Association Between Bowel Urgency and Intestinal Ultrasound Parameters in Ulcerative Colitis: Insights Into Transmural Inflammation and Symptom Pathophysiology.

BACKGROUND: Bowel urgency (BU) is a key symptom of ulcerative colitis (UC), often impairing the quality of life. This study aimed to identify intestinal ultrasound parameters associated with BU, given that UC may also have transmural involvement, and compare these with endoscopic activity and biomarkers. METHODS: In this single-centre prospective study, UC patients undergoing colonoscopy between January 31 and September 27, 2023 were enrolled. Transabdominal and transperineal ultrasound were performed to evaluate bowel wall thickness (BWT), including individual layers (mucosa, submucosa, and muscularis propria), and colour Doppler signal (CDS) in the sigmoid colon and rectum. BU was defined according to the Simple Clinical Colitis Activity Index urgency subscore. RESULTS: Of 59 patients, 33 (56%) reported BU. Compared with those without BU, patients with BU had significantly higher C-reactive protein, Mayo Endoscopic Subscore (MES), BWT (descending colon, sigmoid colon, rectum), CDS (sigmoid colon, rectum), and submucosal and muscularis propria thickness in the sigmoid colon (all p < 0.05). Mucosal thickness and faecal calprotectin were not significantly different (p = 0.11 and p = 0.48, respectively). In MES-adjusted logistic regression, submucosal (p < 0.01) and muscularis propria (p = 0.03) thickness remained associated with BU, whereas mucosal thickness did not (p = 0.97). Receiver operating characteristic analysis showed that sigmoid submucosal thickness had greater diagnostic accuracy than mucosal thickness (AUC 0.77 vs. 0.62, p < 0.05). CONCLUSIONS: Sigmoid submucosal thickening was associated with BU and suggests that transmural inflammation may contribute to symptom pathophysiology. TRIAL REGISTRATION: UMIN000050099.