Acquired hemophilia A associated with IgG4-related lung disease in a patient with autoimmune pancreatitis.

Immunoglobulin G4 (IgG4)-related lung diseases can occur in patients with autoimmune pancreatitis (AIP). However, the causal relationship between AIP and acquired hemophilia A (AH) is unknown. We herein report the first case of AH associated with IgG4-related lung disease that developed in a patient with AIP. A 65-year-old asymptomatic man with a history of AIP and sclerosing cholangitis diagnosed at the age of 57 was admitted to our hospital due to an abnormal reticulonodular shadow on chest X-ray. An examination of lung biopsy specimens revealed IgG4-positive plasma cell infiltration in the interstitium. The serum IgG4 level was elevated. One year later, the patient developed a progressive severe hematoma in the left femoral muscle. On admission, laboratory examinations revealed severe anemia with a markedly prolonged activated partial prothrombin time, a decreased level of factor VIII (FVIII) activity, and the existence of anti-FVIII antibodies. These findings were consistent with a diagnosis of AH. No relapse has been observed over the past 25 months, during which time, corticosteroid therapy has been continuously administered.