Prevalence and evolution of newly diagnosed autoimmune gastritis in a large Spanish retrospective cohort.

Introduction: There is growing interest in autoimmune gastritis (AIG), particularly regarding its prevalence and natural history.

Methods: A retrospective observational study was performed, including all patients with positive parietal cell antibodies who underwent gastroscopy between 2013 and 2023. The first subsequent gastroscopy was defined as follow-up endoscopy and considered for histological comparison. Categorization of histological stages was as follows; stage 0 (potential), stage I (non-atrophic gastritis), stage II (atrophic gastritis) and stage III (dysplasia, neuroendocrine tumor or adenocarcinoma).

Results: A total of 426 patients were included, 316 were female with a median of 54.4 years (IQR 45.3-63.2). During this period, a total of 26798 patients underwent at least one upper endoscopy, so the prevalence of AIG was 1.6% (95% CI 1.4-1.7%). Histologically, 105 patients were classified as potential AIG (24.7%), 99 patients as stage I (23,2%), 215 patients as stage II (50.5%) and 7 patients as stage III (1.6%). 153 patients had a follow-up endoscopy. A significant increase of advanced stage disease was observed at follow-up (difference 18.7% 95% CI 7.6%-29%; p=0.001) and a decrease of potential GAI (difference 20.2% 95% CI 11.8% -28.7%; p<0.001). At baseline, 39 patients exhibited hyperplastic polyps (9.2%), 8 patients fundic gland polyps (1.9%), 3 adenomas with low-grade dysplasia (0.7%) and 3 patients presented G1 neuroendocrine tumors (0.7%). Only one patient (0.2%) was diagnosed with signet-ring cell gastric carcinoma.

Conclusions: AIG has a low prevalence among patients undergoing gastroscopy. Biopsies in patients with positive parietal cell antibodies showed that around half of the population exhibit significant atrophy and a notable progressive disease.