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The myeloproliferative disorders are characterized by abnormal proliferation of one or more hematopoietic cell lines or connective tissue elements. They include
Essential thrombocythemia, primary myelofibrosis, and polycythemia vera are Philadelphia chromosome–negative myeloproliferative disorders. Myeloproliferative disorders, particularly chronic myelocytic leukemia, sometimes lead to acute leukemia; some hematologists also classify hypereosinophilic syndrome and mastocytosis as myeloproliferative disorders. However, most experts argue that these disorders are sufficiently different and omit them.
Each disorder is identified according to its predominant feature or site of proliferation (see Table 1: Myeloproliferative Disorders: Classification of Myeloproliferative Disorders ). Despite overlap, each disorder has a somewhat typical constellation of clinical features, laboratory findings, and course. Although proliferation of one cell line may dominate the clinical picture, each disorder is typically caused by clonal proliferation of a pluripotent stem cell, causing varying degrees of abnormal proliferation of RBC, WBC, and platelet precursors in the bone marrow. This abnormal clone does not, however, produce bone marrow fibroblasts, which can proliferate in polyclonal reactive fashion.
An abnormality of a tyrosine kinase called JAK2, involved in the bone marrow response to erythropoietin, contributes to the cause of polycythemia vera and causes a high proportion of cases of essential thrombocythemia and myelofibrosis.
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Table 1
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PrintOpen table  |
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| Classification of Myeloproliferative Disorders |
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Disorder
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Predominant Feature
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Polycythemia vera
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Erythrocytosis
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Primary myelofibrosis (or myelosclerosis)
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Bone marrow fibrosis with extramedullary hematopoiesis
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Essential thrombocythemia
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Thrombocytosis
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Chronic myelocytic leukemia
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Granulocytosis
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Last full review/revision September 2009 by Josef T. Prchal, MD; Scott Samuelson, MD
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