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PubMed1999

Using surface electromyography to assess sex differences in neuromuscular response characteristics.

OBJECTIVE: To provide an overview of the continuum of muscular responses that typically occur with joint perturbation. The applications and limitations of surface electromyography (sEMG) in evaluating these responses are also addressed. Research applications assessing sex differences in these neuromuscular response characteristics are discussed along with suggestions for future research. DATA SOURCES: MEDLINE was searched from 1969 through 1998. Sport DISCUS was searched from 1975 through 1998. Terms searched included "anterior cruciate ligament," "epidemiology," "neuromuscular control," "neuromuscular performance," "electromyography," "latency," "reflex," "electromechanical delay," "dynamic stability," "intrinsic stiffness," "short-range stiffness," "muscle," "mechanoreceptors," and "reaction time." DATA SYNTHESIS: It is widely accepted that efficient neuromuscular control is essential to dynamic joint stability and protection. Many studies have established the significant role of the muscles, and particularly the hamstrings, in providing knee stability. By observing the timing, phasing, and recruitment of reflexive muscular activation after a loading stress to the knee, we can better understand the coordinative mechanisms necessary to protect the joint and prevent ligament injury. A number of research models have employed the use of sEMG to evaluate neuromuscular responses at the knee after joint loading or perturbation. However, very few studies have specifically addressed potential sex differences in these response characteristics. CONCLUSIONS/RECOMMENDATIONS: From the limited research available, it appears that a sex difference may exist in some aspects of neuromuscular responses. However, further research is needed to explore these differences at the knee and their potential role as predisposing factors to the higher incidence of anterior cruciate ligament injuries in females. Future studies should examine sex differences in neuromuscular response characteristics at the knee under functional, weight-bearing conditions while controlling for training and other confounding variables. The limitations of sEMG should be considered when interpreting neuromuscular response studies.

Journal Article↗

PubMed1954

The value of electromyography in neurology.

By detection of muscular fibrillation, a sign of motor nerve impairment, through electromyography, diseases of the motor nervous system can be distinguished from muscular disorders, malingering, and psychoneurotic states. The site of lesion can be determined and the degree of impairment and progress of recovery can be estimated. The method has been used successfully in amyotrophic lateral sclerosis, poliomyelitis, peripheral neuritis and neuronitis, and root compression syndrome, as also for indirect evidence in muscular dystrophy and other myopathic conditions.

Amyotrophic Lateral Sclerosis↗

PubMed1958

Electromyography; uses and limitations.

A normal muscle at rest emits no detectable electric current, but in action, in diseases of the muscle and in denervation it emits electric impulses characteristic of these states. The impulses can be amplified and studied through the sonic and oscilloscopic patterns they create. These patterns are sufficiently different so that simple atrophy of disuse can be distinguished from the denervation that may be associated with it. Since denervation can be localized to individual muscles and thence to the nerves controlling them, electromyography serves much the same function as myelography, with comparable accuracy and with greater safety and simplicity. It aids in the diagnosis of several muscular diseases of children and adults. Because electromyographic changes due to injury do not appear until 18 to 21 days later, a study made soon after injury can either disclose or rule out preexisting lesions. Then a later study indicating denervation is objective evidence that any disability is due to the injury in question.

Adult↗

PubMed1959

Electromyography in strabismus.

Electromyography of the human extraocular muscles is a new research tool designed to elucidate many problems in ocular physiology. Although at present it affords little clinical help in the diagnosis and treatment of strabismus, it may in time be of value in neuro-ophthalmologic disease.

Electromyography↗

PubMed1975

Myasthenic syndrome studied with single fiber electromyography.

A patient with the myasthenic syndrome was investigated with single fiber electromyography (SFEMG). It was found that 35 of 36 potential pairs had increased "jitter" and that 29 of these demonstrated impulse blockings. There was improvement in neuromuscular transmission with higher rates of innervation. Transmission worsened following rest. The SFEMG findings at the motor end-plate level correlate well with the results of repetitive stimulation and in vitro studies.

Action Potentials↗

PubMed1978

Human botulism studied with single-fiber electromyography.

In two cases of mild human botulism, conventional electromyography (EMG) was normal. In one case, the investigation with reptitive nerve stimulation showed slightly abnormal results, but in the other case the findings were within normal limits. Single-fiber EMG showed abnormal neuromuscular function and at later investigations as well, when the patient no longer showed any muscular fatigability. The jitter was frequency dependent and decreased with higher innervation frequency. The single-fiber EMG findings normalized after three months. The results are in agreement with the known disturbance of acetylcholine release.

Adult↗

PubMed1979

Open-biopsy electromyography. Direct correlation of a pattern of excessively recruited, pathologically small motor unit potentials with histologic evidence of neuropathy.

Open-biopsy electromyography (EMG) of two muscles of a 29-year-old man with slowly progressive proximal weakness demonstrated a striking pattern of excessively recruited, pathologically small motor unit potentials. This pattern is usually equated with myopathy. Histologic study of tissue enclosing the recording sites, however, yielded evidence of neurogenic disease alone. In muscle, this included isolated and small groups of atrophic type I, IIA, and IIB fibers, and in intramuscular nerve a loss of myelinated fibers with connective tissue and Schwann cell proliferation. The EMG pattern is considered to reflect a reduced number of activated muscle fibers within motor units due to random neurogenic involvement of terminal axons.

Adult↗

PubMed1984

Correlation of electromyography with computed tomography in evaluation of lower back pain.

High-resolution computed tomography (CT) of the lumbar spine in 80 consecutive patients with lower back pain was correlated with electromyography (EMG) and with the clinical outcome at one-year follow-up. Forty-two patients had abnormal EMG findings that could be explained on the basis of anatomical defect(s) seen on CT. Nine had normal CT scans but abnormal EMGs, and five patients had normal EMGs but abnormal CT scans. Thirteen of the 80 patients were further investigated with myelography, 22 patients underwent surgical exploration, and the remainder received conservative therapy. In the majority of cases, surgery confirmed the abnormal CT and EMG findings; in some instances, however, myelography and/or surgery confirmed the abnormality only at the level demonstrated on EMG. The CT and EMG often agree. However, an abnormal EMG seems to correlate better with the demonstrated course of radiculopathy than CT.

Adult↗

PubMed1986

Short-latency somatosensory-evoked potentials from radial, median, ulnar, and peroneal nerve stimulation in the assessment of cervical spondylosis. Comparison with conventional electromyography.

A study of data on 30 patients with cervical spondylosis was carried out to determine whether short-latency somatosensory-evoked responses (SEPs) to median, ulnar, radial, and peroneal nerve stimulation provided additional information to that obtained by electromyography (EMG), late responses, and peripheral conduction studies. Peripheral studies, EMG results and SEPs were within normal limits in ten patients with pain, but without objective neurological deficit. By contrast, of ten patients who had objective signs of root compression, conventional EMG results were normal in nine, but abnormalities of the SEPs from radial nerve stimulation were obtained in only five patients, and were normal from ulnar and median nerve stimulation. In ten patients with clinical features of myelopathy, seven had abnormal median SEPs and all had abnormal peroneal SEPs, whereas EMG results were abnormal in only five patients. It is suggested that SEPs and EMG are both of limited use in patients with only symptoms of root compression. In patients with signs of root compression, EMG is the most sensitive procedure; however, some additional information can be obtained from superficial radial SEPs. In patients with cervical myelopathy, SEP was the most useful procedure, especially when upper and lower limbs were studied.

Adult↗

PubMed1978

Design and testing of a new electrode for laryngeal electromyography.

Electromyography of the intrinsic laryngeal muscles has not been widely used, partly because of the difficulty of accurate insertion and stabilization of existing electrodes. The sampling portion of our original electrode has been redesigned. Two needle electrodes, 4 mm in length, protrude from a truncated coneshaped, nonconducting body that has been fashioned to sit in the laryngeal ventricle. The depth of insertion is controlled, and the device resists accidental extrusion.

Electrodes↗

PubMed1985

Anal sphincter electromyography after colectomy, mucosal rectectomy, and ileoanal anastomosis.

Electromyography (EMG) was used to evaluate the external anal sphincter in 27 patients following colectomy, distal mucosal rectectomy, and ileoanal anastomosis. The studies were conducted four months to 58 months (mean, 20 months) following the restoration of intestinal continuity. Nine patients underwent endoanal rectal mucosal stripping, while in 18 patients the rectum was everted to facilitate the stripping. Postoperative continence varied widely, from perfect to frequent and severe mucous of fecal leak. Abnormal motor-unit potentials were identified by EMG in nine patients and this finding was usually associated with poor continence. The sex of the patient, technique of mucosal stripping, and type of anastomosis did not influence the EMG result, but patients at least 40 years old all had abnormal EMGs. We conclude that poor continence after ileoanal anastomosis correlates with an abnormal EMG of the external anal sphincter. The cause of the EMG abnormality is unclear.

Adolescent↗

PubMed1996

Single-fiber electromyography in diabetic peripheral polyneuropathy.

In this study we examined the value of single-fiber electromyography (SFEMG) in assessing the degree of reinnervation in diabetic patients with clinical neuropathy. Relationships between reinnervation and the degree of metabolic control, and/or duration of diabetes were examined. Thirty-six insulin-dependent diabetics and 54 non-insulin-dependent diabetics underwent SFEMG examination of the tibialis anterior muscle, as well as conventional nerve conduction studies of the upper and lower limbs. All patients examined exhibited some abnormality of SFEMG even in the presence of normal nerve conduction studies found in 18% of patients. In diabetic patients, the jitter in the tibialis anterior muscle correlated positively with glycosylated hemoglobin; whereas lower limb nerve conduction studies did not correlate with this measure of diabetic control. These data suggest that SFEMG is a sensitive measure of nerve function and reinnervation and that it may reflect the dynamic changes in metabolic status in diabetic patients.

Adult↗

PubMed1996

The demonstration of the size principle in humans using macro electromyography and precision decomposition.

We set out to study the relationship between a motor unit's size and firing rates and its recruitment threshold and recruitment order. The data were collected from the first dorsal interosseous muscle of 11 normal subjects and analyzed using the precision decomposition and macro electromyography techniques. Our study showed that the recruitment order of a motor unit varies directly with its recruitment threshold (P<0.00005) and that there is a progressive increase in the macro potential size of successively recruited motor units (P=0.002). The firing rates of motor units vary inversely with their recruitment order (P=0.006), the smaller, earlier recruited units consistently reaching higher firing rates than the larger, later recruited units. This study conforms the existence of a size principle of motor unit recruitment in humans and reveals the interactions between a motor unit's size and its firing rate properties.

Adult↗

PubMed1996

AAEM minimonograph #25: single-fiber electromyography.

Single-fiber electromyography (SFEMG) is a selective recording technique in which a needle electrode with a small recording surface in the side is used to identify action potentials from individual muscle fibers. The SFEMG parameters of greatest clinical use are fiber density (FD) and neuromuscular jitter. FD reflects the local organization of muscle fibers within the motor unit; jitter reflects the safety factor of neuromuscular transmission at individual neuromuscular junctions. SFEMG can be of great value in demonstrating or excluding abnormalities in mild or questionable disease of nerve, muscle, or the neuromuscular junction. The neuromuscular jitter may be measured during nerve stimulation, which is particularly useful in uncooperative patients or when it is desirable to control the firing rate precisely, or during voluntary muscle activation, which is less subject to technical artifact. The SFEMG findings may not be specific to a particular disease, but they frequently increase understanding of the disease process by demonstrating abnormal neuromuscular transmission or rearrangement of muscle fibers within the motor unit, which complements information from more conventional EMG examinations.

Electromyography↗

PubMed1997

Stimulated single-fiber electromyography in Lambert-Eaton myasthenic syndrome before and after 3,4-diaminopyridine.

A patient with LEMS unrelated to cancer was studied by stimulated single-fiber electromyography (SFEMG) before and 3 months after the onset of therapy with 3,4-diaminopyridine. All end-plates showed a progressive reduction in blockings and jitter with the increase in stimulation rate. Treatment significantly corrected this feature, but the overall pattern of frequency-improved jitter remained. Such widespread finding is rare but diagnostic for Lambert-Eaton myasthenic syndrome. Stimulated SFEMG can be used to monitor therapy in such patients.

4-Aminopyridine↗

PubMed1997

Electromyography of the external anal sphincter in patients with Parkinson's disease and multiple system atrophy: frequency of abnormal spontaneous activity and polyphasic motor unit potentials.

Electromyographic studies of the external anal sphincter muscle have received increasing attention in the differential diagnosis of patients with parkinsonism. Based on the fact that the external anal sphincter muscle is partly innervated by fibers that originate in Onuf's nucleus in the segments S2-S4 of the spinal cord, an increased duration of the motor unit potentials (MUPs) and an increased polyphasia may reflect neuronal loss of these lower motor neurons characteristic for multiple system atrophy. We report the results of anal sphincter electromyography in 15 patients with clinically probable multiple system atrophy (MSA) and 10 patients with Parkinson's disease (PD). There was no significant difference between patients with MSA and patients with PD concerning the duration of MUPs, mean number of phases, and rate of polyphasic motor potentials. There was a tendency for a longer mean duration and increased polyphasia in patients with MSA compared to patients with PD. Spontaneous activity was recorded in 11 of 15 patients with MSA occurring especially in patients with MSA of the striatonigral type, but not in patients with PD. In this study, the duration of MUPs and the rate of polyphasia were unreliable criteria in the electrophysiological differential diagnosis of patients with parkinsonism. Abnormal spontaneous activity, although difficult to detect, is a more specific marker for neuronal degeneration of Onuf's nucleus occurring in patients with MSA.

Adult↗

PubMed1997

Diagnostic yield of noninvasive high spatial resolution electromyography in neuromuscular diseases.

High Spatial Resolution electromyography (HSR-EMG), a new kind of noninvasive surface EMG based on a spatial filtering technique, was evaluated with respect to the diagnosis of neuromuscular diseases. HSR-EMG measurements were recorded from 61 healthy subjects and 72 patients with different neuromuscular diseases and analyzed quantitatively. The results indicate that a few parameters such as muscular conduction velocity, dwell time over root mean square, autocorrelation function, and chi-value are sufficient to recognize and classify specific signal alterations due to neuromuscular disorders. A diagnostic evaluation procedure calculating automatically the most probable diagnosis from the parameter results could assign the correct diagnosis to about 81% of the investigated patients and healthy subjects. Myopathic disorders were recognized with a sensitivity of 85% (specificity: 97%), neuropathic disorders with a sensitivity of 68% (specificity: 98%). We conclude that HSR-EMG shows a diagnostic validity similar to that described in literature for needle EMG. Moreover, the noninvasive technique provides the advantage of a simple and painless application.

Adolescent↗

PubMed1997

Value of sphincter electromyography in the diagnosis of multiple system atrophy.

It is clinically important, to distinguish between idiopathic Parkinson's disease (IPD) and multiple system atrophy (MSA) not only because of the implications for prognosis but also because urinary incontinence is often an early troublesome feature of MSA and by making the correct neurological diagnosis inappropriate urological surgery may be avoided. Onuf's nucleus in the sacral cord is the location of the anterior horn cells innervating the sphincters, and it is among central nervous system sites affected by neuronal cell loss in MSA but not in IPD. A systematic analysis of motor units recorded from the sphincter looking for changes of chronic reinnervation has therefore been used to distinguish between these conditions. Sphincter electromyography (EMG) was carried out in 126 patients with suspected MSA with review of their case notes up to 2 years later. Of those in whom a diagnosis of MSA was made, 82% had had an abnormal sphincter EMG.

Adult↗