Rubela Ray, MD1, Kristina Patel, MD2, Darshankumar Raval, MD3 1University of Wyoming, Cheyenne, WY; 2University of Arkansas, Texarkana, AR; 3Elmhurst Hospital Center / Icahn School of Medicine at Mount Sinai, Youngstown, OH Introduction: Idiopathic Multicentric Castleman Disease (iMCD) is a rare, non-clonal lymphoproliferative disorder characterized by cytokine excess, systemic inflammation, and multiorgan involvement. While most patients present with lymphadenopathy and constitutional symptoms, GI manifestations such as chronic diarrhea are rare and easily misattributed. We report a diagnostically challenging case where small bowel diarrhea was the dominant presentation, delaying recognition of a life-threatening systemic disease.
Case Description/
Methods: A 45-year-old previously healthy, HIV-negative man presented with four months of profuse, non-bloody diarrhea (6–8 episodes/day), along with fatigue, anorexia, early satiety, bilateral leg edema, and a 25-pound unintentional weight loss. He denied fevers, travel, antibiotic use, or exposures. On exam, he appeared thin and mildly tachycardic, with bilateral inguinal and cervical lymphadenopathy, hepatosplenomegaly, and pitting edema.
Labs revealed normocytic anemia (Hb 8.9 g/dL), thrombocytosis (540K/μL), hypoalbuminemia (2.7 g/dL), elevated CRP (29 mg/L), ESR (81 mm/hr), and polyclonal hypergammaglobulinemia. Stool studies, celiac panel, and thyroid tests were unremarkable. Colonoscopy with biopsies was normal. CT showed diffuse lymphadenopathy and mild ascites. EGD with duodenal biopsies revealed nonspecific inflammation and intraepithelial lymphocytosis, raising suspicion for an immune-mediated small bowel process.
Given persistent symptoms and systemic signs, lymph node excision was performed, revealing regressed germinal centers and interfollicular vascular proliferation—consistent with hyaline vascular Castleman variant. HHV-8 and HIV were negative. Bone marrow showed no malignancy. After excluding mimickers (lymphoma, autoimmune enteropathy, Whipple’s), iMCD was diagnosed. Treatment with siltuximab led to rapid symptom resolution. Discussion: Though not classic for iMCD, diarrhea may result from cytokine-driven mucosal inflammation or lymphatic obstruction. Chronic small bowel diarrhea in the absence of clear GI pathology should prompt consideration of systemic illnesses, especially with lab abnormalities and subtle systemic signs.
Conclusion: GI symptoms may be the initial clue to iMCD. When conventional workups are inconclusive, clinicians should broaden the differential to include infiltrative or inflammatory systemic diseases. Early recognition and IL-6–targeted therapy are key to improved outcomes.
Disclosures: Rubela Ray indicated no relevant financial relationships. Kristina Patel indicated no relevant financial relationships. Darshankumar Raval indicated no relevant financial relationships.
Rubela Ray, MD1, Kristina Patel, MD2, Darshankumar Raval, MD3. P6282 - Beyond the Bowel: Chronic Diarrhea as the Sentinel Symptom of Idiopathic Multicentric Castleman Disease, ACG 2025 Annual Scientific Meeting Abstracts. Phoenix, AZ: American College of Gastroenterology.
