S6384 Collagenous Gastritis in a Patient With Iron Deficiency Anemia and Diffuse Large B-Cell Lymphoma

Introduction: Collagenous gastritis is a rare histopathologic entity characterized by subepithelial collagen deposition typically >10 micrometers in gastric mucosa. This condition has been associated with various systemic disorders and malignancies, though the underlying pathophysiology remains poorly understood. We present a case demonstrating the concurrent presentation of collagenous gastritis with severe iron deficiency anemia and diffuse large B-cell lymphoma. Case Description/Methods: A 63-year-old man with limited medical history presented with 3 weeks of progressive dyspnea. He additionally endorsed 30 lbs weight loss. The patient reported small volume bright red bleeding and recent onset constipation. Initial vitals were stable, but labs showed hemoglobin was critically low at 5.1 g/dL (unknown baseline). Computed tomography (CT) revealed large bilateral adrenal masses (left: 13 cm, right: 5 cm), para-aortic lymphadenopathy, and splenomegaly (16 cm). Esophagogastroduodenoscopy (EGD) demonstrated nodular mucosa in the duodenal bulb. Duodenal biopsy revealed pyloric-type mucosa with features consistent with collagenous gastritis, confirmed by trichrome staining showing prominent subepithelial collagen deposition. Colonoscopy revealed a small rectal hyperplastic polyp, sigmoid diverticulosis and non-bleeding internal hemorrhoids. The patient required multiple transfusions for anemia. Subsequent bone marrow biopsy suggested malignancy, and adrenal biopsy confirmed diffuse large B-cell lymphoma. Outpatient chemotherapy was initiated. Discussion: While collagenous gastritis typically presents with upper gastrointestinal symptoms, our patient's presentation was dominated by severe iron deficiency anemia. The concurrent iron deficiency anemia likely represented malabsorption secondary to an abnormal duodenal mucosa in setting of underlying malignancy. The relationship between collagenous gastritis and malignancy remains incompletely characterized, with limited case reports suggesting potential paraneoplastic associations where the gastric findings may represent an immune-mediated response to the underlying malignancy. Recognition of this rare endoscopic and histopathologic finding may warrant comprehensive malignancy screening, particularly in patients presenting with unexplained systemic symptoms or severe anemia. Further research is needed to elucidate the pathogenetic mechanisms linking collagenous gastritis to hematologic malignancies and optimize diagnostic and therapeutic approaches.