Aplastic anemia is a disorder of the hematopoietic stem cell that results in a loss of blood cell precursors, hypoplasia or aplasia of bone marrow, and cytopenias in two or more cell lines (RBCs, WBCs, and/or platelets). Symptoms result from anemia, thrombocytopenia (petechiae, bleeding), or leukopenia (infections). Diagnosis requires demonstration of peripheral pancytopenia and a bone marrow biopsy revealing a hypocellular marrow. Treatment usually involves immunosuppression with equine antithymocyte globulin and cyclosporine, or bone marrow transplantation.
(See also Overview of Decreased Erythropoeisis.)
The term aplastic anemia commonly implies a panhypoplasia of the marrow with cytopenias in at least two hematopoietic lineages. In contrast, pure RBC aplasia is restricted to the erythroid cell line.
True aplastic anemia (most common in adolescents and young adults) is idiopathic in about half of cases. Recognized causes are
The precise mechanism remains unclear but appears to involve an immune attack on the hematopoietic stem cell.
The onset of aplastic anemia usually is insidious, often occurring over weeks or months after exposure to a toxin, though occasionally it can be acute.
In aplastic anemia, anemia may cause weakness and easy fatigability while severe thrombocytopenia may cause petechiae, ecchymosis, and bleeding from the gums, into the conjunctivae, or other tissues. Agranulocytosis commonly causes life-threatening infections. Splenomegaly is absent unless induced by transfusion hemosiderosis.
Aplastic anemia is suspected in patients, particularly young patients, with pancytopenia. Severe aplastic anemia is defined by the presence of 2 or more of the following:
In aplastic anemia, hematopoietic stem cell transplantation can be curative and is the treatment of choice, particularly in younger patients with a matched donor. At diagnosis, siblings are evaluated for HLA compatibility. Because transfusions pose a risk to subsequent transplantation, blood products are used only when essential.
In those patients unfit for transplant or lacking a donor, immunosuppressive treatment with equine antithymocyte globulin (ATG) combined with cyclosporine produces overall response rates of approximately 60 to 80%. Allergic reactions and serum sickness may occur. In refractory cases, thrombopoietin agonists have shown some efficacy in clinical trials.
Aplastic anemia involves panhypoplasia of the marrow with anemia, leukopenia, and thrombocytopenia.
Many cases are idiopathic, but chemicals, drugs, or radiation may be involved.
Bone marrow examination shows a variable degree of hypocellularity
Treatment is with stem cell transplant or immunosuppression with ATG and cyclosporine.