Autoimmune Gastritis Diagnosed Through Iron-Deficiency Anemia and Gastric Neuroendocrine Tumors in an Older Adult: A Case Report

Background and Clinical Significance: Autoimmune gastritis (AIG) can cause iron-deficiency anemia (IDA) before vitamin B12 deficiency develops. Although AIG-associated IDA is more common in younger individuals, it can also occur in older adults. Type 1 gastric neuroendocrine tumors (gNETs) associated with hypergastrinemia may indicate previously unrecognized AIG; Case Presentation: A 72-year-old woman was referred for microcytic anemia. Laboratory tests revealed severe IDA, with hemoglobin of 4.7 g/dL, mean corpuscular volume of 56 fL, and ferritin of 3.2 ng/mL, despite normal vitamin B12 levels. Gastrointestinal endoscopy identified no bleeding source but revealed extensive gastric mucosal atrophy and a 5 mm gastric lesion. Histopathological examination confirmed a grade 1 gNET. Probable AIG was diagnosed based on a composite clinical assessment of corpus-predominant endoscopic atrophy, anti-parietal cell antibody positivity, and marked hypergastrinemia (1147.2 pmol/L) in the absence of acid-suppressive therapy, although biopsies did not clearly demonstrate the characteristic corpus-predominant histological pattern. The NET G1 was therefore considered consistent with a type 1 gNET. Although the initial biopsy suggested Helicobacter pylori infection, subsequent histology, gastric mucosal polymerase chain reaction, and serum antibody testing were negative. Anemia improved after red blood cell transfusion and intravenous iron therapy. The gNET was completely resected endoscopically. A second gNET detected during follow-up was also completely resected; Conclusions: AIG should be considered in older adults with unexplained IDA, even without vitamin B12 deficiency or macrocytic anemia. A gNET may provide an important clue to underlying AIG. In this case, the diagnosis of probable AIG represented a composite clinical judgment, given the absence of definitive histological findings. Even when H. pylori infection is suspected, gastric mucosal atrophy should not be attributed solely to H. pylori-associated gastritis, and coexisting AIG should be evaluated using integrated serological, endoscopic, and histopathological findings.