Research progress in type I autoimmune pancreatitis

Autoimmune pancreatitis ( AIP) is an increasingly recognized type of chronic pancreatitis, which is clearly distinct from other types of chronic pancreatitis. After it was discovered in 2001 that serum IgG4 concentrations are significantly elevated in AIP patients, the distinctiveness of this disease has been widely recognized. Type 1 AIP, unlike type 2 AIP, accounts for 2% of chronic pancreatitis cases, and it predominantly affects adult males. Patients usually present with obstructive jaundice due to enlargement of the pancreatic head or thickening of the lower bile duct wall. Pancreatic cancer is the leading differential diagnosis for which serological, imaging, and histological examinations need to be considered. Serologically, an elevated level of IgG4 is the most sensitive and specific finding for AIP. Imaging features include irregular narrowing of the pancreatic duct, diffuse or focal enlargement of the pancreas, capsule- like peri- pancreatic rim, and enhancement at the late phase of contrast- enhanced images. Biopsy or surgical specimens show much of the intralobular interstitial tissue has diffuse lymphoplasmacytic infiltration containing many IgG4- positive plasma cells, storiform fibrosis, and obliterative phlebitis. A dramatic response to steroid therapy is another characteristic, and serological or radiological improvements are normally identified within the first 2 or 3 weeks. Type 1 AIP is estimated as a pancreatic manifestation of a systemic IgG4- related disease based on the fact that synchronous or metachronous lesions can develop in multiple organs. Several autoantigens related to type 1 AIP have been identified so far, but the exact role of IgG4 in this disease remains to be clarified.