Associations of muscle mass, adipose tissue mass, and skeletal muscle radiodensity with disease activity in axial spondyloarthritis.

BACKGROUND

Body composition is increasingly recognized as an important modulator of chronic inflammation. However, the association between body composition parameters and disease activity in axial spondyloarthritis (axSpA) remains to be clearly established.

OBJECTIVES

We aimed to investigate the association between muscle, subcutaneous fat composition assessed via computed tomography (CT) imaging, and disease activity in patients with axSpA.

DESIGN

This is a retrospective data registry observational study.

METHODS

This study analyzed 215 patients with axSpA. Body composition parameters were measured from pelvic CT scans. Parameters included the total adipose tissue volume to total skeletal muscle volume ratio (TATV/TSMV), a single-slice subcutaneous adipose tissue to skeletal muscle area ratio (SAT/SM), and skeletal muscle (SM) radiodensity. Disease activity was evaluated using the Ankylosing Spondylitis Disease Activity Score (ASDAS). Associations were analyzed using multivariate linear regression and restricted cubic splines (RCS). The probability of achieving major improvement (MI, ΔASDAS 2.0) was compared using Kaplan-Meier analysis.

RESULTS

After adjusting for age, sex, and disease duration, a higher TATV/TSMV ratio, rather than the single-slice SAT/SM ratio, was independently associated with increased ASDAS-C-reactive protein (β = 0.722, 95% confidence interval (CI): 0.215-1.231, p = 0.004). SM radiodensity showed an inverse, nonsignificant association (p = 0.48). RCS analysis identified a threshold effect of the TATV/TSMV ratio on disease activity at 0.65 (nonlinear p = 0.045). Above this threshold, a higher ratio was significantly associated with elevated ASDAS-CRP (hazard ratio (HR) = 3.64, 95% CI: 1.13-11.71, p = 0.029). Patients with a ratio <0.65 had a significantly higher probability of achieving MI (HR = 1.64, 95% CI: 1.04-2.59, log-rank p = 0.04).

CONCLUSION

The pelvic TATV/TSMV ratio is an independent imaging biomarker associated with higher disease activity and lower odds of clinical improvement in patients with axSpA. A cut-off value of 0.65 may be a promising tool for risk stratification in clinical practice.