ABSTRACT
Thrombotic thrombocytopenic purpura (TTP) and the hemolytic-uremic syndrome (HUS) are rare clinical conditions characterized by microangiopathic hemolytic anemia, consumptive thrombocytopenia, and ischemic dysfunction of several organs, mainly the central nervous system and the kidney. The frequent observation of patients who exhibit features of both TTP and HUS, as well as the morphological findings similar in both syndromes, have led researchers to consider that TTP and HUS are merely different clinical expressions of a unique pathological entity. The routine laboratory tests of hemostasis are normal or near normal in most patients with TTP and HUS. The activation of the plasma coagulation mechanisms may result from either a preceding platelet aggregation phenomenon and/or endothelial cell damage or overstimulation. Activation of the latter cells expose tissue factor and internalize thrombomodulin normally expressed on the luminal surface. The vessel wall endothelial cell is an essential constituent of the maintenance system of the hemostatic balance.
