Annual Trends in the Diagnosis of Autoimmune Gastritis over 11 Years at a Single Facility in Japan

INTRODUCTION: Autoimmune gastritis (AIG), a type of chronic atrophic gastritis, is characterized by positive anti-parietal cell antibodies and mucosal atrophy predominantly in the corpus. In Japan, AIG has garnered increasing attention owing to the recent decline in Helicobacter pylori (HP) infection rates, leading to the proposal of diagnostic criteria. These criteria encompass serological test results, endoscopic findings, and histological findings, emphasizing the need for collaboration between endoscopists and pathologists to make an accurate diagnosis. In the present study, we aimed to clarify the annual number of patients with AIG diagnosed over the past 11 years and analyze their endoscopic and histological characteristics. METHODS: We retrospectively reviewed patients with AIG newly diagnosed at our institution between 2013 and 2023. Patients were categorized into the "prior endoscopically diagnosed group" (ED group) and the "prior pathologically diagnosed group" (PD group). The annual trend in AIG diagnosis was analyzed, and clinicopathological characteristics were compared between the groups. RESULTS: In total, 118 patients were diagnosed with AIG during the study period. The number of diagnoses increased after 2018, when a focused effort to identify AIG began, peaking in 2021 with 32 cases. All patients diagnosed before 2018 belonged to the ED group, but subsequent years saw increases in both groups of patients. The PD group had significantly more cases of coexisting gastric carcinoma (86.3% vs. 26.9%, p < 0.001) or HP-associated gastritis (72.4% vs. 32.8%, p = 0.002) than the ED group, whereas the ED group frequently exhibited typical endoscopic findings, such as atrophic gastritis predominantly in the corpus and adherent mucus. CONCLUSION: Accurate diagnosis of AIG requires familiarity with the diagnostic criteria by endoscopists and pathologists. In cases complicated by gastric carcinoma or HP-associated gastritis, endoscopic findings alone may not suffice for diagnosis, underscoring the critical role of pathologists in interpreting histological findings.