Autoimmune pancreatitis : Diagnostic and immunological aspects

Autoimmune pancreatitis (AIP) is the pancreatic manifestation of a systemic fibro- inflammatory disease, characterized by infiltration with lymphoplasmacytic cells and extensive fibrosis, which leads to morphological changes (swelling, mass forming) and organ dysfunction. Often, but not always, the disease is characterized by elevated levels of serum IgG4 and IgG4 positive plasma cells in the affected tissues. The disease was initially described by Sarles in 1961.4 A major breakthrough was the identification in 2001 of serum IgG4 levels as biomarker. IgG4 levels are elevated in 68 - 95% of patients with AIP. The concept of IgG4-related systemic disease was adopted in 2003. Currently two types of AIP are recognized: type 1 which is associated with IgG4-related disease, and type 2, which has substantial clinical overlap but distinctive pathological features.There are little data on global incidence and prevalence of AIP. Virtually all data regarding epidemiology comes from Japan. Based on these data, the estimated prevalence is 2.2/100.000, with an annual incidence rate of 0.9/100.000. It is believed that AIP accounts for 5 - 6% of all patients with chronic pancreatitis. In patients who underwent resection for presumed malignancy, AIP is found in 2.5%. The male to female ratio is 3.7 and the mean age is 63 years.12 The typical clinical presentation is that of an older man with jaundice, diffuse or focal pancreatic enlargement or mass, substantial weightloss and recent onset diabetes. Other organ involvement is common in the course of AIP. Usually it coincides with or follows the pancreatic manifestation, but sometimes it may herald AIP. The biliary tree, salivary glands, retroperitoneum, kidneys and lymph nodes are involved most frequently, which may lead to sclerosing cholangitis, Sjögren like syndrome, retroperitoneal fibrosis, interstitial nephritis, pseudotumors in lungs or liver and generalized or localized lymphadenopathy.1, Spontaneous remissions and relapses are common. The disease is highly responsive to steroids and this can be used as a diagnostic tool