Background Radiography of the sacroiliac joints (SIJ) in spondyloarthritis (SpA) is a valuable diagnostic tool but is unreliable and unresponsive for assessment of treatment effects. There is an unmet need for imaging tools to assess the potential disease-modifying effects of therapeutic agents early in SpA when disease is still confined to the SIJ. There has been limited validation of MRI-based scores for structural lesions in the SIJ. The SPARCC MRI SIJ Structural Score (SSS) assesses a spectrum of structural lesions and can be used to assess treatment-associated changes in structural damage.
Objectives To determine whether the SSS method has the discriminatory capacity to detect treatment-related structural changes in the SIJ of patients with SpA.
Methods The SSS method assesses fat metaplasia (FAT), erosion (ER), backfill (BF), and ankylosis (ANK) according to standardized and validated definitions. It scores 5 consecutive coronal slices anteriorly through the cartilaginous portion of the joint from the transitional slice, defined as the first slice in the cartilaginous portion that has a visible portion of the ligamentous joint. Lesions are scored dichotomously (present/absent) in SIJ quadrants (fat, erosion) or halves (backfill, ankylosis). Scoring ranges are: FAT (0-40), ER (0-40), BF (0-20), ANK (0-20). After a calibration exercise, two readers independently scored 147 pairs of scans conducted at baseline and 2 years from a prospective cohort of patients with SpA who received either standard (n=69) or anti-TNF (n=78) therapies. Treatment group differences were assessed descriptively and using the Mann-Whitney test. We identified baseline variables associated with change in SSS score by univariate analysis and analyzed the independent effect of treatment by multivariate regression adjusted for severity of baseline structural damage and demographic variables. We also analyzed interaction effects between treatment, patient demographics, and baseline damage scores.
Results A significant increase in mean SSS score for fat metaplasia (p=0.017) and decrease in mean SSS score for erosion (p=0.017) was noted in anti-TNFα treated patients compared to those on standard therapy. There was a significantly higher percentage of patients who developed new fat metaplasia on TNFα inhibitor therapy (38.0%) versus those who received standard therapy (17.6%) (p=0.01). Conversely, more patients on standard therapy had a decrease in fat metaplasia compared to those on TNFα inhibitor therapy (32.3% versus 19.0%, respectively). Significantly more patients on standard therapy developed new erosion compared to those on TNFα inhibitor therapy (26.5% versus 13.9%, respectively, p=0.037). In multivariate analyses, treatment and baseline SSS score for erosion were independently associated with change in SSS erosion score (β=1.75, p=0.003 and β=0.40, p<0.0001, respectively). Change in ASDAS (β=-0.46, p=0.006), SPARCC MRI SIJ inflammation score (β=-0.077, p=0.019), and baseline SSS score for fat metaplasia (β=0.085, p=0.034) were independently associated with development of new fat metaplasia.
Conclusions Anti-TNF therapy may influence structural progression in the SIJ as detected using the SPARCC SSS method, especially by decreasing erosion.
Disclosure of Interest S. Pedersen: None declared, S. Wichuk: None declared, P. Chiowchanwisawakit: None declared, R. Lambert: None declared, W. Maksymowych Grant/research support: Abbvie, Janssen, Consultant for: Abbvie, Amgen, Eli-Lilly, Janssen, Merck, Pfizer, UCB
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