Table 1.
Baseline characteristics of chronic back pain patients suspected of axial spondyloarthritis included in the ASAS cohort
| Characteristics | Data (N = 594) |
|---|---|
| Age at baseline, years | 33.7 (11.7) |
| Male sex | 276 (46%) |
| Duration of back pain, yearsa | 7.1 (9.0) |
| Self-reported ethnicity | |
| White | 348 (59%) |
| Asian | 214 (36%) |
| Otherb | 32 (5%) |
| IBP (according to experts’ definition) | 301/532 (57%) |
| Good response to NSAIDsc | 274 (46%) |
| Peripheral arthritisd | 197 (33%) |
| Enthesitisd | 241 (41%) |
| AAUd | 53 (9%) |
| Dactylitisd | 23 (4%) |
| Psoriasisd | 22 (4%) |
| IBDd | 8 (1%) |
| Positive family history according to ASAS definition | 135 (23%) |
| Positive family history of AS | 87 (15%) |
| Positive family history of AAU | 7 (1%) |
| Positive family history of ReA | 8 (1%) |
| Positive family history of IBD | 12 (2%) |
| Positive family history of Psoriasis | 36 (6%) |
| Total number of SpA-related diseases in first- or second-degree relatives | |
| Number of patients with one disease | 120 (20%) |
| Number of patients with two diseases | 15 (3%) |
| Total number of family members with SpA-related diseases | |
| Number of patients with one relative | 102 (17%) |
| Number of patients with two relatives | 30 (5%) |
| Number of patients with three relatives | 3 (1%) |
| Total number of patients with positive family history in | |
| First-degree relatives only | 100 (17%) |
| Second-degree relatives only | 25 (4%) |
| Both first- and second-degree relatives | 10 (2%) |
| HLA-B27 positivity | 310 (52%) |
| Elevated CRP/ESR | 185 (31%) |
| Definite radiographic sacroiliitise | 119/593 (20%) |
| Presence of active inflammation on MRI-SI | 189/424 (45%) |
| Number of SpA featuresf,g | 2.4 (1.6) |
| Clinical diagnosis of axSpAh | 368 (62%) |
Abbreviations: AAU Acute anterior uveitis, AS Ankylosing spondylitis, ASAS Assessment of SpondyloArthritis international Society, (ax)SpA (Axial) spondyloarthritis, CRP C-reactive protein, ESR Erythrocyte sedimentation rate, HLA-B27 Human leukocyte antigen B27, IBD Inflammatory bowel disease, IBP Inflammatory back pain, MRI-SI Magnetic resonance imaging of the sacroiliac joints, NSAID Nonsteroidal anti-inflammatory drug, ReA Reactive arthritis, SI Sacroiliac joint
Results are presented as mean ± SD unless specified otherwise
a < 5% missing values
b Self-reported ethnicity was missing for five patients, who are included in this category, and other self-reported ethnicities are black, East Indian, Hispanic/Latino, mixed, or Turkish
c Back pain not present anymore or is much better 24–48 hours after a full dose of NSAID
d Past or present condition
e Grade ≥ 2 bilateral or grade ≥ 3 unilateral
f Excluding HLA-B27 carriership and imaging
g < 20% missing values
h Level of confidence regarding the diagnosis is ≥ 6