The objective of this study was to determine the construct validity and sensitivity to change of Belgrade Ultrasound Enthesitis Score (BUSES) in spondyloarthritis patients. Seventy-six spondyloarthritis patients with enthesitis were included in this pilot, prospective, double-blinded ultrasound study. Thirty-four patients received biological and forty-two patients received non-biological therapy. BUSES was determined at the beginning, after 1, 3, and 6 months. Spearman's correlation coefficient was calculated between BUSES and baseline characteristics. Brunner-Langer mixed non-parametric ANOVA was used to examine sensitivity to change of BUSES and effect of biological therapy on BUSES. Effect of time on the presence of each of the ultrasound enthesitis signs (increased thickness, hypoehogenicity, Power Doppler, enthesophytes, and erosions) was assessed using Cochran Q test. There was a weak, positive correlation between BUSES and disease duration, clinical enthesitis score, BASFI, BASDAI, and ASDAS-ESR/CRP. BUSES was higher at the beginning than after 1 month (p = 0.004), after 3 months (p < 0.001) and after 6 months (p < 0.001), as well as BUSES was higher after 1 month than after 3 months (p < 0.001) and after 6 months (p = 0.002). There is no difference in efficiency between non-biological and biological therapies on BUSES. Increased thickness, hypoechogenicity, and Power Doppler have decreased on Achilles tendon's and plantar fascia's enthesis over time. BUSES has a certain degree of construct validity because of the weak, positive correlation with parameters referring to severity of spondyloarthritis. BUSES demonstrated sensitivity to change over time due to decreasing of ultrasound acute enthesitis signs in treated spondyloarthritis patients. BUSES could be useful for monitoring the progression of enthesitis and effectiveness of the treatment.
Keywords: BUSES; Belgrade Ultrasound Enthesitis Score; Construct validity; Enthesitis; Sensitivity to change; Spondyloarthritis; Ultrasound.