Essential thrombocythemia

Essential thrombocytosis (ET, essential thrombocythemia) is a rare and chronic blood disorder characterized by the overproduction of megakaryocytes (the precursor cell for platelets). Most of these patients will have platelet counts over 600,000 per cubic mm. In some cases this disorder may be progressive, and (very rarely) evolves into acute leukemia or myelofibrosis. more...

Pathophysiology

The pathologic basis for this disease is unknown. However, essential thrombosis resembles polycythemia vera in that cells of the megakaryocytic series are more sensitive to growth factors. Platelets derived from the abnormal megakaryocytes do not function properly, which contributes to the clinical features of bleeding and thrombosis.

Recently, in 2005, a mutation in the JAK2 kinase (V617F) was found by multiple research groups (Baxter et al., 2005; Levine et al., 2005) to be associated with essential thrombocytosis. JAK2 is a member of the Janus kinase family. This mutation be helpful in making a diagnosis or as a target for future therapy.

Clinical findings and symptoms

Essential thrombocytosis is the most rare of the myeloproliferative family of diseases. The major symptoms are bleeding and thrombosis. Other symptoms include an enlarged spleen (splenomegaly), epistaxis (nosebleeds) and bleeding from gums and gastrointestinal tract. One characteristic symptom is throbbing and burning of the hands and feet due to the occlusion of small arterioles by platelets (erythromelalgia).

Clinical course

Essential thrombocytosis is a slowly progressing disorder with long asymptomatic periods punctuated by thrombotic or hemorrhagic crises. It is diagnosed at a rate of about 2 to 3 per 100,000 individuals and usually affects middle aged to elderly individuals (although it can affect children and young adults). The median survival time for patients with this disorder is 12 to 15 years.

Treatment

In cases where patients have life-threatening complications, the platelet count can be reduced rapidly through platelet apheresis (a procedure that removes platelets from the blood directly). Long-term decreases in platelet counts can reduce bleeding and clotting complications. Common medications include hydroxyurea, interferon-alpha, or anagrelide. Aspirin may also help decrease clotting.

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