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

Facioscapulohumeral muscular dystrophy (FSHD) is characterized by early and significant involvement of facial muscles; however, objective imaging data focusing on facial muscles are limited. Facial ultrasound can serve as a sensitive imaging biomarker and outcome measure by capturing regional structural changes in facial muscles associated with disease progression in FSHD patients. The aim of this study is to compare facial muscle thickness and echo density between FSHD patients and healthy controls using ultrasound and to examine the relationships between ultrasound findings and clinical parameters. This study will include 20 patients with genetically confirmed FSHD1 diagnosis and 19 age- and sex-matched healthy controls. Using musculoskeletal ultrasound, bilateral evaluation of selected facial muscles (Orbicularis oculi, orbicularis oris, zygomaticus major, and buccinator) will be performed by two different researchers, and muscle thickness and muscle echo density will be recorded. Inter-rater reliability will be assessed using intraclass correlation coefficients. Group comparisons and correlation analyses will be performed with clinical scores, symptom duration, and D4Z4 repeat size. The results will evaluate whether ultrasound can reliably detect structural changes in FSHD that cannot be captured by traditional clinical assessments, and if significant, will suggest that ultrasound can serve as a sensitive imaging biomarker for early and region-specific facial muscle involvement in FSHD.