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Extended report
Low-dose CT detects more progression of bone formation in comparison to conventional radiography in patients with ankylosing spondylitis: results from the SIAS cohort
  1. Anoek de Koning1,
  2. Freek de Bruin2,
  3. Rosaline van den Berg1,
  4. Sofia Ramiro1,
  5. Xenofon Baraliakos3,
  6. Juergen Braun3,
  7. Floris A van Gaalen1,
  8. Monique Reijnierse2,
  9. Désirée van der Heijde1
  1. 1 Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands
  2. 2 Department of Radiology, Leiden University Medical Center, Leiden, The Netherlands
  3. 3 Department of Rheumatology, Rheumazentrum Ruhrgebiet Herne, Herne, Germany
  1. Correspondence to Professor Désirée van der Heijde, Department of Rheumatology, Leiden University Medical Center, 2300 RC Leiden, The Netherlands; mail{at}


Objectives To compare the CT Syndesmophyte Score (CTSS) for low-dose CT (ldCT) with the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS) for conventional radiographs (CR) in patients with ankylosing spondylitis (AS).

Methods Patients with AS in the Sensitive Imaging in Ankylosing Spondylitis cohort had lateral cervical and lumbar spine CR and whole spine ldCT at baseline and 2 years. CR and ldCT images were scored by two readers, paired by patient, blinded to time order, per imaging modality. For the total score analysis, we used average scores of readers per corner on CR or quadrant on ldCT. For the syndesmophyte analysis we used individual reader and consensus scores, regarding new or growing syndesmophyte at the same corner/quadrant.

Results 50 patients were included in the syndesmophyte analysis and 37 in the total score analysis. Mean (SD) status scores for mSASSS (range 0–72) and CTSS (range 0–552) at baseline were 17.9 (13.8) and 161.6 (126.6), and mean progression was 2.4 (3.8) and 17.9 (22.1). Three times as many patients showed new or growing syndesmophytes at ≥3 quadrants on ldCT compared with ≥3 corners on CR for individual readers; for consensus this increased to five times. In 50 patients, 36 new or growing syndesmophytes are seen on CR compared with 151 on ldCT, most being found in the thoracic spine.

Conclusions ldCT, covering the whole spine, detects more progression in the form of new and growing syndesmophytes in patients with AS compared with CR, which is limited to the cervical and lumbar spine. Most progression occurred in the thoracic spine.

  • ankylosing spondylitis
  • outcomes research
  • spondyloarthritis

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  • Handling editor Tore K Kvien

  • Contributors DvdH designed the study. AdK, FdB, RvdB, SR performed the data analyses. XB, JB, FAvG, MR, RvdB performed the data collection. AdK, FdB prepared the first draft of the manuscript. All authors interpreted the results, commented on the draft manuscript and approved the final submission.

  • Funding The authors would like to thank the Dutch Rheumatism Association for providing a grant for the SIAS study. Reumafonds, 9-1-301.

  • Competing interests None declared.

  • Ethics approval Medical Ethics Committee in Leiden and in Herne.

  • Provenance and peer review Not commissioned; externally peer reviewed.