Diagnostic performance of sonographic activity scores for adult terminal ileal Crohn’s disease compared to magnetic resonance and histological reference standards: experience from the METRIC trial

Objectives The simple ultrasound activity score for Crohn’s disease (SUS-CD) and bowel ultrasound score (BUSS) are promising intestinal ultrasound (IUS) indices of CD, but studied mainly in small settings with few sonographers. We compared SUS-CD and BUSS against histological and magnetic resonance enterography (MRE) reference standards in a post hoc analysis of a prospective multicentre, multireader trial. Methods Participants recruited to the METRIC trial (ISRCTN03982913) were studied, including those with available terminal ileal (TI) biopsies. Sensitivity and specificity of SUS-CD and BUSS for TI CD activity were calculated with 95% confidence intervals (CI), from the prospective observations of the original METRIC trial sonographers against the histological activity index (HAI) and the simplified magnetic resonance index of activity (sMARIA). Results We included 284 patients (median 31.5 years, IQR 23–46) from 8 centres, who underwent IUS and MRE. Of these, 111 patients had available terminal ileal biopsies with HAI scoring. Against histology, sensitivity and specificity for active disease were 79% (95% CI 69–86%) and 50% (31–69%) for SUS-CD, and 66% (56–75%) and 68% (47–84%) for BUSS, respectively. Compared to sMARIA, the sensitivity and specificity for active CD were 81% (74–86%) and 75% (66–83%) for SUS-CD, and 68% (61–74%) and 85% (76–91%) for BUSS, respectively. The sensitivity of SUS-CD was significantly greater than that of BUSS against HAI and sMARIA ( p < 0.001), but its specificity was significantly lower than of BUSS against the MRE reference standard ( p = 0.003). Conclusions Particularly when compared to MRE activity scoring, SUS-CD and BUSS are promising tools in a real-world clinical setting. Clinical relevance statement When tested using data from a multicentre, multireader diagnostic accuracy trial, the simple ultrasound activity score for Crohn’s disease (SUS-CD) and bowel ultrasound score (BUSS) were clinically viable intestinal ultrasound indices that were reasonably sensitive and specific for terminal ileal Crohn’s disease, especially when compared to a magnetic resonance reference standard. Key Points The simple ultrasound activity score for Crohn’s disease and bowel ultrasound score are promising intestinal ultrasound indices of Crohn’s disease but to date studied mainly in small settings with few sonographers. Compared to histology and the magnetic resonance reference standard in a multicentre, multireader setting, the sensitivity of simple ultrasound activity score for Crohn’s disease is significantly greater than that of bowel ultrasound score. The specificity of simple ultrasound activity score for Crohn’s disease was significantly lower than that of bowel ultrasound score compared to the magnetic resonance enterography reference standard. The specificity of both indices was numerically higher when the magnetic resonance enterography reference standard was adopted.