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PubMed1998

Surface stimulation single-fiber electromyography.

Stimulation single-fiber electromyography (S-SFEMG) is an alternative method to SFEMG during voluntary contraction (VC-SFEMG). S-SFEMG is preferred to VC-SFEMG in uncooperating patients, children, and patients having severe weakness. Surface stimulation is a viable alternative to needle stimulation in S-SFEMG. In the present study, surface versus needle stimulation of facial nerve has been tested by recording from the orbicularis oculi and frontalis muscles. Jitter values obtained by both methods have been found to be nearly equal.

Adult↗
PubMed1998

Stimulated single-fiber electromyography in the rat.

We constructed an animal model of stimulated single-fiber electromyography (SFEMG) by testing Wistar rats under anesthesia. Stimuli of 1 Hz were applied to the sciatic nerve through an insulated monopolar needle electrode. Single-fiber action potentials were acquired from the gastrocnemius muscle. Jitter was assessed by the mean consecutive difference (MCD). Eighty-seven fibers were obtained from 12 rats. Their MCDs ranged from 2 to 72 micros (17.7+/-13.4). Seven of these values were less than or equal to 5 micros, and three exceeded 50 micros. Neuromuscular blocking agents injected into some of the rats induced considerable increases in jitter and blocking. A rat with one fiber with an MCD less than 5 micros also received an injection of curare. The jitter showed the same pattern of increment, evidence that the small jitter was not attributable to direct muscle stimulation. These results show that SFEMG can be used on rats. In addition, jitter reflects the changes in motor end-plate function. The findings also suggest the presence of an extremely high safety factor in rat neuromuscular junctions.

Action Potentials↗
PubMed1998

Diagnostic yield of stimulation and voluntary single-fiber electromyography in myasthenia gravis.

Voluntary and stimulation single-fiber electromyography were performed in the extensor digitorum communis muscle of 15 myasthenic patients. The increase in mean and individual mean consecutive difference as well as the proportion of blocking in the volitional activation were greater than in the stimulation method. These differences may be explained in part by the different degree of alteration in large as compared with small motor units in patients with myasthenia gravis.

Aged↗
PubMed1999

Single-fiber electromyography of the laryngeal muscles.

Single-fiber electromyography (SFEMG) is useful in the evaluation of disorders of neuromuscular transmission and the assessment of motor unit morphology. Standard EMG techniques are used routinely in the evaluation of laryngeal dysfunction, but the feasibility of laryngeal SFEMG has not been established. We, therefore, performed laryngeal SFEMG in 10 normal individuals to demonstrate the feasibility of the technique and generate preliminary normative data. We also studied 2 patients with amyotrophic lateral sclerosis and 1 patient previously treated with botulinum toxin for comparative purposes.

Adult↗
PubMed1999

Electromyography and magnetic resonance imaging in the evaluation of radiculopathy.

Electromyography (EMG) and magnetic resonance imaging (MRI) are commonly used in the diagnosis of cervical and lumbosacral radiculopathy, but the agreement between the two studies is unknown. We retrospectively studied 47 patients with a clinical history compatible with either cervical or lumbosacral radiculopathy who were evaluated with both an EMG and a spine MRI within 2 months of each other. Among these patients, 55% had an EMG abnormality and 57% had an MRI abnormality that correlated with the clinically estimated level of radiculopathy. The two studies agreed in a majority (60%) of patients, with both normal in 11 and both abnormal in 17; however, only one study was abnormal in a significant minority (40%), suggesting that the two studies remain complementary diagnostic modalities. The agreement was higher in patients with abnormal findings on neurologic examination, underscoring the difficulty of confirming the diagnosis in mild radiculopathy.

Adult↗
PubMed1999

Ocular myasthenia gravis: predictive value of single-fiber electromyography.

Extraocular muscle weakness is the most common presenting sign of myasthenia gravis (MG). More than half of patients presenting with symptoms isolated to these muscles (OMG) develop generalized myasthenia gravis (GMG) over the course of their illness. No clinical, laboratory, or electrophysiological features are recognized that identify these high-risk patients. We have therefore assessed the ability of single-fiber electromyography (SFEMG) to predict the development of GMG in patients presenting with OMG. Thirty-nine consecutive patients presenting with OMG underwent SFEMG of the extensor digitorum communis muscle as well as a battery of other laboratory and imaging studies at the time of diagnosis. All patients were followed prospectively for a minimum of 24 months or until they developed GMG. Two patients were excluded, leaving 37 for assessment. Twenty remained with pure OMG for the entire follow-up period (mean, 55 months). Twenty-six of the 37 had abnormal SFEMG studies at presentation. Eleven of these remained with OMG and 15 developed GMG. Fifty-eight percent of patients with an abnormal SFEMG developed GMG, whereas 82% of those with a normal study remained with OMG. Thus, a normal SFEMG was associated with MG remaining restricted to the extraocular muscles. (P = 0.036, Fisher's exact test), but an abnormal SFEMG was not predictive of subsequent development of GMG.

Adult↗
PubMed2000

Relation between maximum discharge rates on electromyography and motor unit number estimates.

To improve quantitative assessment of motor unit recruitment by standard concentric needle electromyography (CNEMG), hypothenar muscles of 22 healthy subjects, 18 with denervation, and 10 with a myopathy were studied. Discharge rates of motor units were measured in CNEMG recordings comprising action potentials of, at most, 4 motor units. Motor unit number estimation (MUNE) was done using the manual incremental method. In controls, the upper 95% limit of the discharge rate was 16.2/s. In all subjects, a strong nonlinear correlation between the number of motor units and the maximal discharge rate was found (r = 0.88, P < 0.0001). Increased discharge rates were found in all but one of the paretic muscles with denervation, but in none of the myopathic muscles. Measurement of the discharge rate is a simple and reliable procedure. If the discharge rate is high in a hypothenar muscle, loss of motor units can be inferred. Moreover, the discharge rate value gives an estimate of the number of motor units in that muscle. Thus, we suggest that maximal discharge rate be included in electromyographic reports.

Action Potentials↗
PubMed1998

Urethral sphincter needle electromyography in women: comparison of periurethral and transvaginal approaches.

Needle electromyography (EMG) of the striated urethral sphincter is the only technique that permits detection of individual motor unit action potentials (MUAPs) and is a valuable diagnostic tool in the evaluation of women with urinary incontinence and voiding disorders. The purpose of this study was to compare two methods of urethral needle EMG with respect to the number of MUAPs identified, the amount of patient discomfort, and the duration of the examination. Twenty consecutive women referred for electrodiagnostic testing to evaluate symptoms of urinary incontinence and/or voiding dysfunction underwent both methods of the needle examination in a prospective randomized cross-over study design with each patient acting as her own control. A full cross-over analysis was conducted to detect period and sequence effects using analysis of variance with a power of 0.85 and a significance level of P < 0.05. Twice as many MUAPs were identified using the periurethral approach (8.8 versus 3.9) with a mean difference of 5.0 (P=0.0008). There was a non-significant trend to greater patient discomfort with the periurethral approach; however, the discomfort was generally rated as mild to moderate. The length of time required to count all identifiable MUAPs did not vary significantly between the two methods. We conclude that the periurethral approach is superior to the transvaginal approach with respect to the quantity of electrodiagnostic information obtained and propose that this method be standardized to characterize more accurately the neurogenic component of urinary incontinence and voiding dysfunction for future electrodiagnostic studies.

Action Potentials↗
PubMed1999

Simple test of pelvic muscle contraction during pelvic examination: correlation to surface electromyography.

The objective of this work was to evaluate the utility of a "Kegel" contraction test in a primary care setting. Fifty-seven adult women completed a questionnaire, underwent pelvic examination, "Kegel" assessment, and measurement of same by vaginal sensor electromyography. Thirty-seven underwent repeat evaluations within 4 weeks. Inter- and intra-rater reliability of digital scale, intra-rater reliability for sEMG measurement, correlation between raters and sEMG, and correlation between scale scores and sEMG with history and pelvic exam were determined. Fifty-six percent were pre-menopausal, 44% post-menopausal. Urinary (62%) and rectal (37%) dysfunction were reported. Inter-rater reliability, intra-observer reproducibility for both raters and sEMG measurements, and correlation between raters and sEMG were significant (P< 0.05). Comparison of continence status and digital scores showed scores </=4 were more frequently associated with reported urinary incontinence (P<0.05). sEMG data also correlated to hormonal status and parity (P < 0.05). This digital scale is a useful assessment of "Kegel" contraction, correlating well to sEMG vaginal sensor readings and self-reported overall urinary continence status. Neurourol. Urodynam. 18:603-612, 1999.

Adult↗
PubMed1999

Female stress, urge, and mixed urinary incontinence are associated with a chronic and progressive pelvic floor/vaginal neuromuscular disorder: An investigation of 317 healthy and incontinent women using vaginal surface electromyography.

Reduction of the maximum vaginal surface electromyography (EMG) activity has previously been demonstrated in women with stress, urge, and mixed incontinence in comparison with healthy volunteers [Gunnarsson and Mattiasson, Scand J Urol Nephol 157:89-95, 1994]. The present study was performed to investigate if these EMG changes are age dependent and whether healthy parous women in general might show an age-related decrease of vaginal and pelvic neuromuscular activity. A total of 317 women, 144 with urinary incontinence and 173 healthy volunteers, 20 to 76 years of age, were investigated. The maximum EMG activity during repeated short contractions (2 s) was measured. We found that parous women who have maintained continence through the years had a normal pelvic floor function as estimated with vaginal surface EMG. In contrast, all three groups of incontinent women showed a successive decrease of the EMG activity with increasing age. This difference was highly significant (P < 0.001) in women above the age of 50. No significant differences could be seen between groups when stress, urge, and mixed incontinent women were compared. Even though any convincing correlation between the amount of urinary leakage and the reduction of EMG activity was not found, we conclude that a chronic and progressive deterioration of the pelvic-vaginal neuromuscular function occurs in women who develop urinary incontinence. The results support the view that a common pathophysiological mechanism in patients with stress, urge, and mixed incontinence might exist. The findings might help to establish a new perspective for the understanding of the pathophysiology, diagnosis, treatment, and prevention of female incontinence. Neurourol. Urodynam. 18:613-621, 1999.

Adult↗
PubMed2000

Anal sphincter electromyography after vaginal delivery: neuropathic insufficiency or normal wear and tear?

The study was performed to evaluate the potential role of vaginal delivery on innervation of the external anal sphincter (EAS) muscle. Forty-four women, 18 nulliparous and 26 of varying parity (1-4), without genitourinary prolapse, major urogynecological, anorectal, or neurological dysfunction were included. Participants' histories were evaluated by a questionnaire. Quantitative concentric needle electromyography (EMG) using multi-MUP analysis for sampling motor unit potentials (MUPs) in all volunteers, and "turn/amplitude" analysis for interference pattern (IP) analysis in 13 nulliparous and 23 parous women were applied. Pools of MUPs and IPs of parous and nulliparous women were formed and compared using the Mann-Whitney U test. Multiple linear regression analysis was used for evaluation of parity and obstetric variables. No difference between the groups was found in any MUP parameter, while a significant difference was found in two of five IP parameters. On multiple linear regression analysis, the number of deliveries was related to several MUP and IP parameters: the time elapsed since last delivery to MUP, and slight stress urinary incontinence to IP parameters. A group of parous women with (slight) stress incontinence had less "pathologic" MUP parameters, compared to those without. Vaginal delivery is indeed related to EAS muscle EMG abnormalities. However, these are minor and seem not to indicate loss of sphincter function. Our study casts some doubt on the commonly accepted preconception that significant damage to peripheral innervation of the EAS occurs even during uncomplicated deliveries.

Adult↗
PubMed2000

Electromyography in MRI--first recordings of peripheral nerve activation caused by fast magnetic field gradients.

Prior studies on the evaluation of stimulation by MRI were based on the subjective feeling of the volunteers. A wide variety of stimulation thresholds between the subjects was observed. In order to exclude subjective perception levels as a cause of this variation, we developed a method to investigate the activation of peripheral nerves after gradient switching by electromyography (EMG) within the MR-imager. Five healthy volunteers were positioned in the MR-scanner with the bridge of the nose at isocenter. The amplitude of sinusoidal pulse trains of the anterior-posterior gradient (rise-times: 200 or 300 micros, various numbers of oscillations) was increased stepwise. Four surface electrodes were placed on the region where a muscle-twitch was reported. Electric activity of the muscle during stimulation experiments was recorded with an MR-compatible electro-physiologic amplifier. Stimulation thresholds were defined by the appearance of an EMG-signal. Thresholds were sharp and consistent with the report of the subjects.

Adult↗
PubMed2000

Acute care pediatric electromyography.

The recognition of uncommon pediatric motor unit disorders or unusual clinical presentations of common illnesses, such as Guillain-Barré syndrome (GBS), have increased the need for electromyography (EMG) in childhood critical care units. There are two different clinical sets, one appropriate to newborns and infants and the other to older children. Some illnesses that present as an acute floppy infant are not found in the differential diagnosis of motor unit disorders in the older child or adult. These include spinal muscular atrophy, postvaccine poliomyelitis, intrauterine GBS, infantile botulism, and severe myopathies, such as myotonia dystrophy, and some glycogen storage diseases. An appreciation of the neurophysiological maturational norms is essential to an effective pediatric EMG consultation for children ages 0-3 years. Additionally, the neuromuscular complications of extended intubation and sepsis in children are gaining broader recognition. An increased dialogue between clinical neurophysiologists and pediatric neurologists and intensivists in both neonatal and pediatric intensive care units is essential.

Acute Disease↗
PubMed2000

Magnetic resonance imaging of denervated muscle: comparison to electromyography.

The purpose of the study is to further assess the usefulness of short TI (time to inversion) recovery (STIR) magnetic resonance imaging (MRI) in detecting denervation of skeletal muscle compared to needle electromyography (EMG). Ninety subjects with clinical evidence of peripheral nerve injury or radiculopathy underwent STIR MRI and EMG of the affected limb. In 74 (82%) of these subjects, a positive correlation was found between STIR MRI and EMG (P < 0.009). STIR MRI has a relative sensitivity of 84% and specificity of 100% for detecting denervation. A subset of 28 subjects underwent quantitative assessments of signal intensity ratio (SIR) from the STIR MRI. The rank order correlation coefficient between the SIR and abnormal spontaneous activity on EMG was 0.70 (P < 0.001). Increased signal intensity on STIR MRI corresponds closely with spontaneous activity on EMG in denervated muscle. Although less sensitive than EMG in detecting muscle denervation, STIR MRI may be a useful adjunctive diagnostic tool in this setting.

Adult↗
PubMed2000

Standardization of anal sphincter electromyography: effect of chronic constipation.

Severe chronic constipation has been implicated as a cause of damage to the pelvic floor innervation. The aim of the present study was to examine the role of mild to moderate chronic constipation, a condition more relevant for clinical electromyographers, because this complaint is common in patients sent for evaluation of possible neurogenic dysfunction of lower sacral myotomes. A group of 59 subjects without major uroneurological dysfunction, proctological disorders, or neurological abnormalities participated in the study, which involved concentric needle electromyography of the external anal sphincter (EAS). Motor unit potentials (MUPs; sampled using multi-MUP analysis) and interference pattern (IP, sampled using turn/amplitude analysis) of chronically constipated and control subjects were compared. No effect of chronic constipation on MUP/IP parameters compatible with neurogenic injury was found. Our results suggest that mild chronic constipation does not cause damage to the EAS innervation, and that no separate reference values are needed for this group of subjects.

Adult↗
PubMed2001

Surface electromyography using electrode arrays: a study of motor neuron disease.

The use of electromyography (EMG) is limited, particularly in the investigation of children, by the invasive nature of needle electrodes. Surface electrode techniques are an attractive alternative but the detected signals are greatly influenced by volume conductor effects, thus making their interpretation problematic. Using finite element analysis we investigated the relationship between surface potential distribution and motor unit depth, incorporating anisotropic conductivity to model muscle tissue and a range of subcutaneous fat thicknesses. The modeling results were used to analyze data recorded with a 16-channel surface electrode array, from 10 normals subjects and 12 patients with motor neuron disease. Differences in the motor units between the two groups were statistically significant (P < 0.01) and are consistent with reinnervation and increased motor unit territory in the patient group. This noninvasive technique shows promise as a more acceptable alternative to the use of conventional needle electrodes for neurophysiological investigations.

Adult↗
PubMed2001

Relation of electromyography-induced pain to type of recording electrodes.

Pain is an important consideration in the performance of needle electromyography (EMG). Prior investigations have suggested that pain is greater with a concentric needle electrode (CNE) than monopolar needle electrode (MNE). This prospective randomized study tested this hypothesis using improved methodology and disposable rather than reusable needle electrodes. Ninety consecutive outpatients were enrolled and randomized to CNE (diameter = 0.46 mm) or MNE (diameter = 0.41 mm) arms. Subjects underwent a standardized 4 limb-muscle needle EMG protocol during which pretest and posttest verbal analog pain scale (0-10) measures were obtained. As anticipated, EMG-induced pain was significantly higher (P < 0.001) than pre-EMG baseline pain. However, analysis of variance (ANOVA) revealed no significant differences in pain ratings between the CNE and MNE arms. Among other factors analyzed, only gender significantly influenced EMG-induced pain, with females reporting higher levels than males. Thus, pain is not an important selection criterion for type of disposable needle electrode.

Adult↗
PubMed2000

The value of external anal sphincter electromyography for the diagnosis of multiple system atrophy.

OBJECTIVE: To assess the value of external anal sphincter electromyography (ASEMG) for the diagnosis of multiple system atrophy (MSA) among various causes of parkinsonism. ASEMG denervation profiles have previously been proposed as a diagnosis test for MSA, but their specificity is disputed. METHODS: ASEMG variables of 52 parkinsonian patients were analyzed according to the clinical diagnosis: MSA (n = 31) or no MSA (n = 21). Mean motor unit potential duration, percentage of polyphasicity, and the electromyographer's interpretation were analyzed according to clinical diagnosis, disease duration, genitourinary symptoms, gender, parity, and history of pelvic surgery. RESULTS: All patients with MSA showed ASEMG denervation. Mean motor unit potential duration was the most discriminant variable. No patient with MSA had a mean duration less than 12 ms and no patient without MSA had one greater than 16 ms. ASEMG discriminates between patients with MSA and Parkinson's disease. Using a threshold of 13 ms, the sensitivity was 80% and specificity was almost 70% (positive predictive value, 80%) for the diagnosis of MSA. Age, history of pelvic surgery, and to a lesser extent, female gender, parity, disease duration, and presence of urinary symptoms increased the likelihood of abnormal ASEMG. CONCLUSION: ASEMG was highly sensitive and rather specific for the diagnosis of MSA.

Adult↗