The term 'aplastic' means the marrow suffers from an aplasia that renders it unable to function properly. Anemia is the condition of having reduced hemoglobin or red cell concentration in the blood. Typically, anemia refers to low red blood cell counts, but aplastic anemia patients have lower counts of all three blood cell types: red blood cells, white blood cells, and platelets, termed pancytopenia.
In many cases, the etiology is impossible to determine, but aplastic anemia is sometimes associated with exposure to substances such as benzene, radiation, or to the use of certain drugs, including chloramphenicol, carbamazepine, felbamate, phenytoin, quinine, and phenylbutazone. Many drugs are associated with aplasia mainly in the base of case reports but at a very low probability, As an example, chloramphenicol treatment is followed by aplasia in less than 1 in 40,000 treatment courses, and carbamazepine aplasia is even more rare.
Aplastic anemia is present in up to 2% of patients with acute viral hepatitis.
In some animals aplastic anemia may have other causes. For example, in the ferret (mustela putorious furo) aplastic anemia is caused by estrogen toxicity. This is because female ferrets are induced ovulators, so mating is required to bring the female out of heat. Unneutered females, if not mated, will remain in heat, and after some time the high levels of estrogen will cause the bone marrow to stop producing red blood cells.
Medical therapy of aplastic anemia often includes a short course of anti-thymocyte globulin (ATG) or anti-lymphocyte globulin (ALG) and several months of treatment with cyclosporin to modulate the immune system. Mild chemotherapy with agents such as cyclophosphamide and vincristine may also be effective. Antibodies therapy, such as ATG, targets T-cells, which are believed to attack the bone marrow. Steroids are generally ineffective.
In the past, before the above treatments became available, patients with low leukocyte counts were often confined to a sterile room or bubble (to reduce risk of infections), as in the famed case of Ted DeVita.
Occasionally, milder cases of the disease resolve on their own. Relapses of previously controlled disease are, however, much more common.
Well-matched bone marrow transplants from siblings have been successful in young, otherwise healthy people, with a long-term survival rate of 80%-90%. Most successful BMT recipients eventually reach a point where they consider themselves cured for all practical purposes, although they need to be compliant with follow-up care permanently.
Older people (who are generally too frail to undergo bone marrow transplants) and people who are unable to find a good bone marrow match have five year survival rate of up to 75%.
10-33% of all patients develop the rare disease paroxysmal nocturnal hemoglobinuria (PNH, anemia with thrombopenia and/or thrombosis), which has been explained as an escape mechanism by the bone marrow against destruction by the immune system. Flow cytometry testing is performed regularly in people with previous aplastic anemia to monitor for the development of PNH.