[Role of platelet dysfunction in the haemostatic manifestations occurring during essential thrombocythaemia]

Among myeloproliferative disorders, Essential Thrombocythaemia is the most frequent and the one associated with the better prognosis. Although median survival is above 15 years, Essential Thrombocythaemia may be complicated by haemostatic life-threatening manifestations. Occurrence of thromboembolic or haemorrhagic episodes, even both in a same patient, are not predictable and physiopathology of Essential Thrombocythaemia remains misunderstood. Many studies have been conducted to explain the mechanisms responsible for the haemostatic complications and to determine predictive biological factors in order to improve the management of patients. We report here a review of the potential roles of platelets in Essential Thrombocythaemia through their interaction with coagulation and fibrinolysis systems as well as with cellular components (leukocytes and endothelium). Many controversial data have been published so far. However, a deficiency in high molecular multimers of von Willebrand factor is currently admitted, as well as deficiency of platelet membrane proteins and the presence of circulating activated platelets, especially in erythromelalgia. However, no biological abnormality has been correlated with the clinical manifestations. The haemostatic complications are likely to result from a multifactorial process in which accumulated moderated risk factors unbalance the procoagulant/anticoagulant pathways.