感染性・薬剤性大腸炎の内視鏡診断の重要性と限界：ICI治療下での診断とマネジメント

Importance and Limitations of Endoscopic Diagnosis in Infectious and Drug-induced Colitis：Diagnosis and Management during ICI Therapy

要旨●免疫関連有害事象（irAE）大腸炎は，免疫チェックポイント阻害薬使用後に生じる下痢・腹痛・血便を主症状とした副作用である．潰瘍性大腸炎と内視鏡像が類似しており，びまん性の炎症所見（粘液付着，粘膜の発赤，血管透見の消失，顆粒状粘膜，潰瘍形成）を呈することが多い．現在，irAE大腸炎の診断基準はなく，除外診断が重要である．近年，症状だけではなく，罹患範囲・内視鏡所見・病理所見を参考に治療方針を決定するアルゴリズムも提唱されている．他の大腸炎（潰瘍性大腸炎，サイトメガロウイルス腸炎，Clostridioides difficile腸炎など）を合併することもあるが，厳密に区別することは困難である．ただし，irAE大腸炎の治療中に症状が遷延したり，増悪した場合には上記疾患を念頭に置き，内視鏡所見を含めた再精査を行う必要がある．

　Immune-related adverse event（irAE）colitis, a side effect of immune checkpoint inhibitor therapy, is primarily characterized by diarrhea, abdominal pain, and bloody stools. Its endoscopic appearance resembles that of ulcerative colitis, presenting diffuse inflammatory findings（adherent mucus, mucosal erythema, loss of visible vascular patterns, granular mucosa, and ulcer formation）. No established diagnostic criteria exist for irAE colitis, making differential diagnosis crucial. Recently, treatment algorithms incorporating not only symptoms but also the extent of involvement, endoscopic findings, and pathological findings have been proposed. Although irAE may coexist with other colitis-related conditions（ulcerative colitis, cytomegalovirus enteritis, and Clostridioides difficile enteritis）, strict differentiation is challenging. However, the persistence or exacerbation of symptoms during treatment for irAE colitis should warrant the consideration of these conditions, necessitating reevaluation, including repeat endoscopic findings.