[Acquired hemophilia developing after treatment of idiopathic interstitial pneumonia].

A 72-year-old man was diagnosed as having idiopathic interstitial pneumonia (IIP) in May 1999. Immunosuppressive therapy successfully controlled the activity of the IIP. In February 2004, he was referred to our department because of multiple large hematomas. Laboratory examination revealed prolonged activated partial thromboplastin time (APTT; 103.4 seconds), reduced factor VIII activity (7.0%), and the presence of factor VIII inhibitor. Immunosuppressive therapy (prednisolone 1 mg/kg/day) was initiated. After 41 days, APTT decreased to 33.4 seconds and the factor VIII inhibitor disappeared. This is the first reported case of acquired hemophilia which developed during treatment of IIP.