Evaluation of muscle stiffness in Systemic Sclerosis and sarcopenia using Shear Wave Elastography: a cross-sectional study on hand and forearm muscles.

Aims: To assess the impact of systemic sclerosis (SSc) and sarcopenia on muscle stiffness using shear wave elastography (SWE) in hand and forearm muscles, and to determine whether these conditions independently affect muscle mechanical properties.

Material and methods: This cross-sectional study included 39 patients with SSc and 90 controls. Sarcopenia was defined according to EWGSOP2 criteria, using fat-free mass index and handgrip strength. Muscle stiffness was measured by SWE in both relaxed and contracted states at three muscle sites: thenar eminence, flexor pollicis longus, and flexor digitorum profundus. Additional assessments included whole body dual-energy X-ray absorptiometry evaluation, clinical evaluation, and questionnaires. Multiple linear regression and propensity score matching were used to adjust for age, sex, and body mass index. Intra-rater reliability was evaluated using intraclass correlation coefficients (ICCs).

Results: SSc patients showed significantly higher muscle stiffness during contraction across all sites (p<0.05), independent of sarcopenia, age, or bodycomposition. No differences were observed at rest. Sarcopenia showed limited effect on SWE values. ICCs ranged from 0.858 to 0.935, indicating excellent intra-rater reliability.

Conclusions: Muscle stiffness during contraction is increased in SSc and appears to reflect fibrotic changes in the extracellular matrix rather than sarcopenia. SWE under standardized contraction may serve as a sensitive imaging biomarker for muscle involvement in systemic sclerosis. Further studies should include inter-rater reproducibility and clinical phenotyping to validate its diagnostic value.