Objectives: To develop an ultrasound enthesis score, and to assess its validity in the spondyloarthropathies (SpA) diagnostic classification.
Methods: Twenty five SpA patients and 29 healthy controls participated in a blinded, gender-matched, cross-sectional study involving ultrasound assessment. The following enthesis 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. The validity was analyzed by ROC curves. Inter-reader and inter-explorer intraclass correlation coefficients (ICC) 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 17 as the best cut-off point to differentiate between cases and controls. This cut-off point was exceeded by 5 of 29 controls (17 %), and by 21 of 25 SpA patients (84 %). In contrast, 4 of 25 (16 %) SpA cases and 24 of 29 healthy controls (83 %) did not exceed the cut-off point. The sensitivity, specificity, positive likelihood ratio (LR+), and the negative likelihood ratio (LR-) were 83.33%, 82.76%, 4.83%, and 0.201% respectively. The inter-reader and inter-explorer 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.