Autoimmune pancreatitis (AIP) is an infrequently recognized disorder of presumed autoimmune etiology that is associated with characteristic clinical, histologic, and morphologic findings . Most of the early literature pertaining to AIP came from Japan, where the incidence may be increasing, perhaps due to increased recognition . However, it has been described in several countries in Europe as well as the United States and Korea, suggesting that it is a worldwide entity .
AIP can occur as a primary pancreatic disorder or in association with other disorders of presumed autoimmune etiology, including IgG4 cholangitis, salivary gland disorders, mediastinal fibrosis, retroperitoneal fibrosis, tubulointerstitial disease, and inflammatory bowel disease (table 1). Several publications have indicated that AIP is actually an IgG4 systemic disease [4,5]. (See "Overview of IgG4-related disease".)
Autoimmune pancreatitis (AIP) has been referred to by a variety of names including sclerosing pancreatitis, tumefactive pancreatitis, and nonalcoholic destructive pancreatitis, depending in part upon the specific pathologic findings and the presence of extrapancreatic manifestations [6,7]. However, it is generally believed that the pathologic heterogeneity may reflect different stages or manifestations of the same disease [6,7].
Among patients with AIP, IgG4 positive plasma cells are considered a marker for the disease and can be detected in the pancreas and a variety of other tissues [8-12]. In addition, serum IgG4 levels are elevated to more than two times the upper limit of normal in most patients. (See 'Other manifestations' below and 'Serologic testing for IgG4' below.)
Although earlier reports linked autoimmune pancreatitis to primary sclerosing cholangitis (PSC), it is now recognized that intrahepatic and extrahepatic biliary tract abnormalities with strictures are most often due to IgG4-associated cholangitis. Nine to 36 percent of patients with findings indicative of PSC have been found to have elevated IgG4 levels compared with 1 percent in other chronic liver diseases . (See 'Distinction of IAC from PSC' below.)