Context.— Autoimmune gastritis (AG) is a corpus-restricted chronic atrophic gastritis associated with intrinsic factor deficiency, either with or without pernicious anemia. Autoimmune gastritis is a microscopic disease because patients present with no or vague symptoms, and clinicians rarely find endoscopic changes. Autoimmune gastritis only becomes a clinical disease when pathologists diagnose it in gastric biopsies performed for a variety of clinical indications. Unfamiliarity with this disease can result in misdiagnosis of patients, and thus inadequate patient management. Objective.— To review the pathogenesis, clinical features, diagnostic criteria, differential diagnoses, sequelae, and surveillance recommendations for AG. Data Sources.— The sources of the study include a review of the pertinent literature for AG. Conclusions.— Autoimmune gastritis is an important disease characterized by a loss of oxyntic mucosa and presence of metaplastic epithelium and enterochromaffin-like cell hyperplasia. Awareness and proper diagnosis are critical to prevent mismanagement of patients.

Context.— Helicobacter pylori–associated and autoimmune gastritis may coexist in a subset of patients who require treatment for both disorders. Objective.— To delineate findings that identify autoimmune gastritis in the background of H pylori infection. Design.— We examined cases of (1) patients with H pylori–associated gastritis who had successful eradication therapy and subsequent biopsies diagnostic of autoimmune gastritis and (2) H pylori–associated gastritis wherein pathologists noted features of autoimmune gastritis during original interpretation. Control patients underwent H pylori eradication but lacked evidence of autoimmune gastritis or H pylori infection after 10 years of follow-up. Results.— Eight subjects had H pylori–associated gastritis followed by H pylori–negative sampling that showed autoimmune gastritis. Review of original samples showed full-thickness inflammation of oxyntic mucosa in 8 of 8 and oxyntic gland loss in 7 of 8 cases. Enterochromaffin-like (ECL) cell hyperplasia, pyloric metaplasia, and intestinal metaplasia were present in 4 of 8 (80% of 5 tested cases), 4 of 8, and 3 of 8 cases, respectively. Features of autoimmune gastritis were noted at the time of their original H pylori diagnosis in 11 study subjects. Ten of 11 samples displayed full-thickness inflammation of oxyntic mucosa and/or partial loss of oxyntic glands, 8 of 11 had ECL cell hyperplasia (all tested cases), 6 of 11 showed pyloric metaplasia, and 4 of 11 harbored intestinal metaplasia. Except for full-thickness oxyntic mucosa inflammation, these features were absent in control cases. Conclusions.— Full-thickness inflammation combined with oxyntic gland loss and ECL cell hyperplasia may help to identify autoimmune gastritis in patients with concomitant H pylori infection.