Role of through-the-scope catheter–based EUS in inflammatory bowel disease diagnosis and activity assessment

Distinguishing Crohn's disease (CD) from ulcerative colitis (UC) may be difficult when the disease is limited to the colon. Transmural healing is an important adjunctive measure of inflammatory bowel disease activity. The aim of this study was to examine the role of EUS in differentiating CD versus UC and evaluating transmural disease activity.This prospective cohort study enrolled 20 patients with CD (10 active [aCD], 10 inactive), 20 patients with UC (10 active [aUC], 10 inactive), and 20 control subjects who underwent colonoscopy from 2019 to 2021 at a tertiary care center. Measurements of bowel wall layer thickness from the rectum and cecum were obtained using a through-the-scope US catheter (UM-3R-3; Olympus, Center Valley, Penn, USA) at the time of colonoscopy.Compared with control subjects, patients with aCD had thicker rectal submucosa and total wall layer (submucosa median, 1.80 mm [interquartile range {IQR}, 1.40-2.00] vs .60 mm [IQR, .40-.70]; total wall median, 3.70 mm [IQR, 3.52-4.62] vs 2.10 mm [IQR, 1.70-2.40], respectively; P < .01). Similar significant findings were observed for the cecal wall layers. Compared with control subjects, patients with aUC had thicker rectal mucosa and total wall but not submucosa or muscularis propria layers (mucosa median, 1.35 mm [IQR, 1.12-1.47] vs .60 mm [IQR, .57-.70]; total wall median, 3.45 mm [IQR, 2.85-3.75] vs 2.10 mm [IQR, 1.70-2.40], respectively; P < .01). Patients with aCD compared with those with aUC had a significantly thicker rectal submucosa layer (median, 1.80 mm [IQR, 1.40-2.00] vs .55 mm [IQR, .40-.75], respectively, P < .01). Cutoff values of 1.1 mm for rectal submucosa in CD (sensitivity, 1.0; specificity, 1.0) and 1.1 mm for rectal mucosa in UC (sensitivity, .8; specificity, .9) were found to differentiate active from inactive disease.EUS measurements of colon wall layers can help diagnose aCD versus aUC and assess transmural disease activity. (Clinical trial registration number: NCT03863886.).