Autoimmune pancreatitis in Japan: overview and perspective

Since the rediscovery and definition of autoimmune pancreatitis (AIP) by Yoshida et al. in 1995, the disease has been attracting attention because of its unique clinical features and practical issues. This disease shows very impressive imaging findings, serological changes, and characteristic histopathology. It occurs most commonly in elderly males with painless jaundice or mild abdominal pain; resemblance in imaging findings between AIP and pancreatobiliary cancers poses an important practical issue of differentiation. With increasing recognition of AIP and accumulation of cases, another important feature of this disease has been revealed, i.e., association of extrapancreatic organ involvements. Initially misunderstood because it can be accompanied by other autoimmune disorders, such as Sjögren's syndrome or primary sclerosing cholangitis (PSC), AIP is now known to be associated with unique types of sialadenitis and cholangitis distinct from Sjögren's syndrome or PSC. Now the concept of "IgG4-related sclerosing disease" has become widely accepted and the list of organs involved continues to increase. With worldwide recognition, an emerging issue is the clinical definition of other possible types of autoimmune-related pancreatitis called "idiopathic duct-centric chronic pancreatitis (IDCP)" and "AIP with granulocyte epithelial lesion (GEL)" and their relation to AIP with lymphoplasmacytic sclerosing pancreatitis (LPSP). The time has arrived to establish clinical diagnostic criteria of AIP based on international consensus and to discuss regional and racial differences in the clinicopathological features of AIP. Consensus guidelines are also required for the ideal use of steroids in the treatment of AIP to suppress recurrence efficiently with minimal side effects. There are many issues to be settled in AIP; international collaboration of experts in the pancreas field is necessary to clarify the entire picture of this unique and important disease.