Patients with chronic back pain of short duration from the SPACE cohort: which MRI structural lesions in the sacroiliac joints and inflammatory and structural lesions in the spine are most specific for axial spondyloarthritis?
To investigate the extent and performance of MRI lesions in the sacroiliac joint (MRI-SI) and spine (MRI-spine) in patients with suspected axial spondyloarthritis (axSpA).



MRI-SI/spine of patients with chronic back pain (onset <45 years) in the SPondyloArthritis Caught Early (SPACE) cohort were scored by two well-trained readers for inflammation, fatty lesions, erosions, sclerosis/ankylosis and syndesmophytes. MRI performances were tested against the Assessment of Spondyloarthritis international Society (ASAS) axSpA criteria (positive: imaging-arm+ or clinical-arm+; negative: possible axSpA (few spondyloarthritis (SpA) features present) or no SpA). Arbitrary cut-off levels for MRI lesions were set to assure at least 95% specificity (tested in the no SpA group).



In total 126 patients were ASAS criteria positive (73 imaging-arm+ (22 by modified New York criteria (mNY)+; 51 by MRI+mNY-); 53 clinical-arm+) and 161 were ASAS criteria negative (89 possible axSpA and 72 no SpA). On MRI-SI (n=287), at least three fatty lesions (or at least three erosions) were seen in 45.5 (63.6)% of mNY+ patients, 15.7 (47.1)% of MRI+mNY- patients and 15.1 (13.2)% of clinical-arm+ patients versus 3.4 (6.7)% of possible axSpA patients and 2.8 (4.2)% of no SpA patients. A combined rule (at least five fatty lesions and/or erosions) performed equally well. Sclerosis and ankylosis were too rare to analyse. On MRI-spine (n=284), at least five inflammatory lesions (or at least five fatty lesions) were seen in 27.3 (18.2)% of mNY+ patients, 13.7 (21.6)% of MRI+mNY- patients and 3.8 (1.9)% of clinical-arm+ patients versus 4.5 (6.7)% of possible SpA patients and 2.9 (4.3)% of no SpA patients.



The presence of (1) at least five fatty lesions and/or erosions on MRI-SI, (2) at least five inflammatory lesions or (3) at least five fatty lesions on MRI-spine allows an acceptable discrimination of axSpA and no SpA, while assuring >95% specificity.
Rheumatology Department, Leiden University Medical Center, Leiden, The Netherlands.
Manouk
M
de Hooge
Rheumatology Department, Leiden University Medical Center, Leiden, The Netherlands.
Rosaline
R
van den Berg
Rheumatology Department, Leiden University Medical Center, Leiden, The Netherlands Rheumatology Department, University Hospital La Paz, Madrid, Spain.
Victoria
V
Navarro-Compán
Radiology Department, Leiden University Medical Center, Leiden, The Netherlands.
Monique
M
Reijnierse
Rheumatology Department, Leiden University Medical Center, Leiden, The Netherlands.
Floris
F
van Gaalen
Rheumatology Department, Diakonhjemmet Hospital, Oslo, Norway.
Karen
K
Fagerli
Department of Clinical Immunology and Rheumatology, Amsterdam Medical Center, Amsterdam, The Netherlands.
Robert
R
Landewé
Rheumatology Department, Groene Hart Ziekenhuis, Gouda, The Netherlands.
Maikel
M
van Oosterhout
Rheumatology Unit, University of Padova, Padova, Italy.
Roberta
R
Ramonda
Rheumatology Department, Leiden University Medical Center, Leiden, The Netherlands.
Tom
T
Huizinga
Rheumatology Department, Leiden University Medical Center, Leiden, The Netherlands.
Désirée
0000-0002-5781-158X
D
van der Heijde
D000328:Adult; D001368:Axis, Cervical Vertebra / Q000000981:diagnostic imaging; D001416:Back Pain / Q000000981:diagnostic imaging* / Q000209:etiology / Q000473:pathology; D059350:Chronic Pain / Q000000981:diagnostic imaging* / Q000209:etiology / Q000473:pathology; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D012446:Sacroiliac Joint / Q000000981:diagnostic imaging / Q000473:pathology; D058566:Sacroiliitis / Q000150:complications / Q000000981:diagnostic imaging* / Q000473:pathology; D012680:Sensitivity and Specificity; D013131:Spine; D025241:Spondylarthritis / Q000150:complications / Q000000981:diagnostic imaging* / Q000473:pathology; D013997:Time Factors