Sensitivity and specificity of spinal inflammatory lesions assessed by whole-body magnetic resonance imaging in patients with ankylosing spondylitis or recent-onset inflammatory back pain.

Objective: To determine the diagnostic utility of different spinal inflammatory lesions assessed by whole-body magnetic resonance imaging (MRI) in patients with ankylosing spondylitis (AS) or with recent-onset inflammatory back pain (IBP) compared with healthy controls.

Methods: We scanned 35 consecutive patients with AS fulfilling the modified New York criteria, 25 patients with IBP of <24 months' duration (both groups were age < or =45 years and had a Bath Ankylosing Spondylitis Disease Activity Index score > or =4), and 35 healthy age- and sex-matched volunteers using whole-body MRI STIR sequences of the spine. MRIs were independently assessed in random order by 3 readers blinded to patient identity. Inflammatory spinal lesions were recorded consistent with definitions proposed by the Canada/Denmark International MRI Working Group: vertebral corner inflammatory lesions (CIL) and noncorner inflammatory lesions in central sagittal slices and lateral inflammatory lesions (LIL) in lateral slices. Concordantly scored lesions for the 3 possible reader pairs were used in the analysis of sensitivity, specificity, likelihood ratios (LRs), and areas under the curve for the entire spine and by spinal segment.

Results: Diagnostic utility was optimal when > or =2 CIL were recorded (for patients with AS, values for sensitivity, specificity, and positive LR were 69%, 94%, and 12, respectively, and for patients with IBP were 32%, 96%, and 8, respectively). LIL had high specificity (97%) but low sensitivity (31%). Nine controls had > or =1 CIL, but only 2 controls had >2 CIL.

Conclusion: Diagnostic utility of STIR MRI for AS is optimal when > or =2 CIL are present. A single CIL can be found in up to 26% of healthy individuals.