Ultrasound Contrast between the Trapezius and Supraspinatus Muscles as a Potentially Specific Finding of Facioscapulohumeral Muscular Dystrophy.

Objective Facioscapulohumeral muscular dystrophy (FSHD) demonstrates selective muscle involvement, with trapezius muscle affected and rotator cuff muscles relatively preserved in the shoulder girdle. While magnetic resonance imaging of this pattern has been documented, the diagnostic utility of ultrasound remains unclear. This study aimed to determine whether an ultrasound echogenicity analysis can identify this selective involvement pattern in FSHD. Methods This single-center retrospective study examined ultrasound echogenicity differences between the trapezius and supraspinatus muscles in three genetically confirmed FSHD type 1 patients and nine disease controls with shoulder weakness. The trapezius-to-supraspinatus echogenicity difference was calculated, and statistically compared using the Mann-Whitney U test. Results FSHD patients demonstrated significantly higher trapezius-to-supraspinatus echogenicity differences (mean±SD: 113±26) compared to controls (36±11; p<0.05). All three FSHD patients showed values exceeding the control range, with complete separation between the two groups observed. Conclusions Ultrasound may non-invasively detect the characteristic muscle selectivity pattern of FSHD and could serve as a diagnostic adjunct prior to genetic testing.