Objectives: This paper aims to assess the prevalence and relevance of the bursa-synovial lesion in spondyloarthritis (SpA).
Methods: A transversal blind and controlled two-dimensional (2D) and three-dimensional (3D) ultrasound (US) study of Achilles enthesis bursa in early SpA was undertaken. Clinical outcome measures were collected.
Results: Bilateral Achilles enthesis of 66 early SpA patients (34 women) and 46 control patients (23 asymptomatic healthy subjects and 23 rheumatoid arthritis [RA] patients) were analysed. Mean BASDAI, BASFI and BASRI-spine were 4.55±2.08, 2.16±1.95 and 0.65±0.77, respectively. Mean erythrocyte sedimentation rate (ESR) was 10.93±12.35 mm/h and C-reactive protein (CRP) was 6.46±10.09 mg/l. The κ-values for intra-reader agreement for 2D and 3D images and bursa measurement were 0.82 and 0.98, respectively. Bursas were visualised in 89/132 SpA enthesis (67.4%) vs. 27/46 enthesis (58.7%) of healthy controls (p<0.01), and 10/46 enthesis (21.7%) of RA controls (p<0.01). When the thicknesses of the bursas were analysed, the SpA group had a mean of 1.52±1.47 mm versus 0.76±0.76 mm in the healthy control group (p<0.0001), and 0.38±0.62 mm in the RA control group (p<0.0001). A positive likelihood ratio of 4.6 with a cut-off point of bursa >2 was found. No Doppler signal was detected in controls, but 6.6% of SpA Achilles enthesis had Doppler bursitis. Heel pain was more frequent when bursa was present (p<0.05). When Doppler was present, male predominance, HLA B27 positive, heel pain, and higher number of swollen joints, CRP levels, disease activity by the patient and BASDAI questions 2 and 3 achieved statistical significance (p<0.01).
Conclusions: The presence of bursa and Doppler signal at retrocalcaneal bursa level could have a relevant contribution to differentiate SpA patients, and were correlated with clinical outcomes of SpA disease activity.