Table 3

Mean number (percentage) of subjects with a positive sacroiliac joint MRI, positive spine MRI and positive combined MRI, compared with clinical classification as gold standard

CohortA (n=62)B (n=88)
Groupnr-axSpAASNSBPHCnr-axSpAASNSBP
Number of subjects1991420312433
MRI positivity vs clinical classification
SIJ MRI + with confidence range 5–1014.5 (76.3)9.0 (100.0)1.0 (7.1)1.5 (7.5)14.3 (46.0)24.0 (100.0)5.3 (15.9)
SIJ MRI + with confidence range 8–1012.3 (64.5)8.8 (97.2)0 (0)0.5 (2.5)10.5 (33.9)23.0 (95.8)2.8 (8.3)
Spine MRI + with confidence range 5–109.8 (51.3)6.5 (72.2)4.8 (33.9)5.3 (26.3)15.0 (48.4)17.5 (72.9)9.3 (28.0)
Spine MRI + with confidence range 8–106.8 (35.5)5.0 (55.6)2.0 (14.3)1.5 (7.5)9.8 (31.5)15.0 (62.5)3.5 (10.6)
Spine MRI + showing ≥3 CIL*8.3 (43.4)5.5 (61.1)3.5 (25.0)3.5 (17.5)7.8 (25.0)10.3 (42.7)3.5 (10.6)
Spine MRI + showing ≥5 CFL*6.0 (31.6)4.3 (47.2)4.5 (32.1)4.8 (23.8)13.5 (43.5)13.0 (54.2)8.0 (24.2)
Combined MRI + with confidence range 5–1017.0 (89.5)9.0 (100.0)4.5 (32.1)5.0 (25.0)21.0 (67.7)23.8 (99.0)8.0 (24.2)
Combined MRI + with confidence range 8–1015.3 (80.3)8.8 (97.2)2.0 (14.3)2.8 (13.8)15.5 (50.0)23.0 (95.8)5.0 (15.2)
  • MRI data are the mean number (percentage) of subjects over four readers.

  • Confidence range 5–10 reflects a moderate to high level of confidence with a MRI-based classification of spondyloarthritis. Confidence range 8–10 indicates a high level of confidence with a MRI-based classification of spondyloarthritis.

  • *CIL/CFL on ≥1 spinal MRI slices.

  • AS, ankylosing spondylitis; CIL, corner inflammatory lesion (in central spinal MRI slices); CFL, corner fatty lesion (in central spinal MRI slices); HC, healthy control; nr-axSpA, non-radiographic axial spondyloarthritis; NSBP, non-specific back pain; SIJ, sacroiliac joint.