TTP (thrombotic thrombocytopenic purpura): A life-threatening disease involving embolism and thrombosis (plugging) of the small blood vessels in the brain. It is usually caused by inhibition of an enzyme called 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. The use of plasma exchange (running blood through a machine to which the patient is connected which removes the plasma or fluid portion of the blood and returns the cells mixed with new plasma from donors and other fluids) has greatly reduced the death rate from TTP. The mortality (death) rate for promptly treated cases ranges from 10 to 20 percent, down from 90% before the use of plasma exchange technique.