Development and preliminary validation of a paediatric-targeted MRI scoring system for the assessment of disease activity and damage in juvenile idiopathic arthritis

Objectives: To develop and validate a paediatric-targeted MRI scoring system for the assessment of disease activity and damage in juvenile idiopathic arthritis (JIA). To compare the paediatric MRI score with the adult-designed. Outcome Measures in Rheumatology Clinical Trials - Rheumatoid Arthritis MRI Score (RAMRIS), whose suitability for assessing growing joints was tested. Methods: In 66 patients with JIA the clinically more affected wrist was studied. Thirty-nine patients had a 1-year MRI follow-up. Two readers independently assigned the paediatric score and the RAMRIS to all studies. Validation procedures included analysis of reliability, construct validity and responsiveness to change. A reduced version of the bone erosion score was also developed and tested. Results: The paediatric score showed an excellent reproducibility (interclass correlation coefficient >0.9). The interobserver agreement of RAMRIS was moderate for bone erosions and excellent for bone marrow oedema (BMO). The paediatric score and RAMRIS provided similar results for construct validity. The responsiveness to change of the paediatric score was moderate for synovitis and bone erosion, and poor for BMO and did not improve when RAMRIS was applied. The reduced version of the bone erosion was valuable for the assessment of joint damage, and provided time-saving advantages. Conclusion: The results demonstrate that the paediatric MRI score is a reliable and valid method for assessing disease activity and damage in JIA. Unexpectedly, the RAMRIS provides acceptable suitability for use in the paediatric age group. Further work, especially in a longitudinal setting, is required before defining the most suitable MRI scale for assessing growing joints.