The myeloproliferative disorders are a group of diseases characterized by excessive proliferation of the myeloid elements secondary to a defect in the hematopoietic stem cell. As discussed earlier, the myeloid elements consist of erythrocytes, platelets, and the granulocytes, and there are disorders associated with the proliferation of each of these lines. These diseases are chronic in nature but tend to culminate in a more acute picture, such as acute leukemia. We consider four clinical expressions of the myeloproliferative disorders:

1. Chronic myelogenous leukemia (CML), with a predominant increase in the granulocytes
2. Polycythemia vera (PV), with a predominant increase in the red cells
3. Essential thrombocythemia (ET), with a predominant increase in the platelets
4. Myeloid metaplasia with myelofibrosis (MMMF), with a progressive fibrosis of the bone marrow with relocation of hematopoietic tissues to extramedullary sites