Person:

Rutkove, Seward

Objectives: (1) To assess the diagnostic accuracy of EMG in radiculopathy. (2) To evaluate the intrarater reliability and interrater reliability of EMG in radiculopathy. (3) To assess the presence of confirmation bias in EMG. Methods: Three experienced academic electromyographers interpreted 3 compact discs with 20 EMG videos (10 normal, 10 radiculopathy) in a blinded, standardized fashion without information regarding the nature of the study. The EMGs were interpreted 3 times (discs A, B, C) 1 month apart. Clinical information was provided only with disc C. Intrarater reliability was calculated by comparing interpretations in discs A and B, interrater reliability by comparing interpretation between reviewers. Confirmation bias was estimated by the difference in correct interpretations when clinical information was provided. Results: Sensitivity was similar to previous reports (77%, confidence interval [CI] 63%–90%); specificity was 71%, CI 56%–85%. Intrarater reliability was good (κ 0.61, 95% CI 0.41–0.81); interrater reliability was lower (κ 0.53, CI 0.35–0.71). There was no substantial confirmation bias when clinical information was provided (absolute difference in correct responses 2.2%, CI −13.3% to 17.7%); the study lacked precision to exclude moderate confirmation bias. Conclusions: This study supports that (1) serial EMG studies should be performed by the same electromyographer since intrarater reliability is better than interrater reliability; (2) knowledge of clinical information does not bias EMG interpretation substantially; (3) EMG has moderate diagnostic accuracy for radiculopathy with modest specificity and electromyographers should exercise caution interpreting mild abnormalities. Classification of evidence: This study provides Class III evidence that EMG has moderate diagnostic accuracy and specificity for radiculopathy.

Electrical impedance myography (EIM), a non-invasive, electrophysiological technique, has preliminarily shown value as an ALS biomarker. Here we perform a multicenter study to further assess EIM’s potential for tracking ALS. ALS patients were enrolled across eight sites. Each subject underwent EIM, handheld dynamometry (HHD), and the ALS Functional Rating Scale-revised (ALSFRS-R) regularly. Techniques were compared by assessing the coefficient of variation (CoV) in the rate of decline and each technique’s correlation to survival. Results showed that in the 60 patients followed for one year, EIM phase measured from the most rapidly progressing muscle in each patient had a CoV in the rate of decline of 0.62, compared to HHD (0.82) and the ALSFRS-R (0.74). Restricting the measurements to the first six months gave a CoV of 0.55 for EIM, 0.93 for HHD, and 0.84 for ALSFRS-R. For both time-periods, all three measures correlated with survival. Based on these data, a six-month clinical trial designed to detect a 20% treatment effect with 80% power using EIM would require only 95 patients/arm compared to the ALSFRS-R, which would require 220 subjects/arm. In conclusion, EIM can serve as a useful ALS biomarker that offers the prospect of greatly accelerating phase 2 clinical trials.

Objective

Applied electrical current flows preferentially along rather than across muscle fibers, a characteristic called anisotropy. In this study, we investigate the alteration in muscle anisotropy after denervation.

Methods

Eight adult male rats underwent sciatic nerve crush and the gastrocnemius was harvested from 1 to 2.5 weeks later. Muscle from 12 additional healthy rats was also obtained. Multifrequency electrical impedance measurements were made on the tissue and its conductivity and relative permittivity (i.e., its polarizability) calculated. Anisotropy of the tissue was determined by calculating conductivity and permittivity differences, subtracting transverse from longitudinal values. Muscle fiber and blood vessel quantification were also performed.

Results

The mean conductivity difference for sciatic crush animals was higher (p <0.05) than for the healthy animals across the frequency spectrum, due to a greater increase in longitudinal conductivity than in transverse conductivity. For example, at 10 kHz, the conductivity difference was 0.15 S/m for healthy animals and 0.29 S/m for post-crush animals. Relative permittivity difference values, however, were similar between groups. There was a strong correlation of conductivity anisotropy to muscle fiber size but not to blood vessel area.

Conclusions

Anisotropy of muscle conductivity increases markedly after subacute denervation injury.

Significance

This alteration in anisotropy has direct relevance to the clinical application of electrical impedance myography. We also speculate that it may impact other forms of diagnostic testing, including needle electromyography and magnetic resonance imaging.

Objective

Recent developments in electrical impedance myography (EIM) have led to the use of handheld electrode arrays (HEA) for data acquisition. Although preferable for several reasons, this approach tends to be more affected by subcutaneous fat (SF) than the original approach in which the impedance-measuring electrodes are widely spaced. In this study, we seek to identify the EIM parameter least impacted by subcutaneous fat (SF) when using an HEA.

Methods

18 normal subjects underwent 50 kHz EIM and ultrasound of the medial gastrocnemius muscles on the dominant side. Coefficients of determination (R2 values) were calculated for each of the three major EIM variables (reactance, resistance, and phase) and SF thickness.

Results

For both resistance and phase, a strong relationship to SF thickness was observed (R2 = 0.64 and R2 = 0.70, respectively, p < 0.001 for both). In contrast, for reactance, the relationship was non-significant, with R2 = 0.07, p = 0.30.

Conclusions

Unlike resistance and phase, both of which are highly impacted by SF thickness, the reactance shows no significant relationship.

Significance

Future clinical studies employing HEA’s to perform EIM should evaluate alterations in reactance over those in resistance and phase.

Introduction

The current practice of single fiber electromyography (SFEMG) requires that 20 fiber pairs with normal jitter be collected to exclude myasthenia gravis (MG). We applied principles of futility analysis from clinical trials in an attempt to reduce that requirement.

Methods

We utilized conditional power futility analysis to assess the probability of an abnormal 20-pair SFEMG based on ongoing analysis of jitter as each pair is collected. Rules for early test termination in the presence of 0, 1 or 2 abnormal pairs were identified. These rules were then applied to previously collected SFEMG data.

Results

SFEMG could be stopped at just 12 pairs if all are normal and at 17 pairs if 1 is abnormal. The rules successfully determined when SFEMG could be stopped in 104/106 (98%) studies originally reported to be normal.

Discussion

If the first 12 SFEMG pairs have normal jitter, the study can be terminated and interpreted as normal.

Introduction: Electrical impedance myography (EIM) is a non-invasive technique used for assessment of muscle health in which a high-frequency, low-amplitude electric current is applied to the skin overlying a muscle, and the resulting surface voltage is measured. We have previously used adhesive electrodes, application of which is inconvenient. We present data using a handheld electrode array (HEA) that we devised to expedite the EIM procedure in a clinical setting. Methods: Thirty-four healthy volunteers and 24 radiculopathy subjects underwent EIM testing using the HEA and adhesive electrodes. Results: The HEA was shown to have good test-retest reproducibility, with intraclass correlation coefficients as high as 0.99. HEA data correlated strongly with data from adhesive electrodes, ρ = 0.85 in healthy volunteers (p < 0.001) and ρ = 0.75 in radiculopathy subjects (p < 0.001). Discussion: These data support the potential use of a handheld array for performing rapid localized surface impedance measurements.

Localized impedance methods can provide useful approaches for assessing neuromuscular disease. The mechanism of these impedance changes remains, however, uncertain. In order to begin to understand the relation of muscle pathology to surface impedance values, 8 immature rats, 12 mature rats, and 8 mature rats that had undergone sciatic crush were killed. Tissue from the gastrocnemius muscle from each animal was measured in an impedance cell, and the conductivity and relative permittivity of the tissue calculated in both the longitudinal and transverse directions for frequencies of 2 kHz to 1 MHz. In addition, quantitative histological analysis was performed on the tissue. Significant elevations in transverse conductivity and transverse relative permittivity were found with animal growth, but longitudinal values showed no difference. After sciatic crush, both transverse and longitudinal conductivity increased significantly, with no change in the relative permittivity in either direction. The frequency dependence of the values also changed after nerve injury. In the healthy animals, there was a strong linear relation between measured conductivity and relative permittivity with cell area, but not for the sciatic crush animals. These results provide a first step toward developing a comprehensive understanding of how the electrical properties of muscle alter in neuromuscular disease states.

Electrical impedance measurements of skeletal muscle may be sensitive to age-associated declines in muscle health. In an effort to evaluate this concept further, we performed electrical impedance myography (EIM) using a handheld array on 38 individuals aged 19–50 years and 41 individuals aged 60–85 years. Individuals either had 7 upper extremity or 7 lower extremity muscles measured. The 50 kHz reactance, resistance and phase were used as the major outcome variables. Although the phase values were similar in both groups, both reactance and resistance values were lower in the lower extremities of the older individuals as compared to the younger (−23 ± 6%, p = 0.001 for reactance and −27 ± 7%, p = 0.005 for resistance), whereas changes in upper extremity values were not significantly different (−9 ± 5%, p = 0.096 for reactance and +5 ± 9%, p = 0.55 for resistance). When analyzing the genders separately, it became clear that this reduction in lower extremity values was most pronounced in men and less consistently present in women. These findings suggest that age- and gender-associated differences in muscle condition are detectable using EIM. The relationship of these easily obtained parameters to standard functional, imaging, and pathological markers of sarcopenia deserves further study.

We sought to determine whether elec- trical impedance myography (EIM) could serve as a diagnostic procedure for evaluation of radiculopathy. Methods: Twenty- seven patients with clinically and radiologically diagnosed cervi- cal or lumbosacral radiculopathy who met a “gold standard” defi- nition underwent EIM and standard needle electromyography (EMG) of multiple upper or lower extremity muscles. Results: EIM reactance values revealed consistent reductions in the radic- ulopathy-affected myotomal muscles as compared with those on the unaffected side; the degree of asymmetry was associated strongly with the degree of EMG abnormality (P<0.001). EIM had a sensitivity of 64.5% and a specificity of 77.0%; in compari- son, EMG had a sensitivity of 79.7% but a specificity of 69.7%. Conclusions: These findings support the potential for EIM to serve as a new non-invasive tool to assist in diagnosis of radicu- lopathy; however, further refinement of the technique is needed for this specific application.

Nerve conduction studies and electromyograms (EMGs) are most often performed in the outpatient setting in patients with suspected neuromuscular diseases, where they help the physician confirm the clinical diagnosis, assess the localization and severity of the disease, and plan further evaluation and treat- ment. Not infrequently, EMGs are requested on a relatively urgent basis for patients who are admitted to the hospital. Inpatient electrodiagnostic studies are usually requested in two situations: (1) as part of the diagnostic evaluation of patients who present with symptoms of a neuromuscular disorder; or (2) in patients who are admitted to the hospital with non-neuromuscular illnesses but develop symptoms suggestive of a neuromuscular disorder during the course of their illness. The second scenario com- monly occurs in patients who are in the intensive care unit and are unable to be weaned from the ven- tilator. This raises the possibility of a neuromuscular disorder as a cause of respiratory muscle weakness and ventilator dependence. The role of EMG in the evaluation of neuro- muscular disorders in the inpatient setting has not been studied previously. In this study, we evaluated the contribution of EMG to the diagnosis and man- agement of hospital inpatients. We hypothesized that inpatient EMGs (IP-EMGs) would frequently find clinically meaningful diagnoses that would affect the subsequent management of patients. The aims of this study were to compare the results of IP-EMGs with the referring physicians’ clinical diag- noses and to assess how often results of IP-EMGs changed the clinical diagnosis and altered further diagnostic evaluation and treatment.