This study shows that the increased occurrence of stroke in thrombotic thrombocytopenic purpura (TTP) during remission is associated with low ADAMTS13 values.

Background: Thrombotic thrombocytopenic purpura (TTP) is a lifethreatening disorder characterized by thrombocytopenia, microangiopathic hemolysis, and ischemic organ failure. The PLASMIC and French TTP scores can help guide clinical decisions when ADAMTS13 testing is not immediately available. Older individuals often present atypically, but the impact of age on these tools is not known. Study Design and Methods: We calculated the sensitivity and specificity of the PLASMIC and French TTP scores in patients enrolled in the Johns Hopkins thrombotic microangiopathy (TMA) registry. Results: Of 257 patients with TMA enrolled in the registry, we excluded patients less than 18 years of age (n = 19), with prior TMA (n = 81) or who initially presented at another hospital (n = 25). The remaining 132 patients (75 with TTP and 57 with other TMA) were analyzed. Sensitivity of a French score of 2 decreased with age and was 72.2%, 61.5%, and 46.2% for ages 18 to 39, 40 to 59, and ≥ 60 years old, respectively. A PLASMIC score ≥ 5 had higher sensitivity than the French score but this also decreased with age; sensitivity was 91.4% (95% confidence interval [CI], 76.9-98.2), 78.3% (95% CI, 56.3-92.5), and 76.9% (95% CI, 46.2-95.0) for patients 18 to 39, 40 to 59, and ≥ 60 years old, respectively. Older patients had higher platelet counts and serum creatinine than the youngest group, contributing to the loss in sensitivity. Conclusion: The PLASMIC and French TTP scores have reduced sensitivity at age ≥ 60 years and are less reliable in identifying TTP in older patients. A high index of suspicion and availability of rapid ADAMTS13 assays is required to correctly diagnose all patients with TTP.