Collagenous Gastritis: An Atypical Presentation of a Rare Disease.

Collagenous gastritis is a rare inflammatory condition of unknown etiology defined histologically by subepithelial deposition of collagen bands ≥ 10 µm in the lamina propria. Adults typically present with diarrhea, often attributed to concurrent collagenous sprue or collagenous colitis. Children more commonly present with abdominal pain and anemia, with inflammation typically limited to the stomach. Herein, we present a case of collagenous gastritis in a 38-year-old female with a history of iron deficiency and hypothalamic amenorrhea who presented with a one-year history of microcytic anemia. Celiac disease panel, testing, and anti-parietal cell and intrinsic factor antibodies were negative. Esophagogastroduodenoscopy revealed diffusely erythematous and nodular gastric mucosa in the antrum and pylorus. Biopsy from the gastric body showed complete loss of oxyntic glands and deposition of a thick band of collagen under the surface epithelium infiltrated by a few eosinophils, consistent with collagenous gastritis with severe atrophy. She was treated with omeprazole 40 mg daily for six weeks and iron supplementation. Our patient's symptoms and endoscopic findings are consistent with previously described pediatric, but not adult, cases of collagenous gastritis, yielding insight into the variable clinical presentation of this rare disease.