Background: Thrombotic microangiopathy (TM) is characterized by thrombocytopenia and microangiopathic hemolytic anemia in association with diffuse microthrombi in the arteriolar capillaries of various organs. Its clinical manifestation is protean, and a few well-defined clinical syndromes have been recognized. A clear understanding of the consequence of TM is needed to appreciate the unusual clinical syndromes due to atypical presentation of thrombotic thrombocytopenic purpura (TTP). Methods: The medical records of patients with known diagnoses of TTP, hemolytic uremic syndrome (HUS), and the syndrome in which hemolysis, elevated liver enzymes, and low platelet count are found in association with pregnancy were examined retrospectively from 1981 to 1994 and prospectively from 1995 to 2000. Various thrombotic microangiopathic presentations were identified in these patients. Their response to exchange plasmapheresis was evaluated, and their clinical outcome was determined. Results: A total of 74 patients were diagnosed with TM. Among these patients, several well-defined thrombotic microangiopathic presentations were identified. These presentations included TTP in 57 patients, acute respiratory distress syndrome (ARDS) in 13 patients, HUS in 9 patients, the syndrome in which hemolysis, elevated liver enzymes, and low platelet count are found in association with pregnancy in 9 patients, peripheral digit ischemic syndrome (PDIS) in 6 patients, pancreatitis in 3 patients, hepatitis in 3 patients, and nonocclusive mesenteric ischemia (NOMI) in 2 patients. Exchange plasmapheresis was an effective treatment, with a response rate of 79%. A poor prognosis was evident when ARDS was present, with an overall survival rate of 46%. Conclusion: Traditionally, TTP and HUS are considered the main entities of TM. It is evident that other manifestations of TM, if unrecognized in a timely fashion, can lead to fatality. The understanding of the pathophysiologic consequences of TM and the recognition of its atypical presentations are essential to achieve favorable outcomes in patients with this life-threatening disease.

Release of unusually large von Willibrand factor (UL v WF)vmultimers and a deficiency of vWF metalloprotease may result in thrombotic thromocytopenic purpura (TTP), a life threatening disease. Surgery has been associated with TTP, probably by releasing massive amounts of UL v WF. An association bwteeen TTP and orthopedic surgery has never been reported inthe literature. We report a case of TTP following a total knee replacement surgery in which prior use of ticlopidine mighthave played a role.