
- This is why autoimmune markers are checked if indicated [5] and ANA, anti-dsDNA antibodies are part of the workup [8]
| Feature | Distinguishing Clues |
|---|---|
| DIC | Underlying trigger (sepsis, APML, obstetric emergency); ↑ PT/aPTT, ↑ D-dimer, ↓ fibrinogen; schistocytes on PBS |
| TTP/HUS | Microangiopathic haemolytic anaemia (MAHA) + thrombocytopenia ± renal failure ± neurological features; schistocytes on PBS; ↓ ADAMTS13 in TTP |
These typically cause anaemia + thrombocytopenia (not full pancytopenia with neutropenia), and the schistocytes on PBS and coagulation abnormalities are the key differentiators.
| Feature | Distinguishing Clues |
|---|---|
| HLH | High fevers, massive hyperferritinaemia (often > 10,000), hepatosplenomegaly, ↑ triglycerides, ↓ fibrinogen, haemophagocytosis on BM (macrophages engulfing blood cells). Triggers: EBV, other infections, autoimmune disease (MAS), malignancy [9] |
HLH causes pancytopenia through macrophage-mediated phagocytosis and destruction of all blood cell lineages within the marrow and spleen. The clinical picture is much more acute and systemically unwell than AA.
| Infection | Mechanism |
|---|---|
| HIV | Direct infection of haematopoietic progenitors + immune dysregulation; also can cause dysplastic haematopoiesis mimicking MDS [10] |
| Hepatitis viruses | Trigger for post-hepatitis AA (seronegative hepatitis → AA 2–3 months later) [2][5] — this is technically a cause of AA, not just a mimic |
| EBV (Infectious mononucleosis) | Transient marrow suppression; usually self-limiting; atypical lymphocytes on PBS |
| Parvovirus B19 | Selectively infects erythroid precursors → pure red cell aplasia (not full pancytopenia) in immunocompetent; can cause prolonged aplasia in immunosuppressed [1] |
| TB, disseminated fungal infections | Granulomatous infiltration of marrow |
| Differential | BM Cellularity | PBS Clue | Organomegaly | Key Test |
|---|---|---|---|---|
| Aplastic anaemia | Hypocellular (fat) | No abnormal cells [5] | None [1] | BM biopsy (hypocellular, no dysplasia/fibrosis) |
| Hypoplastic MDS | Hypocellular | Dysplastic cells | None | Cytogenetics (abnormal karyotype) [10] |
| AML/ALL | Hypercellular | Blasts ≥ 20% [11] | LN, hepatosplenomegaly (esp ALL) [12] | BM blasts, flow cytometry, cytogenetics |
| Megaloblastic anaemia | Hypercellular | Hypersegmented neutrophils, macro-ovalocytes | None | B12/folate levels |
| Myelofibrosis | Fibrotic (dry tap) | Tear-drop cells, leukoerythroblastic | Massive splenomegaly | BM biopsy (fibrosis), JAK2/CALR |
| Metastatic carcinoma | Infiltrated | Leukoerythroblastic | Variable | BM biopsy (carcinoma cells) |
| Hypersplenism | Normal / hyperplastic | Non-specific | Splenomegaly | Imaging, clinical context |
| PNH | Variable | Polychromasia (haemolysis) | Minimal | Flow cytometry: ↓ CD55/CD59 [5][8] |
| SLE | Normal / variable | Non-specific | Variable | ANA, anti-dsDNA |
| HLH | Haemophagocytosis | Non-specific | Hepatosplenomegaly | Ferritin (massively ↑), sIL-2R, fibrinogen |
When you see a patient with pancytopenia, use this systematic approach:
Step 1: History and examination — look for drug/toxin exposure, viral illness, family history (inherited causes), autoimmune symptoms, constitutional symptoms (malignancy), liver disease (hypersplenism)
Step 2: Peripheral blood smear — this is your most powerful initial tool:
- Blasts → acute leukaemia
- Hypersegmented neutrophils + macro-ovalocytes → megaloblastic anaemia
- Tear-drop cells + leukoerythroblastic → myelofibrosis / marrow infiltration
- Schistocytes → DIC / TMA
- No abnormal cells → AA, hypoplastic MDS, or nutritional causes [5]
Step 3: Reticulocyte count:
- Low → production problem (AA, MDS, megaloblastic, leukaemia)
- High → peripheral destruction (haemolysis, hypersplenism, PNH)
Step 4: Basic blood tests — B12/folate (exclude megaloblastic), LFT (hepatitis), viral serology (HIV, hepatitis), autoimmune markers (ANA), haemolysis screen (LDH, haptoglobin, bilirubin), flow cytometry for PNH [5][8]
Step 5: Bone marrow biopsy — this is the definitive investigation that separates the differentials:
- Hypocellular with fat replacement, morphologically normal residual cells, no fibrosis/malignancy → AA [4][5]
- Hypocellular with dysplasia/abnormal cytogenetics → hypoplastic MDS
- Hypercellular with ≥ 20% blasts → acute leukaemia
- Fibrotic → myelofibrosis
- Infiltrated by non-haematopoietic cells → metastatic cancer
The Three Must-Not-Miss Differentials
-
Acute leukaemia — because it is rapidly fatal if untreated and requires urgent chemotherapy. Distinguished from AA by the presence of blasts (≥ 20%) and often organomegaly.
-
Megaloblastic anaemia — because it is completely reversible with B12/folate replacement. Diagnosing AA and giving immunosuppression when the patient actually has B12 deficiency would be harmful and miss a simple cure.
-
Hypoplastic MDS — because it looks almost identical to AA on clinical grounds and even on initial BM appearance, but carries a high risk of leukaemic transformation and requires different treatment. Only cytogenetics and careful morphological assessment can distinguish them.
High Yield — GC Lecture Point
"Symptoms of pancytopenia (anaemia, neutropenia, thrombocytopenia). NO lymphadenopathy. NO hepatosplenomegaly. In young patients, watch out for the presence of congenital physical abnormalities (inherited bone marrow failure syndromes)" [1]. The absence of organomegaly is a key exam differentiating point — if organomegaly is present, you should be thinking of leukaemia, lymphoma, myelofibrosis, or hypersplenism rather than AA.
High Yield Summary — Differential Diagnosis
Pancytopenia DDx framework: Decreased production (hypocellular BM: AA, hypoplastic MDS, IBMFS; hypercellular BM: leukaemia, MDS, megaloblastic anaemia, myelofibrosis, marrow infiltration) vs. Increased peripheral destruction (hypersplenism, PNH, SLE, DIC/TMA, HLH).
Key differentiators for AA:
- PBS: no abnormal cells, no blasts, no dysplastic changes
- BM: hypocellular with fat replacement, morphologically normal residual cells, no fibrosis, no malignancy
- Clinically: NO lymphadenopathy, NO hepatosplenomegaly
- Reticulocyte count: low (production failure)
Most important differentials:
- Hypoplastic MDS → dysplasia + abnormal cytogenetics on BM
- Acute leukaemia → ≥ 20% blasts + organomegaly
- Megaloblastic anaemia → hypersegmented neutrophils, macro-ovalocytes, low B12/folate, treatable!
- PNH → overlapping condition; screen with flow cytometry for CD55/CD59
- Myelofibrosis → massive splenomegaly + tear-drop cells + fibrotic BM
Always check: B12/folate (exclude megaloblastic), PNH screen (flow cytometry), viral serology (HIV, hepatitis), autoimmune markers, and cytogenetics on BM (exclude MDS).
Active Recall - Differential Diagnosis of Aplastic Anaemia
References
[1] Lecture slides: GC 047. Family history of anaemia.pdf (Aplastic anaemia – clinical features slide) [2] Senior notes: Ryan Ho Haemtology.pdf (p31 — Section 2.4.2 Aplastic Anaemia, causes) [4] Senior notes: Adrian Lui Pediatrics Notes.pdf (p369 — AA clinical features and lab findings) [5] Senior notes: Ryan Ho Haemtology.pdf (p32 — AA pathophysiology, clinical features, diagnostic criteria, lab findings) [7] Senior notes: Maksim Medicine Notes.pdf (p168 — Aplastic anemia and MDS) [8] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p1464–1470 — AA overview, diagnosis, PNH) [9] Senior notes: Ryan Ho Fundamentals.pdf (p390–393 — Pancytopenia causes and evaluation) [10] Senior notes: Ryan Ho Haemtology.pdf (p83 — MDS diagnosis and d/dx with AA) [11] Senior notes: Ryan Ho Haemtology.pdf (p51–54 — Acute leukaemia clinical features, diagnosis) [12] Senior notes: Block A - High white cell count_ acute and chronic leukaemia; bone marrow transplantation; immunogenetics.pdf (p3 — Clinical features of acute leukaemia) [13] Senior notes: Block A - Pallor_ diagnosis of anaemia; nutritional anaemia; anaemia of systemic diseases.pdf (p6, p18 — Megaloblastic anaemia, MCV classification)
Diagnostic Criteria, Algorithm and Investigations for Aplastic Anaemia
1. Diagnostic Criteria — Modified Camitta Criteria
The diagnosis of aplastic anaemia requires two components: (1) demonstration of a hypocellular bone marrow and (2) peripheral blood cytopenias. The severity classification then dictates the urgency and type of treatment.
The key principle: AA is a diagnosis of exclusion superimposed on positive findings (hypocellular marrow + pancytopenia). You must first confirm the marrow is empty, then systematically exclude all other causes of pancytopenia (leukaemia, MDS, megaloblastic anaemia, myelofibrosis, etc.) before diagnosing AA.
The Modified Camitta criteria (also adopted by the British Committee for Standards in Haematology and used internationally) classify AA into three tiers [4][5][7]:
| Severity | Criteria |
|---|---|
| Very Severe AA (vSAA) | Meets Severe AA criteria AND ANC < 0.2 × 10⁹/L [4][5][7] |
| Severe AA (SAA) | BM cellularity < 25% (or 25–50% if < 30% of residual cells are haematopoietic) AND ≥ 2 of the following 3: (1) ANC < 0.5 × 10⁹/L (2) Platelet count < 20 × 10⁹/L (3) Reticulocyte count < 20 × 10⁹/L [4][5][7] |
| Non-severe AA (NSAA) | BM cellularity criteria met (hypocellular marrow consistent with AA) but peripheral blood cytopenias do NOT fulfil criteria for SAA [4][5] |
High Yield — Remember the Numbers
The key numbers to memorise for severity grading: ANC < 0.5 (severe), < 0.2 (very severe); Plt < 20; Retic < 20. You need at least 2 out of 3 peripheral blood criteria PLUS the marrow cellularity criterion to diagnose SAA. The severity classification directly determines treatment — SAA/vSAA requires urgent definitive therapy (HSCT or immunosuppression), while NSAA may be observed with supportive care initially.
- ANC < 0.5 × 10⁹/L: This is the threshold for severe neutropenia, below which the risk of life-threatening bacterial and fungal infection rises dramatically. Below 0.2, the risk of invasive fungal infection (Aspergillus, Candida) becomes extremely high — hence "very severe."
- Platelet < 20 × 10⁹/L: Below this level, the risk of spontaneous mucocutaneous bleeding is significant, and the risk of intracranial haemorrhage becomes real.
- Reticulocyte < 20 × 10⁹/L: A low absolute reticulocyte count confirms that the marrow is not compensating — it cannot mount a reticulocyte response. This distinguishes AA (production failure) from peripheral destruction (where reticulocytes would be elevated).
The diagnosis of AA also requires the absence of [4][5][8]:
- Dysplastic morphology → would suggest MDS
- Blast cells ≥ 20% → would suggest acute leukaemia
- Bone marrow fibrosis → would suggest myelofibrosis
- Malignant infiltration → would suggest leukaemia, lymphoma, or metastatic cancer
- Megaloblastic haematopoiesis → would suggest B12/folate deficiency
"Profoundly hypocellular marrow with decrease in all elements and replacement by fat/stromal cells. Morphologically normal residual haematopoietic cells without megaloblastic haematopoiesis. NO BM infiltration by fibrosis/malignancy" [4][5]
2. Investigation Modalities — Systematic Workup
The workup for suspected AA serves two purposes: (A) confirm the diagnosis (pancytopenia + hypocellular marrow), and (B) exclude alternative diagnoses and identify associated conditions (PNH, inherited causes).
GC Lecture Slide — Key Investigations (High Yield)
"Blood count: pancytopenia; macrocytic anaemia; low reticulocyte count. Blood film. Autoimmune markers. Vit B12 and folate levels. Bone marrow: trephine biopsy is required for the assessment of cellularity. Specialized tests: Flow cytometry for CD55 and CD59 deficient RBC (to rule out PNH). Chromosome breakage with diepoxybutane (to screen for Fanconi anaemia)." [1]
2.1 First-Line Blood Tests
| Parameter | Expected Finding in AA | Interpretation / Why |
|---|---|---|
| Haemoglobin | Low (anaemia) | Erythroid lineage failure → ↓ RBC production |
| MCV | Normal or mildly raised (normocytic or macrocytic) [1][4][5] | Why macrocytic? (i) Stress erythropoiesis — the few remaining erythroid precursors are pushed out prematurely as larger, immature cells ("stress reticulocytes" are larger); (ii) ↑ fetal haemoglobin (HbF) production under stress; (iii) relative folate consumption in the few proliferating cells. NB: it is NOT the marked macrocytosis of megaloblastic anaemia (usually MCV 100–110, not > 120) |
| WBC / ANC | Low (leukopenia with neutropenia) | Myeloid lineage failure → ↓ granulocyte production |
| Platelet count | Low (thrombocytopenia) | Megakaryocyte lineage failure → ↓ platelet production |
| Lymphocyte count | Typically normal [8] | Lymphocytes are produced mainly in lymphoid organs (thymus, lymph nodes, spleen), not primarily dependent on BM HSCs in the short term |
| Reticulocyte count | Low (reticulocytopenia) [1][4][5] | The marrow cannot mount a compensatory response. A low/inappropriately normal reticulocyte count in the setting of anaemia = production failure. This is a critical distinguishing feature from haemolytic anaemia where reticulocytes would be HIGH |
"Pancytopenia; macrocytic anaemia; low reticulocyte count" [1]
Why 'Inappropriately Normal' Reticulocyte Count Matters
In a healthy person, reticulocytes are ~0.5–1.5% of RBCs. When a patient is anaemic, the marrow should compensate by ramping up production, raising the reticulocyte count to 2–5% or higher (or absolute count > 100 × 10⁹/L). In AA, even though the patient is profoundly anaemic, reticulocytes remain low or "inappropriately normal" — the factory simply cannot respond. This is a hallmark of hypo-proliferative anaemia.
| Finding | Interpretation |
|---|---|
| No abnormal cells [4][5][7] | This is what you expect in AA — the problem is the absence of cells, not the presence of abnormal ones |
| No blasts | Excludes acute leukaemia (where you'd see circulating blasts ± Auer rods) |
| No dysplastic changes | Excludes MDS (where you'd see hypogranular/hypolobated neutrophils, giant platelets) |
| No tear-drop cells / leukoerythroblastic picture | Excludes myelofibrosis / marrow infiltration |
| No hypersegmented neutrophils | Excludes megaloblastic anaemia |
| Macrocytosis and anisopoikilocytosis may be present [8] | Non-specific; reflects stress erythropoiesis |
"PBS: normocytic RBCs but may be macrocytic, NO abnormal cells" [5]. The PBS in AA is essentially unremarkable — and that unremarkability IS the clue. Think of it as: "the PBS is boring because the marrow has nothing to give."
| Test | Purpose |
|---|---|
| Vitamin B12 level | Exclude megaloblastic anaemia as a treatable cause of pancytopenia [1][4][8] |
| RBC folate (preferred over serum folate as it reflects tissue stores) | Same — exclude folate deficiency |
Why is this critical? Because megaloblastic anaemia is completely reversible with simple vitamin replacement. Misdiagnosing it as AA and giving immunosuppression or proceeding to HSCT would be a catastrophic error. Always rule out the easily treatable conditions first.
| Test | Purpose |
|---|---|
| LFT (ALT, AST, ALP, bilirubin, albumin) | Detect antecedent or ongoing hepatitis [8] — seronegative hepatitis is a well-known trigger of AA (AA develops 2–3 months after the hepatitis episode). Also useful as a baseline before immunosuppressive therapy |
| Test | Purpose |
|---|---|
| RFT (creatinine, urea, electrolytes) | Baseline assessment; exclude renal disease as a contributing cause of anaemia (↓ EPO); important baseline before nephrotoxic drugs (e.g. ciclosporin) |
| Test | Rationale |
|---|---|
| HIV serology | HIV can cause pancytopenia through direct marrow suppression and dysplastic haematopoiesis [4][8] |
| HAV / HBV / HCV serology | Hepatitis viruses as triggers of post-hepatitis AA [4][8]; also important for transfusion-acquired hepatitis screening |
| EBV / CMV serology | Relevant when HSCT is being considered (reactivation risk) [8]; EBV can also cause transient marrow suppression |
| Parvovirus B19 serology | If pure red cell aplasia is suspected (selective erythroid failure, not full pancytopenia) [8] |
Note: The classic hepatitis-associated AA is caused by seronegative hepatitis (non-A, non-B, non-C) — so standard hepatitis serology will be negative. The diagnosis is clinical: pancytopenia developing 2–3 months after an episode of acute hepatitis with negative standard serologies.
| Test | Purpose | Expected in AA |
|---|---|---|
| LDH | ↑ in haemolysis (released from lysed RBCs) | Normal in pure AA; ↑ if PNH clone present |
| Unconjugated bilirubin | ↑ in haemolysis | Same |
| Haptoglobin | ↓ in intravascular haemolysis (binds free Hb) | Normal in pure AA; ↓ if PNH |
| Reticulocyte count | ↑ in haemolysis | LOW in AA |
| Direct antiglobulin test (DAT/Coombs) | Positive in autoimmune haemolytic anaemia | Negative in AA |
The haemolysis screen serves two purposes: (1) exclude haemolytic anaemia as a primary cause, and (2) detect an associated PNH clone (which causes intravascular haemolysis).
2.2 The Definitive Investigation: Bone Marrow Examination
This is the single most important investigation in the diagnosis of AA. Without it, you cannot diagnose AA [1][4][5][8].
"Bone marrow: trephine biopsy is required for the assessment of cellularity" [1]
| Component | What It Provides | Why It Matters in AA |
|---|---|---|
| BM Aspirate (fluid sample) | Cytology (cell morphology), flow cytometry, cytogenetics (karyotyping, FISH), molecular genetics (NGS), iron staining (Perl's Prussian Blue), microbiological cultures [14] | Allows assessment of cell morphology (are residual cells normal or dysplastic?), immunophenotyping, and genetic studies to exclude MDS/leukaemia |
| Trephine Biopsy (solid core) | Cellularity (the key parameter), architecture, degree of fibrosis, abnormal infiltration, immunohistochemistry [14] | Only way to reliably assess marrow cellularity — aspirate alone cannot tell you how empty the marrow is because you're just sampling fluid. The trephine gives you a cross-section of the intact marrow architecture |
"Trephine biopsy is required for the assessment of cellularity" [1]. This is because cellularity is a structural parameter — you need to see the ratio of haematopoietic cells to fat in the intact bone architecture. An aspirate might return dilute/haemodiluted samples and give a falsely low impression, or conversely, might aspirate from a small remaining island of cellularity and give a falsely high impression.
Practical Point — Dry Tap
In AA, the aspirate may yield a "dry tap" or a markedly hypocellular specimen with very few cells to examine. However, a dry tap is NOT specific to AA — it also occurs in myelofibrosis (where the marrow is replaced by fibrosis rather than fat) and in densely packed marrows (leukaemia). This is another reason why the trephine biopsy is essential — it tells you WHY the aspirate was dry.
| Finding | Description | Significance |
|---|---|---|
| Hypocellular marrow | Cellularity < 25% (or 25–50% with < 30% haematopoietic cells) [5][7] | Confirms marrow failure — the factory is shut down |
| Fat replacement | Prominent fat cells and marrow stroma replacing haematopoietic tissue [4][5][8] | Fat fills the space vacated by destroyed HSCs. This distinguishes AA (replaced by fat) from myelofibrosis (replaced by fibrosis) |
| Morphologically normal residual cells | Residual haematopoietic cells are morphologically normal [4][5][8] | Distinguishes AA from MDS (where residual cells are dysplastic) |
| No megaloblastic haematopoiesis | No nuclear-cytoplasmic dyssynchrony characteristic of B12/folate deficiency [4][5] | Excludes megaloblastic anaemia |
| NO malignant infiltration | No blasts, no malignant lymphoid aggregates, no metastatic carcinoma [4][5][7][8] | Excludes leukaemia, lymphoma, metastatic cancer |
| NO fibrosis | No reticulin or collagen fibrosis [8] | Excludes myelofibrosis |
| Decrease in all elements | All three lineages (erythroid, myeloid, megakaryocytic) reduced [4][5] | Confirms pan-lineage failure |
"BM biopsy: hypocellular with fat infiltration (> 90%), no malignant infiltration" [7]
| Test | Purpose |
|---|---|
| Karyotyping / FISH | Exclude hypoplastic MDS — abnormal karyotype (monosomy 7, del(5q), trisomy 8, del(7q)) in MDS vs normal karyotype in AA [8] |
| Molecular genetics (NGS panel) | Identify somatic mutations. Certain mutations (ASXL1, DNMT3A, BCOR, PIGA) can be found in AA and may have prognostic significance. Mutations more typical of MDS (SF3B1, SRSF2, U2AF1, TP53) help distinguish hypoplastic MDS from AA |
"Perform cytogenetics (karyotyping/FISH) and molecular genetics to exclude hypocellular myelodysplastic syndrome (MDS)" [8]
Key Concept — Why Cytogenetics Is Essential
A hypocellular marrow can look the same on H&E staining whether it is AA or hypoplastic MDS. The karyotype is often the decisive differentiator. Normal cytogenetics + morphologically normal residual cells = AA. Abnormal cytogenetics ± dysplastic morphology = hypoplastic MDS. This distinction has enormous treatment implications.
2.3 Specialised Tests
"Flow cytometry for CD55 and CD59 deficient RBC (to rule out PNH)" [1]
| Parameter | Details |
|---|---|
| What it detects | Deficiency of GPI-anchored proteins (CD55 and CD59) on the surface of blood cells [1][4][5][8] |
| Why it is performed | PNH clones are present in up to 50% of AA patients [8]. PNH can coexist with AA, evolve from it, or present independently. Detection has treatment implications (complement inhibitors, e.g. eculizumab/ravulizumab) |
| Methodology | Modern assays use FLAER (fluorescent aerolysin) — a reagent that directly binds GPI anchors and is more sensitive than anti-CD55/CD59 antibodies, especially for detecting small clones |
| What constitutes a positive result | Presence of a population of cells lacking GPI-anchored proteins (GPI-deficient clone) |
| Additional PNH workup | Urine for haemosiderin (haemosiderosis from chronic intravascular haemolysis) [8]; bilirubin, LDH, haptoglobin for haemolysis markers [8] |
"EXCLUSION of paroxysmal nocturnal haemoglobinuria (PNH). Flow cytometry on peripheral blood or bone marrow sample — MOST useful and accepted method to confirm diagnosis of PNH. Detects deficiency of glycosylphosphatidylinositol (GPI)-anchored proteins including CD55 and CD59 on RBCs" [8]
Why must you screen for PNH in every AA patient? Because (1) the AA–PNH overlap is very common; (2) PNH has specific life-threatening complications (thrombosis in unusual sites — leading cause of death in PNH); and (3) PNH has specific treatment (complement inhibition with eculizumab/ravulizumab) that you would miss if you didn't test.
"Chromosome breakage with diepoxybutane (to screen for Fanconi anaemia)" [1]
| Parameter | Details |
|---|---|
| What it detects | Excessive chromosomal breakage when patient cells are exposed to DNA crosslinking agents (DEB or mitomycin C) [1][4][5][7][8] |
| Why it is performed | Fanconi anaemia has a defect in DNA repair pathways. Normal cells can repair the DNA damage caused by DEB; FA cells cannot → chromosomal breaks, gaps, rearrangements, and radial figures accumulate |
| When to order | Especially in children and young adults with AA [1][4]; consider in any patient < 40 years. Some FA patients may present in adulthood without obvious dysmorphic features |
| Clinical significance | FA patients: (1) are exquisitely radiosensitive → require modified HSCT conditioning; (2) have increased risk of MDS, AML, and solid tumours (squamous cell carcinomas of head and neck, anogenital region) requiring lifelong surveillance [8] |
"Chromosomal breakage test with diepoxybutane (DEB) or mitomycin C (MMC). Hallmark of FA is defective DNA repair. Addition of DEB leads to chromosomal breakage: Normal patient can repair but FA patient cannot (resulting in +ve chromosomal breakage)" [8]
| Test | When to Consider | Purpose |
|---|---|---|
| Telomere length measurement | Suspected dyskeratosis congenita (nail dystrophy, oral leukoplakia, reticular pigmentation) | Very short telomeres confirm DC. Mutations in TERT, TERC, DKC1 genes |
| Genetic testing / NGS | Suspected inherited BM failure syndrome or for prognostic/treatment stratification | Identify specific gene mutations (FANCA-V for FA; SBDS for Shwachman-Diamond; TERT/TERC for DC) [8] |
| HLA typing | All patients with SAA/vSAA at diagnosis | Essential for identifying potential HLA-matched sibling donor for HSCT. Must be done early as HSCT is first-line for young patients with matched donors |
| Pregnancy test | Women of childbearing age | Pregnancy-associated AA (rare) |
| Serum EPO level | Sometimes useful | Expected to be elevated in AA (appropriate response to anaemia); if low/inappropriately normal, consider renal disease as contributing factor |
| Serum iron studies / ferritin | Baseline | Important baseline; patients who require chronic transfusion will develop secondary iron overload [15] |
| CT chest | If thymoma suspected | Thymoma is associated with pure red cell aplasia (not typically full AA) |
Patients with AA who receive chronic red cell transfusions develop secondary iron overload [15]. This is an important long-term complication that requires monitoring:
| Test | Purpose |
|---|---|
| Serum ferritin (serial monitoring) | Rising ferritin indicates iron accumulation; ferritin > 1000 μg/L indicates significant overload |
| MRI (T2 / R2)** of liver and heart | Quantitative assessment of iron deposition in target organs; more accurate than ferritin for assessing organ iron burden |
"Iron-loading anaemias, eg. thalassaemia, aplastic anaemia" are recognised causes of secondary iron overload [15]
The following algorithm represents the systematic approach to a patient with suspected aplastic anaemia:
| Phase | Investigation | Key Finding in AA | Purpose |
|---|---|---|---|
| Phase 1: Confirm pancytopenia | CBC + reticulocyte count | Pancytopenia + reticulocytopenia + normocytic/macrocytic anaemia [1][4][5] | Confirm all three lineages are affected and marrow is not compensating |
| Phase 1: PBS | Peripheral blood smear | No abnormal cells, no blasts, no dysplasia [4][5][7] | Exclude leukaemia, MDS, myelofibrosis, megaloblastic anaemia |
| Phase 2: Exclude mimics | B12 and folate | Normal | Exclude megaloblastic anaemia |
| LFT | May show prior hepatitis | Detect hepatitis trigger | |
| Viral serology | Usually negative (seronegative hepatitis) | Exclude HIV; detect hepatitis | |
| Autoimmune markers | Usually negative | Exclude SLE | |
| Haemolysis screen | Normal unless PNH coexists | Detect associated PNH | |
| Phase 3: Definitive | BM aspirate + trephine biopsy | Hypocellular (< 25%), fat replacement, morphologically normal residual cells, no dysplasia/fibrosis/malignancy [4][5][8] | Confirm diagnosis; trephine essential for cellularity |
| Cytogenetics on BM | Normal karyotype | Exclude hypoplastic MDS | |
| Phase 4: Specialised | Flow cytometry CD55/CD59 | ± PNH clone | Screen for PNH [1][4][5][8] |
| DEB chromosome breakage | Normal in acquired AA; positive in FA | Screen for Fanconi anaemia (especially children/young adults) [1][4][5] | |
| HLA typing | N/A — for donor matching | Plan for potential HSCT | |
| Telomere length | Normal unless DC | Screen for dyskeratosis congenita |
Common Exam Traps
-
"The PBS is normal so it can't be AA" — WRONG. The PBS in AA is supposed to be unremarkable (no abnormal cells). The pathology is in the marrow, not the peripheral blood. "PBS: normal" [7].
-
"MCV is raised so it must be megaloblastic anaemia" — Not necessarily. AA often shows mild macrocytosis (MCV 100–110) due to stress erythropoiesis. Megaloblastic anaemia shows MCV typically > 110–120 with hypersegmented neutrophils and macro-ovalocytes. Always check B12/folate before jumping to conclusions.
-
"Bone marrow aspirate is sufficient for diagnosis" — WRONG. "Trephine biopsy is required for the assessment of cellularity" [1]. The aspirate alone cannot reliably determine how empty the marrow is.
-
Forgetting to screen for PNH — Up to 50% of AA patients have PNH clones. Flow cytometry for CD55/CD59 must be performed in every case [1][4][5][8].
-
Forgetting Fanconi anaemia in a young patient — Even without obvious dysmorphic features, some FA patients present in adolescence/young adulthood. DEB chromosome breakage test should be ordered in all children and young adults with AA [1][4].
High Yield Summary — Diagnosis of Aplastic Anaemia
Diagnostic Criteria (Modified Camitta):
- Severe AA: BM cellularity < 25% + ≥ 2 of: ANC < 0.5, Plt < 20, Retic < 20
- Very Severe AA: SAA + ANC < 0.2
- Non-severe AA: Hypocellular BM but doesn't meet SAA peripheral blood criteria
Key Investigations:
- CBC + reticulocyte count: pancytopenia + reticulocytopenia + normocytic/macrocytic anaemia
- PBS: NO abnormal cells, blasts, dysplasia, tear-drops, or schistocytes
- B12/folate, LFT, viral serology, autoimmune markers: exclude mimics
- BM aspirate + trephine biopsy: ESSENTIAL — hypocellular marrow (< 25%), fat replacement, morphologically normal residual cells, no dysplasia/fibrosis/malignancy
- Cytogenetics on BM: normal karyotype (exclude MDS)
- Flow cytometry CD55/CD59: screen for PNH (up to 50% have clones)
- DEB chromosome breakage: screen for Fanconi anaemia (children/young adults)
- HLA typing: for potential HSCT donor matching
The trephine biopsy is REQUIRED — aspirate alone is insufficient for assessing cellularity.
Active Recall - Diagnosis of Aplastic Anaemia
References
[1] Lecture slides: GC 047. Family history of anaemia.pdf (slides on AA investigations and clinical features) [3] Senior notes: Block A - Hematology Data Interpretation.pdf (p1 — aplastic anaemia discussion) [4] Senior notes: Adrian Lui Pediatrics Notes.pdf (p369 — AA laboratory findings, diagnostic criteria) [5] Senior notes: Ryan Ho Haemtology.pdf (p32 — AA laboratory findings, diagnostic criteria) [7] Senior notes: Maksim Medicine Notes.pdf (p168 — Aplastic anemia laboratory findings, diagnostic criteria) [8] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p1465–1470 — AA etiology, diagnosis, investigations) [9] Senior notes: Ryan Ho Fundamentals.pdf (p391 — BM examination techniques) [14] Senior notes: Block A - Introduction to Haematological investigations (CBP, Clotting).pdf (p15 — BM aspirate vs trephine biopsy) [15] Senior notes: Ryan Ho Chemical Path.pdf (p54 — Iron overload, iron-loading anaemias including AA)
Management of Aplastic Anaemia
Before diving into specific treatments, let's establish the management framework from first principles:
- Remove/treat any identifiable cause — if a drug, toxin, or infection is identified as the trigger, stop it immediately. This alone may be sufficient in mild drug-induced cases.
- Classify severity — the Modified Camitta criteria (SAA/vSAA vs NSAA) dictate the urgency and type of treatment.
- Age and donor availability — these two factors determine whether the patient receives HSCT or immunosuppressive therapy (IST) as first-line definitive treatment.
- Supportive care — all patients need supportive measures regardless of definitive treatment.
- Long-term surveillance — AA can evolve into MDS, AML, or PNH, requiring lifelong monitoring.
"Supportive care: discontinue offending drugs, transfusion, growth factors (G-CSF), broad-spectrum antibiotics. Triple therapy immunosuppression: anti-thymocyte globulin + cyclosporin A ± eltrombopag × 6 months. Definitive treatment: allogenic HSCT (if < 40yo + HLA-matched sibling). Consider androgens. Screen for developing other clonal disorders: MDS, PNH, AML" [7]
GC Lecture Slide — Treatment of Severe AA (High Yield)
"First line — allogeneic haematopoietic stem cell transplantation (for young patients with matched sibling donors). Anti-thymocyte globulin + cyclosporine. Cyclosporine A. Supportive (blood products, iron chelation). Eltrombopag (high dose) + ATG and cyclosporine." [1]
3. Treatment Modalities — Detailed
3.1 Supportive Care (All Patients)
Supportive care is the foundation of AA management and applies to every patient regardless of severity or definitive treatment plan.
| Action | Rationale |
|---|---|
| Discontinue offending drugs [7] | If a drug is the suspected trigger (e.g. chloramphenicol, carbamazepine, NSAIDs, carbimazole), stopping it may allow marrow recovery. In mild drug-induced cases, this alone may be curative |
| Eliminate toxin exposure | Remove from benzene, pesticide, radiation exposure |
| Treat underlying infection | If viral hepatitis triggered AA, supportive care for hepatitis (though the hepatitis itself is usually resolving by the time AA presents 2–3 months later) |
| Parameter | Details |
|---|---|
| Indication | Symptomatic anaemia (fatigue, dyspnoea, angina) or Hb < 70 g/L (threshold varies; higher in elderly/cardiac patients) |
| Goal | Maintain Hb sufficient to relieve symptoms (usually 70–100 g/L) |
| Special considerations | Use leucodepleted, irradiated blood products if HSCT is being considered — why? (1) Leucodepletion reduces HLA alloimmunisation, which could cause graft rejection; (2) Irradiation prevents transfusion-associated graft-versus-host disease (TA-GVHD) by killing donor lymphocytes in the transfused blood [16]; use CMV-negative products if CMV-seronegative and awaiting HSCT |
| Minimise transfusions | Every transfusion increases HLA sensitisation and iron loading. Try to transfuse only when clinically necessary, not to a target number |
"Blood products, iron chelation" are listed as supportive measures [1]
| Parameter | Details |
|---|---|
| Indication | Active bleeding with thrombocytopenia; prophylactic transfusion if platelet < 10 × 10⁹/L (to prevent spontaneous intracranial haemorrhage) |
| Note | Routine prophylactic platelet transfusion in stable, non-bleeding patients with platelets 10–20 is debated. Transfusion thresholds may be higher if the patient is febrile, septic, or undergoing a procedure |
| Special considerations | As above — leucodepleted, irradiated if HSCT candidate |
Why Irradiated Blood Products?
Irradiation of blood products gamma-irradiates the donor lymphocytes to prevent TA-GVHD. In a profoundly immunosuppressed AA patient (or one about to receive HSCT), donor lymphocytes in transfused blood could engraft and attack the recipient's tissues (skin, liver, GI tract, marrow) — this is TA-GVHD, which is almost universally fatal. Irradiation eliminates the donor T cells' ability to proliferate while preserving RBC/platelet function. If irradiated products are not immediately available in an emergency, use the oldest available blood bag — lymphocytes die after ~14 days of storage [16].
| Measure | Rationale |
|---|---|
| Broad-spectrum antibiotics — empirical, immediate, at the first sign of fever in a neutropenic patient [7] | Neutropenic fever (ANC < 0.5 + temperature ≥ 38.3°C single or ≥ 38.0°C sustained for 1 hour) is a medical emergency. Common empirical regimen: anti-pseudomonal β-lactam (e.g. piperacillin-tazobactam or meropenem). Why? Because neutropenic patients cannot mount a normal inflammatory response — infection can progress to septic shock within hours |
| Antifungal prophylaxis | In patients with prolonged, profound neutropenia (ANC < 0.5 for > 7 days), prophylactic antifungals (e.g. posaconazole, voriconazole, or micafungin) are given because invasive fungal infections (Aspergillus, Candida) are a major cause of death in AA [17] |
| Infection prevention measures | Reverse barrier nursing, hand hygiene, face masks, low-bacteria diet (avoid raw food, unpasteurised dairy) [17] |
| G-CSF (granulocyte colony-stimulating factor) [7] | May be used as a temporary measure to boost neutrophil counts during acute infections. "Granulocyte" + "colony-stimulating factor" = stimulates the marrow to produce more granulocytes. However, it does NOT treat the underlying marrow failure and is not a long-term solution. Use judiciously — concern about potential clonal evolution |
| Parameter | Details |
|---|---|
| Why needed | Chronic RBC transfusions lead to secondary iron overload — each unit of packed RBCs contains ~200–250 mg iron. The body has no active excretion mechanism for iron. Excess iron deposits in the liver, heart, and endocrine organs causing organ damage (haemochromatosis, cardiac failure, diabetes, hepatic fibrosis) [15] |
| When to start | Generally after ~20 units of RBC transfusion or when serum ferritin exceeds 1000 μg/L |
| Agents | Deferasirox (oral, once-daily — most commonly used); Deferoxamine (SC/IV infusion — older agent); Deferiprone (oral — less commonly used in AA) |
| Monitoring | Serial serum ferritin; MRI T2* of liver and heart for quantitative iron assessment |
"Iron chelation" is specifically listed as a supportive measure for AA [1]
3.2 First-Line Definitive Treatment: Allogeneic HSCT
"First line — allogeneic haematopoietic stem cell transplantation (for young patients with matched sibling donors)" [1]
Breaking down the term: "allo-" (other) + "geneic" (genetic origin) = from a genetically different individual. "Haematopoietic stem cell transplantation" = infusing donor HSCs to replace the patient's failed marrow with a healthy donor marrow.
The concept: you destroy the patient's diseased/failed marrow (conditioning) and then infuse healthy donor HSCs that engraft, proliferate, and reconstitute normal haematopoiesis.
| Factor | Criteria for HSCT as First-Line |
|---|---|
| Age | Typically < 40 years [7]; some centres extend to < 50 in fit patients. Why the age cut-off? Because HSCT carries significant morbidity/mortality (GVHD, infections, organ toxicity), and outcomes are better in younger patients with fewer comorbidities |
| Donor | HLA-matched sibling donor [1][7] — this is the ideal donor with the lowest risk of GVHD and graft failure. The chance of any sibling being HLA-identical is 25% |
| Disease severity | Severe or very severe AA — NSAA usually does not warrant the risks of HSCT upfront |
"Aplastic anemia" is listed as an adult indication for allogeneic HSCT [17]. In paediatric populations, "Fanconi's anemia" and "Blackfan-Diamond" syndrome are also indications [17].
| Component | Purpose | Details |
|---|---|---|
| Conditioning chemotherapy | Immunosuppression + create "space" in the marrow for donor cells to engraft | For AA, conditioning is typically non-myeloablative or reduced-intensity (e.g. cyclophosphamide ± ATG ± fludarabine). Why reduced intensity rather than full myeloablation? Because the AA marrow is already empty — you don't need to destroy leukaemic cells (as you would in AML). The conditioning primarily serves to suppress the patient's immune system enough to prevent graft rejection |
| Serotherapy (ATG) | Additional immunosuppression to prevent rejection and GVHD | Anti-thymocyte globulin destroys host T cells that might reject the graft |
Special consideration for Fanconi anaemia: FA patients have a defective DNA repair pathway and are exquisitely radiosensitive. They require markedly reduced conditioning doses (low-dose cyclophosphamide + fludarabine, NO radiation or alkylating agents at standard doses) to avoid catastrophic toxicity.
| Outcome | Data |
|---|---|
| Overall survival with matched sibling HSCT | ~75–90% long-term survival in young patients (< 40y) with matched sibling donor |
| Graft failure | 5–10% — higher if patient has been heavily transfused (HLA alloimmunisation) |
| GVHD | Acute: 15–30%; Chronic: 20–40%. Major cause of long-term morbidity |
| Transplant-related mortality | 5–15% |
| Complication | Mechanism | Timeframe |
|---|---|---|
| Graft failure/rejection | Host immune cells reject donor HSCs | Early (weeks) |
| Acute GVHD | Donor T cells attack host tissues (skin rash, diarrhoea, jaundice) | Days 10–100 post-transplant |
| Chronic GVHD | Prolonged donor immune response against host — affects skin, eyes, mouth, lungs, liver (resembles autoimmune disease) | > 100 days post-transplant |
| Infections | Profound immunosuppression during engraftment | Throughout |
| Graft-versus-leukaemia (GvL) effect | Donor immune cells recognise and destroy residual abnormal host cells — actually beneficial | Ongoing |
| Secondary malignancy | Long-term risk from conditioning chemotherapy/radiation | Years later |
| Contraindication | Rationale |
|---|---|
| Age > 40–50 years | Higher transplant-related mortality; GVHD risk increases with age |
| No suitable donor | Without HLA-matched donor, risk of graft failure and GVHD is prohibitive (though haploidentical and matched unrelated donor transplants are increasingly used as second-line) |
| Significant comorbidities | Cardiac, hepatic, pulmonary dysfunction increase transplant-related mortality |
| Non-severe AA | Risk–benefit ratio does not favour HSCT for NSAA |
| Active uncontrolled infection | Must be controlled before proceeding |
3.3 First-Line Definitive Treatment (When HSCT Not Feasible): Immunosuppressive Therapy (IST)
"Anti-thymocyte globulin + cyclosporine" [1] "Eltrombopag (high dose) + ATG and cyclosporine" [1]
IST is the first-line definitive treatment for patients with SAA/vSAA who are not candidates for matched sibling HSCT — i.e. those > 40 years old OR lacking an HLA-matched sibling donor.
Why does immunosuppression work in AA? Because the pathophysiology of idiopathic AA is T-cell–mediated autoimmune destruction of HSCs [3]. By suppressing the aberrant T-cell response, you allow the remaining HSCs to recover and repopulate the marrow. ~65–75% of patients respond to IST.
| Agent | Mechanism | Role | Dosing |
|---|---|---|---|
| Anti-thymocyte globulin (ATG) | Polyclonal antibody raised in horses (hATG) or rabbits (rATG) against human thymocytes ("thymo-" = thymus + "globulin" = antibody). It destroys T lymphocytes — the very cells mediating the autoimmune destruction of HSCs | Rapid, potent T-cell depletion — provides the acute immunosuppression needed to halt HSC destruction | Given IV over 4–5 days as an inpatient; requires premedication (steroids, antihistamines) to prevent allergic/serum sickness reactions |
| Ciclosporin A (CsA) | Calcineurin inhibitor — blocks the calcineurin-NFAT signalling pathway in T cells, preventing IL-2 transcription and T-cell activation/proliferation | Sustained T-cell suppression to maintain the response achieved by ATG and prevent relapse | Oral, continued for 12–24 months then tapered very slowly (rapid taper → relapse risk). Target trough level: 150–250 ng/mL |
| Eltrombopag | Thrombopoietin receptor agonist (TPO-RA). Binds the MPL receptor on HSCs and megakaryocytes. "Eltrombo-" = related to thrombocytes (platelets), "pag" = suffix for receptor agonist | Beyond just stimulating platelet production, eltrombopag has been shown to directly stimulate HSC self-renewal and expansion — it "wakes up" residual dormant HSCs. This is the key insight that led to its addition to IST | Oral, high dose (150 mg/day in trials), started alongside ATG + CsA for approximately 6 months |
"Triple therapy immunosuppression: anti-thymocyte globulin + cyclosporin A ± eltrombopag × 6 months" [7]
Why Eltrombopag Is a Game-Changer
The landmark NIH trial showed that adding eltrombopag to ATG + CsA increased the overall response rate from ~60% to ~85% and the complete response rate from ~10% to ~40% at 6 months. The mechanism is not just platelet stimulation — eltrombopag appears to expand the residual HSC pool by stimulating self-renewal pathways (via the MPL/JAK-STAT pathway on HSCs). This is why current guidelines recommend the triple combination (hATG + CsA + eltrombopag) as the standard IST regimen for SAA.
| Feature | Horse ATG (hATG, e.g. ATGAM) | Rabbit ATG (rATG, e.g. Thymoglobulin) |
|---|---|---|
| Efficacy in treatment-naïve SAA | Superior — higher response rate (~68%) | Lower response rate (~37%) in first-line setting |
| Potency of T-cell depletion | Moderate | More potent — causes more profound lymphopenia |
| Current recommendation | First-line IST: hATG preferred | Second-line (for relapsed/refractory AA after hATG) |
Why is more potent rATG worse for first-line AA? Paradoxically, because rATG causes such profound lymphodepletion, it may eliminate not only the pathogenic T cells but also the regulatory T cells (Tregs) needed to restore immune tolerance. hATG achieves a better balance of suppression without complete Treg ablation.
| Agent | Key Side Effects | Monitoring |
|---|---|---|
| ATG | Serum sickness (fever, rash, arthralgia, myalgia — occurs 7–14 days after administration; caused by immune complex formation against the animal protein). Allergic/anaphylactic reactions. Transient worsening of cytopenias | Premedication with steroids; monitor during infusion; prednisolone taper over 2–4 weeks after ATG course |
| Ciclosporin | Nephrotoxicity (dose-dependent; monitor creatinine and CsA trough levels), hypertension, tremor, gingival hypertrophy, hirsutism, hyperkalaemia, hypomagnesaemia | Drug level monitoring (trough 150–250 ng/mL); regular RFT, BP, electrolytes |
| Eltrombopag | Hepatotoxicity (monitor LFTs), thrombocytosis (rare in AA setting), potential concern about clonal evolution (theoretical risk of stimulating pre-existing MDS/AML clones — but clinical data reassuring so far) | Regular LFTs; CBC monitoring for response |
| Timepoint | Action |
|---|---|
| 3–4 months | Initial response assessment. Some patients show early response; if no response yet, continue treatment |
| 6 months | Main response assessment. If inadequate response → consider second-line therapy |
Response definitions:
- Complete response (CR): Hb normal for age/sex, ANC > 1.5, Platelet > 150, transfusion-independent
- Partial response (PR): No longer meets criteria for SAA, transfusion-independent, but counts not fully normalised
- No response (NR): Still meets SAA criteria or remains transfusion-dependent
For patients who fail first-line IST or who relapse:
| Option | Details |
|---|---|
| Matched unrelated donor (MUD) HSCT | For younger patients (< 50y) who failed IST. MUD HSCT outcomes have improved significantly with better HLA typing and conditioning regimens. Graft failure and GVHD risk are higher than with matched sibling donors, but 5-year survival now approaches 70–80% |
| Haploidentical HSCT | For patients without matched sibling or unrelated donor. Uses a half-matched family member (parent, child, sibling). Requires post-transplant cyclophosphamide (PTCy) to prevent GVHD. Outcomes improving; increasingly used |
| Second course of IST with rATG + CsA | Switch from hATG to rATG for the second course (cross-reactivity concern with repeated hATG). Response rate ~30–40% — lower than first-line |
| Androgens | "Consider androgens" [7]. Androgens (e.g. danazol, oxymetholone) stimulate erythropoiesis via increased EPO production and direct stimulation of erythroid progenitors. Occasionally useful for NSAA or as adjunctive therapy. Also used in telomere biology disorders (androgens upregulate telomerase activity). Side effects: virilisation, hepatotoxicity, peliosis hepatis |
NSAA does not require urgent definitive treatment. The approach is:
| Step | Details |
|---|---|
| 1. Observation | Regular monitoring (CBC every 1–3 months). Some patients remain stable for years; a few may spontaneously improve (especially if drug-related) |
| 2. Supportive care | Transfusion PRN; infection management |
| 3. Ciclosporin monotherapy | If patient becomes transfusion-dependent or cytopenias worsen. CsA alone can produce responses in some NSAA patients |
| 4. Escalation | If NSAA progresses to SAA → treat as SAA (HSCT or IST) |
All AA patients — whether treated with HSCT or IST — require lifelong monitoring for clonal evolution [7]:
| Complication | Screening |
|---|---|
| MDS / AML | Regular CBC, PBS review; BM biopsy if counts change or new cytopenias/dysplasia develop. AA can transform into MDS or AML (5–15% risk over 10 years post-IST) |
| PNH | Periodic flow cytometry for CD55/CD59 (PNH clone may emerge or expand). Clinical monitoring for haemolysis, thrombosis |
| Relapse of AA | Monitor CBC; relapse can occur especially if ciclosporin is tapered too quickly |
| Secondary iron overload | Serum ferritin; MRI T2* of liver/heart in transfusion-dependent patients [15] |
| Ciclosporin toxicity (if on ongoing CsA) | RFT, CsA trough levels, BP |
"Screen for developing other clonal disorders: MDS, PNH, AML" [7]
| Patient Profile | First-Line Treatment | Second-Line if No Response |
|---|---|---|
| SAA/vSAA, age < 40, HLA-matched sibling | Allogeneic HSCT (matched sibling) [1][7] | Repeat HSCT or IST if graft failure |
| SAA/vSAA, age < 40, NO matched sibling | hATG + CsA + Eltrombopag [1][7] | MUD HSCT, haploidentical HSCT, or rATG + CsA |
| SAA/vSAA, age > 40 | hATG + CsA + Eltrombopag [1][7] | rATG + CsA; consider MUD HSCT in fit patients < 50–55y |
| NSAA | Observation + supportive care; CsA if symptomatic | Escalate to IST if progresses to SAA |
| Inherited BM failure (e.g. Fanconi) | HSCT with modified conditioning (reduced intensity) [17] | Gene therapy (investigational) |
High Yield Summary — Management of Aplastic Anaemia
Supportive Care (ALL patients):
- Discontinue offending drugs
- RBC/platelet transfusion (leucodepleted, irradiated if HSCT candidate)
- Infection prevention and treatment (empirical antibiotics for neutropenic fever, antifungal prophylaxis)
- Iron chelation if transfusion-dependent
- G-CSF for acute infection (temporary)
Definitive Treatment — SAA/vSAA:
- First-line for young (< 40y) + matched sibling donor: Allogeneic HSCT
- First-line for older patients / no matched sibling: hATG + Ciclosporin A + Eltrombopag (triple IST)
- Second-line: MUD/haploidentical HSCT; rATG + CsA; androgens
Key Points:
- hATG is preferred over rATG for first-line IST (higher response rate)
- Eltrombopag stimulates HSC self-renewal (not just platelets) → improves CR rate
- CsA must be tapered very slowly over 12–24 months (rapid taper → relapse)
- Lifelong screening for MDS, AML, and PNH (clonal evolution risk 5–15% at 10 years)
- Fanconi anaemia patients require modified conditioning for HSCT (radiosensitive)
- Prognosis: 70% 1y mortality if untreated → 80–90% 5y survival with treatment
Active Recall - Management of Aplastic Anaemia
References
[1] Lecture slides: GC 047. Family history of anaemia.pdf (slide: Severe aplastic anaemia — treatment) [3] Senior notes: Block A - Hematology Data Interpretation.pdf (p1 — AA pathophysiology) [7] Senior notes: Maksim Medicine Notes.pdf (p168 — Management of idiopathic AA) [15] Senior notes: Ryan Ho Chemical Path.pdf (p54 — Iron overload, iron-loading anaemias including AA) [16] Senior notes: Block A - Fever after a blood transfusion_ transfusion and related problems.pdf (p22 — Irradiated blood products indications) [17] Senior notes: Block A - High white cell count_ acute and chronic leukaemia; bone marrow transplantation; immunogenetics.pdf (p9, p28 — HSCT indications, supportive treatment of acute leukaemia) [18] Senior notes: Block A - Family history of anaemia_ inherited causes of anaemia; haemolytic anaemia; aplastic anaemia.pdf (p11 — Treatment of severe AA) [19] Senior notes: Ryan Ho Haemtology.pdf (p153 — HSCT overview, indications, considerations)
Complications of Aplastic Anaemia
The complications of aplastic anaemia arise from three main sources: (A) the disease itself (consequences of pancytopenia), (B) the treatment (IST and HSCT side effects), and (C) clonal evolution (the natural history of the diseased bone marrow over time). Understanding which complication comes from which source is critical for both management and exam questions.
1. Complications of the Disease Itself (Consequences of Pancytopenia)
These are the direct, immediate life-threatening complications and are the primary causes of death in untreated AA. Remember: 70% 1-year mortality if untreated [5].
| Complication | Mechanism / Why | Details |
|---|---|---|
| Bacterial sepsis | ANC < 0.5 × 10⁹/L = severe neutropenia → loss of the first-line innate defence against bacteria. Neutrophils normally phagocytose and kill bacteria via oxidative burst; without them, even commensal flora can cause invasive disease | Infections are typically bacterial (sepsis, pneumonia, UTI) [5]. Common organisms: Gram-negatives (Pseudomonas, E. coli, Klebsiella); Gram-positives (Staphylococcus, Streptococcus) |
| Invasive fungal infections | Prolonged, profound neutropenia (ANC < 0.2 for > 7–10 days) removes the neutrophil barrier that normally prevents fungal hyphae from penetrating tissues | Invasive fungal infection is an important cause of death [5]. Key organisms: Aspergillus species (pulmonary/disseminated aspergillosis), Candida species (candidaemia, hepatosplenic candidiasis). These infections carry > 50% mortality even with treatment |
| Febrile neutropenia | Any fever (≥ 38.3°C single or ≥ 38.0°C sustained for 1 hour) in a patient with ANC < 0.5 is a medical emergency | Must initiate empirical broad-spectrum antibiotics (e.g. piperacillin-tazobactam, meropenem) within 1 hour. Delayed treatment significantly increases mortality [20] |
| Opportunistic infections | With very prolonged immunosuppression (either from the disease or from IST), viral reactivations (CMV, HSV, VZV) and Pneumocystis jirovecii pneumonia can occur | More relevant in patients receiving IST or post-HSCT |
Why fungal infections specifically? Neutrophils are the primary defence against fungal hyphae — they physically attack and kill hyphae through oxidative mechanisms. Without neutrophils, inhaled Aspergillus spores can germinate and invade pulmonary vasculature, causing haemorrhagic infarction and dissemination. This is why antifungal prophylaxis (posaconazole, voriconazole) is critical in prolonged neutropenia.
| Complication | Mechanism / Why | Details |
|---|---|---|
| Mucocutaneous bleeding | Platelets < 20 × 10⁹/L → inadequate primary haemostasis → inability to form an effective platelet plug at sites of vascular injury | Epistaxis, gingival bleeding, petechiae, purpura, menorrhagia |
| Gastrointestinal haemorrhage | Mucosal bleeding from GI tract | Can present as haematemesis, melaena, or haematochezia |
| Intracranial haemorrhage (ICH) | Platelets < 10 × 10⁹/L → risk of spontaneous bleeding into the CNS, where even small bleeds can be fatal due to raised intracranial pressure in a closed compartment | The most feared complication — a leading cause of early death in severe AA. Presents with sudden headache, altered consciousness, focal neurological deficits. Requires urgent platelet transfusion and neurosurgical assessment |
| Retinal haemorrhage | Same mechanism — capillary bleeding in the retina | Can cause visual loss; check fundoscopy in severely thrombocytopenic patients |
| Complication | Mechanism / Why |
|---|---|
| High-output cardiac failure | Chronic severe anaemia → ↓ O₂ carrying capacity → compensatory ↑ cardiac output (↑ HR, ↑ stroke volume) → over time, the heart cannot sustain this → volume overload → congestive heart failure. Particularly in elderly patients with pre-existing cardiac disease |
| Cardiac ischaemia / angina | ↓ O₂ supply to myocardium + ↑ myocardial O₂ demand (from tachycardia and ↑ cardiac output) → supply-demand mismatch → ischaemia |
| Fatigue and functional impairment | ↓ O₂ delivery to tissues → reduced aerobic capacity → profound fatigue affecting quality of life |
2. Complications of Chronic Transfusion Therapy
Patients with AA who are transfusion-dependent (before definitive treatment or while awaiting response) develop complications related to repeated blood product administration.
| Aspect | Details |
|---|---|
| Mechanism | Each unit of packed RBCs contains ~200–250 mg of iron. The body has no active iron excretion mechanism — iron is normally only lost through desquamation of gut epithelial cells (~1 mg/day). After ~20 units of RBC transfusion, iron accumulates beyond the body's storage capacity |
| Target organs | Liver (hepatic fibrosis → cirrhosis), heart (restrictive/dilated cardiomyopathy, arrhythmias — leading cause of death from iron overload), endocrine organs (pancreas → diabetes mellitus; pituitary → hypogonadism, growth failure; thyroid → hypothyroidism) |
| Monitoring | Serial serum ferritin (> 1000 μg/L indicates significant overload); MRI T2 of liver and heart* for quantitative iron assessment (more accurate than ferritin) [15] |
| Prevention / Treatment | Iron chelation therapy: deferasirox (oral), deferoxamine (SC/IV), deferiprone (oral) [15] |
"Iron-loading anaemias, e.g. thalassaemia, aplastic anaemia" are recognised causes of secondary iron overload [15]
Why Is Cardiac Iron Overload the Most Dangerous?
Iron deposited in cardiomyocytes generates reactive oxygen species (ROS) via the Fenton reaction (Fe²⁺ + H₂O₂ → Fe³⁺ + OH· + OH⁻). These free radicals cause lipid peroxidation of cell membranes, mitochondrial dysfunction, and ultimately cardiomyocyte death. This leads to restrictive cardiomyopathy (early) or dilated cardiomyopathy (late) and cardiac arrhythmias — which are the leading cause of death in transfusion-dependent patients worldwide. Cardiac MRI T2* < 20 ms indicates cardiac iron loading; < 10 ms indicates high risk of cardiac complications.
| Aspect | Details |
|---|---|
| Mechanism | Repeated exposure to donor HLA antigens on transfused white cells and platelets triggers recipient antibody formation against non-self HLA molecules |
| Consequences | (1) Platelet refractoriness — transfused platelets are destroyed by anti-HLA antibodies → platelets "don't work" → bleeding despite transfusions; (2) Graft rejection — if the patient later undergoes HSCT, pre-formed anti-HLA antibodies can reject the donor graft → graft failure |
| Prevention | Leucodepleted blood products (filters remove > 99.9% of donor WBCs, dramatically reducing HLA antigen exposure); minimise number of transfusions; use single-donor platelets (fewer HLA exposures than pooled platelets) |
This is why minimising transfusions before HSCT is crucial, and why leucodepleted and irradiated products are standard for AA patients who are potential HSCT candidates [16].
| Complication | Mechanism | Prevention |
|---|---|---|
| Febrile non-haemolytic transfusion reaction (FNHTR) | Recipient antibodies react against donor WBCs and/or cytokines accumulated in stored blood products → fever, rigors | Leucodepleted products; antipyretics |
| Transfusion-associated circulatory overload (TACO) | Volume overload, especially in patients with cardiac compromise from chronic anaemia | Slow infusion rate; diuretics (furosemide); avoid over-transfusion |
| Transfusion-associated GVHD (TA-GVHD) | Donor lymphocytes in transfused blood engraft in the profoundly immunosuppressed AA patient → donor T cells attack recipient tissues (skin, liver, GI, marrow). Almost universally fatal | Irradiated blood products [16]. If unavailable in emergency, use oldest available blood bag (lymphocytes die after ~14 days of storage) [16] |
| Transfusion-transmitted infections | Hepatitis B/C, HIV, CMV, bacterial contamination | Screening of donor blood; CMV-negative products for CMV-seronegative HSCT candidates |
| Allergic / anaphylactic reactions | IgE-mediated reaction against plasma proteins; anaphylaxis particularly in patients with IgA deficiency (anti-IgA antibodies) | Pre-medication with antihistamines; washed red cells for IgA-deficient patients |
3. Complications of Immunosuppressive Therapy (IST)
| Complication | Mechanism | Timing | Management |
|---|---|---|---|
| Serum sickness | ATG is a foreign protein (horse/rabbit immunoglobulin). The recipient's immune system forms immune complexes against the animal protein → Type III hypersensitivity reaction → deposition in joints, skin, kidneys | Day 7–14 after ATG [5] | Prophylactic prednisolone during and after ATG course (taper over 2–4 weeks); NSAIDs for symptoms |
| Allergic/anaphylactic reaction | Type I hypersensitivity to animal protein | During infusion | Test dose first; premedication with steroids, antihistamines, paracetamol; slow infusion; have resuscitation equipment ready |
| Transient worsening of cytopenias | ATG destroys not only pathogenic T cells but also other lymphocytes and cross-reacts with haematopoietic progenitors | Days 1–7 | Supportive — transfusions, infection prophylaxis |
"Serum sickness from ATG as it is from horse (fever, rash, malaise on day 7, decreased by steroids)" [5]
| Complication | Mechanism | Monitoring |
|---|---|---|
| Nephrotoxicity | Ciclosporin causes afferent arteriolar vasoconstriction in the kidney → ↓ renal blood flow → ↓ GFR. Chronic use causes tubulointerstitial fibrosis | Regular RFT (creatinine); CsA trough levels (target 150–250 ng/mL) |
| Hypertension | Same renal vasoconstriction → activation of RAAS → ↑ BP | Regular BP monitoring; treat with amlodipine (NOT ACE-I/ARB initially — drug interaction with CsA) |
| Tremor | Neurotoxicity — mechanism incompletely understood | Dose adjustment |
| Gingival hypertrophy | Stimulation of gingival fibroblast proliferation by CsA | Dental hygiene; dose reduction |
| Hirsutism | Stimulation of hair follicle growth | Cosmetic measures |
| Hyperkalaemia | ↓ Renal potassium excretion (suppression of ROMK channels in collecting duct) | Monitor electrolytes |
| Hypomagnesaemia | ↑ Renal magnesium wasting | Monitor and supplement |
| Relapse on rapid CsA taper | Removing immunosuppression too quickly allows resurgence of pathogenic T cells → recurrence of HSC destruction | Taper CsA very slowly over 12–24 months |
| Complication | Mechanism |
|---|---|
| Hepatotoxicity | Direct hepatocellular toxicity — monitor LFTs regularly |
| Thrombotic events (rare in AA setting) | Theoretical risk from excessive platelet stimulation, though rarely seen at therapeutic doses in AA |
| Concern for clonal evolution | Theoretical: stimulation of pre-existing clonal HSCs could accelerate development of MDS/AML. Clinical trial data so far reassuring, but long-term data still accumulating |
4. Complications of HSCT
These are covered comprehensively in the HSCT lecture notes and apply to all allogeneic HSCT recipients, including AA patients [17][21].
| Complication | Mechanism | Details |
|---|---|---|
| Graft rejection (host-versus-graft) | Recipient's residual immune cells recognise donor HSCs as foreign and destroy them → primary graft failure (never engrafts) or secondary graft failure (engrafts then fails) | Risk increased by HLA mismatch, prior transfusion-related alloimmunisation, inadequate conditioning |
| Acute GVHD | Donor T cells attack host tissues — principally skin (rash), liver (jaundice), GI tract (diarrhoea, abdominal pain) | Graded I–IV; grade III–IV is life-threatening. Prophylaxis: CsA/tacrolimus + methotrexate/mycophenolate. Treatment: steroids |
| Veno-occlusive disease (VOD) of liver | Conditioning regimen damages hepatic venous endothelium → sinusoidal obstruction → hepatic venous outflow obstruction → painful hepatomegaly, ascites, jaundice [21] | Prophylaxis: ursodeoxycholic acid, heparin. Treatment: defibrotide + supportive care |
| Neutropenic infections | Pre-engraftment period (day 0–30): profound neutropenia from conditioning → bacterial and fungal infections | Empirical antibiotics; antifungal prophylaxis |
| Oral mucositis | Conditioning chemotherapy destroys rapidly dividing mucosal epithelial cells | Painful oral ulceration; management: ice cubes, laser therapy, IV palifermin ± TPN [21] |
| Bleeding | Thrombocytopenia from conditioning + delayed platelet engraftment | 26% in first year, 9% life-threatening. Sites: lung (16%), GI (14%), CNS (12%) [21] |
| Complication | Mechanism | Details |
|---|---|---|
| Chronic GVHD | Prolonged donor immune response against host tissues — resembles systemic autoimmune disease (scleroderma-like skin changes, sicca syndrome [dry eyes/mouth], bronchiolitis obliterans [lungs], cholestatic liver disease) | 22% of allogeneic HSCT recipients [21]. Major cause of long-term morbidity. Treatment: steroids, CsA, ruxolitinib |
| Secondary malignancy | (1) Conditioning with alkylating agents/radiation → DNA damage → new cancers years later; (2) Chronic immunosuppression → ↓ immune surveillance → ↑ cancer risk | Post-treatment MDS and acute leukaemia; solid organ tumours (SCC of skin/oral cavity); post-transplant lymphoproliferative disease (PTLD) [21] |
| Endocrine dysfunction | Conditioning (especially TBI) damages endocrine organs | Hypothyroidism; hypogonadism; T2DM (3× risk post-allogeneic HSCT); infertility [21] |
| Cardiovascular disease | Metabolic effects of immunosuppressants + chronic GVHD-related inflammation + concurrent CV risk factors | 5% at 5y, 9% at 15y — most common cause of non-relapse mortality [21] |
| Cataract | Mainly due to total body irradiation (TBI) [17][21] — radiation damages the lens epithelial cells | |
| Osteoporosis and AVN | Chronic steroid use (for GVHD) → ↓ osteoblast activity + ↑ osteoclast activity → bone loss; steroid-induced AVN via disrupted intraosseous blood flow | |
| Immunodeficiency | Post-HSCT immune reconstitution takes 12–24 months. T-cell function is particularly slow to recover → susceptibility to viral reactivation (CMV, VZV, EBV) and encapsulated bacteria | Requires re-vaccination programme; infection prophylaxis |
| Infertility | Gonadal damage from conditioning (especially alkylating agents and TBI) | Discuss fertility preservation (sperm banking, oocyte cryopreservation) BEFORE starting conditioning |
"Complications related to high-dose chemotherapy: infection, haemorrhage, veno-occlusive disease of liver. Complications related to allogeneic HSCT: graft-versus-host disease (acute or chronic), graft rejection. Complications related to late/long-term effects: cataract (mainly due to TBI), immunodeficiency, endocrine dysfunction and infertility, secondary malignancy. Relapse of disease." [17]
5. Clonal Evolution — The Long-Term Natural History Complication
This is a unique and critically important complication of AA that is not seen with most other haematological conditions treated with IST.
| Aspect | Details |
|---|---|
| Incidence | 5–15% of AA patients develop MDS or AML over 10–15 years, particularly those treated with IST (less common after successful HSCT, which replaces the marrow entirely) |
| Mechanism | The residual HSCs in AA patients have undergone significant replicative stress (the few surviving HSCs must work overtime to maintain haematopoiesis). This increases the risk of acquiring somatic mutations. Additionally, the immune pressure that caused AA may have selected for pre-malignant clones that escaped immune destruction. Over time, these clones accumulate additional hits → MDS → AML |
| Risk factors for clonal evolution | Older age at diagnosis; presence of certain somatic mutations on NGS at diagnosis (ASXL1, DNMT3A, BCOR); multiple courses of IST; suboptimal response to IST |
| Monitoring | Regular CBC; if new cytopenias, dysplasia, or rising MCV → repeat BM biopsy with cytogenetics and molecular genetics |
"Screen for developing other clonal disorders: MDS, PNH, AML" [7]
| Aspect | Details |
|---|---|
| Incidence | PNH clones detectable in up to 50% of AA patients at diagnosis; clinical PNH (with significant haemolysis/thrombosis) develops in ~10–15% over long-term follow-up |
| Mechanism | As discussed in pathophysiology: the PIGA-mutant clone escapes autoimmune destruction and has a survival advantage. Over time, this clone may expand sufficiently to cause clinical PNH |
| Complications of PNH | Intravascular haemolysis (↑ LDH, ↓ haptoglobin, haemoglobinuria); thrombosis in unusual sites (hepatic veins [Budd-Chiari syndrome], cerebral veins, mesenteric veins, dermal veins) — thrombosis is the leading cause of death in PNH [8] |
| Monitoring | Periodic flow cytometry for CD55/CD59 (e.g. annually or if new haemolysis/thrombosis develops) |
| Treatment of clinical PNH | Complement inhibition: eculizumab (anti-C5 monoclonal antibody) or ravulizumab (longer-acting anti-C5) |
| Aspect | Details |
|---|---|
| Incidence | ~30–40% of IST responders relapse, most commonly during or after ciclosporin taper |
| Mechanism | The autoimmune T-cell clone is suppressed but not eradicated by IST. When immunosuppression is withdrawn, the pathogenic T cells re-expand and resume HSC destruction |
| Prevention | Very slow ciclosporin taper over 12–24 months; some patients require low-dose maintenance CsA indefinitely |
| Management of relapse | Second course of IST (switch from hATG to rATG); consider MUD/haploidentical HSCT for second relapse |
| Category | Key Complications |
|---|---|
| Disease-related (pancytopenia) | Bacterial sepsis, invasive fungal infections, ICH, mucocutaneous bleeding, high-output HF |
| Transfusion-related | Iron overload (liver, heart, endocrine), HLA alloimmunisation, FNHTR, TACO, TA-GVHD, transfusion-transmitted infections |
| IST-related | Serum sickness (ATG), nephrotoxicity / hypertension / relapse on taper (CsA), hepatotoxicity (eltrombopag) |
| HSCT-related | Graft failure, acute/chronic GVHD, VOD, infections, secondary malignancy, endocrine dysfunction, infertility, cataracts, CVD |
| Clonal evolution | MDS (5–15%), AML, PNH expansion (10–15%), relapse of AA (30–40% of IST responders) |
High Yield Summary — Complications of Aplastic Anaemia
Immediate life-threatening complications (from pancytopenia):
- Infections: bacterial sepsis, invasive fungal infections (Aspergillus, Candida) — major cause of death
- Haemorrhage: ICH (most feared), GI bleeding, mucocutaneous bleeding
- High-output cardiac failure from chronic severe anaemia
Transfusion-related:
- Secondary iron overload — liver cirrhosis, cardiomyopathy, endocrine dysfunction. Prevent with iron chelation (deferasirox)
- HLA alloimmunisation → platelet refractoriness, graft rejection. Prevent with leucodepleted products
- TA-GVHD — almost universally fatal. Prevent with irradiated blood products
Treatment-related:
- IST: serum sickness (ATG day 7–14), CsA nephrotoxicity/hypertension, relapse on rapid CsA taper
- HSCT: graft failure, acute/chronic GVHD, VOD, infections, secondary malignancy, endocrine dysfunction, infertility, cataracts
Clonal evolution (long-term):
- MDS/AML (5–15% over 10 years) — screen with regular CBC ± BM biopsy
- PNH (10–15%) — screen with periodic flow cytometry for CD55/CD59
- Relapse (30–40% of IST responders) — taper CsA slowly
Active Recall - Complications of Aplastic Anaemia
References
[5] Senior notes: Ryan Ho Haemtology.pdf (p32–33 — AA clinical features, management, prognosis) [7] Senior notes: Maksim Medicine Notes.pdf (p168 — Management of idiopathic AA, screen for clonal disorders) [8] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p1464 — AA and PNH overlap) [15] Senior notes: Ryan Ho Chemical Path.pdf (p54 — Iron overload, iron-loading anaemias) [16] Senior notes: Block A - Fever after a blood transfusion_ transfusion and related problems.pdf (p7, p22 — Transfusion complications, irradiated blood products) [17] Senior notes: Block A - High white cell count_ acute and chronic leukaemia; bone marrow transplantation; immunogenetics.pdf (p34 — Complications of HSCT) [20] Senior notes: Learning_Points_All_Lectures.txt (Febrile neutropenia as a medical emergency) [21] Senior notes: Ryan Ho Haemtology.pdf (p156 — Complications and prognosis of HSCT)
High Yield Summary
Definition: Pancytopenia + hypocellular BM (replaced by fat) + NO malignant infiltration/fibrosis.
Epidemiology: 4–6/million/year in Asia (2–3× Western); M:F = 1:1; bimodal age peak (young adults, elderly).
Key Aetiologies: Idiopathic/autoimmune (70–80%); Drugs (chloramphenicol, NSAIDs, anticonvulsants, carbimazole); Seronegative hepatitis (2–3mo after episode); Toxins (benzene); Inherited (Fanconi anaemia — DEB test; Dyskeratosis congenita; Shwachman-Diamond).
Pathophysiology: T-cell–mediated destruction of HSCs (IFN-γ, TNF-α → Fas/FasL apoptosis + direct killing). HLA-DR2 overexpression. PNH clone may survive by escaping immune attack.
Severity (Modified Camitta):
- Severe: BM cellularity < 25% + ≥ 2 of: ANC < 0.5, Plt < 20, Retic < 20
- Very Severe: Severe + ANC < 0.2
- Non-severe: Doesn't meet SAA criteria
Clinical Features: Symptoms/signs of pancytopenia (anaemia + neutropenia/infection + mucocutaneous bleeding). NO lymphadenopathy, NO hepatosplenomegaly. In young patients: look for dysmorphic features (inherited BM failure). Associated PNH: haemolysis + thrombosis.
Prognosis: Fatal if untreated (70% 1y mortality); 80–90% 5y survival with treatment.
High Yield Summary — Differential Diagnosis
Pancytopenia DDx framework: Decreased production (hypocellular BM: AA, hypoplastic MDS, IBMFS; hypercellular BM: leukaemia, MDS, megaloblastic anaemia, myelofibrosis, marrow infiltration) vs. Increased peripheral destruction (hypersplenism, PNH, SLE, DIC/TMA, HLH).
Key differentiators for AA:
- PBS: no abnormal cells, no blasts, no dysplastic changes
- BM: hypocellular with fat replacement, morphologically normal residual cells, no fibrosis, no malignancy
- Clinically: NO lymphadenopathy, NO hepatosplenomegaly
- Reticulocyte count: low (production failure)
Most important differentials:
- Hypoplastic MDS → dysplasia + abnormal cytogenetics on BM
- Acute leukaemia → ≥ 20% blasts + organomegaly
- Megaloblastic anaemia → hypersegmented neutrophils, macro-ovalocytes, low B12/folate, treatable!
- PNH → overlapping condition; screen with flow cytometry for CD55/CD59
- Myelofibrosis → massive splenomegaly + tear-drop cells + fibrotic BM
Always check: B12/folate (exclude megaloblastic), PNH screen (flow cytometry), viral serology (HIV, hepatitis), autoimmune markers, and cytogenetics on BM (exclude MDS).
High Yield Summary — Diagnosis of Aplastic Anaemia
Diagnostic Criteria (Modified Camitta):
- Severe AA: BM cellularity < 25% + ≥ 2 of: ANC < 0.5, Plt < 20, Retic < 20
- Very Severe AA: SAA + ANC < 0.2
- Non-severe AA: Hypocellular BM but doesn't meet SAA peripheral blood criteria
Key Investigations:
- CBC + reticulocyte count: pancytopenia + reticulocytopenia + normocytic/macrocytic anaemia
- PBS: NO abnormal cells, blasts, dysplasia, tear-drops, or schistocytes
- B12/folate, LFT, viral serology, autoimmune markers: exclude mimics
- BM aspirate + trephine biopsy: ESSENTIAL — hypocellular marrow (< 25%), fat replacement, morphologically normal residual cells, no dysplasia/fibrosis/malignancy
- Cytogenetics on BM: normal karyotype (exclude MDS)
- Flow cytometry CD55/CD59: screen for PNH (up to 50% have clones)
- DEB chromosome breakage: screen for Fanconi anaemia (children/young adults)
- HLA typing: for potential HSCT donor matching
The trephine biopsy is REQUIRED — aspirate alone is insufficient for assessing cellularity.
High Yield Summary — Management of Aplastic Anaemia
Supportive Care (ALL patients):
- Discontinue offending drugs
- RBC/platelet transfusion (leucodepleted, irradiated if HSCT candidate)
- Infection prevention and treatment (empirical antibiotics for neutropenic fever, antifungal prophylaxis)
- Iron chelation if transfusion-dependent
- G-CSF for acute infection (temporary)
Definitive Treatment — SAA/vSAA:
- First-line for young (< 40y) + matched sibling donor: Allogeneic HSCT
- First-line for older patients / no matched sibling: hATG + Ciclosporin A + Eltrombopag (triple IST)
- Second-line: MUD/haploidentical HSCT; rATG + CsA; androgens
Key Points:
- hATG is preferred over rATG for first-line IST (higher response rate)
- Eltrombopag stimulates HSC self-renewal (not just platelets) → improves CR rate
- CsA must be tapered very slowly over 12–24 months (rapid taper → relapse)
- Lifelong screening for MDS, AML, and PNH (clonal evolution risk 5–15% at 10 years)
- Fanconi anaemia patients require modified conditioning for HSCT (radiosensitive)
- Prognosis: 70% 1y mortality if untreated → 80–90% 5y survival with treatment
High Yield Summary — Complications of Aplastic Anaemia
Immediate life-threatening complications (from pancytopenia):
- Infections: bacterial sepsis, invasive fungal infections (Aspergillus, Candida) — major cause of death
- Haemorrhage: ICH (most feared), GI bleeding, mucocutaneous bleeding
- High-output cardiac failure from chronic severe anaemia
Transfusion-related:
- Secondary iron overload — liver cirrhosis, cardiomyopathy, endocrine dysfunction. Prevent with iron chelation (deferasirox)
- HLA alloimmunisation → platelet refractoriness, graft rejection. Prevent with leucodepleted products
- TA-GVHD — almost universally fatal. Prevent with irradiated blood products
Treatment-related:
- IST: serum sickness (ATG day 7–14), CsA nephrotoxicity/hypertension, relapse on rapid CsA taper
- HSCT: graft failure, acute/chronic GVHD, VOD, infections, secondary malignancy, endocrine dysfunction, infertility, cataracts
Clonal evolution (long-term):
- MDS/AML (5–15% over 10 years) — screen with regular CBC ± BM biopsy
- PNH (10–15%) — screen with periodic flow cytometry for CD55/CD59
- Relapse (30–40% of IST responders) — taper CsA slowly
Anaemia Of Chronic Disease
Anaemia of chronic disease is a hypoproliferative anaemia arising in the setting of chronic infection, inflammation, or malignancy, mediated largely by hepcidin-induced iron sequestration and impaired erythropoiesis.
Hemolytic Anaemia
Hemolytic anaemia is a condition characterized by the premature destruction of red blood cells at a rate exceeding the bone marrow's compensatory production capacity, leading to reduced circulating erythrocytes.