OBJECTIVES: To compare magnetic resonance imaging (MRI) and conventional radiography of sacroiliac joints (SIJs) for detection of structural lesions typical for axial spondyloarthritis (axSpA).
METHODS: Adult patients from the Assessment of SpondyloArthritis international Society (ASAS) cohort with symptoms suggestive of axSpA and both SIJ MRIs and radiographs available for central reading were included. Radiographs were evaluated by three readers according to the modified New York (mNY) criteria grading system. The presence of structural damage on radiographs was defined as 1) fulfilment of the radiographic mNY criterion and 2) additionally, a lower threshold for sacroiliitis of at least grade 2 unilaterally. MRI scans were assessed for the presence of structural changes indicative of axSpA by 7 readers. Diagnostic performance (sensitivity-Se, specificity-Sp, positive and negative predictive values-PPV and NPV-and positive and negative likelihood ratios-LR+ and LR-) of MRI and radiographs (vs rheumatologist's diagnosis of axSpA) were calculated.
RESULTS: Overall, 183 patients were included, 135 (73.7%) were diagnosed with axSpA. Structural lesions indicative of axSpA on MRI had Se 38.5%, Sp 91.7%, PPV 92.9%, NPV 34.6%, LR + 4.62, LR- 0.67. Sacroiliitis according to the mNY criteria had Se 54.8%, Sp 70.8%, PPV 84.1%, NPV 35.8%, positive LR + 1.88, LR- 0.64. Radiographic sacroiliitis of at least grade 2 unilaterally had Sn 65.2%, Sp 50.0%, PPV 78.6%, NPV 33.8%, LR + 1.30, LR- 0.69.
CONCLUSION: Structural lesions of SIJ detected by MRI demonstrated better diagnostic performance and better inter-reader reliability compared with conventional radiography.