Acquired Hemophilia A in a Patient With Multiple Sclerosis.

Introduction Acquired hemophilia A (AHA) is a rare bleeding disorder caused by autoantibodies against clotting factor VIII. It occurs most commonly in the elderly population. AHA is associated with malignancy, autoimmune diseases, pregnancy, and drugs. However, up to 50% of reported cases remain idiopathic. AHA is very rarely associated with multiple sclerosis. Case Presentation A 56-year-old patient with a history of MS presented with thigh and arm swelling and associated pain. Imaging revealed diffuse iliopsoas hematoma. Laboratory studies showed that prothombin time was not elevated and there was prolongation of activated partial thromboplastin time that was not corrected by mixing studies. Clotting factor VIII activity level was reduced, and the inhibitor level was elevated. He was treated with factor eight inhibitor bypassing agents, rituximab, and steroids. Conclusion AHA should be suspected in any patient with new-onset bleeding in the presence of a prolonged activated partial thromboplastin time. Prompt diagnosis and treatment are important as AHA carries a high mortality rate.