Skip to Main Content

We have a new app!

Take the Access library with you wherever you go—easy access to books, videos, images, podcasts, personalized features, and more.

Download the Access App here: iOS and Android

Chronic myeloproliferative disorder caused by a clonal increase in platelets resulting in thromboembolic and hemorrhagic complications.

Primary Thrombocytosis; Idiopathic Thrombocytosis; Hemorrhagic Thrombocytosis.

Estimated at 1.4-2.5:100,000 per year. Overall, both genders are approximately equally affected; however, there is a predilection for females at younger ages. Although the majority of patients at presentation are approximately 60 years old, approximately 20% of the patients are younger than 40 years. Only rarely has essential thrombocytosis (ET) been described in children.

Rare familial form with autosomal dominant transmission has been described. However, in the vast majority of patients, no genetic background is detectable.

Not fully elucidated yet. ET is caused by proliferation of megakaryocytes, of which the exact pathogenesis remains to be elucidated. However, evidence now indicates that a mutation of the thrombopoietin gene (located on 3q26.3-q27) may play a major role. Thrombopoietin is the key hormone in the regulation of megakaryocyte differentiation and proliferation. The mechanisms by which ET leads to thromboembolic and hemorrhagic complications remain unclear, although different laboratory findings have been used to explain them (intrinsic abnormality of the platelets resulting in hypoaggregation and hyperaggregation of platelets, anomalies or decreased concentrations of “von Willebrand factor,” or deficiencies of proteins C and S and/or antithrombin III).

Based on the clinical findings of a sustained, not otherwise explained platelet count greater than 600 × 109/liter, a hematocrit less than 40 (mild erythrocytosis is present in approximately one third of patients, while others have a mild hypochromic, microcytic anemia), and normal or increased leukocyte count. The mean platelet volume usually is increased, but microcytosis has also been described. Giant platelets can be found in the peripheral blood smear. A bone marrow aspirate and biopsy are needed and show an increased cellularity with megalokaryocytic predominance (often in clumps or sheets). Increased red and white cell hyperplasia are common. The stainable iron in the bone marrow, serum ferritin levels, and mean corpuscular erythrocyte volume are normal. Bone marrow fibrosis is either absent or affects less than one third of the biopsy area. No cytogenetic or morphologic evidence of a myelodysplastic syndrome can be found. No cause for reactive thrombocytosis. Essential thrombocythemia is diagnosed once reactive thrombocytosis has been excluded.

Up to 50% of patients present with microvascular occlusions (e.g., fingers and toes with risk of gangrene if left untreated, priapism), whereas major vessel occlusions (e.g., coronary, renal and femoral arteries, or hepatic-vein thrombosis [Budd-Chiari Syndrome], portal vein, splenic, or femoral vein thrombosis) are less common. Cerebrovascular infarction, transient ischemic attacks, and myocardial infarction, although common in elderly patients, are less common in young patients. Pulmonary embolism is a common finding and may result in chronic pulmonary artery hypertension. Hemorrhage can be a presenting feature, is generally not severe, and often is associated with platelet counts greater than 1000 × 109/liter, with the gastrointestinal tract (duodenum) the most common site ...

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.