Background/Purpose:  The pathology of inflammation in Juvenile Idiopathic Arthritis (JIA), including thickening and vascularization of the synovial membrane, joint effusion and bony erosions, can be detected by musculoskeletal ultrasound (MskUS). Previous studies measured joint effusion and synovial hypertrophy separately. However, it is often hard to distinguish between these two findings within an area of pathology as they are often overlapping and can have similar echogenicity. The objective of this study is to use a novel quantitative approach to characterize MskUS abnormalities in newly diagnosed JIA subjects.

Methods:  Subjects underwent MskUS assessment of bilateral wrists (midcarpal and radiocarpal recesses) and bilateral knees (suprapatellar, medial and lateral recesses) by grey-scale and power Doppler. MskUS scans were performed by an experienced technician. Pathologic lesions were measured across the greatest dimension (mm) independently by two pediatric radiologists blinded to the clinical musculoskeletal exam. Subjects also underwent clinical evaluations including a joint assessment, and calculation of the clinical JIA disease activity score (cJADAS).

Results:  Six subjects (5 oligoarticular and 1 polyarticular JIA) with newly diagnosed DMARD and corticosteroid-naïve JIA by ILAR criteria were evaluated in this cross-sectional study. The median age was 6.3 years (range 2.5, 7.1) and the median disease duration was 5.3 months, (range 2.5, 8.2). There was an equal proportion of male and female subjects. Total number of active joint counts ranged from 1 to 8. Of the 24 bilateral wrists and knees under study, 4 (17%) had clinical synovitis. 58% of the same joints under study had evidence of measurable MskUS pathology. Measurements of lesions ranged from 0.5 to 10mm. The interclass correlation between two independent raters for measurements of pathologic lesions in the suprapatellar recesses was 0.95. The Pearson correlation between cJDAS and total measurements of pathologic lesions was not significant.

Conclusion:  Ultrasonography is a useful tool for joint assessment in JIA. Subclinical ultrasonographic abnormalities are common in this cohort of newly diagnosed JIA subjects. Quantitative measurement of total joint pathology is reliable and reproducible. It may be a useful tool to characterize ultrasonographic abnormalities in JIA when it is difficult to distinguish between synovial hypertrophy and joint effusion. Future longitudinal studies are necessary to determine if quantitative measures of ultrasonographic lesions are reliable in monitoring JIA disease activity across time.