Extraintestinal manifestations of autoimmune pancreatitis.

The term autoimmune pancreatitis (AIP) was first used in Japan in 1995 to describe a newly recognized form of chronic pancreatitis, after the description of Yoshida and colleagues. But Sarles in 1961, first described a form of idiopathic chronic inflammatory sclerosis of the pancreas, suspected to be due to an autoimmune process. AIP has become a widely accepted term because clinical, serologic, histologic, and immunohistochemical findings suggest an autoimmune mechanism. Most affected patients have hypergammaglobulinemia and increased serum levels of IgG, particularly IgG4. Recently published International Consensus Diagnostic Criteria for Autoimmune Pancreatitis include Guidelines of the International Association of Pancreatology, classifying AIP into types 1 and 2, using five cardinal features of AIP, namely imaging of pancreatic parenchyma and duct, serology, other organ involvement, pancreatic histology, and an optional criterion of response to steroid therapy. Extrapancreatic presentations can include sclerosing cholangitis, retroperitoneal fibrosis, sclerosing sialadenitis (Küttner tumor), lymphadenopathy, nephritis, and interstitial pneumonia. Increased IgG4+ plasma cell infiltrate has been reported in sclerosing lesions from other organ sites, including inflammatory pseudotumors of the liver, breast, mediastinum, orbit, and aorta, and it has been observed with hypophysitis and IgG4-associated prostatitis. Abundant IgG4+ plasma cells were also confirmed in Riedel thyroiditis, sclerosing mesenteritis, and inflammatory pseudotumor of the orbit and stomach. Extrapancreatic lesions could be synchronously or metachronously diagnosed with AIP, sharing the same pathological conditions, showing also a favorable result to corticosteroid therapy and distinct differentiation between IgG4-related diseases from the inherent lesions of the corresponding organs.