Proposal of simplified CT syndesmophyte score (sCTSS) and comparison with CTSS in patients with ankylosing spondylitis

The CT syndesmophyte score (CTSS) can evaluate spinal progression more precisely than mSASSS in ankylosing spondylitis (AS); however, it is complex and time consuming. Here, we propose a simplified CTSS (sCTSS) for measuring spinal structural changes in AS. Patients with AS were recruited from a single tertiary hospital. Baseline and 2-year follow-up whole spine CT images were used to calculate CTSS and sCTSS. The sCTSS used the anterior and posterior vertebral corners, and ranged 0–184. Intraclass correlation coefficients (ICC) were calculated, as well as the smallest detectable changes. Fifty AS patients were included. For reader 1, the mean sCTSS at baseline and 2-year follow-up were 11.7 ± 14.6 and 15.8 ± 16.1, whereas those for reader 2 were 12.0 ± 12.5 and 15.8 ± 15.7, respectively. The ICCs for CTSS at baseline and at 2-year follow-up were 0.97 (95% confidence interval [CI] 0.96–0.99) and 0.98 (0.97–0.99), respectively, and that for changes over the 2 years was 0.48 (95% CI 0.23–0.67). For sCTSS, the ICCs were 0.96 (95% CI 0.92–0.97), 0.97 (95% CI 0.94–0.98), and 0.58 (95% CI 0.36–0.74), respectively. Detection rates for syndesmophyte progression were comparable between CTSS and sCTSS. The detection rate for syndesmophytes on only lateral side was 13.2 and 11.4%, and 11.4 and 15.2% at baseline and 2-year follow-up (reader 1 and 2). sCTSS and CTSS showed similar detection rates for syndesmophyte progression. sCTSS may be a reliable method for evaluating spinal structural damage in AS.