[The two types of auto-immune pancreatitis]

Autoimmune pancreatitis (AIP) is a rare disease (less than 5% of all chronic pancreatitis). AIP concept was first described 20 years ago but usual diagnostic criteria were published in 2006 (HISORt criteria). Since 2 years, a new AIP concept was described distinghing two AIP types because of differences between Asian and Western series. This new classification is based on pathological features. AIP type 1 is a systemic IgG4-related disease, defined by periductal lymphoplasmacytic infiltrate with obliterative phlebitis and storiform fibrosis and/or lymphoplasmacytic infiltrate with abundant IgG4 positive-plasma cells at immunostaining. AIP type 1 fits the classic description of the disease reported in Asian series. It appears to be a pancreatic manifestation of an IgG4-associated systemic disease which could affect numerous organs with abundant infiltration of IgG4 positive-plasma cells (biliary tree, salivary glands, lymph nodes, retroperitoneum, kidney…), associated with elevated IgG4 serum levels. AIP type 2 is characterized by the presence of granulocyte epithelial lesion on pathological examination. The inflammatory infiltrate is usually devoid of IgG4 positive-plasma cells and the IgG4 serum levels are normal. AIP type 2 represents the main pattern in Western series. No association with extra-pancreatic involvement has been described, except for inflammatory bowel disease (IBD) in 20-30% of the cases. AIP diagnosis is based on association of clinical, biological and morphological features. MRI is essential to argue for AIP diagnosis. The consensual treatment is a steroid therapy (4 weeks) according to symptoms and relapses.