Ultrasound Detection of Early Facial Muscle Changes in FSHD: Thickness and Echo Intensity Findings

Facioscapulohumeral muscular dystrophy (FSHD) is a hereditary neuromuscular disorder characterized by progressive muscle weakness, showing early and significant involvement of facial muscles. Despite their diagnostic and functional importance, facial muscles are often underrepresented in imaging-based assessments of disease involvement. This observational, cross-sectional study was designed to compare structural changes in selected facial muscles of individuals with genetically confirmed FSHD with healthy controls using musculoskeletal ultrasound. The study focuses on the quantitative assessment of muscle thickness and the qualitative assessment of muscle echo density as indicators of atrophy and fat infiltration. Bilateral ultrasound examinations will be performed on facial muscles, including the orbicularis oculi, orbicularis oris, zygomaticus major, and buccinator muscles, which play a role in facial expression and oral function. Imaging findings will be evaluated in relation to clinical features to investigate whether facial muscle ultrasound can provide region-specific information not captured by global disease severity scores. This study aims to characterize facial muscle involvement using a non-invasive and accessible imaging method, contribute to the understanding of early and subclinical facial muscle changes in FSHD, and support the potential role of ultrasound as an imaging biomarker in neuromuscular disorders.