Autoimmune pancreatitis: an underdiagnosed autoimmune disease with clinical, imaging and serological features.

Since Sarles et al. [Sarles H, Sarles JC, Muratore R, Guien C. Chronic inflammatory sclerosis of the pancreas-an autonomous pancreatic disease? Am J Dig Dis 1961; 6: 688-698.] reported a case of pancreatitis associated with hypergammaglobulinemia, many cases have been described, which led to the current concept of "autoimmune pancreatitis (AIP)". Lymphoplasmacytic infiltration and fibrosis on histology together with elevated IgG levels or the presence of autoantibodies on laboratory examinations supported the concept of AIP. In recent years, based on histological and immunohistochemical examination of various organs of patients with AIP, a novel clinicopathological entity, IgG4-related slerosing disease, has been proposed. AIP is a systemic disease that is characterized by dense infiltration of IgG4-positive plasma cells and T lymphocytes in various organs. Clinical manifestations are related with pancreas dysfunction but other organs may be affected such as bile duct, gallbladder, salivary gland, retroperitoneum, kidney, lung and prostate. Increased serum IgG4 levels, the presence of several autoantibodies such as anti-carbonic anhydrase II antibodies (ACA-II), immunostaining IgG4 positive in pancreas tissue and a very good response to steroid therapy are useful for the diagnosis of AIP that can mimic pancreatic cancer.