Diagnostic utility of whole spine and thoracic spine MRI corner inflammatory lesions in axial spondyloarthritis.

Background: The presence of > 3 corner inflammatory lesions has been proposed as the definition of a positive spinal magnetic resonance imaging (MRI) for axial spondyloarthritis (axSpA), but subsequent studies showed inconclusive findings. Our objective was to evaluate whether locations of corner inflammatory lesions (CILs) would affect the diagnostic utility of MRI in axSpA. Method: Two groups were consecutively recruited from eight rheumatology centers in Hong Kong. The 'axSpA' group included 369 participants with a known diagnosis of axSpA. The 'non-specific back pain' (NSBP) control group consisted of 117 participants. Clinical, biochemical, and radiological parameters were collected and all patients underwent MRI of the spine and sacroiliac joints. CILs were assessed based on their locations (cervical, thoracic or lumbar) to determine the optimal cutoff for diagnosis. Results: The cutoff of >= 5 whole spine CILs (W-CILs) and >= 3 thoracic spine CILs (T-CILs) had comparable specificity to MRI sacroiliitis. Of 85/369 axSpA patients without sacroiliitis on conventional radiograph or MRI, 7 had >= 5 W-CILs and 11 had >= 3 T-CILs. Incorporating the proposed cutoffs into Assessment of SpondyloArthritis international Society axSpA criteria, >= 5 W-CILs and >= 3 T-CILs had similar performance when added to the imaging criteria for sacroiliitis (sensitivity 0.79 versus 0.80, specificity 0.92 versus 0.91). Conclusion: Spinal MRI provided little incremental diagnostic value in unselected axSpA patients. However, in patients without sacroiliitis on MRI or radiographs, 8-13% might be diagnosed by spinal MRI. Thoracic and whole spine MRI had similar diagnostic performance using the proposed cutoff of >= 5 W-CILs and >= 3 T-CILs.