Page 67 - Recognizing axial spondyloarthritis - Janneke de Winter

and high SPARCC scores.
Statistical analysis
Categorical data are presented as the number (percent), and continuous data are presented as the mean ± SD or as the median (interquartile range) as appropriate. The chi-square test and Mann-Whitney U test were used for comparing categorical and continuous data, respectively. Interreader agreement on positive/negative MRI of the SI joints was investigated using Cohen’s kappa coefficient and interpreted according to the standards of Landis and Koch (16). Interreader agreement on SPARCC scores was evaluated using intraclass correlation coefficients (ICCs). We performed all analyses in SPSS version 24.0.
RESULTS
Study participants
In total, we evaluated 141 MRIs of the SI joints of 47 healthy participants from the Maasstad MRI project, matched with 47 patients with axial SpA with MRIs positive for sacroiliitis and 47 controls with chronic back pain irrespective of MRI outcome from the SPACE cohort. We also included MRIs of the SI joints of 24 runners from the Maasstad MRI project and 7 women with postpartum back pain (4 from the Maasstad MRI project and 3 from the SPACE cohort). The baseline characteristics of the study population are shown in Table 1.
Scoring agreement
The 3 readers agreed moderately well on the absence or presence of BME (absolute agreement within the 3 reader pairs 75%, 76%, and 80%, respectively; Cohen’s k = 0.48, 0.50, and 0.59, respectively). Readers correlated far better on absolute SPARCC scores (ICCs of 0.82, 0.82, and 0.96, respectively).
Scoring results
Scoring according to the ASAS definition
Figure 1 shows the proportion of subjects with MRIs positive for sacroiliitis according to the ASAS definition in the different groups. Of the 47 healthy participants, 11 (23.4%) had a positive MRI. Of the 47 positive controls with axial SpA, 43 (91.5%) had a positive MRI, and of the 47 controls with chronic back pain, only 3 (6.4%) had a positive MRI. Of the 24 runners, 3 (12.5%) had a positive MRI, and of the 7 women with postpartum back pain, 4 (57.1%) had a positive MRI.
MRI IN HEALTHY INDIVIDUALS
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