Table 1

Demographic, clinical, laboratory and radiological characteristics of patients and classification criteria at baseline

CharacteristicAll (n=118)SpA (n=51)Non-SpA (n=48)p Value*Not classified (n=19)*
Sex ratio, men/women0.60.50.5NS1.1
Age at inclusion in years, median (minimum-maximum)40.3 (18.2–85.3)38.3 (18.5–68.5)41.6 (18.2–85.3)NS36.5 (19–58.3)
Median (minimum-maximum) disease duration at inclusion, years2.2 (0–20.4)2.2 (0.2–20.4)2.3 (0–20.3)NS1.9 (0.3–19.4)
Age at diagnosis in years, median (minimum-maximum)41.6 (19.3–85.9)39 (19.3–68.8)43.5 (20.1–85.9)NSNA
Primary inclusion criterion, n (%)
 IBP48 (41)23 (45)20 (42)NS5 (26)
 Arthritis/arthralgia38 (32)12 (24)18 (38)NS8 (42)
 Enthesitis/dactylitis12 (10)4 (8)5 (10)NS3 (16)
 HLAB27+ AAU20 (17)13 (25)5 (10)NS2 (11)
All manifestations, n (%)
 IBP73 (62)36 (71)25 (52)NS12 (63)
 Isolated inflammatory buttock pain19 (16)13 (25)4 (8)0.022 (11)
 Arthritis34 (29)16 (31)12 (25)NS6 (32)
 Inflammatory arthralgia33 (28)19 (37)8 (17)NS6 (32)
 Enthesitis49 (42)25 (49)18 (37)NS6 (32)
 Dactylitis5 (4)4 (8)0NS1 (5)
 Psoriasis26 (22)17 (33)8 (17)NS1 (5)
 IBD5 (4)4 (8)1 (2)NS0
 Family history of SpA25 (21)18 (35)5 (10)0.0012 (10)
 Efficacy of NSAIDs71 (60)36 (71)22 (46)0.0113 (68)
 HLAB27+ AAU20 (17)13 (25)5 (10)NS2 (11)
Radiological and laboratory findings
 HLA-B27, n positive/n tested (% positive)46/116 (40)26/51 (51)11/47 (23)0.0059/18 (50)
 Pelvic x-rays, n doubtful/n tested (% doubtful)22/113 (19)12/50 (24)8/47 (17)NS2/16 (13)
 Pelvic CT scan, n positive/n tested (% positive)5/23 (22)5/19 (26)0/7 (0)NS0/2 (0)
 Pelvic or lumbar MRI, n positive/n tested (% positive)17/83 (20)14/39 (36)3/34 (9)0.0060/10 (0)
Classification criteria, n (%)
 Amor criteria45 (38)31 (61)6 (12)<0.00018 (42)
 ESSG criteria63 (53)40 (78)18 (37)<0.00015 (26)
 Berlin criteria, n positive/n tested (% positive)§20/48 (42)14/23 (23)4 /20 (20)<0.00012 (11)
 Axial ASAS criteria, n positive/n tested (% positive)§21/48 (44)15/23 (65)4/20 (20)0.0032/5 (40)
 Peripheral ASAS criteria, n positive/n tested  (% positive)9/33 (27)6/12 (50)2/15 (13)0.041/6 (17)
  • See online supplement for explanation of primary inclusion criterion.

  • IBP was the primary inclusion criterion for 48 patients and it was a secondary inclusion criterion for 21/38 patients with arthritis, 5/12 patients with enthesitis and 12/20 patients with B27+ uveitis as the primary inclusion criterion.

  • * Comparison between SpA and non-SpA patients was performed with a t test or Kruskall–Wallis test depending on sample size for continuous and ordinal data, and by χ2 test (Fisher exact test, when appropriate) for categorical data.

  • Manifestations present and recorded at inclusion.

  • Manifestations retrieved from past medical history.

  • § Both ASAS axial and Berlin criteria were applied to patients for whom a pelvic MRI was available and presenting with IBP at baseline.

  • ASAS peripheral criteria were applied to patients with clinically confirmed peripheral manifestation at baseline.

  • AAU, acute anterior uveitis; ASAS, Assessment of SpondyloArthritis international Society; ESSG, European Spondylarthropathy Study Group; IBD, inflammatory bowel disease; IBP, inflammatory back pain; NSAIDs, non-steroidal anti-inflammatory drugs; SpA, spondyloarthritis.