Autoimmune gastritis associated with well-differentiated type 1 gastric neuroendocrine tumor: A Case Report and Brief Literature Review

Autoimmune gastritis (AIG) is an immune-mediated inflammatory disorder characterized by the progressive destruction of gastric parietal cells, leading to achlorhydria, intrinsic factor deficiency, and compensatory hypergastrinemia. This condition predisposes patients to severe micronutrient deficiencies and significantly increases the risk of developing type 1 gastric neuroendocrine tumors. 
We present the case of a 58-year-old female with a history of Hashimoto’s thyroiditis who presented with progressive fatigue, early satiety, and neurologic symptoms initially managed as irritable bowel syndrome. Diagnostic evaluation revealed severe vitamin B12 and iron deficiency anemia, hypergastrinemia, and positive anti-parietal cell antibodies. Upper endoscopy demonstrated severe corpus-restricted atrophic gastritis with multiple small polyps. A multidisciplinary tumor board guided the management, leading to the endoscopic mucosal resection of the dominant 8-millimeter lesion, which was histologically confirmed as a well-differentiated type 1 gastric neuroendocrine tumor (G-NET) with enterochromaffin-like cell hyperplasia. 
This case highlights the gradual, often subtle progression of autoimmune gastritis and the importance of recognizing the thyro-entero-gastric autoimmune association. It also underscores the need for early endoscopic screening and surveillance in patients with combined iron and vitamin B12 deficiency anemia, as timely intervention may prevent progression from enterochromaffin-like cell hyperplasia to neuroendocrine neoplasia and reduce the risk of gastric adenocarcinoma.