Characteristics of the patients according to subgroups. Values are n (%) unless otherwise specified.
| Characteristics | N | All Patients, n = 393 | AxSpA, n = 142 | Possible SpA, n = 140 | No SpA, n = 111 | p |
|---|---|---|---|---|---|---|
| Male | 393 | 138 (35) | 69 (49) | 39 (28) | 30 (27) | < 0.001α,β |
| Age, yrs, mean (SD) | 393 | 31.1 (8.3) | 29.7 (8.0) | 32.0 (8.3) | 31.7 (8.4) | 0.04α |
| Height, cm, mean (SD) | 373 | 175 (9) | 177 (10) | 172 (9) | 175 (9) | 0.01α |
| Overweight (BMI ≥ 25.0) | 372 | 147 (40) | 43 (33) | 63 (48) | 41 (38) | 0.04α |
| Age at onset of back pain, yrs, mean (SD) | 391 | 29.4 (8.2) | 28.1 (7.9) | 30.4 (8.3) | 30.0 (8.4) | 0.05 |
| Duration of back pain, mos, mean (SD) | 392 | 13.1 (7.2) | 13.2 (7.4) | 12.4 (6.8) | 13.7 (7.4) | 0.39 |
| Back pain intensity, NRS 0–10, mean (SD) | 352 | 5.0 (2.3) | 4.2 (2.3) | 5.3 (2.3) | 5.6 (2.2) | < 0.001α,β |
| Location of back pain | ||||||
| Buttock | 389 | 212 (55) | 88 (63) | 70 (50) | 54 (49) | 0.03α,β |
| Lumbar | 393 | 333 (85) | 108 (76) | 124 (89) | 101 (91) | 0.01α,β |
| Thoracic | 393 | 137 (35) | 48 (34) | 42 (30) | 47 (42) | 0.12 |
| SpA features | ||||||
| IBP | 393 | 246 (63) | 114 (80) | 74 (53) | 58 (52) | < 0.001α,β |
| Positive family history | 393 | 150 (38) | 72 (51) | 55 (39) | 23 (21) | 0.01β,γ |
| HLA-B27+ | 387 | 147 (38) | 123 (89) | 20 (15) | 4 (4) | < 0.001α,β, γ |
| Good response to NSAID | 386 | 136 (35) | 62 (45) | 46 (34) | 28 (25) | 0.01β |
| Elevated CRP/ESR | 383 | 86 (23) | 38 (28) | 48 (35) | 0 | < 0.001β, γ |
| Heel enthesitis | 393 | 64 (16) | 31 (22) | 33 (24) | 0 | < 0.001β, γ |
| Peripheral arthritis | 388 | 54 (14) | 27 (19) | 27 (20) | 0 | < 0.001β, γ |
| Psoriasis | 392 | 38 (10) | 18 (13) | 20 (14) | 0 | < 0.001β, γ |
| IBD | 393 | 33 (8) | 9 (6) | 24 (17) | 0 | < 0.001α,β, γ |
| Uveitis | 393 | 31 (8) | 23 (16) | 8 (6) | 0 | < 0.001α,β, γ |
| Dactylitis | 393 | 21 (5) | 11 (8) | 10 (7) | 0 | 0.01β, γ |
| Sacroiliitis present on imaging | 354 | 62 (17) | 58 (45) | 4 (3) | 0 | < 0.001α,β |
| Radiograph | 19 (5) | 17 (13) | 2 (2) | 0 | ||
| MRI | 31 (9) | 30 (23) | 1 (1) | 0 | ||
| Radiograph and MRI | 12 (3) | 11 (8) | 1 (1) | 0 | ||
| Current use of medication | ||||||
| NSAID | 393 | 273 (70) | 105 (74) | 90 (64) | 78 (70) | 0.21 |
| DMARD | 378 | 24 (9) | 11 (8) | 13 (10) | 0 | 0.01 β,γ |
↵Statistically significant subgroup difference between α axSpA and possible SpA, β axSpA and no SpA, γ possible SpA and no SpA. BMI: body mass index; axSpA: axial spondyloarthritis; CRP: C-reactive protein; DMARD: disease-modifying antirheumatic drug; ESR: erythrocyte sedimentation rate; IBD: inflammatory bowel disease; IBP: inflammatory back pain; MRI: magnetic resonance imaging; NRS: numerical rating scale; NSAID: nonsteroidal antiinflammatory drug; SpA: spondyloarthritis.