The French-American-British (FAB) investigative group devised a working classification for the MDSs in 1981 based on a study of 50 cases.7 This classification was groundbreaking work and presented the first formal body of knowledge on this group of disorders.In 1997, the World Health Organization (WHO) revised this work and presented their classification of the MDSs based on the additional knowledge gained from molecular, immunological, and cytogenetic studies. Although both classifications will be presented, only the WHO classification will be elaborated on6 (Table 14.2).
Specific Features of the World Health Organization Classification
Refractory anemia (RA) is primarily a disorder of red cells, with an anemia resistant to treatment. Less than 1% myeloblasts in the peripheral blood and less than 5% myeloblasts are seen in the bone marrow. The marrow shows hyperpla-sia with megaloblastoid features, such as multi-nuclearity, etc.
Refractory anemia with ringed sideroblasts (RARS) is a refractory anemia in which 15% or more of red cell precursors are ringed sideroblasts (Fig. 14.5). The bone marrow shows erythroid hyper-plasia and less than 5% myeloblasts, and the liver and spleen may show changes related to iron overload.
Refractory anemia with multilineage dysplasia shows bone marrow failure with two or more myeloid cell lines affected. Fifty percent of patients are
Figure 14.4 Degenerating neutrophil.
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