Collagenous gastritis with elevated fecal calprotectin in a pediatric patient

Collagenous gastritis is a rare and chronic inflammatory condition of undetermined etiology characterized histologically by thickened subepithelial collagen bands and increased intraepithelial lymphocytes. Here, we present a collagenous gastritis case in a 16-year-old female with chronic abdominal pain, persistently elevated fecal calprotectin (507 and 796 mcg/g), and resolved iron deficiency anemia. The patient's history, laboratory tests, endoscopy, and magnetic resonance imaging ruled out common causes of elevated fecal calprotectin, including Helicobacter pylori and gastrointestinal infections, medications, celiac disease, and inflammatory bowel disease, as well as less common causes such as collagenous colitis. Esophagogastroduodenoscopy revealed significant antral nodularity. Gastric biopsies showed thickened subepithelial collagen band and surface epithelium damage with increased intraepithelial lymphocytes. The ileocolonoscopy was normal. This is among the first reported cases of collagenous gastritis with elevated fecal calprotectin levels that could solely be attributed to this condition.