P.13.13 Electrical impedance myography in DMD: A multi-center study of reliability and relationships to strength and function

Abstract

Determine reliability of electrical impedance myography (EIM) in boys with Duchenne muscular dystrophy (DMD) and healthy controls and compare results to measures of strength and function. EIM is a non-invasive, rapid to apply, painless, and quantifiable technique that is sensitive to muscle pathology. It could potentially serve as a biomarker of disease in DMD. Sixty-one boys with DMD and 31 healthy boys, aged 3–12 years, were recruited and evaluated at five centers. Assessments included EIM of unilateral arm and leg muscles (EIM system1103, Convergence Medical Devices, Inc.), six minute walk test (6MWT), North Star Ambulatory Assessment (NSAA), timed functional tests (TFT), and strength (hand held dynamometry). EIM measurements were repeated by a second examiner. EIM, TFT, and dynamometry data were normalized based on the healthy subject data and percent predicted of normal values were calculated. All boys tolerated testing well. Although results of EIM from single muscles showed good reliability and correlation with function and strength, an average measure of EIM from each subjects biceps brachii, wrist flexors, quadriceps, and tibialis anterior muscles was found to be especially promising. Average EIM had high inter-rater reliability (intraclass correlation coefficient of 0.97), was lower on average in boys with DMD than controls (56.1 (22.1)% vs. 99.8 (19.8)%, p < 0.001), differentiated DMD from controls (area under the curve = 0.94), and correlated with measures of function (6MWT: r = 0.48; NSAA: r = 0.62; TFT: r = −0.58) and strength (r = 0.49) (all p ⩽ 0.001). EIM is a promising ancillary measure for use in clinical trials in DMD. EIM measures were reliably obtained from multiple centers, differentiated healthy from DMD boys, and correlated with strength and function. Longitudinal studies comparing EIM to other outcome measures over time in DMD are warranted. Determine reliability of electrical impedance myography (EIM) in boys with Duchenne muscular dystrophy (DMD) and healthy controls and compare results to measures of strength and function. EIM is a non-invasive, rapid to apply, painless, and quantifiable technique that is sensitive to muscle pathology. It could potentially serve as a biomarker of disease in DMD. Sixty-one boys with DMD and 31 healthy boys, aged 3–12 years, were recruited and evaluated at five centers. Assessments included EIM of unilateral arm and leg muscles (EIM system1103, Convergence Medical Devices, Inc.), six minute walk test (6MWT), North Star Ambulatory Assessment (NSAA), timed functional tests (TFT), and strength (hand held dynamometry). EIM measurements were repeated by a second examiner. EIM, TFT, and dynamometry data were normalized based on the healthy subject data and percent predicted of normal values were calculated. All boys tolerated testing well. Although results of EIM from single muscles showed good reliability and correlation with function and strength, an average measure of EIM from each subjects biceps brachii, wrist flexors, quadriceps, and tibialis anterior muscles was found to be especially promising. Average EIM had high inter-rater reliability (intraclass correlation coefficient of 0.97), was lower on average in boys with DMD than controls (56.1 (22.1)% vs. 99.8 (19.8)%, p < 0.001), differentiated DMD from controls (area under the curve = 0.94), and correlated with measures of function (6MWT: r = 0.48; NSAA: r = 0.62; TFT: r = −0.58) and strength (r = 0.49) (all p ⩽ 0.001). EIM is a promising ancillary measure for use in clinical trials in DMD. EIM measures were reliably obtained from multiple centers, differentiated healthy from DMD boys, and correlated with strength and function. Longitudinal studies comparing EIM to other outcome measures over time in DMD are warranted.