Page 73 - Recognizing axial spondyloarthritis - Janneke de Winter

A final strength of this study is that it combined several groups of individuals with and individuals without symptoms in one setting. It allows us to speculate that runners may not show higher rates of MRI positivity than asymptomatic individuals, but that postpartum patients with back pain potentially do.
Our study also has limitations. First, the clinical and demographic information on healthy participants, runners, and women with postpartum back pain was rather limited. Individuals who we considered asymptomatic could still have had SpA- related symptoms that would have been revealed if more data had been obtained according to a study protocol (such as the SPACE protocol). It is unlikely that the 25% of MRIs that were classified as positive were related to undiagnosed or early axial SpA, since individuals with any sign of current or past back pain were excluded. Second, the groups of runners and women with postpartum back pain were rather small, due to reasons of convenience, and therefore conclusions should be drawn with caution. Third, this study focused exclusively on inflammatory lesions. To date, however, it is unclear if potential refining of SpA-specific inflammatory lesions or alternatively combining information on inflammation and structural changes may help in the diagnosis of axial SpA (14). Fourth, the arbitrary threshold of back pain starting within 3 months after delivery in the group of women with postpartum back pain was not supported by the literature. However, it was our aim to include only women in whom incident back pain was most likely related to delivery. Fifth, in this study, different MRI scanners were used, which in theory may violate the blinding of the readers and thus contribute to a biased result, but several MRI scanners were used across subgroups, and the same type of MRI scanner was used in different subgroups, so we conclude that such a form of expectation bias is highly unlikely.
Finally, readers agreed only moderately on the presence or absence of BME. Interreader agreement is dependent on several factors, including the quality of the images, the presence of a unique protocol, and the level of training of the readers. This study included patients and individuals from different sources, scanned with different machines, by different technicians, using slightly different protocols, as in common clinical practice. This level of variability has an impact on measurement error. While readers were trained in a standardized manner, the variability in the quality of the images likely resulted in kappa values that were slightly lower than values obtained in, for example, randomized controlled trials or cohort studies conducted under a protocol. Given these limitations and considering the high level of interreader agreement on SPARCC scores, the interreader agreement in this study is still very acceptable.
We conclude that a substantial proportion of healthy and asymptomatic individuals, runners, and women with postpartum back pain may have positive findings on MRI of the SI joints that are highly suggestive, but not reflective, of axial SpA. Patients with axial SpA have more extensive lesions (reflected by SPARCC scores ≥5 and the presence of deep lesions) than healthy, asymptomatic individuals.
MRI IN HEALTHY INDIVIDUALS
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