Validity of enthesis ultrasound assessment in spondyloarthropathy

Objectives: To develop an ultrasound enthesis score and to assess its validity in the diagnostic classification of the spondyloarthropathies (SpAs). Methods: Twenty-five patients with SpA and 29 healthy controls participated in a blinded, gender-matched, cross-sectional study involving ultrasound assessment. The following entheses were explored bilaterally: proximal plantar fascia, distal Achilles tendon, distal and proximal patellar ligament, distal quadriceps and brachial triceps tendons. The ultrasound score evaluated enthesis thickness, structure, calcifications, erosions, bursae and power Doppler signal. The value of each elemental lesion was calculated using a three-model analysis. Validity was analysed by receiver operating characteristic (ROC) curves. Inter-reader and interexplorer intraclass correlation coefficients (ICCs) were calculated. Results: The logistic regression model overestimated the score of three elemental lesions: calcification (0-3), Doppler (0 or 3) and erosion (0 or 3), while scoring tendon structure, tendon thickness and bursa as 0 or 1. ROC curves established an ultrasound score of >= 18 as the best cut-off point for differentiation between cases and controls. This cut-off point was exceeded by 5/29 controls (17%) and by 21/25 patients with SpA (84%). The sensitivity, specificity, positive and negative likelihood ratios (LR+, LR-) were 83.3%, 82.8%, 4.8% and 0.2%, respectively. The inter-reader and interexplorer ICCs were 0.60 and 0.86, respectively. Conclusion: The findings suggest that the ultrasound enthesis score could be a valid tool in the diagnosis of SpA.