0394: In Radiographic Axial Spondyloarthritis Spinal Mobility Measures Correlate Well with the Whole Spine CT Syndesmophyte Score (CTSS)

Rosalinde Stal¹, Sofia Ramiro¹, Xenofon Baraliakos², Juergen Braun³, Monique Reijnierse¹, Rosaline van den Berg¹, Désirée van der Heijde⁴ and floris van Gaalen¹, ¹Leiden University Medical Center, Leiden, Netherlands, ²Rheumazentrum Ruhrgebiet Herne, Herne, Germany, ³Rheumazentrum Ruhrgebiet, Herne, Germany, ⁴Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands, Leiden, Netherlands

Background/Purpose: The modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) is the best validated and widely used method for assessing radiographic progression in axial spondyloarthritis (axSpA) and is known to correlate with spinal mobility measures. The recently developed Computed Tomography Syndesmophyte Score (CTSS) assesses syndesmophyte presence and size on whole spine low dose CT but correlation with spinal mobility measures has not been investigated.

Methods: AxSpA patients from the SIAS cohort meet the Modified New York criteria and have ≥1 and < 18 syndesmophytes on mSASSS at baseline. Correlations were tested for each of 8 spinal mobility measures (occiput to wall distance (OWD), tragus to wall distance (TWD) (calculated as OWD+11.1), lateral spinal flexion, mSchober, cervical rotation, chest expansion, intermalleolar distance (IMD) and Bath Ankylosing Spondylitis Metrology Index (BASMI)) with CTSS and mSASSS using Spearman's rank correlation coefficients. A cumulative probability plot shows the relationship between BASMI and CTSS on the patient level.

Results: Forty-one patients (mean age 48 (SD 9), 83% male, 85% HLA-B27+) had scores for both CTSS and mSASSS and all spinal mobility measures. The CTSS showed substantial correlation with OWD/TWD (r_s=0.68), lateral spinal flexion (r_s=-0.72), cervical rotation (r_s=-0.61) and BASMI (r_s=0.73)(figure 1). Patient level data is shown for BASMI with CTSS (figure 2). CTSS correlated moderately with the mSchober (r_s=-0.46) and chest expansion (r_s=-0.52) but not with IMD (r_s=-0.12). The mSASSS also had significant correlations with all measures except IMD but all correlations were lower than with CTSS.

Conclusion: The CTSS correlates with 7 out of 8 spinal mobility measures. Lateral spinal flexion and total BASMI correlated best with both methods. The lack of correlation with IMD was expected since hip range of motion is not affected by spinal structural changes. These observed correlations compared favourably to mSASSS and support the construct validity of the CTSS.

Figure 1: Spearman correlations for eight spinal mobility measures with the CTSS and mSASSS
Correlations are color coded according to the strength of the association.

Figure 2: cumulative probability plot showing patient-level data of the BASMI and the CTSS. Patients are ordered on the X-axis according to their CTSS.
The value of the CTSS is shown on the left Y-axis, and the value of the BASMI on the right Y-axis.
Disclosures: R. Stal, None; S. Ramiro, AbbVie/Abbott, Eli Lilly, Galapagos, Merck/MSD, Novartis, Pfizer, UCB, Sanofi; X. Baraliakos, AbbVie, Lilly, Galapagos, MSD, Novartis, Pfizer, UCB, Bristol-Myers Squibb, Janssen, Roche, Sandoz, Sanofi; J. Braun, None; M. Reijnierse, ASAS, International Skeletal Society; R. van den Berg, None; D. van der Heijde, AbbVie, Bayer, BMS, Cyxone, Eisai, Galapagos, Gilead, Glaxo-Smith-Kline, Janssen, Novartis, Pfizer, UCB, Imaging Rheumatology bv, Lilly; f. van Gaalen, Stichting vrienden van Sole Mio, Stichting ASAS, Jacobus stichting, Novartis, UCB, MSD, AbbVie, Bristol Myers Squibb, Eli Lilly.