Are There Two Distinct Mechanistic Pathways That Explain the Varying Clinical Presentations, Laboratory Findings, and Outcomes of Thienopyridine-Associated Thrombotic Thrombocytopenic Purpura (TTP)?

Introduction: The antiplatelet agents ticlopidine and clopidogrel are thienopyridine derivatives that are commonly used for secondary prevention of cerebrovascular events, prevention of coronary artery stent thrombosis, and for treatment of acute coronary syndrome. While these chemically related agents are the first and third most common causes of drug-associated TTP respectively, clinical presentations, laboratory findings, and outcomes suggest that there may be two distinct mechanistic pathways. Methods: Clinical and laboratory data for 60 cases of ticlopidine-associated TTP and 35 cases of clopidogrel associated TTP were reviewed. Results: Type 1 thienopyridine-associated TTP, characterized by onset of disease > 5 days after drug initiation, occurred in 98% of the ticlopidine patients versus 63% of the clopidogrel patients. Laboratory studies identified severe deficiency of ADAMTS13 activity and the presence of IgG inhibitors in 7 ticlopidine (Tsai, et al.; Annals of Internal Medicine, 2000) and 2 clopidogrel (Bennett, et al.; NEJM, 2000) patients. Survival was 68% in the ticlopidine patients versus 91% in the clopidogrel patients. Type 2 thienopyridine-associated TTP, consisting of TTP onset within 5 days of drug initiation, occurred in 2% of the ticlopidine patients versus 37% of the clopidogrel patients. Laboratory studies failed to identify deficient ADAMTS13 activity or the presence of IgG inhibitors in 1 clopidogrel patient (Zheng, et al.; Blood, 2004). Survival was 0% in the ticlopidine patients versus 38% in the clopidogrel patients. Conclusion: The proposed type 1 and type 2 thienopyridine-associated TTP may be distinguished on the basis of clinical presentation, ADAMTS13 levels, and outcome. Type 1 thienopyridine-associated TTP—characterized as occurring after > 5 days of thienopyridine treatment, severely deficient ADAMTS13 activity and presence of IgG inhibitors, and high survival rates with plasmapheresis—is more likely to occur in patients receiving ticlopidine. Type 2 thienopyridine-associated TTP—characterized as occurring within 5 days of thienopyridine therapy initiation, normal ADAMTS13 activity and undetectable IgG inhibitors, and poor survival rates despite plasmapheresis—is more likely to occur in patients receiving clopidogrel. Additional confirmatory studies on larger numbers of patients are needed.