IgG4 immunostaining of duodenal papillary biopsy specimens may be useful for supporting a diagnosis of autoimmune pancreatitis

Background: Autoimmune pancreatitis (AIP) is now considered to be part of an immunoglobulin G4 (IgG4)-related systemic fibroinflammatory disease. Objective: We evaluated whether IgG4 immunostaining of duodenal papillary biopsy specimens is useful for supporting a diagnosis of AIP. Design: A prospective study. Setting: A tertiary academic center. Patients/Interventions: We obtained 2 forceps biopsy specimens from the major duodenal papilla (MDP) of 19 symptomatic AIP patients during ERCP before steroid administration. As a control, biopsy specimens were obtained from the MDP of patients with pancreatic cancer (n = 35), cholangiocarcinoma (n = 20), ampullary cancer (n = 11), ordinary chronic pancreatitis (n = 18), and AIP in remission (n = 16) and immunohistochemically examined. Main Outcome Measurements: Specimens were considered positive for IgG4 immunostaining if there were more than 10 IgG4-positive plasma cells per high-power field. Results: Positive IgG4 immunostaining of the MDP was found in 10 (53%) of 19 symptomatic AIP patients, but was absent in the control groups. Among symptomatic ALP patients (n = 19), 5 (83%) of 6 AIP patients with elevated serum IgG4 levels exhibited positive IgG4 staining of the MDP, whereas 5 (38%) of 13 AIP patients with normal serum IgG4 levels showed positive IgG4 staining of the 'ADP. Nine of 19 symptomatic AIP patients also underwent pancreatic biopsy, and positive IgG4 immunostaining of the MDP was observed in patients with positive pancreas IgG4 staining (4/6, 67%), but not in patients with negative pancreas IgG4 staining (0/3). Limitations: Small symptomatic AIP patient population. Conclusions: Positive IgG4 immunostaining of the MDP was an extremely specific and moderately sensitive tool for the diagnosis of AIR IgG4 immunostaining of the MDP may be useful for supporting a diagnosis of AIP, especially when AIP is suspected clinically but serum IgG4 levels are normal or pancreatic tissue is not available. (Gastrointest Endosc 2010;71:960-6.)