Acquired Hemophilia A Presenting as a Spontaneous Soft Tissue Hematoma in an Elderly Male

Acquired hemophilia A (AHA) is a rare but potentially life-threatening autoimmune bleeding disorder characterized by autoantibodies against factor VIII. It often presents with spontaneous bleeding in patients without a personal or family history of coagulopathy, making diagnosis particularly challenging. We present a case of a 60-year-old male with a remote history of right total hip arthroplasty (THA) who developed a spontaneous intra-articular hematoma, initially mistaken for a periprosthetic infection. He later re-presented with expanding ecchymosis and anemia, ultimately diagnosed with AHA following hematology evaluation. This case highlights the diagnostic pitfalls and emphasizes the importance of considering acquired coagulopathies in unexplained bleeding.