Essential thrombocytosis (primary thrombocythemia), first described by Epstein and Goedel in 1934, is a nonreactive, chronic myeloproliferative disorder | 1 Essential thrombocytosis (primary thrombocythemia) is associated with sustained megakaryocyte proliferation that increases the number of circulating platelets. Traditionally, essential thrombocytosis (primary thrombocythemia) was considered a clonal disorder that involved pluripotent stem cells; however, studies have indicated that some patients may have polyclonal hematopoiesis

Essential thrombocytosis (primary thrombocythemia) is characterized by a platelet count greater than 600,000/?L, megakaryocytic hyperplasia, splenomegaly, and a clinical course complicated by thrombotic and/or hemorrhagic episodes.

Platelet survival is normal in essential thrombocytosis (primary thrombocythemia). Megakaryocytes increase the production of platelets, causing thrombocytosis. The cause of this increase in platelet production remains unclear, though it may be a result of autonomous production, increased sensitivities to cytokines (eg, interleukin-3 [IL-3]), decreased inhibition to platelet-inhibiting factors (eg, transforming growth factor [TGF] beta), or defects in accessory cell microenvironment

Bone marrow megakaryocytic precursors (colony-forming unit-megakaryocyte [CFU-Meg]) from patients with essential thrombocytosis (primary thrombocythemia) form colonies in the absence of exogenous thrombopoietin (Tpo). JAK2 mutations possibly turn receptor on permanently, but this could possibly occur even before the mutation becomes detectable as JAK-2mutation is only seen in 50% of patients The mechanism by which thrombocythemia produces hemorrhage or thrombosis is not well defined.

Several defects have been described, including a decrease in aggregation, hyperaggregation, and intracellular concentration of various chemicals. In addition, reports show a decrease in von Willebrand ristocetin cofactor activity and high molecular weight von Willebrand factor multimers.

Some researchers speculate that the incidence rate may be several times higher.

Patients with essential thrombocytosis (primary thrombocythemia) have a 10-year survival rate of 64-80%, which may not be significantly different from that of the age-matched general population. Transformation to acute myelogenous leukemia (AML) occurs in 0.6-5% of patients and may accelerate if the patient takes chemotherapeutic agents.

Myeloproliferative Disease . Thrombocytosis [in the Pediatrics: General Medicine section]. Thrombocytosis, Secondary . Clinical Trials. Polycythemia Vera, Myelofibrosis and Essential Thrombocythemia: Identification of PV, MF & ET Genes . Primary Thrombocythaemia 1 Trial (PT-1) .

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