Thrombotic thrombocytopenic purpura

Thrombotic thrombocytopenic purpura (TTP or Moschcowitz syndrome) is a rare disorder of the blood-coagulation system, causing extensive microscopic clots to form in the small blood vessels throughout the body. These small blood clots, called thrombi, can damage many organs including the kidneys, heart and brain. In the era before effective treatment with plasma exchange, the fatality rate was about 90%. With plasma exchange, this has dropped to 10% at six months. Immunosuppressants, such as glucocorticoids, rituximab, cyclophosphamide, vincristine, or cyclosporine, may also be used if a relapse or recurrence follows plasma exchange.

Most cases of TTP arise from inhibition of the enzyme ADAMTS13, a metalloprotease responsible for cleaving large multimers of von Willebrand factor (vWF) into smaller units. The increase in circulating multimers of vWF increase platelet adhesion to areas of endothelial injury, particularly at arteriole-capillary junctions.

A rarer form of TTP, called Upshaw-Schülman syndrome, is genetically inherited as a dysfunction of ADAMTS13. If large vWF multimers persist, a tendency for increased coagulation exists.

Red blood cells passing the microscopic clots are subjected to shear stress which damages their membranes, leading to intravascular hemolysis, which in turn leads to anaemia and schistocyte formation. Reduced blood flow due to thrombosisand cellular injury results in end organ damage. Current therapy is based on support and plasmapheresis to reducecirculating antibodies against ADAMTS13 and replenish blood levels of the enzyme.