Electrical impedance myography in duchenne muscular dystrophy and healthy controls: A multicenter study of reliability and validity

Introduction: Electrical impedance myography (EIM) is a non-invasive, painless, objective technique to quantify muscle pathology. Methods: We measured EIM in 8 arm and leg muscles in 61 boys with Duchenne muscular dystrophy (DMD) and 31 healthy boys, ages 3-12 years, at 5 centers. We determined the reliability of EIM and compared results in boys with DMD to controls and to 6-minute walk distance (6MWD), North Star Ambulatory Assessment (NSAA), timed functional tests (TFTs), and strength (hand-held dynamometry). Results: EIM was well tolerated and had good inter- and intrarater reliability (intraclass correlation coefficient 0.81-0.96). The averaged EIM phase value from all muscles was higher (P<0.001) in controls (10.45±2.29) than boys with DMD (7.31±2.23), and correlated (P≤0.001) with 6MWD (r=0.55), NSAA (r=0.66), TFTs (r=-0.56), and strength (r=0.44). Conclusion: EIM is a reliable and valid measure of disease severity in DMD. Longitudinal studies comparing EIM with other assessments over time in DMD are warranted.