Walsh & Hoyt: Essential Thrombocythemia

Essential thrombocythemia (primary thrombocythemia, hemorrhagic thrombocythemia, idiopathic thrombocythemia) is a chronic myeloproliferative disorder in which the predominant laboratory feature is a persistent, striking thrombocytosis with elevation of the platelet count to values in excess of 1,000,000 per microliter (mL). It is a clonal neoplasm. The median age at diagnosis is 60 years, and women are affected more commonly than men. Young adults are less commonly affected. Diagnostic criteria include a platelet count equal to or greater than 6 x 105/mL and the absence of conditions associated with reactive thrombocytosis. Most patients are asymptomatic at the time of diagnosis, although one-third have vasomotor complaints, including vascular headache, dizziness, visual disturbances, and erythrocelalgia (burning paresthesis of the palms and soles accompanied by erythema). Other clinical manifestations of essential thrombocythemia result from thrombotic events, hemorrhagic events, or both. Some patients have easy bruising, epistaxis, unexplained gastrointestinal bleeding, and an excessive tendency to bleed postoperatively. Splenomegaly is found in fewer than 50% of patients at diagnosis but in 80% during the course of the disease. Other patients develop evidence of microvascular occlusion in the extremities, the heart, and in about two-thirds of patients the CNS