病理組織学的所見からみた分類不能腸炎（IC/IBDU）の特徴

Characteristics of Indeterminate Colitis/Inflammatory Bowel Disease Unclassified Based on Histopathological Findings

要旨●IC（indeterminate colitis）/IBDU（inflammatory bowel disease unclassified）は潰瘍性大腸炎とCrohn病の鑑別診断困難症例とされるが，これらの疾患概念や定義は時代とともに変遷しており，その病理学的な特徴についても明確になっていないのが現状である．したがって，ICの病理診断においては，各種鑑別疾患やさまざまな修飾因子を考慮し，臨床医との密な連携のもと，慎重な診断を行っていく必要がある．本稿では，潰瘍性大腸炎とCrohn病の典型的な肉眼像・病理組織像やその鑑別疾患，修飾因子について概説するとともに，これまで自施設において経験したICと考えられる症例を提示し，考察を加える．

　IC（indeterminate colitis）/IBDU（inflammatory bowel disease unclassified）is a term used to describe patients with chronic colitis who clearly have IBD but lack definitive pathological or clinical features of UC（ulcerative colitis）or CD（Crohn's disease）. However, the concept and definition of IC/IBDU have changed over the years, but the pathological features of the disease remain unclear. For the pathological diagnosis of IC, various differential diseases and modifying factors should be considered, and a careful diagnosis should be made in close collaboration with clinicians. Furthermore, in this section, we review the typical gross and histological features of UC and CD as well as their differential diseases and modifying factors ; in addition, we present two cases of IC encountered by us.