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. 2025 Sep 7;6(1):e70187.
doi: 10.1002/deo2.70187. eCollection 2026 Apr.

A Rare Case of Immune-related Adverse Events Localized to the Small Intestine

Ryo Morikawa  1 , Ryosuke Kanaya  1 , Hiromichi Shimizu  1 , Masayoshi Fukuda  1 , Yasuhiro Nemoto  1 , Toshimitsu Fujii  1 , Towako Taguchi  2 , Kurara Yamamoto  3 , Kazuo Ohtsuka  1 , Ryuichi Okamoto  1
Affiliations

A Rare Case of Immune-related Adverse Events Localized to the Small Intestine

Ryo Morikawa et al. DEN Open. .

Abstract

Enterocolitis is a common gastrointestinal manifestation of immune-related adverse events (irAEs); however, only a few studies have reported on irAE enteritis with localized active inflammation in the small intestine. Here, we report the case of a 74-year-old man who developed diarrhea, abdominal pain, and oral intake difficulty and was subsequently hospitalized after receiving atezolizumab for pulmonary adenocarcinoma. Computed tomography and enterocolonoscopy revealed active inflammation in the small intestine but not in the colon, leading to the final diagnosis of irAE enteritis. After initiating prednisolone at a dose of 60 mg/day, his symptoms improved rapidly, and a follow-up enterocolonoscopy revealed a marked reduction in inflammation. Being a relatively rare gastrointestinal toxicity, irAE enteritis often goes unrecognized due to diagnostic challenges, but can lead to serious AEs such as perforation. Therefore, even if colonoscopy findings are normal, a thorough examination of the small intestine is essential for patients who develop gastrointestinal symptoms while undergoing immune checkpoint inhibitor therapy. We herein report a rare case of irAE enteritis confirmed through endoscopic and pathological examination, which has not been previously reported.

Keywords: endoscopy; immune checkpoint inhibitor; immune‐related adverse events; prednisolone; small intestine.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

FIGURE 1
FIGURE 1
(a) and (b) Images of abdominal computed tomography prior to prednisolone treatment. Computed tomography revealed wall thickening in the small intestine but no significant abnormalities in the colon.
FIGURE 2
FIGURE 2
Endoscopic images of (a) small intestine and (b) colon prior to prednisolone treatment. (a) Endoscopy showed mucosal edema, erythema, and scattered erosions, and atrophied villi in the small intestine (b) and mucosal edema without any erosions or ulcers in the colon.
FIGURE 3
FIGURE 3
Histopathological findings of hematoxylin and eosin staining prior to prednisolone treatment for (a) small intestine and (b) colon. The small intestine showed inflammatory cell infiltration in the lamina propria and crypt abscesses, with no apoptotic features. In contrast, the colonic mucosa showed no active inflammatory changes.
FIGURE 4
FIGURE 4
Endoscopic images of (a) small intestine and (b) colon after prednisolone treatment. Endoscopy showed improvement in the inflammatory findings in the small intestine and no edema in the colon.
See this image and copyright information in PMC

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