Incidence and risk factors for thrombotic complications in a historical cohort of 100 patients with essential thrombocythemia.

The purpose of this study was to determine which factors were associated with an increased risk of thrombo-hemorrhagic complications in a historical cohort of 100 consecutive and unselected patients with essential thrombocythemia (ET) in whom busulfan treatment was given when platelets were more than 1,000 x 10(9)/L and/or a major thrombotic or hemorrhagic event occurred. The incidence of major hemorrhagic complications was very low (0.33%/person-time at risk [pt-yr]) in comparison with that of thrombotic episodes (6.6%/pt-yr). In an adequate and appropriate control historical group of 200 patients, no severe hemorrhages were recorded and the incidence of thrombotic events was 1.2% pt-yr. Thus, the analysis of risk factors was restricted to this latter group of events. Age, a previous thrombotic event, and long duration of thrombocytosis were identified as major risk factors for thrombosis, while smoking, diabetes mellitus, hyperlipidemia, and hypertension did not influence the rate of thrombotic episodes.