Electrical impedance myography for discriminating traumatic peripheral nerve injury in the upper extremity

Electrical impedance myography combined with quantitative assessment techniques in paretic muscle of stroke survivors: Insights and challenges

Aging is a non-modifiable risk factor for stroke and the global burden of stroke is continuing to increase due to the aging society. Muscle dysfunction, common sequela of stroke, has long been of research interests. Therefore, how to accurately assess muscle function is particularly important. Electrical impedance myography (EIM) has proven to be feasible to assess muscle impairment in patients with stroke in terms of micro structures, such as muscle membrane integrity, extracellular and intracellular fluids. However, EIM alone is not sufficient to assess muscle function comprehensively given the complex contributors to paretic muscle after an insult. This article discusses the potential to combine EIM and other common quantitative methods as ways to improve the assessment of muscle function in stroke survivors. Clinically, these combined assessments provide not only a distinct advantage for greater accuracy of muscle assessment through cross-validation, but also the physiological explanation on muscle dysfunction at the micro level. Different combinations of assessments are discussed with insights for different purposes. The assessments of morphological, mechanical and contractile properties combined with EIM are focused since changes in muscle structures, tone and strength directly reflect the muscle function of stroke survivors. With advances in computational technology, finite element model and machine learning model that incorporate multi-modal evaluation parameters to enable the establishment of predictive or diagnostic model will be the next step forward to assess muscle function for individual with stroke.

Electrical Impedance Methods in Neuromuscular Assessment: An Overview

Electrical impedance methods have been used as evaluation tools in biological and medical science for well over 100 years. However, only recently have these techniques been applied specifically to the evaluation of conditions affecting nerve and muscle. This specific application, termed electrical impedance myography (EIM), is finding wide application as it can provide a quantitative index of muscle condition that can assist with diagnosis, track disease progression, and assess the beneficial impact of therapy. Using noninvasive surface methods, EIM has been studied in a number of conditions ranging from amyotrophic lateral sclerosis to muscular dystrophy to disuse atrophy. Data support that the technique is sensitive to disease status and can offer the possibility of performing clinical trials with fewer subjects than would otherwise be possible. Recent advances in the field include improved approaches for using EIM as a "virtual biopsy" and the development of combined needle impedance-electromyography technology.

Assessing Hand Muscle Structural Modifications in Chronic Stroke

The purpose of the study is to assess poststroke muscle structural alterations by examining muscular electrical conductivity and inherent electrophysiological properties. In particular, muscle impedance and compound muscle action potentials (CMAP) were measured from the hypothenar muscle bilaterally using the electrical impedance myography and the electrophysiological techniques, respectively. Significant changes of muscle impedance were observed in the paretic muscle compared with the contralateral side (resistance: paretic: 27.54 ± 0.97 Ω, contralateral: 25.46 ± 0.91 Ω, p < 0.05; phase angle: paretic: 8.81 ± 0.61°, contralateral: 10.79 ± 0.69°, p < 0.05). In addition, impedance changes correlated moderately with the CMAP amplitude in the paretic hand (phase angle: r = 0.66, p < 0.05; reactance: r = 0.58, p < 0.05). The study discloses significant muscle rearrangements as a result of fiber loss or atrophy, fat infiltration or impaired membrane integrity in chronic stroke.

Recording characteristics of electrical impedance myography needle electrodes

OBJECTIVE

Neurologists and physiatrists need improved tools for the evaluation of skeletal muscle condition. Here we evaluate needle electrical impedance myography (EIM), a new minimally invasive approach to determine muscle status that could ultimately become a bedside tool for the assessment of neuromuscular disorders.

APPROACH

We design and study the recording characteristics of tetrapolar EIM needle electrodes combining theory and finite-element model simulations. We then use these results to build and pilot in vivo an EIM needle electrode in the rat gastrocnemius muscle ([Formula: see text]). The dielectric properties of muscle are reported (mean  ±  standard deviation).

RESULTS

The numerical simulations show that the contribution of subcutaneous fat and muscle tissues to needle EIM data is <3% and >97%, respectively, and the sensed volume is [Formula: see text] cm³. Apparent resistivity [Formula: see text] [Formula: see text] cm and relative permittivity [Formula: see text] (dimensionless) measured at 10 kHz are in good agreement with in vivo dielectric properties reported in the literature.

SIGNIFICANCE

The results presented show the feasibility of measuring muscle impedivity in vivo using a needle electrode from 10 kHz to 1 MHz. The development of needle EIM technology can open up a new field of study in electrodiagnostic medicine, with potential applications to both disease diagnosis and biomarker assessment of therapy.