Autoimmune Pancreatitis

Abstract Autoimmune pancreatitis (AIP) is a type of chronic pancreatitis which is likely caused by immune dysregulation. There are two types of AIP. Type 1 AIP is a pancreatic manifestation of immunoglobulin G4 (IgG4)-related disease. It presents with painless obstructive jaundice and diffuse swelling of the pancreas on imaging. It is seen more commonly in elderly males. Approximately two-thirds of patients with type 1 AIP have elevated serum IgG4 levels. It is characterized histologically by dense lymphoplasmacytic infiltration, storiform fibrosis, and obliterated phlebitis. Type 1 AIP responds very well to steroids but has a high risk of relapse and patients frequently need steroids, immunomodulators, or rituximab to maintain remission. Type 2 AIP primarily affects the pancreas. It affects male and female patients equally in the third to fourth decade of life. These patients do not typically have elevated serum IgG4 levels or any other biomarkers, and tend to have more focal or segmental involvement than diffuse involvement of the pancreas. It is characterized histologically by lymphoplasmacytic infiltration and intraluminal and intraepithelial neutrophils in the small and medium ducts. These patients respond to steroids and the likelihood of relapse is low.