Pancytopenia with hypocellular bone marrow most often is caused by idiopathic aplastic anemia, but can be caused by inherited bone marrow failure syndromes, drugs, infections, nutritional deficiencies, and rheumatologic disease. Aplastic anemia (AA) can remain stable for years but can become severe or transform into a myelodysplastic syndrome, acute leukemia, or paroxysmal nocturnal hemoglobinuria. Corticosteroids and erythropoietin are ineffective for management of aplastic anemia; and granulocyte colony-stimulating factor is only indicated in severe infections that do not improve with antibiotics. Supportive care with leukocyte-poor red blood cell transfusions reduces HLA antigen alloimmunization and platelet transfusion refractoriness. Horse or rabbit antithymocyte globulin plus cyclosporine typically is first-line therapy for patients with nonsevere AA who are transfusion-dependent, patients older than 40 years with severe AA, and patients with severe AA who lack an HLA antigen-matched sibling for bone marrow transplantation. The overall 5-year survival rate among patients taking antithymocyte globulin plus cyclosporine therapy is 75% to 85%. Bone marrow transplantation from an HLA antigen-matched sibling is considered the treatment of choice for severe AA in children and adults younger than 40 years. Less than approximately 33% of patients with AA have an HLA antigen-matched sibling donor, so matched unrelated donor hematopoietic stem cells are increasingly used. Umbilical cord stem cell transplantation is in clinical trials.
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