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.
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 ≤45 years and had a Bath Ankylosing Spondylitis Disease Activity Index score ≥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.
Diagnostic utility was optimal when ≥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 ≥1 CIL, but only 2 controls had >2 CIL.
Diagnostic utility of STIR MRI for AS is optimal when ≥2 CIL are present. A single CIL can be found in up to 26% of healthy individuals.