[Pathogenesis of thrombotic and hemorrhagic complications in myeloproliferative and myelodysplastic syndromes].

Chronic myeloproliferative disorders (CMD) and Myelodisplastic Syndromes (MDS) represents a group of clonal pluripotent stem-cell pathologies. During their natural history, the clinical picture reveals both thrombosis and hemorrhage. The thrombosis could affect the microvessels, and also the large vessels, including even less usual territories (suprahepatic veins, porta vein, pulmonary vein). There are many factors contributing to thrombosis in myeloproliferative chronic disorders--the associated comorbidities, the numeric alterations of blood elements and also the disorders of the platelet's function. Thus, there were described quantitative and qualitative anomalies of platelet's receptors: GP Ib, GP IIb/IIIa, GP IV, GP VI, thrombopoietin receptor of the platelet cMPL, the increase of platelet activation; the increase of P selectin and thrombospondin and the increase on GP IIb/IIIa expression--they were all correlated with thrombosis. An important role has been attributed to JAK2 mutation, which affects the platelet receptor for thrombopoietin cMPL. Regarding the hemorrhage in chronic myeloproliferative syndrome, it is favored by many disorders in platelet's function, such as: the decrease of von Willebrand factor's receptor of the platelet, which leads to acquired Bernard Soulier syndrome; quantitative and qualitative disorders of dense granules of the platelet, decrease of the secretion and platelet aggregation after epinephrine, ADP and collagen stimulation. It was also described the acquired von Willebrand syndrome, most frequently type 2.