Background/Purpose: The assessment of structural damage progression is an important part of outcome assessment in axial SpA (axSpA). In order to test whether interventions can potentially inhibit structural damage progression, an outcome measurement instrument that is sensitive to change is essential. We aimed at comparing the sensitivity to change of different methods assessing structural lesions on conventional radiographs and on MRI of the sacroiliac joints (SIJ) and the spine in patients with early axSpA.

Methods: Patients with chronic back pain (≥3 months; ≤2 years; onset < 45 years) from the SPondyloArthritis Caught Early (SPACE) cohort received a rheumatologist’s diagnosis of axSpA or non-axSpA after two years follow-up. Only patients with an axSpA diagnosis were included in this analysis. Radiographs and MRIs of the SIJ (MRI-SIJ) and spine (MRI-spine) were obtained at baseline, 3 months, 1 and 2 years of follow-up, and scored for structural lesions (Table 1) by at least 2 and a maximum of 3 readers in two reading rounds. All patients with ≥1 score from ≥1 reader from ≥1 timepoint from ≥1 reading round were included in the analysis. To allow comparison across outcomes, the standardized rate of change was calculated using integrated multilevel generalized estimating equations while considering the individual readers and reading round. To facilitate the comparison across imaging outcomes, the relative standardized rate of change was calculated by dividing the standardized rate of change of the imaging outcome by that of an outcome chosen as the reference. Additionally, one outcome was chosen as a reference for each anatomic site for comparison of the outcomes at the site level. The imaging outcome with the highest standardized rate of change per year was chosen as reference, both overall and for each anatomic site. A sensitivity analysis was conducted in patients with all scores from ≥2 timepoints available.

Results: In total, 332 patients with axSpA (mean age 30 (SD 8) years; 53% males) were included in the main analysis, of which 295 (89%) had all scores from ≥2 timepoints. The yearly (relative) standardized rate of change of each imaging outcome is shown in Table 1. From all outcomes, MRI-SIJ total structural lesions without sclerosis had the highest standardized rate of change per year, also meaning that SIJ structural lesions were more sensitive to change than spinal lesions. From the spine outcomes, MRI total fat lesions had highest standardized rate of change. In addition, total fat lesions were highly sensitive both in the SIJ and spine (Figure 1). In contrast, outcomes with erosions or (partial) ankylosis were less sensitive to change. The sensitivity analysis showed similar findings.

Conclusion: Compared to MRI-spine and radiographs SIJ and spine, MRI-SIJ structural lesions are generally most sensitive to change. Fat lesions are most sensitive to change, especially on the MRI-SIJ. Erosions and ankylosis are less sensitive outcomes.

Figure 1. Relative rate of mean change using a reference per anatomic site with total structural lesions without sclerosis set as the reference. The total of structural lesions in the MRI of the sacroiliac joints is a sum of erosions, fat lesions, (partial) ankylosis, and sclerosis. The total of structural lesions in the MRI of the spine is a sum of erosions, fat lesions, bone spurs and ankylosis. mNY, modified New York criteria; No., number; mSASSS, modified Stoke Ankylosing Spondylitis Spinal Score.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/which-instrument-measuring-structural-damage-progression-in-axial-spa-is-most-sensitive-to-change-analyses-from-the-spondyloarthritis-caught-early-cohort/