Autoimmune Pancreatitis

Autoimmune pancreatitis (AIP), also referred to as nonalcoholic destructive pancreatitis and sclerosing pancreatitis, is a rare condition characterized histologically by chronic inflammation of the pancreas and clinically by various symptoms related to biliary and pancreatic pathologies. Recurrent acute pancreatitis or painless jaundice should prompt an evaluation for autoimmune pancreatitis. AIP can be a primary pancreatic disorder or a systemic autoimmune disease associated with other autoimmune conditions, such as immunoglobulin G subclass 4 (IgG4)–related diseases. Autoimmune pancreatic disease is the only pancreatic condition treated effectively with corticosteroids. Three types of AIP are clinically recognized: IgG4-related pancreatitis, associated with a serum IgG4 concentration greater than twice the normal reference range in most affected individuals. Diagnostic findings include infiltration with greater than 10 IgG4-positive plasma cells per high-power field (HPF), a cartwheel pattern of fibrosis, lymphocytic and plasma cell inflammation of venules, and a histologic description of lymphoplasmacytic sclerosing pancreatitis. The most common clinical presentation of type 1 AIP is painless jaundice with laboratory studies suggesting biliary obstruction and hyperglycemia. Other cases present with abdominal pain or are discovered in asymptomatic individuals with a pancreatic mass, pancreatic duct stricturing, or an enlarged pancreas. Acute pancreatitis is an unusual presentation in type 1 AIP, but it can result in exocrine and endocrine pancreatic insufficiency. The pancreas may be the only organ affected, or there may also be other organs involved with corresponding clinical presentations, including: Bile ducts (secondary sclerosing cholangitis). Retroperitoneal fibrosis. Kidneys (tubulointerstitial nephritis). Lungs. Submandibular and parotid glands (Sjögren disease). Sublingual glands (sclerosing sialadenitis). Orbits and lacrimal glands (IgG4-related dacryoadenitis and sialoadenitis, formerly Mikulicz disease) . Joints (rheumatoid arthritis). Histologically, this is idiopathic duct-centric pancreatitis with granulocytic epithelial lesions within the pancreatic duct, small numbers of IgG4–positive plasma cells (fewer than 10/HPF), and no extrapancreatic involvement. Type 2 AIP is often associated with inflammatory bowel disease and is twice as common in patients with ulcerative colitis or proctitis as in those with Crohn disease. Unlike patients with type 1 AIP, about half of those with type 2 AIP present with abdominal pain or acute pancreatitis. Immune checkpoint inhibitor-induced pancreatic injury is a type of progressive immune-mediated pancreatitis, an adverse effect of cancer treatment with immune checkpoint inhibitor drugs. The risk of this immune response is heightened when multiple immune checkpoint inhibitors are used. Most patients with type 3 AIP are asymptomatic.