Purpura, thrombotic thrombocytopenic (TTP): 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 in the blood called ADAMTS13 which breaks down another protein in the blood 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 (in which a patient is attached to a machine which filters the blood, removing the plasm- or fluid portion of the blood and returns the blood cells mixed with fresh plasma from donors and other fluids).The mortality (death) rate for promptly treated cases ranges from 10 to 20 percent, down from 90% before use of plasma exchange.