Autoimmune pancreatitis is closely associated with gastric ulcer presenting with abundant IgG4-bearing plasma cell infiltration

Background: Autoimmune pancreatitis is characterized by high serum IgG4 concentrations and lymphoplasmacytic infiltration. Because of the diversity of extrapancreatic involvement in this disease, the present study sought to identify other associated GI-tract lesions. Methods: EGD findings were compared between a group of 23 patients with autoimmune pancreatitis undergoing ERCP for obstructive jaundice and 230 age- and gender-matched control patients. To clarify the histopathologic differences found between these two groups, the histopathologic findings (Updated Sydney System) and the immunohistochemistry of each IgG subclass were compared between 8 patients with autoimmune pancreatitis and gastric ulcer, and 23 control patients with gastric ulcer from which biopsy specimens had been obtained. Results: Gastric ulcer was found significantly more frequently in patients with autoimmune pancreatitis compared with control patients (34.8% vs. 13.5%; p = 0.007). There was no significant difference between the groups with respect to the frequency of other GI lesions. Four of 8 gastric ulcers in patients with autoimmune pancreatitis were linear, with the long axis perpendicular to the incisura on the lesser curvature of the stomach. The activity score for the gastric lesions was significantly lower in patients with autoimmune pancreatitis compared with control patients (mean score 0.38 vs. 1.08; p = 0.012). There were no significant differences in histopathologic findings with respect to inflammation, atrophy, metaplasia, or Helicobacter pylori scores between the two groups. IgG4-bearing plasma cells were significantly more abundant in gastric lesions in patients with autoimmune pancreatitis compared with those in control patients (mean score 1.75 vs. 0.39; p = 0.0008). Conclusions: Autoimmune pancreatitis is closely associated with gastric ulcer with abundant IgG4-bearing plasma cell infiltration.