S6057 Russell Body Duodenitis in a 60-Year-Old Man With Upper Gastrointestinal Bleeding: A Rare Mimicker of Malignancy

Introduction: Russell body duodenitis (RBD) is a rare plasma cell-rich inflammatory condition defined by Mott cells containing eosinophilic immunoglobulin inclusions known as Russell bodies. Though most commonly described in the gastric mucosa, duodenal involvement is exceedingly rare and may mimic neoplastic processes. Recognition of this benign entity is essential to avoid unnecessary interventions. Case Description/Methods: A 60-year-old man with a history of alcohol and tobacco use, atrial fibrillation on apixaban, coronary artery disease, and peripheral arterial disease presented with melena and chronic anemia. He was pale but hemodynamically stable. Laboratory evaluation revealed a hemoglobin of 9.8 g/dL and elevated pro-BNP. Esophagogastroduodenoscopy showed an edematous, nodular duodenal bulb without active bleeding, along with diffuse gastritis and moderate portal hypertensive gastropathy. Duodenal biopsies were obtained. Histologic analysis revealed preserved villous architecture with chronic inflammation and numerous Mott cells containing eosinophilic Russell bodies. Immunohistochemistry showed CD138-positive plasma cells with polytypic kappa and lambda light chain expression. Special stains for Helicobacter pylori and D2-40 were negative. There was no evidence of HIV, autoimmune disease, or gastrointestinal malignancy. The patient improved with supportive care and was discharged in stable condition. Discussion: Fewer than 10 published cases of RBD have been reported. Proposed mechanisms include chronic antigenic stimulation, endoplasmic reticulum (ER) stress impairing immunoglobulin secretion, and altered plasma cell differentiation. Although rare associations with malignancies have been documented, these appear incidental. Histologic evaluation, particularly with immunohistochemical staining for CD138 and light chains, is critical to distinguish RBD from plasma cell neoplasms and avoid unnecessary oncologic workup. This case reinforces the importance of including RBD in the differential diagnosis of nodular duodenal lesions, particularly in patients with upper GI symptoms and chronic mucosal changes.