Sociodemographic data, clinical characteristics, disease activity and disease burden across the three clusters with regard to the location of the arthritis
| Cluster 1A N=3830 | Cluster 2A N=115 | Cluster 3A N=520 | |
| Rheumatologist’s diagnosis | |||
| Axial spondyloarthritis | 2572 (67.2%) | 24 (20.9%) | 123 (23.7%) |
| Peripheral spondyloarthritis | 362 (9.5%) | 11 (9.7%) | 60 (11.5%) |
| Psoriatic arthritis | 658 (17.2%) | 71 (61.7%) | 304 (58.5%) |
| ReA or IBD-SpA | 142 (3.7%) | 2 (1.7%) | 24 (4.6%) |
| Juv-SpA or others | 96 (2.5%) | 7 (6.0%) | 9 (1.7%) |
| Classification criteria | |||
| ASAS axial criteria | 2704 (70.6%) | 56 (48.7%) | 193 (37.1%) |
| ASAS peripheral strict criteria | 391 (10.2%) | 26 (22.6%) | 136 (26.2%) |
| ASAS peripheral ‘non-strict’ | 962 (25.1%) | 47 (40.9%) | 262 (50.4%) |
| CASPAR criteria | 695 (18.1%) | 73 (63.5%) | 275 (52.9%) |
| Demographic characteristics | |||
| Age, mean (SD) | 43.4 (13.8) | 50.4 (13.4) | 51.2 (13.3) |
| Disease duration | 13.9 (11.1) | 18.7 (12.6) | 16.4 (12.0) |
| Sex (male) | 2449 (63.9%) | 59 (51.3%) | 216 (41.5%) |
| Ever smoker | 1618/3826 (42.3%) | 48 (41.7%) | 234 (45.0%) |
| Ever alcohol | 1561/3827 (40.8%) | 51 (44.3%) | 200 (38.5%) |
| Phenotype | |||
| HLA-B27+ | 1941/2782 (79.8%) | 27/56 (48.2%) | 98/282 (34.8%) |
| Axial involvement (ever) | 3097 (80.9%) | 63 (54.8%) | 268 (51.5%) |
| Enthesitis (ever) | 1635 (42.7%) | 74 (64.3%) | 275 (52.9%) |
| Dactylitis (ever) | 451 (11.8%) | 55 (47.8%) | 179 (34.4%) |
| Uveitis (ever) | 699 (18.3%) | 18 (15.7%) | 45 (8.7%) |
| Psoriasis (ever) | 890 (23.2%) | 78 (67.8%) | 310 (59.6%) |
| IBD (ever) | 242 (6.3%) | 4 (3.5%) | 35 (6.7%) |
| Treatment | |||
| csDMARDs (ever) | 2393 (62.5%) | 110 (95.7%) | 484 (93.1%) |
| bDMARDs (ever) | 2250 (58.7%) | 80 (69.6%) | 317 (61.0%) |
| Disease activity and severity | |||
| BASDAI, mean (SD) | 3.7 (2.4) | 4.7 (2.6) | 4.9 (2.6) |
| ASDAS-CRP, mean (SD) | 2.5 (1.1) | 2.9 (1.3) | 2.8 (1.2) |
| BASFI, mean (SD) | 2.8 (2.6) | 4.1 (2.9) | 4.0 (2.9) |
| ASAS-HI, mean (SD) | 6.3 (4.5) | 9.0 (5.0) | 8.2 (4.7) |
| Concomitant fibromyalgia* | 576/3523 (16.3%) | 37/107 (34.6%) | 162/497 (32.6%) |
All results are presented as mean and SD and percentages for continuous and categorical variables, respectively.
*Presence of fibromyalgia defined by the fulfilment of the Fibromyalgia Rapid Screen Tool (FiRST).13
ASAS-HI, ASAS Health Index; ASDAS-CRP, Ankylosing Spondylitis Disease Activity Score; BASDAI, Bath Ankylosing Disease Activity Index; BASFI, Bath Ankylosing Spondylitis Functional Index; IBD, inflammatory bowel disease; Juv-SpA, juvenile SpA; ReA, reactive arthritis.