Myelodysplastic Syndromes and Aplastic Anemia: Pathologic and Immunologic Implications

The Myelodysplastic Syndromes (MDS) represent a heterogeneous group of bone marrow diseases of uncertain etiology characterized by a variable degree of cytopenias, predominantly but not exclusively anemia that is often macrocytic (1). The cytopenias reflect both ineffective hematopoiesis (marrow dysplasia or accelerated apoptosis) and increase in marrow leukemic blasts (2). In 85% of cases the marrow is normo to hypercellular but in 15% the marrow cellularity can be below 30% and, on occasion, below 15%, which raises the differential diagnosis with acquired aplastic anemia (3). In such instances it is necessary to depend on the morphologic identification of significant dysplasia of one or more of the myeloid cell lines or the identification of small clusters of blasts on a bone marrow biopsy. Over 50% of all cases occur in patients over the age of 70 years. Each year some 15,000 individuals will be diagnosed with MDS, although this may well be an underestimate. In a recent national survey of elderly patients with anemia (4) some 17% met the criteria for unexplained anemia and leucopenia or thrombocytopenia. This would amount to a prevalence of 163,000 individuals who might have MDS with a more careful evaluation.