Evolving Autoimmune Gastritis Initially Hidden by Active Helicobacter pylori Gastritis

Autoimmune gastritis (AIG) and Helicobacter pylori (H. pylori) gastritis are considered different diseases but exhibit overlapping features. We herein report a case of evolving AIG that had been initially hidden by active H. pylori gastritis. The patient was diagnosed with active H. pylori gastritis and received first-line eradication therapy in 2014 and successful second-line therapy in 2017. She was suspected of having early-stage AIG in 2019 based on the endoscopic finding of salmon roe-like nodular lesions on the greater curvature of the corpus. Parietal cell antibody was positive and the serum gastrin level was slightly elevated. Although subsequent endoscopy in 2020 revealed no significant changes in gastric atrophy, a sharp rise in the serum gastrin level was noted. A biopsy specimen taken from a nodular lesion showed pseudohypertrophy of residual parietal cells, lymphocytic infiltration, and enterochromaffin-like (ECL) cell hyperplasia. Upon retrospective reviews, endoscopic and serological findings obtained before eradication were consistent with active H. pylori gastritis. However, endoscopic salmon roe-like nodular lesions were detected in close-up views. In addition, lymphocytic destruction of fundic glands, pseudopyloric metaplasia, and ECL cell hyperplasia was histopathologically identified on a background of full-thickness inflammation, which suggested that early-stage AIG had coexisted with active H. pylori gastritis.