A variant form of autoimmune pancreatitis successfully treated by steroid therapy, accompanied by von Meyenburg complex.

Diagnostic criteria for autoimmune pancreatitis (AIP) have been proposed and used clinically because, despite its unique clinicopathological features, AIP does not have disease-specific serological tests for confirmation. However, diagnosis of a patient with pancreatic lesions mimicking cancer who deviates from these diagnostic criteria is still difficult. We present herein a patient with a variant form of AIP successfully diagnosed by fine-needle biopsy, whose response to steroid therapy was excellent. A 55-year-old Japanese man was admitted to hospital because of jaundice and pancreatic head mass. AIP was considered as one of the differential diagnoses; however, as the patient showed neither pancreatic duct narrowing nor immunological abnormalities, he did not meet the Japanese diagnostic criteria for AIP. Histopathology of the pancreatic mass demonstrated abundant infiltration by lymphocytes and interstitial fibrosis, which suggested AIP. Immunoreaction to IgG4, which is supposed to be specific to AIP, was not observed; however, response to subsequent prednisolone therapy was good, with dramatic pancreatic head mass regression. Aside from the pancreatic head mass, diffusely spreading small lesions were observed throughout the liver. The likelihood of a potential association with extrapancreatic lesions of AIP was considered and led us to carry out a liver biopsy, which revealed biliary hamartoma, also called von Meyenburg complex (VMC). As IgG4-positive plasma cell infiltration was not demonstrated in the hamartomatous regions, the hepatic condition was thought to have occurred incidentally; however, to the best of our knowledge, this is the first report in which the association between AIP and VMC was investigated and discussed.