Delayed Recovery of a Disintegrin-Like and Metalloproteinase With Thrombospondin Type 1 Motif 13 (ADAMTS13) Activity in Immune Thrombotic Thrombocytopenic Purpura Treated With Caplacizumab and Rituximab.

An 81-year-old man was admitted with fever, impaired consciousness, thrombocytopenia, and hemolytic anemia after severe acute respiratory syndrome coronavirus 2 infections. Laboratory findings showed reduced a disintegrin-like and metalloproteinase with thrombospondin type 1 motif 13 (ADAMTS13) activity with the presence of ADAMTS13 inhibitor, confirming immune thrombotic thrombocytopenic purpura (TTP). Initial treatment with plasma exchange (PE), corticosteroids, and caplacizumab attenuated symptoms; however, ADAMTS13 activity remained low. Refractory TTP was managed with rituximab. Thrombocytopenia recurred during treatment, indicating relapse, which was treated with additional PE, corticosteroids, caplacizumab, and rituximab. The patient achieved remission on day 57. The careful monitoring of rituximab efficacy is necessary because caplacizumab may delay ADAMTS13 recovery.