**Background:** Collagenous colitis is a form of microscopic colitis typically seen in middle-aged adults and is rare in the pediatric population. Collagenous gastroenteritis with colonic involvement is even less common. Protein-losing enteropathy is a known presentation in children but is infrequently associated with collagenous gastroenteritis. The differential diagnosis for protein-losing enteropathy includes malabsorption, nephrotic syndrome, inflammatory bowel disease, celiac disease, infection, and lymphatic abnormalities, among others. There is no standardized treatment strategy for pediatric collagenous gastroenteritis.
**Methods:** This is a single-patient case report. The patient was a 3-year-old White girl who presented initially to the emergency department with 2 weeks of liquid diarrhea (3 times daily), poor oral intake, and decreased urination. She had no significant medical history, no recent medications or travel, and no family history of gastrointestinal disease. Initial workup included abdominal x-ray, urinalysis, and a complete metabolic panel. After discharge, she returned with fatigue, anuria, and nonpitting bilateral lower extremity edema. Laboratory evaluation revealed hypoalbuminemia of 2.0 g/dL (reference 3.2–4.5 g/dL). Gastrointestinal and respiratory multiplex PCR were negative. Urine protein was negative. Complete blood count, C-reactive protein, immunoglobulins (IgA, IgM, IgG), and transglutaminase IgA were within normal limits. Over the following month, the patient continued to have 2–5 large, explosive brown stools per day and lost 1.9 kg. Further workup showed a triglyceride level of 834 mg/dL (reference 0–74 mg/dL), ceruloplasmin at 11.5 mg/dL (reference 21.7–43.3 mg/dL), low IgG at 151 mg/dL (reference 453–916 mg/dL), elevated IgA at 108 mg/dL (reference 20–100 mg/dL), elevated stool alpha-1-antitrypsin at 64 mg/dL (reference ≤54 mg/dL), and elevated calprotectin at 329 μg/g (reference ≤50 μg/g). Abdominal ultrasound, echocardiogram, and EKG were unremarkable. Endoscopy showed normal esophageal and gastric mucosa with mild duodenal congestion and villous blunting. Colonoscopy revealed diffuse erythema from rectum to cecum with distal congested mucosa. Biopsies showed chronic gastritis with eosinophil prominence and thickening of the subepithelial collagen table in the stomach, severe villous blunting with subepithelial collagen thickening in the duodenum and terminal ileum, and collagenous colitis of the left colon. MOC31, BerEP4, and CD10 stains of duodenal tissue were normal. Electron microscopy showed no microvillus abnormalities. No signs of autoimmune enteropathy were found.
**Key Results:** A diagnosis of collagenous gastroenteritis and colitis was made. Budesonide was prescribed for 8 weeks. The patient took the medication for only 1 week before refusal, during which diarrhea lessened to once daily with firmer stools. Diarrhea resolved completely within a few weeks. Repeat laboratory tests demonstrated normalization of albumin, triglycerides, and immunoglobulins.
**Clinical Implications:** Collagenous colitis is rare in children, and the combination of collagenous gastroenteritis and colitis is even less documented. This case demonstrates that collagenous colitis should be considered in the differential diagnosis for children with persistent diarrhea of unknown etiology and for protein-losing enteropathy. Corticosteroid treatment, particularly budesonide, is supported by the literature; one pediatric study cited in the report showed that 8 of 9 patients treated with corticosteroids (prednisone or budesonide) reached full or partial remission within 8 weeks. The patient's improvement even after a short course of budesonide suggests that treatment can be effective in pediatric cases.