Posttransfusion purpura with antibodies against human platelet antigen‐4a following checkpoint inhibitor therapy: a case report and review of the literature

BACKGROUND Posttransfusion purpura (PTP) is a rare condition characterized by severe thrombocytopenia following receipt of blood products. Most reported PTP cases involve alloantibodies directed against human platelet antigen (HPA)‐1a. We present a case of PTP‐mediated severe thrombocytopenia associated with alloantibodies directed against HPA‐4a in the setting of combination checkpoint inhibitor therapy. CASE REPORT A 62‐year‐old woman with rectal melanoma that progressed on combination checkpoint inhibitors (ipilimumab and nivolumab) was admitted for abdominoperineal resection. She received multiple blood products during surgery, and between the sixth and eighth days post‐surgery her platelet (PLT) count decreased from 126 × 10 9 /L to a nadir of 1 × 10 9 /L. She received intravenous immunoglobulin (IVIG), steroids, and romiplostim with eventual recovery of her PLT count to 50 × 10 9 /L 20 days after surgery. She tested positive for anti‐HPA‐4a and was shown not to express HPA‐4a, confirming a diagnosis of PTP. CONCLUSION Alloantibodies strongly reactive to HPA‐4a were detected in this patient who received multiple blood products during abdominoperineal resection surgery. Her thrombocytopenia improved with prompt administration of IVIG, steroids, and romiplostim. PTP must always be considered in patients with acute severe thrombocytopenia after receipt of blood products, and treatment should not be delayed while awaiting laboratory confirmation. To our knowledge, this is the second reported case of PTP with antibodies against HPA‐4a.