Determination of optimal cutoff value of ulcerative colitis intestinal ultrasound index to estimate endoscopic improvement in ulcerative colitis

Background The ulcerative colitis intestinal ultrasound (UC-IUS) index (UII) has been reported as a sonographic scoring system correlating with the Mayo endoscopic subscore (MES). Endoscopic improvement (EI) of UC (MES <= 1) is a crucial therapeutic target in clinical practice. However, the cutoff value for estimating EI using the UII has not been established. Methods We established test and validation cohorts comprising patients with UC undergoing IUS and endoscopy within a 15-day interval at our institution. IUS findings (bowel wall thickness, bowel blood flow, bowel wall structure, haustrations, and inflammatory fat) and endoscopic activity (MES) of each colon segment (ascending, transverse, descending, and sigmoid colon) were assessed. Results In the test cohort (74 segments), UII was correlated with MES (r = 0.645, p < 0.0001). The median UII was 1.0 and 6.0 among participants with MES <= 1 and MES >= 2, respectively. A UII of 2 was identified as the threshold for estimating MES <= 1 with receiver operating characteristic analysis. In the validation cohort (122 segments), UII was correlated with MES (r = 0.675, p < 0.0001) and the estimation ability of UII <= 2 for EI had a positive predictive value of 85.4% and negative predictive value of 79.0%. This estimation ability of UII for EI was numerically lower but not statistically different from the previously reported Milan Ultrasound Criteria and Kyorin Ultrasound Criterion for UC. Conclusion UII <= 2 can be a simple, feasible criterion for estimating EI. Correlation with MES is an advantage of the UII compared with other criteria. Proper use of various sonographic criteria is important.