A 59-year-old man presented to our institution with complaints of anorexia and nausea. He had malignant pleural mesothelioma and had received nivolumab five months prior to presentation. An esophagogastroduodenoscopy (EGD) demonstrated diffuse erythema and edema of the gastric and duodenal bulb mucosa. Mucosal biopsy revealed inflammatory cells, mucosal erosion on HE-staining, and a predominance of CD8-positive intraepithelial lymphocytes on immunostaining. A diagnosis of immune-related adverse effect (irAE) diffuse gastritis was made and treatment with intravenous prednisolone was initiated. Thereafter, his anorexia and nausea improved. EGD was repeated on the 34th day of admission and improvement in mucosal erythema and edema were observed. Herein, we report a case of irAE gastritis where corticosteroid therapy was effective in ameliorating symptoms and endoscopic findings.
