Colonoscopic evaluation of diarrhea/colitis occurring as an immune-related adverse event.

Objective: Diarrhea is often observed as an immune-related adverse event. In this study, we conducted a retrospective review of the severity of diarrhea, its treatment and the endoscopic findings in patients developing diarrhea as an immune-related adverse event.
Methods: From August 2015 to June 2019, a total of 369 patients received treatment with immune checkpoint inhibitors at our hospital. For this study, development of grade 2 or more diarrhea in these patients was defined as an immune-related adverse event. We analyzed the histopathological severity of the bowel lesions according to the Nancy histological index for ulcerative colitis.
Results: Of the 369 patients, 27 (7.3%) developed diarrhea as an immune-related adverse event. Of these 27 patients, 18 received steroid treatment. Colonoscopy was performed in 17 patients and culture of the feces in 18. The tests revealed evidence of bacterial colitis (Aeromonas hydrophila) in two patients. The Nancy histological index was 4, 3, 2, 1 and 0 in two, three, two, two and seven patients, respectively. No findings on colonoscopy were observed in 7 of the 17 patients (41%) who underwent colonoscopy, and most of these patients recovered without steroid treatment. Patients with lower values of the Nancy histological index tended to show better responses to steroid treatment.
Conclusions: To avoid unnecessary steroid administration, colonoscopic evaluation is essential in patients receiving treatment with immune checkpoint inhibitors who present with diarrhea as an immune-related adverse event. In addition, the endoscopic findings could be useful to predict the response to steroid treatment.
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