LAUSR

BACKGROUND Cross-sectional imaging is important in the assessment of transmural inflammation in Crohn's disease (CD). Small bowel involvement is often more extensive in pediatric CD. We undertook to develop a magnetic resonance enterography (MRE)-based index that would measure inflammation in all segments of the intestine, without rectal contrast METHODS: Children with CD underwent ileocolonoscopy and MRE and half were followed for 18 months when MRE was repeated. Item generation and reduction were performed by a Delphi panel of pediatric radiologists, a systematic literature review, a cross-sectional study of 48 MREs and a steering committee. Formatting and weighting were performed by multivariate modeling adjusted by a steering committee. MREs were read locally and centrally. Reliability, validity and responsiveness were determined utilizing several clinimetric and psychometric approaches. RESULTS Thirty items were initially generated and reduced to five by regression analysis on 159 MREs: wall thickness, wall diffusion weighted imaging, ulcerations, mesenteric edema and comb sign. In the validation cohort of 81 MREs, the weighted global PICMI correlated well with the radiologist global assessment (r=0.85, p<0.001) and with the simple endoscopic score in a sub-sample with ileocolonic disease (SES-CD; r=0.63, p<0.001). Interobserver and test-retest reliability were high (interclass correlation coefficients, 0.84 [95% [CI 0.79-0.87] and 0.81 [0.65-0.90], respectively; both p<0.001). Excellent responsiveness was found at repeated visits (n=116 MREs; area under the ROC curve (AUROC) 0.96 [95%CI, 0.93-0.99]). Transmural healing was defined as PICMI≤10 and response as a change of >20 points with excellent discriminative validity (AUROC=0.96 [95%CI 0.93-0.99]). CONCLUSION The PICMI is a valid, reliable and responsive index for assessing transmural inflammation in pediatric CD. It scores the entire bowel length and does not require intravenous contrast or rectal enema and therefore is suitable for use in children.