Diagnostic Accuracy Study of the Pediatric-Specific Ultrasound Scoring System for the Knee Joint in Children With Juvenile Idiopathic Arthritis.

OBJECTIVE: We undertook this study to validate the Pediatric Arthritis Ultrasound Scoring System for the knee joint (PAUSS-knee) in children with juvenile idiopathic arthritis (JIA). METHODS: Children with JIA were enrolled to prospectively receive a musculoskeletal ultrasound (MSUS) examination of the knee and a physical examination to determine presence/absence of clinical arthritis. MSUS images were scored using the PAUSS-knee, a semiquantitative MSUS scoring system (0-3, normal to severe) for B-mode and power Doppler mode. In addition to MSUS, a subset of participants also received magnetic resonance imaging (MRI) of the knee, which was scored according to the combined Juvenile Arthritis MRI Scoring (JAMRIS) system. Spearman's correlations (r(s) ) were used to calculate associations between variables. Test characteristics of the PAUSS-knee were calculated with MRI as the reference standard. Inflammatory biomarkers were assessed in synovial fluid from involved knees. RESULTS: Eighty children with JIA contributed 112 MSUSs and 25 MRIs of the knee. Of the knees, 41% (n = 46) had clinical evidence of arthritis. The B-mode PAUSS-knee score moderately correlated with clinically determined arthritis (r(s) = 0.54, P < 0.001) and strongly correlated with the JAMRIS score (r(s) = 0.75, P < 0.001). Compared with MRI, the area under the curve for the B-mode PAUSS-knee was 0.92. For a cutoff of >1, the B-mode PAUSS-knee had a sensitivity of 83% and specificity of 82%. Biomarker analysis indicates that interleukin-2R levels correlate with PAUSS score. CONCLUSION: Our data indicate that the PAUSS-knee has excellent accuracy for the diagnosis of arthritis when compared with MRI. The PAUSS-knee has the potential to effectively inform JIA medical decision-making in real time.