Table 1

Baseline characteristics of patients with chronic back pain in the SPACE cohort and stratified by total number of SpA features after medical history taking, physical examination and measurement of acute phase reactants but before HLA-B27 testing and imaging

CharacteristicAll patients, n=500Patients with ≤1 feature, n=159Patients with 2 features, n=143Patients with 3 features, n=79Patients with ≥4 features, n=119
Age, years29.3 (8.3)29.7 (8.8)28.8 (8.3)29.1 (8.0)29.5 (7.9)
Symptom duration, months13.4 (7.4)12.9 (7.3)14.6 (7.7)13.3 (7.0)12.7 (7.4)
Male185 (37)51 (32)56 (39)24 (30)54 (45)
IBP329 (66)43 (27)103 (72)71 (90)112 (94)
Good response to NSAIDs*208 (42)13 (8)50 (35)47 (60)98 (82)
Positive family history SpA†206 (41)26 (16)57 (40)43 (54)80 (67)
Peripheral arthritis‡74 (15)2 (1)15 (11)11 (14)46 (39)
Dactylitis‡26 (5)0 (0)1 (1)3 (4)22 (19)
Enthesitis‡108 (22)4 (3)12 (8)15 (19)77 (65)
Anterior uveitis‡38 (8)2 (1)9 (6)6 (8)21 (18)
IBD‡35 (7)8 (5)7 (5)7 (9)13 (11)
Psoriasis‡57 (11)2 (1)7 (5)8 (10)40 (34)
Elevated CRP (mg/L)/ESR (mm)§132 (26)12 (8)25 (18)26 (33)69 (58)
HLA-B27 positive198 (40)36 (23)65 (46)41 (52)56 (47)
Imaging¶
 X-SI positive58 (12)9 (6)16 (11)5 (6)28 (24)
 MRI-SI positive146 (29)33 (21)37 (26)29 (37)47 (40)
 Diagnosis of axSpA**250 (50)38 (24)62 (43)49 (62)101 (85)
  • Results are presented as mean±SD or number (%).

  • *Back pain not present anymore or is much better 24–48 hours after a full dose of NSAID.

  • †Presence in first-degree or second-degree relatives of any of the following: ankylosing spondylitis, psoriasis, acute anterior uveitis, reactive arthritis or IBD.

  • ‡Past or present condition, either confirmed or diagnosed by a physician.

  • §Values greater than the upper limit of normal.

  • ¶According to global assessment radiologist (local reading).

  • **Diagnosis based on information after full diagnostic workup: medical history, physical examination, imaging and laboratory testing.

  • AxSpA, axial spondyloarthritis; CRP, C reactive protein; ESR, erythrocyte sedimentation rate; HLA-B27, human leucocyte antigen B27; IBD, inflammatory bowel disease; IBP, inflammatory back pain; MRI-SI, MRI of sacroiliac joints; NSAIDs, non-steroidal anti-inflammatory drugs; SpA, spondyloarthritis; SPACE, SPondyloArthritis Caught Early; X-SI, radiograph of sacroiliac joints.