Baseline characteristics of patients with chronic back pain included in the Leiden SPACE cohort
| All patients (n=261) | Patients diagnosed with axSpA (n=107) | Patients not diagnosed with axSpA (n=154) | |
|---|---|---|---|
| Demographical and back pain characteristics | |||
| Age at inclusion, mean (SD), in years | 31.0 (8.8) | 30.4 (8.3) | 31.4 (9.2) |
| Male, n (%) | 86 (33.0%) | 43 (40.2%) | 43 (27.9%) |
| Duration of back pain, mean (SD), in months | 13.4 (7.3) | 13.1 (7.2) | 13.7 (7.5) |
| Age at onset <40 years, n (%) | 217 (83.1%) | 90 (84.1%) | 127 (82.5%) |
| Certainty of diagnosis, mean (SD) | 7.1 (2.4) | 7.2 (2.5) | 7.0 (2.2) |
| Fulfilling ASAS axSpA criteria, n (%) | 79 (30.3%) | 63 (58.9%) | 16 (10.4%) |
| SpA features | |||
| HLA-B27+, n (%) | 79 (30.3%) | 57 (53.3%) | 22 (14.3%) |
| Positive family history of SpA, n (%) | 95 (36.4%) | 50 (46.7%) | 45 (29.2%) |
| Psoriasis, n (%) | 25 (9.6%) | 14 (13.1%) | 11 (7.1%) |
| Dactylitis, n (%) | 8 (3.1%) | 7 (6.5%) | 1 (0.6%) |
| Enthesitis, n (%) | 25 (9.6%) | 20 (18.7%) | 5 (3.2%) |
| Uveitis, n (%) | 17 (6.5%) | 13 (12.1%) | 4 (2.6%) |
| IBD, n (%) | 19 (7.3%) | 10 (9.3%) | 9 (5.8%) |
| CRP (mg/L), mean (SD) | 6.9 (11.1) | 9.8 (15.3) | 4.9 (6.1) |
| ESR (mm/hour), mean (SD) | 10.5 (12.0) | 14.2 (16.3) | 8.1 (7.1) |
| Elevated CRP/ESR, n (%) | 45 (17.2%) | 28 (26.2%) | 17 (11.0%) |
| Good response to NSAIDs, n (%) | 69 (26.4%) | 36 (33.6%) | 33 (21.4%) |
| Sacroiliitis on radiographs, n (%) | 22 (8.4%) | 16 (15.0%) | 6 (3.9%) |
| Sacroiliitis on MRI, n (%) | 27 (10.3%) | 26 (24.3%) | 1 (0.6%) |
| IBP* (ASAS), n (%) | 152 (58.2%) | 78 (72.9%) | 74 (48.1%) |
| Inflammatory back pain features | |||
| Improvement of back pain by rest, n (%) | 60 (23.0%) | 24 (22.4%) | 36 (23.4%) |
| Improvement of back pain by exercise, n (%) | 164 (62.8%) | 79 (73.8%) | 85 (55.2%) |
| Buttock pain, n (%) | 128 (49.0%) | 60 (56.1%) | 68 (44.2%) |
| Alternating buttock pain, n (%) | 67 (25.7%) | 25 (23.4%) | 42 (27.3%) |
| Night pain, n (%) | 164 (62.8%) | 71 (66.4%) | 93 (60.4%) |
| Pain in second half of night, n (%) | 78 (29.9%) | 35 (32.7%) | 43 (27.9%) |
| Insidious onset, n (%) | 228 (87.4%) | 95 (88.8%) | 133 (86.4%) |
| Morning stiffness, n (%) | 199 (76.2%) | 88 (82.2%) | 111 (72.1%) |
*IBP definition by ASAS criteria.35
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 (Crohn's disease/ulcerative colitis); IBP, inflammatory back pain; NSAIDs, non-steroidal anti-inflammatory drugs; SPACE, SPondyloArthritis Caught Early.