Mapping of Lumbar Multifidus Stiffness Quantification in Ankylosing Spondylitis with Shear-wave Elastography

Background: Lower back pain and stiffness are the typical symptoms of ankylosing spondylitis (AS). In this study, muscle mass was assessed by muscle density, mechanical elasticity, and area. We investigated the characteristics of lumbar paraspinal-muscle (PSM) mass using muscle ultrasound shear-wave elastography (SWE), as well as the validity of this method for identifying patients with AS. Methods We recruited a representative cohort of 30 AS patients, and 27 healthy volunteers who were age- and sex-matched to the patient study group. Results Young’s modulus (YM) of SWE in AS patients was significantly higher than that in volunteers. Percentage change in lumbar multifidus (LM) muscle cross-sectional area (CSA) and thickness were significantly lower in AS patients than in healthy volunteers on the left side of the body. Correlation analysis showed a positive correlation between percentage change in CSA and thickness in both volunteers and AS patients. In AS patients, YM was negatively correlated with percentage change of CSA and thickness on the right side, while increased disease duration in AS was associated with increased YM on the left. Conclusion AS patients showed reductions in LM muscle mass and function as the disease progressed, SWE could reflect these changes well. Trial registration: Chinese Clinical Trial Registry, ChiCTR2000031476. Registered 02/04/2020. http://www.chictr.org.cn/index.aspx.