Patients with autoimmune metaplastic atrophic gastritis (AMAG) have antibodies to parietal cells and their components (which include intrinsic factor and the proton pump H+,K+-ATPase). AMAG is inherited as an autosomal dominant trait. Some patients also develop Hashimoto thyroiditis and 50% have thyroid antibodies; conversely, parietal cell antibodies are found in 30% of patients with thyroiditis.
Hypochlorhydria leads to G-cell hyperplasia and elevated serum gastrin levels (often > 1000 pg/mL [> 481 pmol/L]). Elevated gastrin levels lead to enterochromaffin-like cell hyperplasia, which occasionally undergoes transformation to a carcinoid tumor.
In some patients, AMAG may be associated with chronic Helicobacter pylori infection, although the relationship is not clear. Gastrectomy and chronic acid suppression with proton pump inhibitors cause similar deficiencies of intrinsic factor secretion.
The areas of atrophic gastritis in the body and fundus may manifest as metaplasia. Patients with AMAG have a 3-fold increased relative risk of developing gastric adenocarcinoma.
Patients with gland atrophy and/or intestinal metaplasia distributed multifocally, including to the lesser curvature of the corpus and fundus, have a phenotype called multifocal atrophic gastritis. Multifocal involvement is considered "extensive", in contrast to "marked," which refers to severity at a specific site. Risk of gastric adenocarcinoma is higher among patients who have multifocal atrophic gastritis.
Diagnosis of autoimmune metaplastic atrophic gastritis is made by endoscopic biopsy. Serum B12 levels should be obtained. Parietal cell antibodies can be detected but are not measured routinely.
The issue of surveillance endoscopy for cancer screening is unsettled. A guideline for the management of precancerous conditions and lesions in the stomach from a European multidisciplinary group recommended that patients with extensive gastric atrophy and/or intestinal metaplasia (ie, multifocal atrophic gastritis) should be offered endoscopic surveillance every 3 years but that patients with mild to moderate atrophy or intestinal metaplasia confined to the antrum do not need surveillance. The cost-effectiveness of this strategy has not been established.
Guideline for the management of precancerous conditions and lesions in the stomach (MAPS) from the European Society of Gastrointestinal Endoscopy (ESGE), European Helicobacter Study Group (EHSG), European Society of Pathology (ESP), and the Sociedade Portuguesa de Endoscopia Digestiva (SPED)