Essential thrombocythaemia (ET) refers to an acquired myeloproliferative neoplastic state characterized by an expansion of the megakaryocytic lineage, leading to an isolated elevation of platelets. It falls under the group of myeloproliferative disorders. It increases the risk of both thrombosis and hemorrhage.
The disease has traditionally been a diagnosis of exclusion, requiring the absence of reactive conditions and other clonal disorders that may present with thrombocytosis. The discovery of mutations in JAK2 and MPL now allows for the positive identification of ET in more than one-half of all cases.
Diagnosis is often when there is an "unexplained and persistent thrombocytosis" (platelet count > 450 × 109/L). Several diagnostic criteria have been put forward, e.g. WHO 2008 and BCSH 2010 2.
Can be variable depending on the organ involved and usually suspected when there are thrombosis of various vessels or ischemic events such as recurrent strokes.
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