[Diagnostic principles of colonoscopy in ulcerative colitis].

Colonoscopy plays a most important role in the diagnosis and management of ulcerative colitis (UC). It is generally performed in UC for defining the degree of disease activity, grading endoscopic disease severity, and surveillance to detect early cancer and/or dysplasia. Colonoscopic findings of UC are characterized by diffuse and continuous inflammation of mucosa. Loss of vascular pattern, erythema, petechiae and mucosal friability are features of relatively mild disease. As the severity of inflammation increases, spontaneous bleeding, erosions and/or ulcerations are observed. Although UC can be easily diagnosed by these typical findings, colonoscopic findings are modified in a variable and complicated manner at the different clinical stages. Thus it is important for endoscopists to understand the findings in each clinical stage of UC.