Thrombotic thrombocytopenic purpura.

Platelet thrombus formation in small vessels is triggered by certain stimuli, including vascular injury, primary platelet agglutination, or both. The formation and dissolution of platelet thrombi is modulated by proteolysis, plasma factors, PGI2 synthesis and stability, and immune mechanisms. Some recent evidence now suggests that there is a subset of thrombotic thrombocytopenic purpura (TTP) patients possessing a specific platelet agglutinating factor that triggers the intravascular platelet agglutination. Identification and classification of TTP patients into subgroups with common triggering agents, and further clarification of the role of modifying factors will enable us to understand the disease better and to improve therapy.