Baseline patient and disease characteristics in the entire ‘eligible population’ and across all subgroups according to BASDAI/ASDAS category
| Variables | Overall (n=594) | ASDAS≥2.1 | ASDAS<2.1 | P value* | ||
| BASDAI≥4 (n=487) | BASDAI <4 (n=64) | BASDAI≥4 (n=4) | BASDAI <4 (n=39) | |||
| Age in years, mean±SD | 49±13 | 49±12 | 48±14 | 42±9 | 48±15 | 0.66 |
| Gender (male), n (%) | 326 (55) | 251 (51) | 49 (77) | 1 (25) | 25 (64) | <0.01 |
| BMI in kg/m2, mean±SD (n=300) | 25.9±4.7 | 26.0±4.8 | 24.7±4.5 | . (.) | 26.0±3.6 | 0.28 |
| Current smokers, n (%) | 114 (22) | 98 (23) | 10 (19) | 0 (0) | 6 (19) | <0.01 |
| Age at diagnosis in years, mean±SD (n=449) | 36±12 | 36±12 | 34±11 | 29±15 | 40±13 | 0.08 |
| Disease duration in years, mean±SD† | 12.8±10.3 | 12.9±10.1 | 14.1±12.4 | 13.1±6.9 | 8.3±8.2 | 0.08 |
| HLA-B27, n (%)† | 347 (67) | 278 (65) | 44 (79) | 2 (67) | 23 (68) | 0.24 |
| Radiographic sacroiliitis (mNY), n (%) (n=487) | 391 (80) | 322 (80) | 44 (85) | 3 (100) | 22 (76) | 0.63 |
| Sacroiliitis on MRI-SIJ, n (%) (n=225) | 137 (61) | 114 (60) | 9 (50) | 2 (100) | 12 (86) | 0.12 |
| Number of SpA features±SD† | 2.5±1.2 | 6.4±1.5 | 2.9±1.0 | 5.3±0.8 | 1.9±1.3 | 0.96 |
| BASDAI (0–10), mean±SD | 5.8±2.1 | 6.4±1.5 | 2.9±0.9 | 5.3±0.8 | 1.9±1.3 | <0.01 |
| ASDAS-CRP, mean±SD | 3.5±1.0 | 3.8±0.8 | 3.0±0.6 | 1.9±0.3 | 1.6±0.4 | <0.01 |
| ASDAS inactive disease, n (%) | 9 (2) | 0 (0) | 0 (0) | 0 (0) | 9 (23) | <0.01 |
| ASDAS low disease activity, n (%) | 28 (5) | 0 (0) | 0 (0) | 3 (75) | 25 (64) | |
| ASDAS high disease activity, n (%) | 272 (46) | 213 (44) | 53 (83) | 1 (25) | 5 (13) | |
| ASDAS very high disease activity, n (%) | 285 (48) | 274 (56) | 11 (17) | 0 (0) | 0 (0) | |
| CRP, mg/dL, mean±SD† | 2.1±2.9 | 2.1±2.9 | 2.9±3.5 | 0.1±0.0 | 0.5±0.7 | 0.03 |
| Elevated CRP, n (%)‡ | 376 (71) | 325 (70.4) | 47 (88.7) | 0 (0.0) | 4 (33.3) | <0.01 |
| BASFI (0–10), mean±SD† | 5.2±2.5 | 5.6±2.2 | 3.0±2.0 | 4.7±0.6 | 2.1±2.0 | <0.01 |
| bDMARD therapy | (n=529) | (n=462) | (n=53) | (n=2) | (n=12) | § |
| Infliximab, n (%) | 130 (25) | 112 (24) | 12 (23) | 0 (0) | 130 (25) | |
| Adalimumab, n (%) | 164 (31) | 142 (31) | 18 (34) | 0 (0) | 164 (31) | 0.18 |
| Etanercept, n (%) | 135 (26) | 116 (25) | 18 (34) | 2 (26) | 135 (26) | |
| Golimumab, n (%) | 91 (17) | 83 (18) | 5 (9) | 0 (0) | 91 (17) | |
| Certolizumab pegol, n (%) | 5 (1) | 5 (1) | 0 (0) | 0 (0) | 5 (1) | |
| Secukinumab, n (%) | 4 (1) | 4 (1) | 0 (0) | 0 (0) | 4 (1) | |
| Co-medication (bDMARD-treated), n (%) | ||||||
| NSAIDs | 211 (40) | 184 (40) | 21 (40) | 1 (50) | 5 (42) | 0.99 |
| csDMARDs | 271 (51) | 234 (51) | 28 (53) | 2 (100) | 7 (58) | 0.52 |
| Oral corticosteroids | 108 (20) | 95 (21) | 11 (21) | 1 (50) | 1 (8) | 0.54 |
Overall (‘Eligible population’): axSpA patients, irrespective of being treated with bDMARDs, with complete 6 months of follow-up and BASDAI/ASDAS data at baseline (irrespective of having ASDAS/BASDAI at any other time point).
*Comparison across all subgroups according to BASDAI/ASDAS category of disease activity (ANOVA test for continuous variables and χ2 test for categorical variables). P values in bold are significant (<0.05).
†Variables with <15% of missing data.
‡Defined as ≥0.5 mg/dL.
§P value of <0.01 for the categorical variable (treated or not with bDMARD).
ASDAS, Ankylosing Spondylitis Disease Activity Score; axSpA, axial spondyloarthritis; BASDAI, Bath Ankylosing Spondylitis Disease Activity Index; BASFI, Bath Ankylosing Spondylitis Functional Index; bDMARD, biologic disease-modifying antirheumatic drug; BMI, body mass index; CRP, C reactive protein; csDMARDs, conventional synthetic disease-modifying antirheumatic drugs; HLA-B27, human leucocyte antigen B27; mNY, modified New York criteria for ankylosing spondylitis; MRI-SIJ, MRI of sacroiliac joints; NSAIDs, non-steroid anti-inflammatory drugs.