Background Systemic sclerosis (SSc) is an autoimmune connective tissue disease characterized by progressive cutaneous and visceral fibrosis, and disseminated vasculopathy [1]. Due to clinical features, SSc patients may present low muscle mass, which impacts negatively on their daily activities and physical function [2,3]. There are several methods to assess muscle mass such as magnetic resonance imaging (MRI), computed tomography (CT) and dual-energy radiological absorptiometry (DXA). However, the high costs of the equipment and the lack of portability make them uncommon tools in clinical practice. In this sense, ultrasonography has been used to evaluate muscle mass in different populations [4].

Objectives To assess the quadriceps muscle thickness and to verify associations with clinical features, muscle strength and physical performance in SSc women.

Methods In this cross-sectional study, patients with SSc according to the 2013 ACR-EULAR classification criteria were included. Age in years (y), disease duration (y), modified Rodnan skin score (mRSS), the European Scleroderma Trials and Research Group (EUSTAR) SSc activity index (EScSG-AI), and the health assessment questionnaire (HAQ) were assessed. The muscle thickness was assessed by a real-time ultrasound device (Esaote S.p.A MyLab 50 X Vision; SãoPaulo, Brazil). An experienced ultrasound evaluator analyzed the muscle thickness of vastus lateralis (VL, cm), rectus femoris (RF,cm), vastus intermedius (VI,cm), and vastus medialis (VM,cm). Muscle strength was assessed by handgrip (HGS,kg) and physical performance was assessed by short physical performance battery (SPPB,points). Frequency analysis and Pearson’s or Spearman’s correlation coefficients were explored as appropriate. The significance was considered when p<0.05.

Results We included 45 patients with SSc, 32 (71.1%) with diffuse disease. The median age was 62.00 (54.50-66.50) years and the disease duration was 10.91 (4.88-18.68) years. The median of EScSG-AI was 1.33 (0.33-2.34), the mRSS was 4.00 (2.00-8.00) and the HAQ was 0.62 (0.25-1.06). The mean of muscle thickness were: VL 1.38 + 0.32 cm, RF 1.06±0.35 cm, VM 1.16±0.47 cm, and VI 1.17±0.33 cm. The mean of HGS was 18.64±9.71kg and the median SPPB was 10.00 (9.00-11.50) points. The disease activity by EScSG-AI was negatively associated with VL (r = -0.410, p = 0.016) and VI (r= -0.394, p = 0.021). In addition, HGS was positively associated with VM (r= 0.435, p = 0.003) and SPPB was positively associated with VL (r= 0.354, p = 0.017).

Conclusion Low quadriceps muscle thickness is associated with higher disease activity. As expected, our findings suggest that there are positive associations between muscle thickness with strength and physical performance in SSc women. Our findings highlight the importance of aiming for disease activity control because it may indirectly influence the muscle mass of SSc women.

References [1]Denton CP et al. Lancet 2017.

[2]Caimmi C, et al. Clin Rheumatol. 2018.

[3]Hax V et al. PLoS One. 2021

[4]Abe T, et al. Ultrasound. 2015.

Acknowledgements We thank the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) and the Fundo de Incentivo à Pesquisa e Eventos (FIPE) for the financial support to the development of this project. Also, we thank Hospital de Clínicas de Porto Alegre for providing infrastructure to the conduction of this project.

Disclosure of Interests None Declared.