Objective. To compare magnetic resonance imaging (MRI), conventional radiography, and ultrasonography in identifying bone erosions in patients with juvenile idiopathic arthritis (JIA), and to determine the validity and reliability of an MRI scale in detecting and grading joint damage. Methods. In 26 JIA patients, the clinically more affected wrist was studied with MRI, radiography, and ultrasonography, coupled with standard clinical assessment and biochemical analysis. MR images were assessed independently by 2 readers according to an apposite devised scoring system. Results. Of 26 patients, 25 (96.1%) had 1 or more erosions as detected by MRI, whereas conventional radiography and ultrasonography revealed erosions in 13 (50%) of 26 and 12 (50%) of 24 patients, respectively. The ability of MRI to detect erosive changes was significantly higher with respect to conventional radiography (P = 0.002 with Bonferroni correction [P B]) and ultrasonography (P B = 0.0002) in the group of patients with s = 0.82) and with wrist limited range of motion score (r s = 0.69). The interreader intraclass correlation coefficient (ICC) for MRI score was excellent (0.97); intrareader ICCs were good for both investigators (0.97 and 0.79). Conclusion. MRI seems to be a powerful tool to detect early structural damage in JIA. The proposed MRI scale for bone erosions appears promising in terms of reliability and construct validity. The pathophysiologic meaning and the prognostic value of bone erosions revealed only by MRI remain to be established in longitudinal studies.
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