S6081 Triple-Site Collagenous Gastroenteropathy With Biopsy-Confirmed Glomerulonephritis: A Rare Immune-Mediated Overlap

Introduction: Collagenous colitis is a form of microscopic colitis marked by subepithelial collagen deposition and chronic watery diarrhea. Collagenous gastritis and enteritis are rare, particularly in adults, and simultaneous involvement of the upper and lower gastrointestinal (GI) tract is exceptional. We report a case of triple-site collagenous gastroenteropathy in a patient with biopsy-confirmed glomerulonephritis, suggesting a possible shared immune-mediated mechanism. Case Description/Methods: A 50-year-old woman with a prior left hemicolectomy for colon cancer presented with bilateral lower extremity edema and nephrotic-range proteinuria. Renal biopsy revealed glomerulonephritis of unclear etiology. She was discharged without immunosuppressive therapy. Following discharge, she developed progressive severe non-bloody diarrhea, prompting readmission. Stool infectious studies and celiac serologies were negative. Fecal calprotectin was elevated (631 μg/g). Upper GI endoscopy revealed scalloping and fissuring of the duodenal bulb; colonoscopy revealed normal colonic mucosa. Histopathology demonstrated subepithelial collagen thickening (>10 µm), surface epithelial injury, and lamina propria inflammation in the gastric body, duodenum, and right colon—consistent with collagenous gastritis, enteritis, and colitis, respectively. Given her concurrent glomerulonephritis, prednisone was initiated instead of budesonide, leading to marked improvement in both diarrhea and proteinuria. Repeat upper endoscopy 4 months later confirmed histologic resolution of gastric and duodenal changes, with persistence of collagenous colitis. The patient remained clinically stable on a tapering regimen of budesonide. Discussion: While renal involvement is recognized in Crohn disease and ulcerative colitis, its association with microscopic colitis is poorly described. To our knowledge, this is the first reported case of nephrotic syndrome due to glomerulonephritis occurring in conjunction with diffuse collagenous involvement of the gastrointestinal tract. This case supports the hypothesis that collagenous gastroenteropathy may exist within a broader spectrum of systemic immune-mediated disorders. Recognition of extraintestinal involvement may support the use of systemic immunosuppression in select cases. Artificial Intelligence Disclosure: Portions of this abstract were revised with the assistance of generative artificial intelligence (ChatGPT, OpenAI). All content was reviewed, verified, and finalized by the authors.