The Mayo endoscopic subscore (MES) is a major endoscopic scoring system used to assign a status of mucosal inflammation and disease activity to patients with ulcerative colitis (UC). Using interobserver reliability (IOR), this study clarified the difficulties for endoscopic observers imposed by MES parameters used for the endoscopic evaluation of UC in histological remission. First, 42 endoscopists of four observer groups examined each MES parameter, which were evaluated from endoscopically obtained images of 100 cases as Grade 0 or 1 of the Nancy histological index of histopathological inflammation. Then, IOR was assessed using multiple κ statistics for each finding of MES. The results showed that IOR among all the observers was slight or fair for all the parameters, indicating a low IOR. The experts of the UC practice group had "moderate" or higher IOR for seven of the nine parameters, whereas "slight" or "fair" results were found for all parameters by the trainee group. The IOR for each MES parameter was calculated separately for the observer groups. All the groups showed "slight" or "fair" for "Erythema" and "Decreased vascular pattern". Large differences between the endoscopists were found in the IOR for the MES parameters in UC in histological remission. Even among UC practice experts, the IOR was low for "Erythema" and "Decreased vascular pattern".
Keywords: Mayo endoscopic subscore; endoscopic remission; histological remission; interobserver reliability; ulcerative colitis.