Thrombotic thrombocytopenic purpura (TTP): A life-threatening disease involving embolism and thrombosis (plugging) of the small blood vessels in the brain and kidneys and other organs. It is most commonly caused by inhibition of the enzymes ADAMTS13 which normally serves to break up a blood protein called Von Willebrand Factor into smaller pieces. TTP is characterized by platelet microthrombi (tiny traveling clots composed of platelets, the clotting cells in the blood), thrombocytopenia (lack of platelets), hemolytic anemia (from the breakup of red blood cells), fever, renal (kidney) abnormalities and neurologic changes such as neurological signs such as aphasia, blindness, and convulsions.
TTP is fortunately rare. It occurs at a rate of 3.7 cases per year per million persons. Plasma exchange (running blood through a machine to which patient is connected to remove the plasma- or fluid portion of the blood and returning it mixed with fresh plasma from donors and other fluids) has greatly reduced the death rate in this disorder. The mortality (death) rate for promptly treated cases ranges from 10 to 20 percent as compared to 90% before plasma exchange was used.
Many drugs have been associated with TTP. One is the antiplatelet drug clopidogrel (Plavix).