Assessment of active inflammation in juvenile dermatomyositis: a novel magnetic resonance imaging-based scoring system

Methods. Forty-eight children (33 girls) underwent retrospective assessment of their MRI studies by two musculoskeletal paediatric radiologists for the presence of disease activity. Each observer performed the readings on two separate occasions. The degree of concordance between the two observers and between the two readings was assessed using kappa analysis. The reproducibility of the total score was determined using Bland-Altman analysis. Results. There was fair to moderate agreement between the two observers for all the examined disease activity markers in all muscle groups. There was good intra-observer agreement between the two readings. There was no difference according to the side evaluated. The mean total score (out of 20) for Observer 1 was 7.9 and for Observer 2 was 7.5 (mean difference -0.4, 95% limits of agreement -6.8 to 6.0), while the mean total scores for Observer 1 were 9.0 for the first reading and 7.9 for the second reading (mean difference 1.0, 95% limits of agreement -2.6 to 4.6). Conclusion. Markers of inflammatory change in JDM can be observed on MRI in a reliable fashion and have been used to make a reliable and objective scoring system. The accuracy of the proposed scoring system is acceptable for the single reader, although there is more variability between two different individuals.