Background The definition of a “positive” or “negative” MRI of the SIJ-joints (MRI-SIJ) according to ASAS is recommended for use in daily practice1. However, in several clinical trials the Spondyloarthritis Research Consortium of Canada (SPARCC)-score is used2. It would be useful to know which SPARCC-score is the best cut-off value as surrogate for the ASAS definition.
Objectives To investigate which SPARCC cut-off value best matches the ASAS definition for a positive MRI-SIJ.
Methods All MRI-SIJs of two time points of patients included in the SPondyloArthritis Caught Early (SPACE)-cohort in the Leiden University Medical Center (LUMC) were scored independently by 3 readers. The readers, blinded to the time sequence, scored the MRI-SIJs according to the ASAS definition (ASAS-pos) and the SPARCC-score. An MRI-SIJ was marked ASAS-pos if 2/3 readers scored positive. In this analysis, mean SPARCC-scores of the readers that also scored ASAS-pos for that particular case were used. Cross-tabs were used to analyse agreement between several SPARCC-score cut-off values (≥1, ≥2, ≥3 and ≥4) and ASAS-pos, which served as gold standard in this comparison.
Results All available MRI-SIJs were used (n=238 in total; n=148 baseline MRI-SIJs; n=90 follow-up MRI-SIJs). The results of the different tested SPARCC cut-off values are presented in the table. A SPARCC cut-off value ≥2 resulted in 11 (4.6%) false-positive classifications and no false-negative classifications compared to ASAS-pos, while a cut-off of ≥4 resulted in 9 (3.8%) false-negative and 1 (0.4%) false-positive classifications. A SPARCC cut-off value ≥3 resulted in 1 (0.4%) false-positive classification and 4 (1.7%) false-negative classifications. We found very similar results if baseline MRI-SIJs and follow-up MRI-SIJs were analysed separately.
Conclusions SPARCC cut-off values of ≥2, ≥3 or ≥4 have all high percentages of correctly classified patients (95.4%, 97.9% and 95.8%, respectively). A SPARCC cut-off value ≥3 shows most balanced misclassification and the highest agreement with the ASAS definition for positive MRI-SIJ.
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Disclosure of Interest None Declared