Aplastic anaemia
- Lesion
The marrow empties of blood-forming cells and fills with fat. All counts fall; most cases are an immune attack on the stem cells.
What it is
Aplastic anaemia is marrow failure with pancytopenia and a hypocellular, fatty marrow, caused by loss of haematopoietic stem cells rather than replacement by tumour. Most acquired cases are idiopathic and immune-mediated: activated T cells release interferon-γ and TNF that kill stem cells, and immunosuppression restores counts in many patients. Other causes are drugs and chemicals (dose-related or idiosyncratic), viral infections (especially seronegative hepatitis), radiation and inherited syndromes such as Fanconi anaemia and telomerase defects.
Structure
- Marrow biopsy: less than about a quarter of normal cellularity, mainly fat with scattered lymphocytes and plasma cells.
- Aspirate: often dry or diluted; residual cells are not dysplastic.
- Blood: normocytic or slightly macrocytic anaemia, neutropenia, thrombocytopenia, low reticulocytes.
Step by step
- A drug, virus or unknown trigger alters stem cells or presents new antigens.
- Autoreactive T cells (Th1 and cytotoxic) are activated.
- Interferon-γ and TNF trigger apoptosis of stem and progenitor cells.
- Alternatively, inherited DNA repair or telomere defects exhaust the stem cell pool.
- Fat replaces the marrow; all lineages fall: anaemia, infections, bleeding.
Causes of aplastic anaemia
| Group | Examples | Key point |
|---|---|---|
| Inherited: Fanconi anaemia | FANC gene defects in DNA crosslink repair | Congenital anomalies, cancer risk |
| Inherited: telomere biology disorders | Dyskeratosis congenita, TERT and TERC mutations | Nail dystrophy, oral leukoplakia, lung fibrosis |
| Acquired immune (idiopathic) | Most adult cases | Responds to immunosuppression |
| Drugs, chemicals, radiation, viruses | Chemotherapy, benzene, chloramphenicol, radiation, seronegative hepatitis | Some dose-related and reversible, some idiosyncratic |
Clinical notes
- Pallor, petechiae, bleeding gums and repeated infections in a patient without splenomegaly.
- Stem cell transplantation is the treatment of choice when a donor exists; immunosuppression otherwise.
Test yourself
Think of the answer, then tap the question to see it.
What finding on biopsy separates aplastic anaemia from hypocellular MDS or leukaemia?
A fat-filled hypocellular marrow without dysplasia or excess blasts.
What evidence supports an immune cause of most acquired aplastic anaemia?
Many patients recover counts after antithymocyte globulin and cyclosporine, and T cells produce interferon-γ that kills stem cells.
Which physical finding argues against aplastic anaemia?
Splenomegaly.
Elsewhere in DurgiPedia
Connections
Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Aplastic Anemia | MedlinePlus (MedlinePlus, US National Library of Medicine, 2026); Fanconi anemia: MedlinePlus Genetics (MedlinePlus, US National Library of Medicine, 2026).
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Representative model, for educational purposes only.