Case Report: Concurrent autoimmune gastritis and high-grade dysplasia in a gastric hyperplastic polyp.

Autoimmune gastritis (AIG) is an under-recognized, corpus-predominant autoimmune loss of oxyntic glands that creates a metaplastic, inflamed field in which hyperplastic polyps are common, while epithelial dysplasia is uncommon but management-defining. We report a 35-year-old woman with corpus-predominant atrophy and three pedunculated polyps removed by endoscopic mucosal resection (EMR); initial pathology called a hyperplastic polyp with focal low-grade dysplasia (LGD). On tertiary review, the background was identified as AIG (corpus-restricted oxyntic atrophy with pseudopyloric, also called oxyntic, metaplasia and mild intestinal metaplasia) and a small polyp-head focus was upgraded to high-grade dysplasia (HGD); margins were negative. Helicobacter pylori was negative on histology/immunohistochemistry and urea breath testing. Targeted serology at index and follow-up showed persistently elevated anti-parietal-cell antibodies and fasting gastrin, with intrinsic-factor antibody negative and vitamin B12 within range. Early follow-up confirmed a healed EMR site with a persistent corpus-predominant background, and a small body polyp that proved to be a hyperplastic polyp without dysplasia. This case highlights that concurrent AIG and HGD shift management from routine post-polypectomy care to definitive excision plus corpus-focused surveillance, and it argues for actively considering AIG when dysplasia is found in a body polyp-and considering dysplasia when AIG is present.