Exacerbation of previously undetected ulcerative colitis in a patient undergoing nivolumab for metastatic melanoma: A case report.

rationaleIn patients receiving immune checkpoint inhibitors, subclinical inflammatory bowel disease can be unmasked, leading to severe colitis. Ulcerative colitis, in particular, may remain undetected when initial symptoms are mild. This report describes a patient with metastatic melanoma whose previously unrecognized ulcerative colitis flared severely after initiating nivolumab. PATIENT CONCERNS: A 35-year-old man presented with chronic mild diarrhea, persisting for several months, which was initially overlooked. Three months after starting nivolumab therapy, he developed frequent diarrhea and hematochezia that required hospitalization. DIAGNOSES: Sigmoidoscopy demonstrated ulcerations with bleeding in the rectosigmoid junction and rectum. Histopathology revealed crypt architectural distortion and inflammatory infiltrates, consistent with ulcerative colitis. Infectious etiologies were excluded.

interventionsHigh-dose intravenous corticosteroids were administered, followed by an oral steroid taper and 5-aminosalicylic acid. Nivolumab was briefly held during acute exacerbations but was ultimately resumed to continue melanoma management. OUTCOMES: Two months after resuming nivolumab, the patient experienced a diffuse ulcerative colitis flare, now involving the entire colon. A second course of high-dose pulse steroid therapy was initiated, and a further hold on nivolumab is currently under consideration. LESSONS: Mild ulcerative colitis can be unmasked and exacerbated by immune checkpoint inhibitors such as nivolumab, emphasizing the importance of early evaluation for inflammatory bowel disease in patients with persistent diarrhea.