A Handheld Electrical Impedance Myography probe for the assessment of neuromuscular disease

Electrical impedance myography for the early detection of muscle ischemia secondary to compartment syndrome: a study in a rat model

Acute Compartment Syndrome (ACS) is one of the most devastating orthopedic conditions, affecting any of the body's many compartments, which, if sufficiently severe, may result in disability and amputation. Currently, intra-compartmental pressure measurements serve as the gold standard for diagnosing ACS. Diagnosing limbs at risk for ACS before irreversible damage to muscle and nerve is critical. Standard approaches for diagnosing impending compartment syndrome include clinical evaluation of the limb, such as assessment for "tightness" of the overlying skin, reduced pulses distally, and degree of pain, none of which are specific or sensitive. We have proposed a novel method to detect ACS via electrical impedance myography (EIM), where a weak, high-frequency alternating current is passed between one pair of electrodes through a region of tissue, and the resulting surface voltages are measured via a second pair. We evaluated the ability of EIM to detect early muscle ischemia in an established murine model of compression-induced muscle injury, where we collected resistance, reactance, and their dimensionless product, defined as Relative Injury Index (RII) during the study. Our model generated reproducible hypoxia, confirmed by Hypoxyprobe™ staining of endothelial regions within the muscle. Under conditions of ischemia, we demonstrated a reproducible, stable, and significant escalation in resistance, reactance, and RII values, compared to uninjured control limbs. These data make a reasonable argument for additional investigations into using EIM for the early recognition of muscle hypoperfusion and ischemia. However, these findings must be considered preliminary steps, requiring further pre-clinical and clinical validation.

Characterizing spinal muscular atrophy with electrical impedance myography

Electrical impedance myography (EIM) is a non-invasive, painless technique for the evaluation of neuromuscular disease, and here we evaluate its potential application in spinal muscular atrophy (SMA). Twenty-one SMA patients and 18 healthy children underwent EIM of biceps brachii and tibialis anterior using a commercially available impedance device. Hand-held dynamometry and ultrasound assessment of subcutaneous fat thickness were also performed. All EIM parameters differed significantly between both SMA patients and normal subjects and between type 2 and type 3 SMA patients. In addition, EIM had an accuracy level as high as 93% for correctly categorizing patients as type 2 or type 3. Multiple regression analyses confirmed a strong association between EIM and dynamometry. These results confirm that EIM can accurately categorize patients with SMA. Because EIM requires no patient effort and is rapid to apply, it may serve a useful role in future SMA clinical trials.

Quantifying muscle asymmetries in cervical dystonia with electrical impedance: a preliminary assessment

OBJECTIVE

Cervical dystonia (CD) lacks an objective quantitative measure. Electrical impedance myography (EIM) is a non-invasive assessment method sensitive to changes in muscle structure and physiology. We evaluate the potential role of EIM in quantifying CD, hypothesizing that patients would demonstrate differences in the symmetry of muscle electrical resistance compared to controls, and that this asymmetry would decrease after botulinum neurotoxin (BoNT) treatment.

METHODS

EIM was performed on the sternocleidomastoid (SCM) and cervical paraspinal (PS) muscles of CD patients and age-matched controls. 50 kHz resistance was analyzed, comparing side-to-side asymmetry in patients and controls, and, in patients, before and after BoNT treatment.

RESULTS

Sixteen patients and 10 controls were included. Resistance asymmetry was on average 3-5 times higher in patients than controls. Receiver operating characteristic analysis demonstrated 91% accuracy of discriminating CD from normal. From pre-treatment to maximum BoNT effect, asymmetry decreased from 20.8(13.9-26.1)% to 6.2(3.1-9.9)% (SCM), and from 16.0(14.3-16.0)% to 8.4(7.0-9.2)% (PS), p<0.05 (median, interquartile range).

CONCLUSIONS

EIM effectively differentiates normal subjects from CD patients by revealing asymmetries in resistance values and detects improvement in muscle symmetry after treatment.

SIGNIFICANCE

These results suggest that EIM, a painless, non-invasive measure, can provide a useful quantitative metric in CD evaluation and deserves further study.

A portable system for the assessment of neuromuscular diseases with electrical impedance myography

PRIMARY OBJECTIVE

To create a system for the acquisition of multi-angle, multifrequency muscle impedance data.

RESEARCH DESIGN

Device development and preliminary testing.

METHODS AND PROCEDURES

The system presented here employs an interrogating signal composed of multiple tones with frequencies between 10 kHz and 300 kHz. The use of a composite signal makes possible measurement of impedance at multiple frequencies simultaneously. In addition, this system takes impedance measurements at multiple orientations with respect to the muscle fibres by means of an electronically reconfigurable electrode array. The required measurement time is reduced by taking advantage of muscle's linearity with respect to the flow of electrical current.

MAIN OUTCOMES AND RESULTS

The system was tested in normal subjects, a patient with amyotrophic lateral sclerosis, and one with inclusion body myositis; unique impedance signatures were identified the two patients.

CONCLUSIONS

Early data suggest that this system is capable of high-quality data collection and may detect changes in neuromuscular disease; study of additional normal subjects and patients with a variety of neuromuscular diseases is warranted.

Electrical impedance myography: Background, current state, and future directions

Electrical impedance myography (EIM) is a non-invasive technique for the evaluation of neuromuscular disease that relies upon the application and measurement of high-frequency, low-intensity electrical current. EIM assesses disease-induced changes to the normal composition and architecture of muscle, including myocyte atrophy and loss, edema, reinnervation, and deposition of endomysial connective tissue and fat. With application of single-frequency electrical current, EIM can be used to help grade the severity of neuromuscular disease. Assessing electrical impedance across a spectrum of applied frequencies and with current flow at multiple orientations relative to major muscle fiber direction can provide a more complete picture of the condition of muscle. EIM holds the promise of serving as an indicator of disease status. It may be useful in clinical trials and in monitoring effectiveness of treatment in individual patients; ultimately, it may also find diagnostic application. Ongoing efforts have been focused on obtaining a deeper understanding of the basic mechanisms of impedance change, studying EIM in a variety of clinical contexts, and further refining the methods of EIM data acquisition and analysis.