Development and validation of an endoscopic activity score for canine inflammatory bowel disease

•The endoscopic activity score correlates with the endoscopist's assessment of abnormal mucosal appearance.•Mucosal assessment is consistent when evaluated in patients different than that used for score development.•The activity score incorporates mucosal variables intuitively considered as important by experienced endoscopists.•The activity score incorporates mucosal variables previously shown to be reproducibly collected, and is itself reproducible.•The activity score is simple to calculate. The aim of this study was to develop and prospectively validate a simple endoscopic score of disease activity for dogs with inflammatory bowel disease (IBD). Archived endoscopic still images and video recordings of gastric, duodenal, and colonic endoscopic examinations were displayed to novice and experienced endoscopists for assessment of inflammatory activity using established descriptions. The mucosal appearances evaluated were normal tissue, erosions, friability, increased granularity, lymphangiectasia (duodenum), and mass (colon). Fleiss and Cohen's Kappa statistics were used to estimate the inter-observer agreement of the index. For duodenal assessment, there were statistically significant (P