Autoimmune pancreatitis is a rare, inflammatory disorder of the pancreas.  This disorder occurs in the elderly with a male predominance. It presents clinically with jaundice, weight loss, and anorexia. Abdominal pain and associated diabetes mellitus are variable. Extrapancreatic symptoms include sclerosing sialadenitis, retroperitoneal fibrosis, and autoimmune sclerosing cholangitis. Less commonly, interstitial nephritis or mediastinal adenopathy may occur. The laboratory profile is consistent with cholestasis (elevated alkaline phosphatase and hyperbilirubinemia). Pancreatic enzymes (amylase and lipase) may be normal or only mildly elevated. An elevated serum IgG4 is the most sensitive and specific marker for diagnosing autoimmune pancreatitis. On dual-phase helical CT imaging, the pancreas may be diffusely enlarged or present with a focal mass. A well defined capsule-like rim which surrounds the pancreas or isolated pancreatic mass is another radiographic characteristic. ERCP or MRCP may reveal either segmental or diffuse narrowing of the main pancreatic duct and biliary duct strictures (long strictures with prestenotic dilatation).

The main concern is to rule out the more common pancreatic cancer when autoimmune pancreatitis presents as a pancreatic mass. Pancreatic cancer is suggested by an elevated CA 19-9 and diagnosed with core biopsy.  Histopathologic findings in autoimmune pancreatitis include diffuse fibrosis, parenchymal and periductal lymphoplasmacytic infiltration with CD4+ and CD8+ lymphocytes plus IgG4+ plasma cells, and obliterative phlebitis.

Therapy is with oral prednisone starting at 40 mg/day for the first 4 weeks and then tapering by 5 mg every 1 to 2 weeks. The response to therapy is rapid with radiographic clearing in as early as 2 to 3 weeks. This rapid response is a diagnostic characteristic. In fact, when patients fail to respond, the diagnosis should be reconsidered and the case re-evaluated for surgical exploration.