Quantitative muscle ultrasound detects disease progression in Duchenne muscular dystrophy.

OBJECTIVE: We assessed changes in quantitative muscle ultrasound data in boys with Duchenne muscular dystrophy (DMD) and healthy controls to determine whether ultrasound can serve as a biomarker of disease progression. Two approaches were used: gray scale level (GSL), measured from the ultrasound image, and quantitative backscatter analysis (QBA), measured directly from the received echoes. METHODS: GSL and QBA were obtained from 6 unilateral arm/leg muscles in 36 boys with DMD and 28 healthy boys (age = 2-14 years) for up to 2 years. We used a linear mixed effects model with random intercept and slope terms to compare trajectories of GSL, QBA, and functional assessments. We analyzed separately a subset of boys who initiated corticosteroids. RESULTS: Compared to healthy boys, increasing GSL in DMD boys >7.0 years old was first identified at 6 months (eg, anterior forearm slope difference of 1.16 arbitrary units/mo, p = 0.004, 95% confidence interval [CI] = 0.38-1.94); in boys ≤ 7 years old, differences in GSL first appeared at 12 months (0.82 arbitrary units/mo, p = 0.04, 95% CI = 0.075-1.565, in rectus femoris). QBA performed similarly to GSL (eg, DMD boys > 7 years old: 0.41dB/mo, p = 0.01, 95% CI = 0.096-0.72, in anterior forearm at 6 months). Ultrasound identified differences earlier than functional measures including 6-minute walk and supine-to-stand tests. However, neither QBA nor GSL showed an effect of corticosteroid initiation. INTERPRETATION: QBA performs similarly to GSL, and both appear more sensitive than functional assessments for detecting muscle deterioration in DMD. Additional studies will be required to determine whether quantitative muscle ultrasound can detect therapeutic efficacy. Ann Neurol 2017;81:633-640.

Electrical impedance myography for assessment of Duchenne muscular dystrophy.

OBJECTIVE: Sensitive, objective, and easily applied methods for evaluating disease progression and response to therapy are needed for clinical trials in Duchenne muscular dystrophy (DMD). In this study, we evaluated whether electrical impedance myography (EIM) could serve this purpose. METHODS: In this nonblinded study, 36 boys with DMD and 29 age-similar healthy boys underwent multifrequency EIM measurements for up to 2 years on 6 muscles unilaterally along with functional assessments. A linear mixed-effects model with random intercept and slope terms was used for the analysis of multifrequency EIM values and functional measures. Seven DMD boys were initiated on corticosteroids; these data were analyzed using a piecewise linear mixed-effects model. RESULTS: In boys > 7.0 years old, a significant difference in the slope of EIM phase ratio trajectories in the upper extremity was observed by 6 months of -0.074/month, p = 0.023, 95% confidence interval (CI) = -0.013, -0.14; at 2 years, this difference was -0.048/month, p < 0.0001, 95% CI = -0.028, -0.068. In boys ≤ 7.0 years old, differences appeared at 6 months in gastrocnemius (EIM phase slope = -0.83 °/kHz/mo, p = 0.007, 95% CI = -0.26, -1.40). EIM outcomes showed significant differences earlier than functional tests. Initiation of corticosteroids significantly improved the slope of EIM phase ratio (0.057/mo, p = 0.00019, 95% CI = 0.028, 0.086) and EIM phase slope (0.14 °/kHz/mo, p = 0.013, 95% CI = 0.028, 0.25), consistent with corticosteroids' known clinical benefit. INTERPRETATION: EIM detects deterioration in muscles of both younger and older boys by 6 months; it also identifies the therapeutic effect of corticosteroid initiation. Because EIM is rapid to apply, painless, and requires minimal operator training, the technique deserves to be further evaluated as a biomarker in DMD clinical therapeutic trials. Ann Neurol 2017;81:622-632.

Sensitivity distribution simulations of surface electrode configurations for electrical impedance myography.

INTRODUCTION: Surface-based electrical impedance myography (EIM) is sensitive to muscle condition in neuromuscular disorders. However, the specific contribution of muscle to the obtained EIM values is unknown. METHODS: We combined theory and the finite element method to calculate the electrical current distribution in a 3-dimensional model using different electrode array designs and subcutaneous fat thicknesses (SFTs). Through a sensitivity analysis, we decoupled the contribution of muscle from other surrounding tissues in the measured surface impedance values. RESULTS: The contribution of muscle to surface EIM values varied greatly depending on the electrode array size and the SFT. For example, the contribution of muscle with 6-mm SFT was 8% for a small array compared with 32% for a large array. CONCLUSIONS: The approach presented can be employed to inform the design of robust EIM electrode configurations that maximize the contribution of muscle across the disease and injury spectrum. Muscle Nerve 56: 887-895, 2017.

Optimizing electrical impedance myography of the tongue in amyotrophic lateral sclerosis.

INTRODUCTION: Electrical impedance myography (EIM) can quantify muscle health at a range of frequencies, including that most commonly employed, 50 kHz. However, disease-related changes in EIM data suggest the distinction between normal and patient EIM values could be more apparent at frequencies of >50 kHz. We investigated at what other selected frequencies tongue EIM may differentiate healthy individuals and amyotrophic lateral sclerosis (ALS) patients, remain reliable, and correlate with a standard metric of bulbar function. METHODS: Tongue EIM phase data from 30 volunteers and 11 ALS patients were analyzed at 6 discrete frequencies from 50 to 500 kHz. RESULTS: Of the frequencies assessed, EIM demonstrated maximal separation and reliability at 100 kHz, where phase value was also significantly correlated with the bulbar subscore on the revised version of the ALS Functional Rating Scale. CONCLUSIONS: One hundred kilohertz could serve as an optimal frequency at which to measure EIM phase values of the tongue in ALS. Muscle Nerve 55: 539-543, 2017.

Functional Mixed-Effects Modeling of Longitudinal Duchenne Muscular Dystrophy Electrical Impedance Myography Data Using State-Space Approach.

OBJECTIVE: Electrical impedance myography (EIM) is a quantitative and objective tool to evaluate muscle status. EIM offers the possibility to replace conventional physical functioning scores or quality of life measures, which depend on patient cooperation and mood. METHODS: Here, we propose a functional mixed-effects model using a state-space approach to describe the response trajectories of EIM data measured on 16 boys with Duchenne muscular dystrophy and 12 healthy controls, both groups measured over a period of two years. The modeling framework presented imposes a smoothing spline structure on EIM data collected at each visit and taking into account of within subject correlations of these curves along the longitudinal measurements. The modeling framework is recast in a state-space approach, thereby allowing for the employment of computationally efficient diffuse Kalman filtering and smoothing algorithms for the model estimation, as well as the estimates of the posterior variance-covariance matrix for the construction of the Bayesian [Formula: see text] confidence bands. RESULTS: The proposed model allows us to simultaneously adjust for baseline variables, differentiate the longitudinal changes in the smooth functional response and estimate the subject and subject-time specific deviations from the population-averaged response curves. The code is made publicly available in the supplementary material. SIGNIFICANCE: The modeling approach presented will potentially enhance EIM capability to serve as a biomarker for testing therapeutic efficacy in DMD and other clinical trials.

Single and modeled multifrequency electrical impedance myography parameters and their relationship to force production in the ALS SOD1G93A mouse.

OBJECTIVE: The relationship between muscle force production in ALS SOD1G93A mice and single and modeled multifrequency electrical impedance myography (EIM) parameters is unknown. We evaluated the relationship between multifrequency EIM data and paw grip and in situ force measurements, as well to standard measures including body weight and compound motor action potential (CMAP) amplitude. METHODS: Twenty-nine SOD1 G93A mice aged 13-18 weeks (approximately 4-5 per week) and a group of similarly aged wild-type mice (N = 7) were studied with single and multifrequency EIM, CMAP, front and hind-limb paw grip measures, and in situ force measurements of the gastrocnemius. RESULTS: Significant differences among WT, presymptomatic, and symptomatic ALS animals were identified for all standard measures and single 50 kHz frequency EIM parameters. Of the modeled multifrequency measures, the center frequency, fc , an index of cell size, showed the strongest relationship to force output. The two other multifrequency parameters corresponding to cell size distribution and cell density showed consistent although mostly non-significant differences. CONCLUSION: Reductions in force are reflected in single 50 kHz impedance values and in the fc. These data support the construct validity of EIM as an assessment tool of muscle dysfunction in diseases associated with motor neuron loss.

Guidelines to electrode positioning for human and animal electrical impedance myography research.

The positioning of electrodes in electrical impedance myography (EIM) is critical for accurately assessing disease progression and effectiveness of treatment. In human and animal trials for neuromuscular disorders, inconsistent electrode positioning adds errors to the muscle impedance. Despite its importance, how the reproducibility of resistance and reactance, the two parameters that define EIM, are affected by changes in electrode positioning remains unknown. In this paper, we present a novel approach founded on biophysical principles to study the reproducibility of resistance and reactance to electrode misplacements. The analytical framework presented allows the user to quantify a priori the effect on the muscle resistance and reactance using only one parameter: the uncertainty placing the electrodes. We also provide quantitative data on the precision needed to position the electrodes and the minimum muscle length needed to achieve a pre-specified EIM reproducibility. The results reported here are confirmed with finite element model simulations and measurements on five healthy subjects. Ultimately, our data can serve as normative values to enhance the reliability of EIM as a biomarker and facilitate comparability of future human and animal studies.

Electrical Impedance Myography to Detect the Effects of Electrical Muscle Stimulation in Wild Type and Mdx Mice.

OBJECTIVE: Tools to better evaluate the impact of therapy on nerve and muscle disease are needed. Electrical impedance myography (EIM) is sensitive to neuromuscular disease progression as well as to therapeutic interventions including myostatin inhibition and antisense oligonucleotide-based treatments. Whether the technique identifies the impact of electrical muscle stimulation (EMS) is unknown. METHODS: Ten wild-type (wt) C57B6 mice and 10 dystrophin-deficient (mdx) mice underwent 2 weeks of 20 min/day EMS on left gastrocnemius and sham stimulation on the right gastrocnemius. Multifrequency EIM data and limb girth were obtained before and at the conclusion of the protocol. Muscle weight, in situ force measurements, and muscle fiber histology were also assessed at the conclusion of the study. RESULTS: At the time of sacrifice, muscle weight was greater on the EMS-treated side than on the sham-stimulated side (p = 0.018 for wt and p = 0.007 for mdx). Similarly, in wt animals, EIM parameters changed significantly compared to baseline (resistance (p = 0.009), reactance (p = 0.0003) and phase (p = 0.002); these changes were due in part to reductions in the EIM values on the EMS-treated side and elevations on the sham-simulated side. Mdx animals showed analogous but non-significant changes (p = 0.083, p = 0.064, and p = 0.57 for resistance, reactance and phase, respectively). Maximal isometric force trended higher on the stimulated side in wt animals only (p = 0.06). Myofiber sizes in wt animals were also larger on the stimulated side than on the sham-stimulated side (p = 0.034); no significant difference was found in the mdx mice (p = 0.79). CONCLUSION: EIM is sensitive to stimulation-induced muscle alterations in wt animals; similar trends are also present in mdx mice. The mechanisms by which these EIM changes develop, however, remains uncertain. Possible explanations include longer-term trophic effects and shorter-term osmotic effects.

An improved electrical impedance myography (EIM) tongue array for use in clinical trials.

OBJECTIVES: Electrical impedance myography (EIM) measurements of the tongue could provide valuable information about bulbar dysfunction in amyotrophic lateral sclerosis (ALS). A prototype tongue depressor EIM array produced gag reflexes. The objectives of this study were to determine the reliability, mean phase values, and tolerability of tongue EIM measurements using a smaller electrode array. METHODS: Tongue EIM measurements were performed in a total of 31 healthy individuals and four neuromuscular patients with lingual abnormalities. Reliability was assessed by calculating the intraclass correlation coefficient (ICC) and percent difference in addition to performing Bland-Altman analyses. Standard descriptive statistics, including results of a Mann-Whitney test, were also determined. RESULTS: At the 50 kHz frequency, the ICCs for intra- and inter-rater reliability were 0.76 with 5.17% difference and 0.78 with 5.34% difference respectively. The mean EIM phase values of healthy participants (11.61° ± 1.00°) and patients (9.87° ± 1.28°) were significantly different (p=0.0051). None of the participants experienced gag reflexes or discomfort. CONCLUSIONS: The small tongue array provided good inter- and intra-rater reliability, could preliminarily distinguish between healthy and diseased muscle, and was well-tolerated. SIGNIFICANCE: Biomarker information about tongue health could be more comfortably obtained with a smaller EIM array.

Tongue electrical impedance in amyotrophic lateral sclerosis modeled using the finite element method.

OBJECTIVE: Electrical impedance myography (EIM) of the tongue has demonstrated alterations in patients with amyotrophic lateral sclerosis (ALS) compared to normal subjects. Whether these differences are due to reduced tongue size or diseased-associated alterations in the electrical characteristics of intrinsic tongue muscles is uncertain. METHODS: We employed computer simulations using the finite element method, inputting data from healthy and ALS mouse muscle, to help answer that question, comparing our modeled results to human data. RESULTS: The models revealed that much of the electrical current flows superficially in the tongue and that tongue thickness only begins to have a major impact on the measured impedance when substantial atrophy is present. Modeled values paralleled the human tongue data. CONCLUSIONS: These findings suggest that the observed changes in tongue impedance in ALS are mainly due to alterations in the electrical properties of the tongue and are not a mere consequence of tongue volume loss. SIGNIFICANCE: Further development of EIM for evaluation of bulbar dysfunction in ALS may provide useful information on drug efficacy and could serve as a biomarker in future clinical trials.

Loss of electrical anisotropy is an unrecognized feature of dystrophic muscle that may serve as a convenient index of disease status.

OBJECTIVE: We sought to understand the alteration in the anisotropic, or direction dependent, character of muscle as measured by electrical impedance myography (EIM) in subjects with Duchenne muscular dystrophy (DMD) and its potential to serve as a biomarker of disease status. METHODS: Thirty-six boys with DMD and 27 healthy controls were measured with EIM, with electrical current applied both parallel and perpendicular to the major muscle fiber direction. In addition, muscle extracted from 10 mdx and 10 wild-type mice were measured analogously. RESULTS: Normalized reactance anisotropy, a direction-dependent measure of membrane charge storage capability, was significantly lower in the four muscles of DMD subjects as compared to controls (p<0.01). Normalized reactance anisotropy also decreased with increasing age in DMD subjects (r=-0.36, p=0.031), but not in healthy boys. Analogous changes were observed in mdx mouse gastrocnemius as compared to wild type (p=0.019). CONCLUSION: These results support that loss of electrical anisotropy is a previously unrecognized feature of dystrophic muscle. SIGNIFICANCE: Anisotropic alterations may offer novel indices to assist in neuromuscular disease diagnosis and to serve as easy-to-obtain biomarkers in clinical therapeutic trials.

Evaluation of Electrical Impedance as a Biomarker of Myostatin Inhibition in Wild Type and Muscular Dystrophy Mice.

OBJECTIVES: Non-invasive and effort independent biomarkers are needed to better assess the effects of drug therapy on healthy muscle and that affected by muscular dystrophy (mdx). Here we evaluated the use of multi-frequency electrical impedance for this purpose with comparison to force and histological parameters. METHODS: Eight wild-type (wt) and 10 mdx mice were treated weekly with RAP-031 activin type IIB receptor at a dose of 10 mg kg-1 twice weekly for 16 weeks; the investigators were blinded to treatment and disease status. At the completion of treatment, impedance measurements, in situ force measurements, and histology analyses were performed. RESULTS: As compared to untreated animals, RAP-031 wt and mdx treated mice had greater body mass (18% and 17%, p < 0.001 respectively) and muscle mass (25% p < 0.05 and 22% p < 0.001, respectively). The Cole impedance parameters in treated wt mice, showed a 24% lower central frequency (p < 0.05) and 19% higher resistance ratio (p < 0.05); no significant differences were observed in the mdx mice. These differences were consistent with those seen in maximum isometric force, which was greater in the wt animals (p < 0.05 at > 70 Hz), but not in the mdx animals. In contrast, maximum force normalized by muscle mass was unchanged in the wt animals and lower in the mdx animals by 21% (p < 0.01). Similarly, myofiber size was only non-significantly higher in treated versus untreated animals (8% p = 0.44 and 12% p = 0.31 for wt and mdx animals, respectively). CONCLUSIONS: Our findings demonstrate electrical impedance of muscle reproduce the functional and histological changes associated with myostatin pathway inhibition and do not reflect differences in muscle size or volume. This technique deserves further study in both animal and human therapeutic trials.