Spontaneous Hemarthrosis and Compartment Syndrome in an Elderly Female With Acquired Hemophilia A: A Case Report.

Acquired hemophilia A (AHA) is a rare but life-threatening bleeding disorder caused by autoantibodies against factor VIII. Unlike congenital hemophilia, AHA often presents in older adults without a prior bleeding history, manifesting with spontaneous, severe bleeding into soft tissues, muscles, or joints. We report the case of a 79-year-old woman with osteoporosis and osteoarthritis who presented with progressive right elbow pain and swelling, initially suspected to be septic arthritis or synovial tumor. Her course was complicated by massive hemarthrosis, intramuscular hematoma, and compartment syndrome requiring fasciotomy. Laboratory evaluation revealed a prolonged activated partial thromboplastin time (aPTT), markedly reduced factor VIII activity, and the presence of inhibitors, confirming the diagnosis of AHA. The patient was successfully managed with prothrombin complex concentrate, corticosteroids, and surgical intervention. This case highlights the importance of early recognition of AHA in patients with unexplained bleeding and prolonged aPTT, as misdiagnosis can delay life-saving treatment.