LAUSR

Immune-mediated thrombotic thrombocytopenic purpura (iTTP) is characterized by recurring episodes of thrombotic microangiopathy causing ischemic organ impairment. Blacks are overrepresented in iTTP cohorts in the United States but racial disparities in iTTP outcomes and response to therapy have not been studied. Using the United States Thrombotic Microangiopathy (USTMA) Consortium iTTP Registry, we evaluated the impact of race on mortality and relapse-free survival (RFS) in confirmed iTTP in the US from 1995 to 2020. We separately examined the impact of rituximab therapy and presentation with newly diagnosed (de novo) or relapsed iTTP on RFS by race. 645 participants with 1308 iTTP episodes were available for analysis. Acute iTTP mortality did not differ by race. When all episodes of iTTP were included, Black race was associated with shorter RFS [hazard ratio (HR) of 1.60 (95% CI 1.16-2.21)]; the addition of rituximab to corticosteroids improved RFS in White [HR 0.37 (95% CI 0.18-0.73)] but not Black patients [HR 0.96 (95% CI 0.71-1.31)]. In de novo iTTP, rituximab delayed relapse, but Blacks had shorter RFS than Whites regardless of treatment. In relapsed iTTP, rituximab significantly improved RFS in White but not Black patients. Race affects overall relapse risk and response to rituximab in iTTP. Black patients may require closer monitoring, earlier retreatment, and alternative immunosuppression following rituximab treatment. How race, racism, and the social determinants of health contribute to the disparity in relapse risk in iTTP deserve further study.