[Immune-mediated thrombotic thrombocytopenic purpura successfully diagnosed and treated through repeated ADAMTS13 inhibitor testing].

Immune-mediated thrombotic thrombocytopenic purpura (TTP) is characterized by systemic thrombosis and organ damage due to a significant reduction in ADAMTS13 enzyme activity caused by the production of anti-ADAMTS13 autoantibodies. The standard frontline treatments are supplementation of ADAMTS13 and the removal of inhibitory antibodies by plasma exchange, suppression of inhibitor generation by corticosteroid, and suppression of thrombosis formation by caplacizumab. Additionally, in recurrent or refractory cases, favorable outcomes have been reported using rituximab. It has been reported that low ADAMTS13 inhibitor titers result in false negatives, and these rise to detectable levels due to a reaction to the ADAMTS13 factor in the fresh frozen plasma used in plasma exchange. Here, we report a case where the ADAMTS13 activity was <10%, but the ADAMTS13 inhibitor was negative at the initial measurement. It is difficult to distinguish between congenital and immune-mediated TTP. We experienced a rare case in which the patient's life was saved by continuing treatment for immune-mediated TTP while conducting a thorough examination of differential diagnoses. This rare case is presented together with a review of the relevant literature.