Sociodemographic data, clinical characteristics, disease activity and disease burden across the two clusters with regard to the location of all the peripheral musculoskeletal manifestations
| Cluster 1 (predominant axial phenotype) N=3984 | Cluster 2 (predominant peripheral phenotype) N=481 | |
| Rheumatologist’s diagnosis | ||
| Axial spondyloarthritis | 2617 (65.7%) | 102 (21.2%) |
| Peripheral spondyloarthritis | 380 (9.5%) | 53 (11.0%) |
| Psoriatic arthritis | 738 (18.5%) | 295 (61.3%) |
| ReA or IBD-SpA | 147 (3.7%) | 21 (4.4%) |
| Juv-SpA or others | 102 (2.6%) | 10 (2.1%) |
| Classification criteria | ||
| ASAS axial criteria | 2758 (69.2%) | 195 (40.5%) |
| ASAS peripheral ‘strict’ criteria | 429 (10.8%) | 124 (25.8%) |
| ASAS peripheral ‘non-strict’ criteria | 1046 (26.3%) | 225 (46.8%) |
| CASPAR criteria | 770 (19.3%) | 273 (56.8%) |
| Demographic characteristics | ||
| Age, mean (SD) | 43.8 (13.9) | 50.2 (13.4) |
| Disease duration | 14.1 (11.2) | 16.3 (11.8) |
| Sex (male) | 2515 (63.1%) | 209 (43.5%) |
| Ever smoker | 1695/3980 (42.6%) | 205 (42.6%) |
| Ever alcohol | 1619/3981 (40.7%) | 193 (40.1%) |
| Phenotype | ||
| HLA-B27+ | 1973/2874 (68.6%) | 93/246 (37.8%) |
| Axial involvement (ever) | 3176 (79.7%) | 252 (52.4%) |
| Arthritis (ever) | 2061 (51.7%) | 480 (99.8%) |
| Enthesitis (ever) | 1692 (42.5%) | 292 (60.7%) |
| Dactylitis (ever) | 474 (11.9%) | 211 (43.9%) |
| Uveitis (ever) | 715 (17.9%) | 47 (9.8%) |
| Psoriasis (ever) | 975 (24.5%) | 303 (63.0%) |
| IBD (ever) | 252 (6.3%) | 29 (6.0%) |
| Treatment | ||
| csDMARDs (ever) | 2534 (63.6%) | 453 (94.2%) |
| bDMARDs (ever) | 2342 (58.8%) | 305 (63.4%) |
| Disease activity and severity | ||
| BASDAI, mean (SD) | 3.7 (2.4) | 4.9 (2.6) |
| ASDAS-CRP, mean (SD) | 2.5 (1.1) | 2.9 (1.2) |
| BASFI, mean (SD) | 2.9 (2.6) | 4.0 (2.9) |
| ASAS-HI, mean (SD) | 6.3 (4.5) | 8.6 (4.9) |
| Concomitant fibromyalgia* | 620/3671 (16.9%) | 155/456 (34.0%) |
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.