Collagenous gastritis is an exceedingly rare gastrointestinal disorder characterized by atypical gastric mucosa with an inflamed or nodular appearance. Histologic analysis reveals an irregular thickened collagenous subepithelial band, dilated entrapped capillaries, and intraepithelial inflammatory cells. This disease is very rare, with only 60 reported cases in the medical literature, based on which it is divided into pediatric-onset and adult-onset phenotypes.

Pediatric-onset collagenous gastritis – Presents with abdominal pain and severe anemia with an inflamed and/or nodular stomach and normal-appearing colon. There is no known etiology.

Adult-onset collagenous gastritis – Associated with collagenous colitis and presents with voluminous nonbloody diarrhea. Etiology is possibly secondary to autoimmune, infectious, and medication-induced causes.

Esophagogastroduodenoscopy (EGD) is important for diagnosis and to rule out other causes of symptoms.