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PubMed2002

Clinical impact of single-fiber electromyography.

The major clinical impact of single-fiber electromyography has been from its role in confirming, or excluding, the diagnosis of myasthenia gravis (MG). Jitter measurements also have a clinical role in demonstrating changes in disease severity in patients with MG and Lambert-Eaton myasthenic syndrome, in demonstrating subtle changes in motor unit architecture and physiology in patients with nerve and muscle diseases, and in demonstrating the remote effects of locally injected botulinum toxin. In addition to these clinical roles, the ability to identify the activity from single muscle fibers makes it possible to mark the discharges of single motor units. This, along with information gained by jitter and fiber-density measurements, has uniquely increased our understanding of motor unit organization and function in normal and disease states.

Electromyography↗
PubMed2002

Scanning electromyography.

A special electromyography (EMG) method, scanning EMG, was introduced by Stålberg and Antoni in 1980 to study the electrophysiological cross sections and sizes of motor units. Scanning EMG gives a new approach for the evaluation of the electrical properties of motor units, providing new data on the normal anatomical distribution of muscle fibers and its changes in different pathologies of the muscle. The description of scanning EMG recordings required the introduction of new parameters (lengths of motor unit cross sections, fractions of motor units, and silent areas), in addition to those used with conventional EMG recordings, and the traditional parameters (duration, amplitude, etc.) acquired new and more accurate explanations. Normal scanning EMG recordings are available for biceps brachii, anterior tibial, and masseter muscles. The findings in normal muscles agree with the nonrandom distribution of muscle fibers in motor units and confirm the suggestion that muscle fibers within motor units tend to be arranged in clusters. In muscular dystrophies, the sizes of motor unit territories do not differ significantly from the normal values. However, the configuration of motor units changes considerably. Abrupt changes in amplitude and duration, segments of short and long duration, increased numbers of fractions, and silent areas have been revealed, showing that dystrophic motor units are definitely fragmented. Scanning EMG supports the assumption that there is clustering of muscle fibers within the dystrophic motor unit, with local grouping of muscle fibers. In neurogenic lesions, the length of motor units is normal or only slightly increased. Reinnervated motor units are restricted to the fascicles in which they are originally found. Reinnervation does not result in an increase in the number of fractions, but the amplitude of the potentials, the length of polyphasic sections, and the duration increase. The increase in the number and length of polyphasic sections can differentiate normal motor units from abnormal ones. However, other features (amplitude, duration, number of fractions, and presence of silent areas) are also necessary to distinguish neurogenic processes from myogenic ones.

Animals↗
PubMed2002

New attempts to quantify concentric needle electromyography.

Quantitative motor unit potential (MUP) analysis, which is a leading method of quantitative evaluation of concentric needle electromyography, has several inherent limitations. First, the most essential features of neurogenic or myogenic changes manifest as recruitment abnormalities, rather than as changes in MUP morphology. Second, two factors related to MUP sampling, focusing and level of contraction, greatly influence the parameters of sampled MUPs. Third, the MUP duration, considered to be the cardinal parameter in MUP analysis, has several drawbacks, including low stability and low discriminant sensitivity. We developed a new MUP parameter, the size index (SI), which is calculated from the MUP amplitude and area/amplitude ratio (thickness). The SI remained almost constant during electrode movements, as demonstrated by manual scanning of MUPs. It is a stable and robust parameter and achieved an extremely high ability to discriminate between normal and large neurogenic MUPs. It identifies features related to the sound produced by the MUP on the audio monitor, which is often used by trained electromyographers for qualitative assessments of MUPs.

Electromyography↗
PubMed2002

Story of electromyography equipment.

It all started in 1950 with the introduction of the first commercially available electromyography (EMG) system. From 1950 to 1973 was the era of the analog EMG systems: EMG signals were recorded, and subsequent analyses were carried out manually on film or paper. From 1973 to 1982, the first modular digital EMG systems were introduced. Dedicated analysis modules were introduced, but detailed analysis was still done on paper. In 1982, the first system controlled by a microprocessor was introduced. From 1982 to 1993, many new ways of analyzing EMG signals and basic reporting features were implemented in the EMG systems. Since 1993, personal computer technology has been used in EMG systems. Standard software and hardware components are used to record, analyze, and document EMG examinations. Since 1950, many people have influenced the development of new features in commercial EMG systems. However, within the last 3 decades, Erik Stålberg has always been in the forefront and has shown ways of implementing new methods for analyzing EMG activity or nerve signals. The development of new commercial EMG systems has been dependent on the technology introduced to the market at that particular period of time. This article only refers to systems that have been sold or are now being sold worldwide.

Computers↗
PubMed2002

Defining extensible markup language standards for electromyography data transmission across the world-wide web.

Different electromyography (EMG) machines store their data in different formats that vary from manufacturer to manufacturer and even between different EMG machines from the same manufacturer. As advanced as these machines are today, it is necessary in most cases to use faxes, scanners, or a common interface such as Adobe's file format to exchange data between them. A possible solution to this problem is to translate the EMG machine's data output into a common format that can be read (and displayed) by commonly available programs or, even better, by a Web browser. We describe an EMG-extensible markup language (XML) translation program that takes proprietary data from an EMG machine and translates the data into XML, a common language format. Predefined extensible stylesheet language (XSL) style sheets allow the display of the data in user-defined formats for EMG machines, personal digital assistants such as Palm Pilots, and even cellular phones.

Electromyography↗
PubMed2002

Electromyography of human cricopharyngeal muscle of the upper esophageal sphincter.

The cricopharyngeus (CP) is a striated muscle sphincter situated at the pharyngoesophageal junction. The upper esophageal sphincter is comprised of the striated CP muscle and nonmuscular components at the level of the cricoid cartilage. This review describes the basic anatomy and physiology of the CP muscle, its central and peripheral relationship, methods of investigating it, and electrophysiological properties related to deglutition. The main function of the CP muscle is to control flow between the pharynx and esophagus. The CP sphincter muscle is tonically contracted at rest and relaxes during swallowing, belching, and vomiting. Electromyography (EMG) of the CP sphincter muscle has been undertaken frequently in a variety of subhuman species with the aim of understanding deglutition, whereas it has seldom been reported in healthy human subjects and patients. Increased knowledge of the physiology and anatomy of the human CP sphincter muscle is not only important scientifically but is necessary for advancing the diagnosis and treatment of oropharyngeal dysphagia, for which neurological causes are responsible in 80% of cases.

Animals↗
PubMed2003

Iatrogenic complications and risks of nerve conduction studies and needle electromyography.

Electrodiagnostic procedures are routinely performed in patients with a variety of neuromuscular disorders. These studies are generally well tolerated and rarely thought to be associated with any significant side effects. However, needle electromyography is an invasive procedure and under certain situations has the potential to be associated with iatrogenic complications, including bleeding, infection, nerve injury, pneumothorax, and other local trauma. Similar complications are possible if needles are used for either stimulating or recording. In addition, like all other electrical devices and monitoring equipment connected to patients, electrodiagnostic testing carries the risk of stray leakage currents that under certain circumstances can result in electrical injury, especially in patients in the intensive care setting. Similarly, certain precautions are required during nerve conduction studies (NCS) in patients with pacemakers and other similar cardiac devices. In this review, we address the known and theoretical complications of NCS and needle electrode examination, and the possible methods to avoid such hazards.

Electromyography↗
PubMed2003

Acute compartment syndrome of the leg following diagnostic electromyography.

Acute compartment syndrome of the lower extremity is typically associated with some form of trauma, either fracture or blunt injury. Accurate diagnosis and urgent treatment of this condition is required for preservation of the viability of the limb. We report the case of a 73-year-old man who developed an acute compartment syndrome of the leg after diagnostic electromyography. Potential causes and treatment are discussed.

Acute Disease↗
PubMed2003

Decomposition-based quantitative electromyography: methods and initial normative data in five muscles.

Quantitative electromyographic (EMG) techniques provide clinically useful information to aid in the diagnosis and follow the course or response to treatment of diseases affecting the motor system. The purpose of this study was to describe a decomposition-based quantitative electromyography method (DQEMG) designed to obtain clinically applicable information relating to motor unit potential (MUP) size and configuration, and motor unit (MU) firing characteristics. Additionally, preliminary normative data were obtained from the deltoid, biceps brachii, first dorsal interosseous, vastus medialis, and tibialis anterior muscles of 13 control subjects. DQEMG was capable of efficiently and accurately extracting MUP data from complex interference patterns during mild to moderate contractions. MUP amplitude, surface-detected MUP (S-MUP) amplitude, MUP duration, number of phases, and MU firing frequencies varied significantly across muscles. The mean parameter values for the individual muscles studied were similar to previous reports based on other quantitative methods. The main advantages of this method are the speed of data acquisition and processing, the ability to obtain MUPs from MUs with low and higher recruitment thresholds, and the ability to obtain both S-MUP or macro-MUP data as well as MU firing rate information.

Adult↗
PubMed2004

Sphincter electromyography in diagnosis of multiple system atrophy: technical issues.

Possible technical reasons for the controversy over the role of sphincter electromyography (EMG) in the diagnosis of multiple system atrophy (MSA) were analyzed. In a review of the literature, a high sensitivity (>60%) was found reported in 11 studies that included late components, and no value of the test was found in 4 studies that excluded them. This was also corroborated in a pilot study of 5 patients with probable MSA. With late components included, the mean motor unit potential (MUP) duration was prolonged in all 4 patients with an adequate single-MUP analysis sample and, with late components excluded, in 2 of 5 patients on multi-MUP analysis. At least in diagnostic EMG of MSA patients, late components should be included in the measurement of MUP duration.

Action Potentials↗
PubMed2003

Laryngeal electromyography: an evidence-based review.

This article reports on an evidence-based review of laryngeal electromyography (EMG) as a technique for use in the diagnosis, prognosis, and treatment of laryngeal movement disorders including the laryngeal dystonias, vocal fold paralysis, and other neurolaryngological disorders. The authors performed a systematic review of the medical literature from 1944 through 2001 on the clinical application of EMG to laryngeal disorders. Thirty-three of the 584 articles met the predefined inclusion criteria. The evidence demonstrated that in a double-blind treatment trial of botulinum toxin versus saline, laryngeal EMG used to guide injections into the thyroarytenoid muscle in persons with adductor spasmodic dysphonia was beneficial. A cross-over comparison between laryngeal EMG-guided injection and endoscopic injection of botulinum toxin into the posterior cricoarytenoid muscle in abductor spasmodic dysphonia found no significant difference between the two techniques and no significant treatment benefit. Based on the evidence, laryngeal EMG is possibly useful for the injection of botulinum toxin into the thyroarytenoid muscle in the treatment of adductor spasmodic dysphonia. There were no evidence-based data sufficient to support or refute the value of laryngeal EMG for the other uses investigated, although there is extensive anecdotal literature suggesting that it is useful for each of them. There is an urgent need for evidence-based research addressing the use of laryngeal EMG for other applications.

Electrodiagnosis↗
PubMed2004

Muscle-fiber conduction velocity and electromyography as diagnostic tools in patients with suspected inflammatory myopathy: a prospective study.

Combinations of different techniques can increase the diagnostic yield from neurophysiological examination of muscle. In 25 patients with suspected inflammatory myopathy, we prospectively performed needle electromyography (EMG) and measured muscle-fiber conduction velocity (MFCV) in a single muscle, using a technique with direct muscle-fiber stimulation and recording. Results of MFCV were compared with final diagnosis, EMG, and needle muscle biopsy. Diagnostic accuracy of combined MFCV and EMG studies was 72%, compared to 60% for EMG alone. This improvement was due to a gain in specificity. The MFCV did not prove useful in discriminating inflammatory myopathy from other myopathies. Furthermore, we found a correlation of 92% between variability of MFCV and myopathic changes in muscle biopsy. We conclude that the utility of electrodiagnostic examination can be increased if EMG examination is combined with MFCV studies.

Action Potentials↗
PubMed2001

Stimulated single fiber electromyography in the mouse: techniques and normative data.

As the number of new transgenic mouse models of human neuromuscular disease continues to increase, the development of sophisticated electrophysiologic techniques for assessing the peripheral nervous system in these models has become important. Neuromuscular junction (NMJ) dysfunction, in particular, is often not detectable by morphologic or other techniques. To enable sensitive testing of murine NMJ function, we developed and tested a method for stimulated single fiber electromyography (S-SFEMG) in the gastrocnemius muscles of anesthetized mice. Jitter was assessed by measuring the mean consecutive latency difference (MCD) of single fiber responses to sciatic nerve stimulation at 2 HZ. Mean MCD values in normothermic mice were in the range of 6-8 micros for different strains, with no MCD values exceeding 25 micros. Reduced core temperature (to 29 degrees--30 degrees C) resulted in increased jitter, whereas intubation and mechanical ventilation of mice did not alter these values. Intraperitoneal and intravenous injection of vecuronium, however, resulted in progressively increased jitter followed by blocking in continuously monitored fibers. These observations validate the utility of S-SFEMG in mice as an index of NMJ function under a variety of physiologic conditions, and suggest that a high safety factor for neuromuscular transmission exists at mouse NMJs.

Animals↗
PubMed2001

Standardization of anal sphincter electromyography: utility of motor unit potential parameters.

Advanced electromyography systems offer quantitative analysis of a number of motor unit potential (MUP) parameters. However, only limited data are available on the diagnostic usefulness of these parameters. In the present study, we compared the sensitivities of MUP parameters in revealing "neuropathic" changes in the external anal sphincter (EAS) muscles in 56 patients examined 5-240 months after damage to the cauda equina or conus medullaris. Using multi-MUP analysis, 20 MUPs were obtained from patients' EAS muscles. Their MUP parameters were compared with normative data from 64 controls. The diagnostic sensitivities of mean values/"outliers" of MUP parameters for detecting neuropathic EAS muscles were calculated (area 25%/30%; number of turns 18%/29%; size index 13%/24%; thickness 18%/18%; amplitude 17%/17%; spike duration 20%/9%; duration 15%/12%; number of phases 15%/11%; and their combination 51%/52%). Altogether, the cumulative sensitivity of multi-MUP analysis using both mean values and "outliers" was 62%. The combination of MUP parameters improves the diagnostic yield of MUP analysis, but the influence on specificity remains unknown.

Adult↗
PubMed2005

Anal sphincter electromyography: editing of sampled motor unit action potentials.

During multi-motor unit action potential (MUAP) analysis of the tonically contracted external anal sphincter (EAS), a mild interference pattern often obscures the baseline, affecting the algorithm's ability to determine accurate boundaries of detected MUAPs. To assess the equivalence of methods of editing and selecting candidate MUAPs from the EAS, 17 nulliparous women underwent concentric needle electromyography (EMG) of the EAS using multi-MUAP software. The selected MUAPs either were accepted without question ("automated"), or a subset was deleted due to a noisy baseline ("manual-deletion") or manually marked ("manual-mark"). A second examiner repeated the analysis. Each examiner found that the two editing methods were equivalent and yielded results that differed from those obtained by automated analysis of unedited data. However, there was a moderate difference in MUAP amplitude when the manual-deletion method was compared between the two examiners. Editing of selected EAS MUAPs during multi-MUAP analysis is required, and development of common protocols is essential to enable meaningful comparisons between similar studies.

Action Potentials↗
PubMed2005

Decomposition-based quantitative electromyography: effect of force on motor unit potentials and motor unit number estimates.

Decomposition-based quantitative electromyography (DQEMG) allows for the collection of motor unit potentials (MUPs) over a broad range of force levels. Given the size principle of motor unit recruitment, it may be necessary to control for force when using DQEMG for the purpose of deriving a motor unit number estimate (MUNE). Therefore, this study was performed to examine the effect of force on the physiological characteristics of concentric needle- and surface-detected MUPs and the subsequent impact on MUNEs obtained from the first dorsal interosseous (FDI) muscle sampled using DQEMG. Maximum M waves were elicited in 10 subjects with supramaximal stimulation of the ulnar nerve at the wrist. Intramuscular and surface-detected EMG signals were collected simultaneously during 30-s voluntary isometric contractions performed at specific percentages of maximal voluntary contraction (MVC). Decomposition algorithms were used to identify needle-detected MUPs and their individual MU firing times. These MU firing times were used as triggers to extract their corresponding surface-detected MUPs (S-MUPs) using spike-triggered averaging. A mean S-MUP was then calculated, the size of which was divided into the maximum M-wave size to derive a MUNE. Increased levels of contraction had a significant effect on needle- and surface-detected MUP size, firing rate, and MUNE. These results suggest that force level is an important factor to consider when performing quantitative EMG, including MUNEs with this method.

Adult↗
PubMed2006

Which patients need referral for anal sphincter electromyography?

Needle electromyography (EMG) of lower sacral myotomes is useful in certain patients with urinary, bowel, or sexual dysfunction. The aim of the study was to identify the clinical profile of patients who require such testing. Medical records were retrospectively reviewed, and findings evaluated using bivariate and multivariate statistics. A neuropathic condition affecting the lower sacral segments was diagnosed by quantitative concentric needle EMG of the external anal sphincter (EAS) muscle. Neuropathic changes in the EAS were found in 85 (44%) of 193 patients studied. On ordinal logistic regression analysis, bladder-emptying difficulties and perineal sensory loss were significantly related to the presence of a neuropathic EMG. No guidelines for referral for anal sphincter EMG could be defined that would include all patients with neuropathic abnormalities in the lower sacral segments. However, patients with bladder-emptying difficulties and perineal sensory loss seem to be the most suitable candidates for testing.

Adolescent↗
PubMed2006

Single-fiber electromyography in limb and facial muscles in muscle-specific kinase antibody and acetylcholine receptor antibody myasthenia gravis.

We examined the findings from single-fiber electromyography in extensor digitorum communis (EDC) and orbicularis oculi (OOc) in 13 myasthenia gravis (MG) patients with muscle-specific kinase antibodies (MuSK-MG) and 12 MG patients with acetylcholine receptor antibodies (AChR-MG) with similar clinical scores. More than 70% of AChR-MG patients had abnormal jitter in both EDC and OOc, but the majority of MuSK-MG patients had normal jitter in EDC despite abnormal jitter in OOc. These findings demonstrate clear differences between the neurophysiology of MuSK-MG and AChR-MG.

Acetylcholinesterase↗