Development and Validation of the OMERACT Juvenile Idiopathic Arthritis MRI- Sacroiliac Joint Score (OMERACT JAMRIS-SIJ): Phase 3

Objective The OMERACT JAMRIS working group has defined a spectrum of MRI lesions in the sacroiliac joint (SIJ) in pediatric cases with spondyloarthritis (SpA) that match domains for inflammation and structural damage. We aimed to assess longitudinal construct validity using two available instruments, the Spondyloarthritis Research Consortium of Canada (SPARCC) and JAMRIS scores, in two longitudinal cohorts of youth with SpA treated with a tumor necrosis factor inhibitor (TNFi) according to the OFISA framework. Methods Two cohorts recruited 60 youth with SpA who had MRI prior to and after TNFi. MRI lesions were assessed blinded to timepoint by 7 readers (5 MSK radiologists, 2 rheumatologists). Analyses compared data from JAMRIS-all slice versus SPARCC selected slices for descriptive variables, reliability, and responsiveness. Results Pre- and post-treatment scans (mean (SD) duration between scans 46.6 (47.1) weeks) were available from 60 cases. The major contributor to change in inflammatory lesion scores was bone marrow edema (BME) followed by inflammation in an erosion cavity (IEC), though differences between the two instruments were minimal. For change in structural lesions, minimal differences were evident between SPARCC and JAMRIS-all slice instruments. Reliability for detection of change scores and responsiveness were comparable between SPARCC and JAMRIS-all slice methodologies. Combining scores for inflammatory lesions did not enhance responsiveness compared to BME alone. Conclusions BME is the most responsive lesion to treatment with TNFi in axJSpA followed by IEC and then erosion. Validation according to the OFISA framework demonstrates that the JAMRIS-all slice and SPARCC instruments have comparable performance characteristics.