Despite the relatively high rate of complications seen in patients with Roux-en-Y reconstruction, ERCP with a "short" DBE is effective in patients who have undergone bowel reconstruction.

Recent studies have suggested the existence of two subtypes of autoimmune pancreatitis (AIP): type 1 AIP, related to IgG4 (lymphoplasmacytic sclerosing pancreatitis); and type 2 AIP, related to a granulocytic epithelial lesion (idiopathic duct-centric chronic pancreatitis). Compared with type 2 AIP, the clinicopathological features of type 1 AIP, with increased serum IgG4/IgE levels, abundant infiltration of IgG4 + plasmacytes and lymphocytes, autoantibodies, and steroid responsiveness, are more suggestive of abnormal immunity such as allergy or autoimmunity. Moreover, patients with type 1 AIP often have extrapancreatic lesions, such as sclerosing cholangitis, sclerosing sialadenitis, or retroperitoneal fibrosis, showing pathological features similar to those of the pancreatic lesions. Based on these findings, an international concept of and diagnostic criteria for AIP have been proposed recently. Of interest, many synonyms have been proposed for the conditions of AIP and extrapancreatic lesions associated with IgG4, such as "multifocal idiopathic fibrosclerosis," "IgG4-related autoimmune disease," "IgG4-related sclerosing disease," "systemic IgG4-related plasmacytic syndrome (SIPS)," and "IgG4-related multiorgan lymphoproliferative syndrome," all of which may refer to the same conditions. Therefore, the Japanese Research Committee for "Systemic IgG4-Related Sclerosing Disease" proposed a disease concept and clinical diagnostic criteria based on the concept of multifocal fibrosclerosing disease, in 2009, in which the term "IgG4-related disease" was agreed upon as a minimal consensus to cover these conditions. Although the significance of IgG4 in the development of "IgG4-related disease" remains unclear, we have proposed a hypothesis for the development of type 1 AIP, one of the IgG4-related diseases. The concept and diagnostic criteria of "IgG4-related disease" will be changed in accordance with future studies.

The IgG4/IgG1 ratio in the liver may be a useful marker for differential diagnosis of IgG4-SC and PSC. In IgG4-SC, abundant infiltration of regulatory T cells (Tregs) may affect the switching of B cells to IgG4-producing plasmacytes, and there is a possibility that the function of Tregs is different in IgG4-SC and other liver diseases (PSC, AIH, and PBC).

IgG4 related cholangiopathy, a distinctive type of cholangitis of unknown origin, is characterized by increased serum levels of IgG4, massive infiltration of IgG4-positive plasma cells with storiform fibrosis and/or obliterative phlebitis in the thickened bile duct wall, and good response to steroids. Patients with IgG4-cholangiopathy are frequently associated with autoimmune pancreatitis; IgG4-cholangiopathy is recognized as a biliary manifestation of IgG4-related disease. This condition can be diagnosed by a combination of imaging, serology, histopathology, and steroid responsiveness; however, cholangiographic features are often difficult to differentiate from primary sclerosing cholangitis, pancreatic cancer, or cholangiocarcinoma. The Japanese clinical diagnostic criteria for IgG4-related sclerosing cholangitis established in 2012 are useful in the diagnosis of IgG4-cholangiopathy. Although the precise pathogenic mechanism remains unclear, the development of IgG4-cholangiopathy may involve: susceptible genetic factors, abnormal innate and acquired immunity, decreased naïve regulatory T cells, and specific B cell responses. Further studies on genetic backgrounds, disease specific antigens, and the role of IgG4 are necessary to clarify the pathogenesis.

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Increased quantities of inducible costimulator-positive Tregs may influence IgG4 production in IgG4-related AIP.

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Xanthogranulomatous inflammation (XGI)