Unveiling Risankizumab's Rare Side Effect: A Case of Severe Thrombocytopenia in Psoriatic Arthritis.

Drug-induced thrombocytopenia (DITP) is a rare but serious immune-mediated reaction characterized by drug-dependent antibodies that bind platelet surface glycoproteins, leading to severe thrombocytopenia. Biologic therapies, including IL-23 inhibitors like risankizumab, have been implicated in such adverse events. We present the case of a 47-year-old male with a history of psoriasis and prior deep vein thrombosis, who developed severe bleeding manifestations shortly after initiating risankizumab therapy for psoriatic arthritis. Clinical evaluation included mucocutaneous bleeding, petechiae, and a precipitous drop in platelet count to 3 x 10^3/uL. Management strategies involved platelet transfusions, high-dose steroids, intravenous immunoglobulin (IVIG), and thrombopoietin receptor agonists due to inadequate initial response. Despite aggressive treatment, the patient's thrombocytopenia persisted, necessitating prolonged hospitalization and consideration of alternative therapies. This case underscores the critical importance of recognizing and managing rare hematologic complications associated with biologic therapies. Vigilance in monitoring platelet counts during IL-23 inhibitor therapy is essential to mitigate severe adverse outcomes.