Case Report: Collagenous gastritis presenting with refractory dyspepsia and diffuse gastric atrophic-appearing...

Collagenous gastritis (CG) is a rare fibroinflammatory disorder that may present with heterogeneous endoscopic findings. We report a 35-year-old woman with a 7-year history of refractory dyspepsia who had previously received a provisional diagnosis of seronegative AIG at another hospital because of Helicobacter pylori-negative, corpus-predominant gastric atrophy, iron deficiency, vitamin B12 deficiency, and concomitant thyroid autoimmunity. Persistent symptoms despite vitamin B12 and iron supplementation prompted referral to our center for further evaluation. Comprehensive reassessment revealed diffuse gastric atrophic-appearing changes, together with several findings discordant with established AIG, including persistent hypogastrinemia and magnifying endoscopic features inconsistent with typical AIG. Magnifying endoscopy with narrow-band imaging showed effacement of the surface microarchitecture and disorganized microvessels rather than the typical "cast-off skin" appearance of AIG, while acetic acid-enhanced imaging revealed residual central pits within the atrophic mucosa. Histopathological review with Masson trichrome staining demonstrated thickened subepithelial collagen bands with entrapped capillaries in both corpus and antral biopsies, confirming CG. After initiation of proton pump inhibitor therapy, the patient reported marked symptomatic improvement within 8 weeks. This case highlights CG as an overlooked differential diagnosis in unexplained diffuse gastric atrophic-appearing changes; nodular mucosal changes, atypical magnifying NBI findings, and subtle subepithelial pink material on routine histology should prompt collagen-specific staining to avoid diagnostic anchoring to more common forms of atrophic gastritis.