Acquired Factor VIII (FVIII) Deficiency: A Case of Idiopathic Hemorrhage.

We report the case of a 34-year-old female with no prior medical history or known bleeding disorders who presented with a large, spontaneous right arm hematoma developing gradually over 10 days, without preceding trauma. She also had multiple ecchymoses and a history of a right calf hematoma three months earlier, initially misdiagnosed and managed as deep venous thrombosis and later as muscle cramp. Laboratory evaluation revealed anemia (hemoglobin: 9.9 g/dL) and a markedly prolonged activated partial thromboplastin time (aPTT) that failed to correct with mixing studies. Factor VIII activity was severely reduced at 4%, with an inhibitor titer of 3.1 Bethesda units, confirming acquired hemophilia A. Imaging demonstrated an intramuscular hematoma within the biceps. The patient was treated with high-dose intravenous methylprednisolone for three days, a single dose of cyclophosphamide, and transitioned to oral prednisolone and azathioprine. Within 24 hours, her aPTT improved to near-normal, and at one-month follow-up, she demonstrated complete resolution of symptoms, normalized FVIII activity, and no recurrence. This case underscores the importance of prompt recognition and combined laboratory, imaging, and clinical assessment in diagnosing acquired hemophilia, particularly in atypical presentations without mucocutaneous bleeding. Early targeted immunosuppressive therapy can result in rapid inhibitor eradication and favorable outcomes.