Collagenous gastritis: a rare case in young adult with iron deficiency anemia.

Collagenous gastritis (CG) is an extremely rare chronic inflammatory gastropathy with non-specific symptoms and high misdiagnosis rate. We report a 21-year-old female with 6-month postprandial epigastric discomfort, anorexia, dizziness, fatigue, and severe iron deficiency anemia. Endoscopy showed diffuse erythema, erosions, and typical nodular elevation-depression lesions in the gastric corpus. Histopathology and Masson's trichrome staining verified subepithelial collagen band thickening (>10 μm), confirming CG. After 8-week oral iron and proton pump inhibitor treatment, clinical symptoms resolved and hematological parameters improved markedly, but histological changes persisted. This case indicates that CG should be considered in young adults with unexplained iron deficiency anemia and atypical endoscopic features, and nodule-depression pattern serves as a key diagnostic clue.