Thrombotic thrombocytopenic purpura (TTP) is characterized by the pentad of 
fever, thrombocytopenia, microangiopathic hemolytic anemia, fluctuating 
neurologic symptoms, and renal dysfunction. Thrombotic thrombocytopenic purpura 
has recently been reported in association with rheumatic diseases (RDs). The 
authors present a patient with TTP and polymyositis and speculate on the 
pathophysiology linking these two conditions. Thrombotic thrombocytopenic 
purpura and RDs may present with overlapping clinical and laboratory features. 
It is important to identify TTP as a cause of thrombocytopenia and hemolysis 
when occurring in patients with RDs since management, treatment, and prognosis 
differ. Early recognition and prompt institution of plasmapheresis may improve 
the outcome in patients with TTP.