Acquired hemophilia associated with autoimmune bullous diseases: a report of two cases and a review of the literature.

Acquired hemophilia (AHA) is a relatively rare and life-threatening disease caused by autoantibodies against factor VIII. Autoimmune bullous diseases (ABD) are also caused by autoantibodies against specific skin proteins. We herein report two cases of AHA associated with ABD. These coincidences are extremely rare, and only 14 documented cases have been reported previously. We further analyzed the properties of the autoantibodies in our patients. The epitopes were the A2 domain in patient 1, and both the A2 domain and the light chain in patient 2. Their isoforms were predominantly IgG4. Cross-reactivity could not be demonstrated. An accumulation of cases is required to unveil the pathogenesis of AHA.