Autoimmune Pancreatitis and Other Organ Involvement

Autoimmune pancreatitis (AIP) is a peculiar form of pancreatitis that should be differentiated from pancreatic cancer. AIP is divided into two subtypes: type 1 and type 2. The histologic characteristic of type 1 AIP is lymphoplasmacytic sclerosing pancreatitis (LPSP) showing abundant infiltration of lymphocytes and IgG4-positive plasma cells, storiform fibrosis, and obliterative phlebitis, while that of type 2 AIP is idiopathic duct-centric chronic pancreatitis (IDCP) showing granulocytic infiltration of the pancreatic duct wall (GEL). AIP is diagnosed by combination of imaging, serological, histopathological findings; other organ involvement; and steroid responsiveness according to international consensus diagnostic criteria. Type 1 AIP is a pancreatic manifestation of IgG4-related disease, and frequently has elevation of serum IgG4 levels and other IgG4-related diseases. Type 2 AIP is rare in Asia compared to Europe and North America. In contrast to type 1 AIP, type 2 AIP is seen in younger patients, and typical affects males and females equally. Abdominal pain and acute pancreatitis are more frequent in type 2 AIP patients. Although type 1 AIP is rarely associated with inflammatory bowel disease, type 2 AIP frequently has inflammatory bowel disease.