Table 1 Baseline characteristics of patients

Age, mean (SD), years

39.69 (13.02)

38.71 (12.75)

42.88 (13.40)

< 0.001

Disease duration, mean (SD), years

5.00 (6.17)

5.46 (6.36)

3.48 (5.22)

< 0.001

HLA-B27 positivity (n = 1,617) (%)

1451 (89.73)

1131 (91.88)

320 (82.9)

< 0.001

nr-axSpA (%)

170 (9.7)

118 (8.79)

52 (12.68)

0.020

Cigarette smoking (%)

< 0.001

No smoker

881 (50.26)

507 (37.75)

374 (91.22)

Ex-smoker

365 (20.82)

351 (26.14)

14 (3.41)

Current smoker

507 (28.92)

485 (36.11)

22 (5.37)

ESR, mean (SD), mm/h

37.08 (29.93)

35.13 (29.12)

43.47 (31.63)

< 0.001

CRP (n = 1,733), mean (SD), mg/dL

2.14 (2.89)

2.23 (2.92)

1.85 (2.78)

< 0.001

Inflammatory back pain (n = 1,748) (%)

1475 (84.38)

1134 (84.69)

341 (83.37)

0.521

Peripheral arthritis (n = 1,735) (%)

492 (28.36)

341 (25.66)

151 (37.19)

< 0.001

Enthesitis (n = 1,738) (%)

278 (16)

197 (14.81)

81 (19.85)

0.015

Uveitis (n = 1,740) (%)

164 (9.43)

112 (8.41)

52 (12.75)

0.009

Psoriasis (n = 1,738) (%)

41 (2.36)

34 (2.56)

7 (1.72)

0.328

Crohn’s disease (n = 1,734) (%)

10 (0.58)

7 (0.53)

3 (0.74)

0.708

Family history of SpA (n = 1,721) (%)

196 (11.39)

138 (10.47)

58 (14.39)

0.030

Hypertension (%)

274 (15.63)

213 (15.86)

61 (14.88)

0.632

DM (%)

87 (4.96)

69 (5.14)

18 (4.39)

0.542

Ischemic heart disease (n = 1,752) (%)

21 (1.2)

20 (1.49)

1 (0.24)

0.039

CKD^a (%)

15 (0.86)

12 (0.89)

3 (0.73)

> 0.99

Type of TNFi^b (%)

< 0.001

Adalimumab

696 (39.7)

546 (40.66)

150 (36.59)

Etanercept

273 (15.57)

214 (15.93)

59 (14.39)

Golimumab

387 (22.08)

309 (23.01)

78 (19.02)

Infliximab

397 (22.65)

274 (20.4)

123 (30)

Number of biologic agents used previously (%)

0.474

0

1,385 (79.01)

1,053 (78.41)

332 (80.98)

1

270 (15.4)

211 (15.71)

59 (14.39)

More than two

98 (5.59)

79 (5.88)

19 (4.63)

Time interval between baseline to first follow-up, mean (SD), months

11.13 ± 3.78

11.22 ± 3.74

10.84 ± 3.90

0.077