Magnetic resonance imaging assessment of ASAS-defined active sacroiliitis in patients with inflammatory back pain and suspected axial spondyloarthritis: a study of reliability

Objective The main purpose was to investigate the intra-and inter-rater reliability of the Assessment of SpondyloArthritis international Society (ASAS) definition of positive MRI for active sacroiliitis (ASAS-positive MRI), in a sample of patients with inflammatory back pain (IBP) and suspected axial spondyloarthritis (axSpA), who underwent sacroiliac joints (SIJ) MRI. We also evaluated the intra-and inter-rater reliability for the detection of the recently ASAS-refined findings indicating inflammatory activity. Methods We retrospectively identified 105 consecutive patients with IBP and suspected axSpA who underwent SIJ MRI. Two radiologists in two distinct reading sessions assessed the prevalence of ASAS-positive MRI and of ASAS-defined signs of inflammatory activity. We determined the intra-rater and inter-rater reliability of the above-mentioned variables by means of prevalence-adjusted bias-adjusted kappa (PABAK) statistic, and verified whether there was any significant difference in providing the diagnosis of ASAS-positive MRI on an inter-rater basis (McNemar test). Results We observed substantial reliability in assessing a SIJ MRI as ASAS-positive both on intra-rater basis (PABAK ranging 0.70-0.77) and inter-rater basis (PABAK 0.71 for the first reading, and 0.64 for the second reading). No significant difference in the rate of diagnosis between raters was found (p>0.99 for both reading sets). Intra-rater and inter-rater reliability for inflammatory activity signs ranged from moderate to almost perfect. Conclusion The substantial intra-and inter-rater reliability in assessing the ASAS-positive MRI supports its use for classification purposes. The variable reliability of inflammatory activity signs suggests they are suboptimal as a complement to the current definition of ASAS-positive MRI.

Automated summary

The study found substantial intra-and inter-rater reliability in assessing ASAS-positive MRI in patients with IBP and suspected axSpA, while the reliability of inflammatory activity signs varied.