Differences in spinal structural lesions between patients with early axSpA and non-axSpA chronic back pain: 2-year SPACE cohort results

Objectives: To compare spinal structural lesions on radiography and magnetic resonance imaging (MRI) over 2 years, between patients with early axial spondyloarthritis (axSpA) and non-axSpA chronic back pain. Methods: Patients from the SPACE cohort with available radiography or MRI at both baseline and 2-year were included. Spinal lesions on radiography were assessed by the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS), corner MRI lesions by the modified Canada-Denmark scoring system. Baseline spinal structural lesions and 2-year changes were compared between axSpA and non-axSpA. Generalized Estimating Equations were used to assess the change over 2-year, adjusting for age, sex, NSAID-use, and diagnosis. Results: Radiography data from 318 patients (67% axSpA), MRI data from 351 patients (69% axSpA) were included. At baseline, the mean (SD) mSASSS was 0.6 (1.1) for both axSpA and non-axSpA. Over 2 years, mSASSS progression was minimal (0.01 units/year) in both groups. On MRI, axSpA patients had a mean of 1.4 (2.9) total structural lesions compared with 0.7 (2) in non-axSpA at baseline (p= 0.12). Significant 2Y increase in structural lesions [0.5 (1.8)] was mainly due to fat lesions [0.5 (1.6)] in axSpA. On MRI, fat lesions changed at a rate of 0.16 units/year in axSpA (p= 0.002), and -0.02 units/year in non-axSpA (p= 0.70). Conclusion: Over 2 years, spinal structural damage typical for axSpA progressed minimally on radiography in axSpA and non-axSpA. On MRI, axSpA showed a significant increase in fat lesions, while non-axSpA had no progression. Fat lesions may be important to assess spinal changes from early disease onwards.