Autoimmune pancreatitis (AIP) is an increasingly recognized type of chronic pancreatitis that can be difficult to distinguish from pancreatic carcinoma but which responds to treatment with corticosteroids, particularly prednisone. There are two categories of AIP: Type 1 and Type 2, each with distinct clinical profiles.

Type 1 AIP is now regarded as a manifestation of IgG4-related disease, and those affected have tended to be older and to have a high relapse rate. Type 1 is associated with pancreatitis, Sjogren syndrome, Primary sclerosing cholangitis and inflammatory bowel disease. Patients with Type 2 AIP do not experience relapse, tend to be younger and not associated with systemic disease. AIP occurring in association with an autoimmune disorder has been referred to as "secondary" or "syndromic" AIP. AIP does not affect long-term survival. Autoimmune pancreatitis may cause a variety of symptoms and signs, which include pancreatic and biliary (bile duct) manifestations, as well as systemic effects of the disease. Two-thirds of patients present with either painless jaundice due to bile duct obstruction or a "mass" in the head of the pancreas, mimicking carcinoma. As such, a thorough evaluation to rule out cancer is important in cases of suspected AIP.

Type 1 AIP typically presents in a 60-70 year old male with painless jaundice. In some cases, imaging reveals a mass in the pancreas or diffuse pancreatic enlargement. Narrowing in the pancreatic duct called strictures may occur. Rarely, Type 1 AIP presents with acute pancreatitis. Type 1 AIP presents with manifestations of autoimmune disease (IgG4 related) in at least half of cases. The most common form of systemic involvement is cholangitis, which occurs in up to 80 percent of cases of Type 1 AIP. Additional manifestations include inflammation in the salivary glands, in the lungs resulting in scarring (pulmonary fibrosis) and nodules, scarring within the chest cavity (mediastinal fibrosis) or in the anatomic space behind the abdomen (retroperitoneal fibrosis) and inflammation in the kidneys (tubulointerstitial nephritis).

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