Pathologic findings of autoimmune pancreatitis and IgG4-related disease

Autoimmune pancreatitis (AIP) is pathologically characterized by lymphoplasmacytic infiltration and fibrosis. However, AIP is not a single entity, but rather includes two histological types-lymphoplasmacytic sclerosing pancreatitis (LPSP) and idiopathic duct-centric chronic pancreatitis (IDCP)- of which the former constitutes the pancreatic manifestation of IgG4-related disease. The inflammation seen in peripancreatic adipose tissue and the interlobular area in LPSP, such as dense lymphoplasmacytic infiltration with fibrosis, storiform fibrosis, and obliterative phlebitis, is common among the various lesions that belong to IgG4-related disease. However, some lesions in the family of IgG4-related disease, such as IgG4-related sclerosing sialadenitis and lymphadenopathy, often lack prominent fibrosis, suggesting the histological variation of this entity. Nonetheless, histological features are important in the formation of a pathological diagnosis of IgG4-related disease because the presence of numerous IgG4-positive plasma cells is not necessarily specific to this disease.