A myeloproliferative disorder characterised by increased platelets due to clonal proliferation of megakaryocytes in the bone marrow.
Platelets although increased in number have disrupted function causing them to clump intravascularly leading to thrombosis, and to fail to aggregate causing bleeding.
Essential thrombocythaemia presents with bruising, bleeding and cerebrovascular symptoms. Initially there is splenomegaly but recurrent splenic thromboses lead to a small atrophic spleen.
The blood film shows increased numbers of platelets and giant platelets. Bone marrow aspiration demonstrates increased megakaryocytes.
Mild disease may be treated with long term aspirin. Patients with a higher risk of thrombosis are treated with hydroxyurea. Patients with life-threatening haemorrhagic or thrombotic events should be treated with thrombocytopheresis in addition to hydroxyurea. Angrelide is occasionally used.
Essential thrombocythaemia may eventually transform to myelofibrosis or acute leukaemia but the disease may not progress for many years.