Aplastic anaemia

Definition

A gross reduction or absence of haemopoietic precursors in all 3 cell lineages in bone marrow resulting in pancytopenia in peripheral blood. 122 Although this encompasses all situations in which there is myelosuppres-sion, the term is generally used to describe those in which spontaneous marrow recovery is unusual.

Incidence

Rare ~5 cases per million population annually. Wide age range, slight increase around age 25 years and >65 years. 10X more common in Orientals.

Causes

Divided into categories where aplasia is regarded as:

• Inevitable

- TBI dose of >1.5Gy (note: >8Gy always fatal in absence of graft rescue).

- Chemotherapy e.g. high dose busulfan.

• Hereditary

- Fanconi syndrome—stem cell repair defect resulting in abnormalities of skin, facies, musculo-skeletal system and urogenital systems.

- BM failure often delayed until adulthood.

• Idiosyncratic

- Chronic benzene exposure.

- Drug-induced, but not dose related—mainly gold, chloramphenicol, phenylbutazone, NSAIDs, carbamazepine, phenytoin, mesalazine.

- Genetic predisposition demonstrated for chloramphenicol.

- Parvoviral infections—classically red cell aplasia but may be all elements. Devastating in conjunction with chronic haemolytic anaemia e.g. aplastic sickle crisis.

- Hepatitis viruses A, B and C, CMV and EBV.

• Idiopathic

- Constitute the majority of cases.

Classification

• According to severity most clinically useful.

• Defines highest risk groups.

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