Increased IgG4+ cells in duodenal biopsies are not specific for autoimmune pancreatitis.

Endoscopic ampullary biopsies showing increased immunoglobulin (Ig) G4+ plasma cells have been reported as an alternative to pancreatic biopsy in diagnosing autoimmune pancreatitis (AIP). This study assessed whether increased IgG4+ cells can be seen outside the context of AIP. Fifty-four cases (45 duodenal or ampullary biopsies, 9 ampullae from pancreatic resections) were selected, and all specimens were immunostained for IgG4 and IgG. Duodenal or ampullary biopsies containing normal duodenal mucosa (n = 6) and increased intraepithelial lymphocytes without villous blunting (n = 7) were negative for IgG4. Increased IgG4+ cells (>10 per high-power field) were found in 7 cases of 18 serologically confirmed celiac disease patients and in 3 of 14 patients with duodenitis or gastric heterotopias. Two of 6 ampullae from patients with pancreatic cancer showed increased IgG4+ cells. In summary, 12 of 51 patients without AIP had duodenal biopsies or ampullae showing increased IgG4+ plasma cells. The finding of increased IgG4+ cells in duodenal biopsies is not specific for AIP without the correct clinical context.