Case Report: Olmesartan-induced Enteropathy Mimicking Amyloidosis in the Setting of NewMultiple Myeloma Diagnosis

Olmesartan-induced enteropathy is an uncommon but important cause of severe chronic diarrhea and weight loss that can mimic celiac disease and infiltrative gastrointestinal disorders. We report a 71-year-old man on long-term olmesartan who presented with months of diarrhea, nausea/vomiting, profound weakness, and ~100 pounds of unintentional weight loss. EGD demonstrated duodenal villous blunting with lamina propria lymphoplasmacytic inflammation and rare periodic acid–Schiff (PAS)–positive macrophages. An empiric three-week gluten-free diet trial was ineffective. Celiac serologies, infectious stool studies, and HIV testing were negative. Laboratory evaluation revealed anemia, elevated creatinine, hypercalcemia, and a gamma gap; serum and urine protein electrophoresis showed an M-protein, and bone marrow biopsy confirmed multiple myeloma. Repeat duodenal biopsies again showed villous blunting, while Congo red staining was negative, arguing against gastrointestinal amyloidosis. Olmesartan-induced enteropathy was favored; olmesartan was discontinued and budesonide started. Within one month, gastrointestinal symptoms resolved and the patient gained 20 pounds. Recognition of this drug effect is critical, particularly when concurrent hematologic disease raises concern for infiltrative etiologies.