Characteristics of patients with axSpA and chronic back pain due to unknown causes
| ASAS classification 2/3 readers | No SpA | Possible axSpA | Clinical arm only | MRI+mNY− | mNY+ |
|---|---|---|---|---|---|
| No. of patients | 72 | 89 | 53 | 51 | 22 |
| Age (years) at onset of back pain, mean±SD | 30.6 (±0.98) | 30.4 (±0.93) | 27.5 (±1.07) | 30.5 (±1.08) | 25.7 (±1.53) |
| Duration of back pain (months), mean±SD | 14.6 (±0.86) | 12.4 (±0.72) | 11.7 (±0.92) | 13.1 (±1.09) | 13.1 (±1.85) |
| Male, n (%) | 20 (27.8) | 24 (27.0) | 19 (35.8) | 27 (52.9) | 13 (59.1) |
| HLA-B27 positive, n (%) | 2 (2.8) | 9 (10.2) | 53 (100) | 31 (60.8) | 15 (65.2) |
| Positive family history, n (%) | 14 (19.4) | 37 (42.0) | 33 (62.3) | 18 (35.3) | 9 (39.1) |
| IBP, n (%) | 40 (55.6) | 56 (63.6) | 47 (88.7) | 34 (66.7) | 17 (73.9) |
| Psoriasis, n (%) | 0 | 15 (17.0) | 8 (15.1) | 4 (7.8) | 3 (13.4) |
| Peripheral arthritis, n (%) | 0 | 20 (22.7) | 12 (22.6) | 10 (19.6) | 2 (8.7) |
| Dactylitis, n (%) | 0 | 9 (10.2) | 5 (9.4) | 4 (7.8) | 1 (4.3) |
| Heel enthesitis, n (%) | 0 | 27 (30.7) | 13 (24.5) | 8 (15.7) | 4 (17.4) |
| Uveitis, n (%) | 0 | 6 (6.8) | 10 (18.9) | 5 (9.8) | 3 (13.4) |
| IBD, n (%) | 0 | 14 (15.9) | 2 (3.8) | 6 (11.8) | 3 (13.4) |
| Good response to NSAIDs, n (%) | 21 (29.2) | 31 (35.2) | 26 (49.1) | 18 (35.3) | 14 (60.9) |
| Elevated ESR/CRP, n (%) | 0 | 26 (29.5) | 13 (24.5) | 11 (21.6) | 7 (30.4) |
| CRP, mean±SD | 3.9 (±0.40) | 6.7 (±1.21) | 7.6 (±1.68) | 6.7 (±1.01) | 7.1 (±1.33) |
| Radiographic sacroiliitis, n (%) | 0 | 1 (1,1) | 0 | 0 | 22 (100) |
| Sacroiliitis on MRI, n (%) | 0 | 4 (4.5) | 0 | 51 (100) | 12 (52.2) |
ASAS, Assessment of Spondyloarthritis international Society; axSpA, axial spondyloarthritis; CRP, C-reactive protein; ESR, erythrocyte sedimentation rate; HLA, human leucocyte antigen; IBD, inflammatory bowel disease; IBP, inflammatory back pain; mNY, modified New York criteria; NSAIDs, non-steroidal anti-inflammatory drugs; SpA, spondyloarthritis.