Characteristics of the study population patients compared with the patients who had not had an US at baseline
| Baseline characteristics | Patients with US: n=402 | Patients without US: n=306 |
| Age, year, med (IQR) | 33.5 (26.7–39.4) | 33.1 (26.6–40.6) |
| Male (%) | 195 (48.5) | 132 (43.1) |
| Symptom duration, months, med (IQR) | 17.1 (8.7–27.8) | 16.7 (10.0–24.8) |
| Number of patients with at least one clinical enthesitis (%) | 259 (64.4) | 200 (65.3) |
| BASDAI, med (IQR) | 45 (29–60) | 47 (28–62) |
| ASDAS-CRP, med (IQR) | 2.55 (1.89–3.23) | 2.64 (1.88–3.26) |
| MASES, med (IQR) | 2 (0–4) | 2 (0–4) |
| HLA B27 positivity, number (%) | 233 (58.0) | 177 (57.8) |
| Meeting diagnostic criteria for axial SpA*, n (%) | 375 (93.3) | 275 (89.9) |
| mSASSS, med (IQR) | 0 (0–0) | 0 (0–0) |
| Patients with positive MRI sacro-iliitis†, number (%) | 134 (33.3) | 85 (27.8) |
| SPARCC, med (IQR) | 0 (0–3.5) | 0 (0–2.5) |
| Berlin score, med (IQR) | 0 (0–0) | 0 (0–0) |
| NSAIDs intake, number (%) | 366 (91.0) | 272 (88.9) |
| CRP (mg/L), med (IQR) | 3.5 (2.0–7.3) | 3.1 (2.0–7.0) |
*One criteria set for axial SpA: patients meeting at least one of the following diagnostic criteria set for axial SpA: modified New York criteria, 2009 ASAS criteria, Amor criteria, ESSG criteria.
†positive sacro-iliac joint MRI according to ASAS definition.
ASDAS-CRP, Ankylosing Spondylitis Disease Activity Score with C reactive protein; BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; Berlin score: spine MRI scoring system; ESSG, European Spondylarthropathy Study Group; MASES, Maastricht Ankylosing Spondylitis Enthesitis Score; mSASSS, modified Stoke Ankylosing Spondylitis Spine Score; NSAIDs, non-steroidal anti-inflammatory drugs; SPARCC, Spondyloarthritis Research Consortium of Canada scoring system (sacro-iliac joints MRI scoring system); US, ultrasound.