Autoimmune pancreatitis‐related cholecystitis: a morphologically and immunologically distinctive form of lymphoplasmacytic sclerosing cholecystitis

Abstract

Gallbladder involvement in autoimmune pancreatitis (AIP) is reported to be histologically similar to that seen in primary sclerosing cholangitis (PSC) and biliary obstruction secondary to pancreatic ductal adenocarcinoma (PDAC). The aim was to identify unique morphological and immunological features that could help distinguish gallbladders of AIP from those associated with PSC and PDACs. Archival gallbladders from well-characterized individuals with AIP (n = 22), PSC (n = 13) and PDAC (n = 23) were examined. Quantitative immunohistochemical analysis for IgG and IgG4 plasma cells was performed and an IgG4/IgG ratio was derived. Dense extramural infiltrates were almost exclusively seen in AIP cases (41%), but seen in only 4% of PDAC-associated cases and 0% of PSC cases (P = 0.001). Phlebitis was more frequently noted in AIP cases (41%) (P = 0.03). Inflammatory nodules were almost exclusively seen in AIP (27%) (P = 0.04). AIP gallbladders showed higher IgG4/IgG ratios (P = 0.0001) than PDAC-associated and PSC gallbladders. The findings support our hypothesis that gallbladder involvement in AIP is a primary manifestation of this disease and not a secondary phenomenon related to biliary obstruction. In conjunction with imaging and serology, examination of the gallbladder could provide collaborative evidence of AIP. Evaluation of the gallbladder could also distinguish PSC from AIP-related cholangitis.