Autoimmune pancreatitis is an unusual cause of pancreatitis, in which the immune system attacks the pancreas, resulting in inflammation of the organ. It has two subtypes. Type 1, or lymphoplasmacytic sclerosing pancreatitis, which is the most common type, is characterized histologically by lymphocyte and plasma cell infiltration with fibrosis. It usually presents in older men with obstructive jaundice, with or without a pancreatic mass; diffuse pancreatic enlargement on imaging; and pancreatic ductal strictures. Abdominal pain occurs in less than 50% of cases. It is associated with elevated serum IgG4 (more than two times the upper limit of normal) and can present as an isolated disease or as part of an IgG4-related systemic disorder with other organ involvement, such as the biliary system, lacrimal and salivary glands, kidneys, lymph nodes, and retroperitoneum.
Type 2 or idiopathic duct-centric pancreatitis is the less common type. Typically, patients present at a younger age, and 75% have abdominal pain. IgG4 is only mildly elevated. It is also the more frequent type in patients with inflammatory bowel disease. The diagnosis is made using the International Consensus Diagnostic Criteria, which include serology, imaging of pancreatic parenchyma and duct, pancreatic histology, other organ involvement, and response to corticosteroid therapy as an optional criterion. The patient in this case is relatively young, with a serum IgG4 level less than twice the upper limit of normal, and he has a normal bilirubin level. He also has no other organ involvement besides the pancreas and no family history of inflammatory bowel disease. His imaging studies show no evidence of pancreatic masses or diffuse enlargement. Thus, autoimmune pancreatitis is less likely.
Drug-induced pancreatitis is unlikely because none of his medications are known to cause pancreatitis. In addition, his alcohol intake is not high enough to cause alcoholic pancreatitis; however, a skillful history of intake should be obtained. Hereditary pancreatitis is a genetic disorder in which acute recurrent pancreatitis develops in childhood or early adolescence and usually progresses to chronic pancreatitis by early adulthood. The most common type is secondary to a mutation in the trypsinogen gene (PRSS1), which is inherited in an autosomal dominant pattern. The patient in this case had his first episode of pancreatitis in his fifth decade of life and does not have any family history of pancreatitis, except for his uncle, who probably has chronic pancreatitis due to alcohol abuse. Hereditary pancreatitis is thus unlikely.
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