TTP can occur soon after birth (usually in the inherited form) or in adult life (usually in the acquired form). Patients can suffer from a single episode of the disease in their entire life (70-80%) or experience one or multiple recurrences (20-30%). Recurrence of TTP may happen at any time after the first episode, although it is more likely to occur within six months.
TTP can be associated with diseases such as autoimmune diseases, blood malignancies or other tumors, treatment with some drugs (ticlopidine, clopidogrel, mitomycin and others), pregnancy and bone marrow transplantation.
TTP was first described in 1924 by Moschowitz and its cause remained unknown until recently when the occurrence of the disease was found to be associated with the deficiency of a circulating blood protein: ADAMTS13.
In healthy people ADAMTS13 is believed to cut into fragments von Willebrand Factor (VWF), an important factor that regulates platelets aggregation and is involved in blood coagulation. If VWF cutting does not occur, either for inherited or acquired ADAMTS-13 deficiency, VWF accumulates in the blood in its uncut and large form and causes platelets to aggregate in the characteristic thrombi. Consumption of platelets in thrombus formation results in reduced number of circulating platelets (thrombocytopenia). Red blood cells are fragmented into capillaries as they pass through platelet aggregates causing a low number of circulating red blood cells and hemolytic anemia (low level of circulating hemoglobin caused by destruction of red blood cells) which is typically present in the laboratory profile of TTP patients.
Hemolysis and ischemic necrosis (cellular death caused by lack of oxygen) lead to LDH increase in patients' plasma, detectable by blood analysis.
Two forms of TTP are recognized: a genetic one and an acquired one associated with ADAMTS13 deficiency. In the genetic form ADAMTS13 deficiency is genetically inherited, in the acquired form it is caused by presence of antibodies directed on one's own ADAMTS13.