Introduction: Thrombotic thrombocytopenic purpura (TTP) is a clinical syndrome characterized by microangiopathic hemolytic anemia and thrombocytopenia, which has a low mortality if treated with therapeutic plasma exchange (TPE). One aim of our current study was to evaluate the clinical outcomes of patients with idiopathic TTP. Methods: SERF-TTP is a multi-center prospective study that enrolled patients with a first episode of idiopathic TTP. Each case is identified upon referral for TPE, all cases had evidence of microangiopathic hemolytic anemia and platelet count <100,000. Exclusion criteria include solid organ or allogeneic stem cell transplant, anti-neoplastic therapy or metastatic carcinoma. ADAMTS13 activity was measured on pre-TPE samples by collagen-binding assay in a central lab. Hierarchically optimal classification tree analysis (CTA) was used to construct a non-linear multi-attribute ''tree'' model for predicting outcome variables.
Results: 90 cases of idiopathic TTP were enrolled. Mean age is 43 years, and 82% are female. The median duration of symptoms prior to hospitalization was 5 days. Duration of symptoms prior to diagnosis was not predictive of severity of thrombocytopenia, renal failure or neurologic abnormalities. Presenting features included fever (T>101.38F) 3%, neurologic abnormalities 56% and acute renal failure (Cr > 2.0) 31%. All patients underwent TPE at least once daily as prescribed by the treating physicians. 52% received cryoprecipitate-poor plasma during the exchange and 63% were treated with corticosteroids. 24% received adjunctive therapies, including Rituximab 12% and vincristine 10%. The mean time to response (platelet recovery >150,000) was 10.6 days in all patients. CTA model for response identified platelet count as a root attribute. In patients who did not receive adjunctive therapies and had an initial platelet count < 27,000, 81 % had a response by day 6. While in those with initial platelet > 27,000 only 38 % achieved a response by day 6.