OP0114 Low dose computed tomography detects more progression of bone formation in comparison to conventional radiography in patients with ankylosing spondylitis: results from the sias cohort
Authors: A de Koning, F de Bruin, R van den Berg, S Ramiro, X Baraliakos, J Braun, FA van Gaalen, M Reijnierse, D van der Heijde
Journal: Annals of the Rheumatic Diseases (2017)

<h3>Background</h3> Recently we presented the good interreader reliability and sensitivity to detect changes with a newly developed scoring method of bone formation on low dose computed tomography (LD-CT) of the whole spine in patients (pts) with Ankylosing Spondylitis (AS)<sup>1</sup>. Next step in the validation is the comparison with conventional radiographs (CR). <h3>Objectives</h3> To compare the assessment of syndesmophyte formation and growth on CR and LD-CT in pts with AS. <h3>Methods</h3> Pts from the SIAS (Sensitive Imaging of Axial Spondyloarthritis) cohort from Leiden and Herne were analysed. Inclusion criteria were modified NY criteria, ≥1 syndesmophytes on either the cervical and/or lumbar spine on CR, and ≥1 inflammatory lesion on MRI-spine. Pts had CR of the lateral cervical and lumbar spine and LD-CT (approximately 2–3mSV) of the entire spine at baseline and two years. Two readers independently assessed both CR and CT in separate sessions. Images were paired per patient, blinded to time order, patient information, and result of the other imaging technique. CR was assessed using the mSASSS scoring method. On CT, syndesmophytes were scored in the coronal and sagittal planes for all "corners" per view, thus scoring 8 "corners" per vertebral unit. Syndesmophytes were scored as absent (score 0), &lt;50% of the intervertebral disc height (IVDH) (score 1), ≥50% of the IVDH but no bridging (score 2) or as bridging the IVDH (score 3)<sup>1.</sup> The formation of new syndesmophytes (CR score 0 or 1→2 or 3, CT 0→1 or 2 or 3) and growth of existing syndesmophytes (CR score 2→3, CT 1→2 or 3, or 2→3) and the combination of both was calculated per vertebral corner. Consensus about each of these outcomes was defined by agreement of both readers on the same vertebral level. Data of CR and CT was compared per reader and for the consensus score. <h3>Results</h3> 50 patients (mean age 48.6 years; 84% male; 80% HLA-B27) were included in the analysis. The number (%) of pts with newly formed, growth or combined newly formed and growth of syndesmophytes for separate readers and consensus score are presented in table 1. In all comparisons, CT detected more patients with progression. This is especially apparent in case of growth and for cut-offs of a higher number of (newly formed or growth of) syndesmophytes per patient. E.g. with the strictest comparison of the consensus score for both CR and CT, 30% of the patients show bony proliferation (newly formed and growth) at ≥3 sites on CT compared with only 6% on CR. <h3>Conclusions</h3> LD-CT covering the whole spine, is a more sensitive method for assessing the formation and growth of syndesmophytes than CR which is limited to cervical and lumbar spine in pts with AS and is a promising method of assessment for clinical research. <h3>References</h3> de Bruin F et al. A&amp;R 2016; 68 (suppl 10). <h3>Disclosure of Interest</h3> None declared