A pancytopenia due to a loss of haematopoetic precursors from the bone marrow.
Aplastic anaemia can be either congenital or much more commonly acquired:
· There are several forms of congenital aplastic anaemia the most common of which is Fanconi’s anaemia. This is an autosomal recessive aplastic anaemia with limb deformities.
· Idiopathic acquired aplastic anaemia is the most common form. It is thought to be due to an immune mechanism.
· Secondary acquired aplastic anaemia may result from direct injury to stem cells by external radiation or cytotoxic drugs. Other drugs may cause aplastic anaemia through dose dependent (e.g. gold) or idiosyncratic (e.g. nonsteroidal anti-inflammatory drugs) reactions, or by both mechanisms (e.g. chloramphenicol). Other causes include solvents, pesticides, industrial chemicals and insecticides and viruses (e.g. parvovirus B19 and HIV).
Patients present with the features of pancytopenia:
· Symptoms and signs of anaemia.
· Recurrent infections due to leucopenia.
· Bruising and purpura due to thrombocytopenia.
Full blood count and blood film will demonstrate a pancytopenia with absence of reticulocytes. A bone marrow aspirate and trephine shows a hypocellular marrow with no increased reticulin (fibrosis).
Treatment should include withdrawal of any causative agents, supportive care (blood and platelet transfusions) and some form of definitive therapy. Blood and platelet transfusions should be used selectively in patients who are candidates for stem cell transplantation to avoid sensitisation.
Stem cell transplantation is the treatment of choice in young patients with acquired severe aplastic anaemia who have an HLA identical sibling.
Immunosuppressive therapy is used as first line treatment in patients over 35–45 years, younger patients without an HLA identical sibling or those with less severe aplastic anaemia. Regimens include antithymocyte globulin and cyclosporine. Androgens may be used as additional therapy.
The course is dependent on the severity of the disease and the age of the patient. In young patients who undergo stem cell transplantation the 3-year survival rate is 75–85%. Immunosuppressive therapy has a similar 3 year survival but there is a significant risk of developing paroxysmal nocturnal haemoglobinuria, myelodysplastic syndrome or acute myeloid leukaemia.