We investigate whether EIM parameters are associated with microscopic and macroscopic muscle structure measured by magnetic resonance imaging, muscle histology, and transcriptomic analysis.

Electrical impedance myography (EIM) has been proposed as an efficient, noninvasive biomarker of muscle composition in facioscapulohumeral muscular dystrophy (FSHD).

We performed a multi-center cross-sectional study enrolling 33 patients with FSHD. EIM measurements were recorded from bilateral vastus lateralis, tibialis anterior (TA), and medial gastrocnemius muscles and compared to MRI quantitative Dixon fat fraction (FF).  EIM measurements of the TA were further compared to dorsiflexion strength, muscle biopsy histology, and transcriptomic analysis of muscle and fat content.

EIM phase at multiple frequencies was negatively associated to the amount of fat replacement of muscle measured by MRI (ρ = -0.53 to -0.73,) and transcriptomic analysis (ρ = -0.42, P < .001 in only the TAs); and positively associated with strength measured by quantitative muscle testing (ρ = 0.47 to 0.58, p <0.01).

This study supports the hypothesis that EIM is associated to disease features of FSHD at the functional level (strength), macroscopic level (fatty fibrous replacement measured by MRI), and microscopic level (RNAseq), and these data provide further convergent validity for the usage of EIM as an interesting biomarker to assess muscle health in muscle diseases.