Background/Purpose: Radiographic damage is one of the core outcomes recommended by the Assessment in Spondyloarthritis international Society (ASAS) for follow-up of patients with axial SpA. So far, the evolution of radiographic damage over a long period has not been described in detail. We aimed to describe the evolution of radiographic abnormalities over time in a prevalence cohort of patients with ankylosing spondylitis (AS).

 Methods: The modified Stoke AS Spine Score (mSASSS) was calculated using 2-yearly radiographs of patients followed for 12 years in the Outcome in AS International Study (OASIS). Two readers independently scored the x-rays and scores were averaged. Status and progression scores (2- and 12-year-progression) were computed for patients with at least one 2-year interval available (n=186) and for those with an mSASSS at 12-years (n=68). New syndesmophytes at vertebral corners (VCs) “at risk” (i.e. without a previous syndesmophyte or bridge) were computed. Radiographic progression over time was investigated using generalized estimating equations. Relevant interactions with time were explored. Time was modeled in different forms (linear and non-linear) and the best model fit was assessed using the quasi-likelihood information criterion.

 Results: 809 radiographs of 186 patients (70% males, mean (SD) age 43(12) years, mean disease duration 11.0(8.8) years and 83% HLA-B27 positive) were included. The mean (SD) mSASSS at baseline was 11.6 (16.2) [11.2 (15.7) in patients with mSASSS at 12-years]. The mean (SD) 2-year interval progression score (in 520 2-year intervals) was 2.0 (3.5) [2.2 (3.9) for the subset of 12-year-completers]. Over the 12 years, the mean (SD) progression was 11.7 (11.5). A new syndesmophyte was assessed in 38% by one reader (R1) and 39% by reader 2 of all 2-year intervals and, throughout follow-up, in 55% (R1) and 63% (R2) of the patients with at least one VC “at risk”. In 24% of the patients (39% of the 2-year intervals) there was no progression in mSASSS. A progression ≥1 mSASSS occurred in 72% of the patients (54% of the intervals) and a progression ≥5 mSASSS in 22% of the patients (12% of the intervals). At the group level, a linear time course model fitted the observed data the best. Time was positively associated with radiographic progression, with an increase of 0.98 mSASSS/year (≈1.96 mSASSS in 2 years) (Table). Radiographic progression occurred significantly faster in males (vs females) and in HLA-B27 positive patients (vs HLA-B27 negative). HLA-B27 positive male (but not female) patients had a significantly higher progression than HLA-B27 negative males. Progression was independent of disease- and symptom duration.

Conclusion: Long-term radiographic progression in AS is more severe in HLA-B27-positive males. About 60% of all patients have at least one new syndesmophyte. Radiographic progression is dependent on time and, at the group level, linear.

Table – Progression of radiographic damage over time

	Univariable regression analysis Β (95% CI)	P-value
Time (years)	0.98 (0.84; 1.12)	<0.001
Time X HLAB27		0.052
–       Time in HLAB27 negative	0.70 (0.48; 0.90)	<0.001
–       Time in HLAB27 positive	1.03 (0.88; 1.19)	<0.001
Time X gender		0.005
–       Time in women	0.69 (0.57; 0.80)	<0.001
–       Time in men	1.11 (0.93; 1.29)	<0.001
Time X HLAB27 in women		0.958
Time X HLAB27 in men		0.044
–       Time in female HLAB27 positive	0.69 (0.34; 1.03)	<0.001
–       Time in male HLAB27 positive	1.18 (0.98; 1.38)	<0.001
Time X disease duration		0.701
Time X symptom duration		0.214

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/radiographic-damage-in-ankylosing-spondylitis-over-12-years-of-follow-up-a-longitudinal-analysis/