Sclerosing cholangitis associated with autoimmune pancreatitis.

Autoimmune pancreatitis is a unique form of chronic pancreatitis characterized by irregular narrowing of the pancreatic duct, pancreatic swelling, and a favorable response to corticosteroids, in which the autoimmune mechanism is postulated in the pathogenesis. High serum immunoglobulin (Ig)G4 concentrations and various types of extrapancreatic involvement are prominent features of this disease. Sclerosing cholangitis is a major extrapancreatic lesion of autoimmune pancreatitis that has been regarded as primary sclerosing cholangitis (PSC) complicating chronic pancreatitis. Because sclerosing cholangitis associated with autoimmune pancreatitis (SC-AIP) also favorably responds to corticosteroid therapy, it should be differentiated from PSC. Useful points regarding the differentiation between SC-AIP and PSC are as follows: (i) PSC occurs in younger and SC-AIP in older individuals; (ii) obstructive jaundice is more frequently seen in SC-AIP; (iii) PSC is complicated with inflammatory bowel disease, whereas SC-AIP is complicated with so called extrapancreatic lesions of AIP; (iv) high serum IgG4 concentrations are frequently seen in SC-AIP; (v) a cholangiogram may differentiate the two conditions to some extent; (vi) abundant IgG4-bearing plasma cell infiltration is seen in SC-AIP; and (vii) steroid therapy is effective for SC-AIP. IgG4-related sclerosing cholangitis without pancreatic lesion may be a metachronous phenotype of SC-AIP, and also should be differentiated from PSC. The pathogenesis of AIP and SC-AIP remains unclear. The complement activation system of the classical pathway may be contributing in some cases.