Practice Question # 755.
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Polycythemia vera, or primary polycythemia, is a proliferative disorder in which the myeloid stem cells seem to have escaped normal control mechanisms. The bone marrow is hypercellular, and the RBC, WBC, and platelet counts in the peripheral blood are elevated.
However, the RBC elevation is predominant; the hematocrit can exceed 60%. This phase can last for an extended period (10 years or longer). The spleen resumes its embryonic function of hematopoiesis and enlarges. Over time, the bone marrow may become fibrotic, with a resultant inability to produce as many cells (“burnt out” or spent phase). The disease evolves into myeloid metaplasia with myelofibrosis or AML in a significant proportion of patients; this form of AML is usually refractory to standard treatments.