Pediatric Eosinophil-Predominant Collagenous Gastritis: From Conventional Therapy to Dupilumab: A Case Report.

Background and Clinical Significance: Collagenous gastritis (CG) is a rare disorder characterized by subepithelial collagen deposition, typically presenting in children with iron deficiency anemia (IDA) and abdominal pain. Its pathogenesis remains unclear, and no standardized treatment exists. Case Presentation: A female patient developed IDA at 4.5 years of age, requiring repeated intravenous iron infusions, and recurrent epigastric pain. CG was diagnosed at 13.5 years, with marked gastric eosinophilia (peak 685 eosinophils/mm2) and subepithelial collagen thickening (103.6 μm). Extensive evaluation excluded alternative causes. Proton pump inhibitor (PPI) therapy failed to meaningfully improve symptoms, endoscopic findings, or histology. A 10-week course of oral systemic corticosteroids resolved abdominal pain and normalized hemoglobin and ferritin levels, but endoscopic abnormalities persisted, histologic improvement was limited, and pain recurred after withdrawal. Dupilumab was initiated as a steroid-sparing, histology-targeted therapy. Over 15 months, the patient remained asymptomatic, hemoglobin and ferritin levels remained normal without intravenous iron or routine oral iron supplementation, and endoscopic abnormalities improved although residual histologic abnormalities persisted. Dupilumab achieved a decrease in gastric eosinophil counts and subepithelial collagen thickness by 41% and 33%, respectively; steroids achieved decreases of 17% and 13%, respectively, and PPIs achieved decreases of 23% and 0.6%, respectively. Conclusions: Dupilumab was associated with sustained clinical and hematologic remission together with gradual endoscopic and histologic improvement in pediatric CG with prominent eosinophilic inflammation. To our knowledge, this is the first reported pediatric case of CG treated with dupilumab. These findings suggest that dupilumab may represent a promising steroid-sparing therapeutic option and support further evaluation in larger case series and controlled studies.