Abstract
Low-risk essential thrombocythemia patients in clude patients aged 18 to < 80 years with no vascular risk fac tor or previous thrombosis, no associated disease, a normal life expectancy, and a platelet count between 400 and 1,000 x 109/L up to 1,500 x 109/L. Asymptomatic essential thrombo cythemia patients may be at risk for microvascular circulation disturbances. The indication for low-dose aspirin in asymptom atic essential thrombocythemia patients is uncertain, therefore randomization for aspirin 50 mg versus placebo is recom mended. Symptomatic essential thrombocythemia patients with erythromelalgia and its ischemic complications, atypical tran sient ischemic attacks, minor stroke, visual disturbances and "superficial thrombophlebitis" in the absence of bleeding, vas cular risk factors, or vascular disease have a clear indication for aspirin in a regular dose. To determine whether 50 mg/day is as effective as 100 mg/day for the prophylaxis of microvascular circulation disturbances in essential thrombocythemia, a ran domized trial comparing low-dose aspirin 50 mg versus 100 mg at platelet counts between 400 and 1,000 up to 1,500 x 109/L is recommended. To address the question whether reduction of the platelet count to normal (<350 x 109/L) is as effective as low-dose aspirin for the long-term relief of microvascular cir culation disturbances, a randomized study comparing low-dose aspirin with the correction of platelet count to normal by anagrelide is recommended. High-risk essential thrombocythe mia patients have a clear indication for platelet reductive therapy, including: (a) platelets >1,500 x 109/L, history of ma jor thrombosis (myocardial infarction, stroke, peripheral occlu sive vascular disease), or presence of vascular disease (e.g., arteriosclerosis); (b) history or presence of spontaneous or ma jor bleedings, bleedings elicited by low-dose aspirin for the secondary prevention of vascular complications in essential thrombocythemia at platelet counts <1500 x 109/L, and side effects of long-term aspirin treatment such as gastritis; and © progression from low- to high-risk essential thrombocythemia patients during follow-up or progressive myeloproliferative disease such as significant splenomegaly, myelofibrosis, leu kocytosis, etc. To address the question of optimal treatment of high-risk essential thrombocythemia patients, randomization for anagrelide versus interferon at < 65 years of age and anagrelide versus hydroxyurea at an age > 65 years is recom mended.