Background The pathogenesis of new bone formation in ankylosing spondylitis (AS), is largely unknown. One emerging hypothesis implies that inflammation and fatty degeneration (Fat), play a role in syndesmophyte formation.
Objectives Using data from the golimumab (GLM) AS study (GO-RAISE), we assessed how fatty and inflammatory lesions as detected by magnetic resonance imaging (MRI) related to new bone formation on x-rays.
Methods In GO-RAISE, 98 of 356 patients with definite AS, BASDAI ≥4, who had been randomized to SC GLM 50mg, 100mg, or PBO q4wks and who underwent conventional radiography of the cervical and lumbar spine at baseline (BL), wks104 and 208, also had serial spine MRI scans taken in the sagittal plane using 1.5T scanners with T1 and short tau inversion recovery (STIR) sequences at BL, wk14, and wk104 in specialized centers. MRI reads were performed by two readers blinded to treatment and time order of the images, who evaluated vertebral corners on x-rays for syndesmophytes/bridging and on MRIs for active inflammation (Infl) and Fat on the level of predefined vertebral units (VU), including notation of the location by VU quadrant (upper, lower, anterior, posterior). The present analysis focused on the percentage of VU quadrants (VUq) with new syndesmophytes/bridging visible on x-ray, and on how this percentage varied by presence or absence of prior Infl or Fat in the corresponding VUq at BL and wk14.
Results There were 91 patients in the substudy representing 4,368 VUq with evaluable images. Using only concordant scores of both readers, the percentage of VUq with new syndesmophytes at wk 104 or 208 was greater if Fat at BL and persisted wk14. New syndesmophytes were significantly more likely to develop in VUq with Fat present at both, BL and wk14, in comparison to those that did not have persistent fat (odds ratios for wk208 syndesmophyte/bridging Reader 1:, 3.27; Reader 2: 2.42). The combined presence of Fat and Infl lesions in a VUq at BL further increased the chance of new syndesmophytes which developed at the corresponding VUq (6.6% and 2.6% of corners with new syndesmophytes at wk104 for VU with BL Fat+Infl/wk14 Fat vs. BL Fat-no Infl/wk14 Fat, respectively. Conversely, for VUq without Fat or Infl at BL but wk14 Fat present, only 0-1.5% of VUq developed new syndesmophytes later.
Conclusions This detailed analysis of radiographs and MRI at the vertebral level of the spine supports the hypothesis that in the spine of pts with AS, fatty degeneration and active inflammation favor progression towards subsequent growth of syndesmophytes and ankylosis.
Disclosure of Interest X. Baraliakos Grant/research support: Janssen R & D, LLC, K.-G. Hermann Grant/research support: Janssen R & D, LLC, S. Xu Employee of: Janssen R & D, LLC, B. Hsu Employee of: Janssen R & D, LLC, J. Braun Grant/research support: Janssen R & D, LLC