Aplastic Anemia : Review of Etiology and Treatment

Abstract

bone marrow to produce blood cell components. The hallmarks of the disease are pancy-topenia and a hypocellular bone marrow. Aplastic anemia is a rare disease, and approximately 2000 patients are diagnosed in the United States every year. 1 The estimated incidence is approximately two cases per million in Europe, and the incidence in Asia is two to three times higher. 2 This geographic variation is more likely caused by environmental rather than genetic elements, although individual susceptibility is an important factor. ETIOLOGY The most common causes of aplastic anemia are listed in Table 1. Inherited forms of the disorder are rare and consist of Fanconi's anemia, dyskeratosis congenita, and Schwachman syndrome. Among patients with the acquired disorder, idiopathic aplastic anemia, in which no cause is apparent, accounts for approximately 65% of all cases of aplastic anemia. Secondary aplastic anemia occurs after exposure to environmental factors and in certain disorders. The following factors have been implicated as causes of secondary aplastic anemia: chemicals, drugs, infectious agents, radiation, rheumatic disease, and pregnancy. Chemicals. A definitive linkage between benzene and aplastic anemia has been established from clinical and epidemiologic data, as well as from animal and in vitro studies. 3,4 Despite this association, benzene is still widely used as a solvent and in the manufacture of other chemicals, drugs, dyes, explosives, leather goods, and rubber. Chemicals used in insecticides (chlorophe-nothane), glue (toluene), and Stoddard solvent (petroleum distillates) have also been associated with aplastic anemia. Drugs. Chloramphenicol was, at one point, the most common cause of drug-induced aplastic anemia in the United States. Anticonvulsant medications, in particular carbamazepine and hydantoins, are also associated with the development of aplastic anemia. The toxic metabolic intermediate of carbamazepine has been implicated in fatal cases of aplastic anemia. 5 Treatment with anti-neoplastic cytotoxic agents carries a high risk of aplastic anemia, and drugs such as gold salts, D-penicillamine, phenylbutazone, quinacrine, and acetazolamide have also been implicated. Commonly used drugs such as penicillin, furosemide, allopurinol, and nonsteroidal anti-inflammatory drugs (NSAIDs) are linked to a lesser degree with aplastic anemia. Infectious agents. Some viral infections, notably infectious mononucleosis caused by Epstein-Barr virus, have been associated with aplastic anemia. Whether anemia results from a direct effect by the virus on the bone marrow or from a host immunologic response is unclear. The association between hepatitis and aplastic anemia is also strong, but anemia does not appear to be related to infection …

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