Effectiveness of anagrelide in the treatment of symptomatic patients with essential thrombocythemia.

We prospectively evaluated the effect of anagrelide on platelet counts and the clinical manifestations of microvascular circulation disturbances in 17 newly diagnosed patients with essential thrombocythemia. Ten patients had symptoms related to thrombocythemia, eight at the time of starting anagrelide treatment. The platelet counts before anagrelide treatment and during maintained remission of essential thrombocythemia by anagrelide were 980 (range, 610-2030) and 378 (range, 212-546) x 10(9)/L, respectively. Spontaneous platelet aggregation was found in 6 patients (35%), which disappeared on remission of essential thrombocythemia in five cases (P = 0.02). Essential thrombocythemia-related microvascular thrombotic and hemorrhagic symptoms disappeared with the normalization of platelet count in all cases during maintained remission of essential thrombocythemia by long term continuous anagrelide treatment with a follow-up period of between 2 and 6 years. However, ET-related symptoms reappeared in three patients, coinciding with increased platelet count up to 600 x 10(9)/L caused by anagrelide dose reduction. We conclude that reduction of increased platelet to normal (< 400 x 10(9)/L) in symptomatic patients with essential thrombocythemia through use of maintained anagrelide treatment is associated with the disappearance of spontaneous platelet aggregation and the complete relief of thrombotic and hemorrhagic manifestations.