Automatic analysis of the EMG interference pattern

Physiological Effects of Voice Therapy for Aged Vocal Fold Atrophy Revealed by EMG Study

OBJECTIVES

Age-related voice changes are characterized as breathy, weak and strained, and a deterioration in vocal function in the elderly has been putatively linked to a reduced intensity of speech. They contribute to undesirable voice changes known as presbyphonia. These changes are caused by histological alterations in the lamina propria of the vocal fold mucosa and atrophy of the thyroarytenoid muscle, as well as by decreased respiratory support. There are several clinical studies on presbylarynx dysphonia showing the effectiveness of voice therapy. However, physiological changes of the presbylarynx following voice therapy have not been verified. The purpose of this prospective study was to demonstrate the clinical effectiveness of voice therapy for rehabilitating presbylarynx dysphonia, using vocal function assessments and thyroarytenoid muscular activity detection on laryngeal electromyography (LEMG).

METHODS

10 patients who were diagnosed with aged vocal fold atrophy from ages 60 to 87 years (mean age: 72 years) underwent approximately 12 weeks of voice therapy, mainly using forward-focused voice and vocal resistance training. Stroboscopic examination, aerodynamic assessment, acoustic analysis, Voice Handicap Index (VHI)-10, and LEMG were performed pre- and post-voice therapy. Vocal fold vibratory amplitude (VFVA) was measured by image analysis from the stroboscopic examinations. Turns analysis during steady phonation on LEMG was also assessed.

RESULTS

Maximum phonation time, subglottic pressure, jitter, shimmer, VFVA, and VHI-10 significantly improved after voice therapy. The number of turns per second on LEMG also significantly increased.

CONCLUSION

Our data suggest that voice therapy may improve vocal function and thyroarytenoid muscle activity in patients with aged vocal fold atrophy.

A scoping review of current and emerging techniques for evaluation of peripheral nerve health, degeneration, and regeneration: part 1, neurophysiology

Peripheral neuroregeneration research and therapeutic options are expanding exponentially. With this expansion comes an increasing need to reliably evaluate and quantify nerve health. Valid and responsive measures that can serve as biomarkers of the nerve status are essential for both clinical and research purposes for diagnosis, longitudinal follow-up, and monitoring the impact of any intervention. Furthermore, such biomarkers can elucidate regeneration mechanisms and open new avenues for research. Without these measures, clinical decision-making falls short, and research becomes more costly, time-consuming, and sometimes infeasible. As a companion to Part 2, which is focused on non-invasive imaging, Part 1 of this two-part scoping review systematically identifies and critically examines many current and emerging neurophysiological techniques that have the potential to evaluate peripheral nerve health, particularly from the perspective of regenerative therapies and research.

Quantitative electrodiagnosis of the motor unit

Electromyography (EMG) focuses on assessment of the motor unit (MU), and a given muscle has several hundred MUs, each innervating hundreds of muscle fibers. Assessment is limited by the recording radius of electrodes, 1-2 fibers with single-fiber electrodes and 7-15 fibers with concentric or monopolar electrodes. Routine qualitative EMG studies rely on observing MUs in free-run mode and qualitatively estimating common metrics. In contrast, quantitative EMG (QEMG) applied to routine studies includes assessment of individual MUs by software available in modern EMG machines with extraction of discrete values for common metrics, and also derived metrics. This results in greater precision and statistical interpretation. Other QEMG techniques assess muscle fiber density within the MU and time variability at the neuromuscular junction. The interference pattern can also be assessed. The number of MUs innervating a muscle can be estimated. Advanced signal processing, called near-fiber EMG, allows for extraction of underlying muscle fiber contributions to MU waveforms. It is also possible to use QEMG to make statistical probabilities of the state of a muscle as to whether normal, myopathic, or neuropathic. Time to acquire QEMG data is minimal. QEMG is most useful in situations where pathology is uncertain.

Childhood muscular dystrophies

Infancy- and childhood-onset muscular dystrophies are associated with a characteristic distribution and progression of motor dysfunction. The underlying causes of progressive childhood muscular dystrophies are heterogeneous involving diverse genetic pathways and genes that encode proteins of the plasma membrane, extracellular matrix, sarcomere, and nuclear membrane components. The prototypical clinicopathological features in an affected child may be adequate to fully distinguish it from other likely diagnoses based on four common features: (1) weakness and wasting of pelvic-femoral and scapular muscles with involvement of heart muscle; (2) elevation of serum muscle enzymes in particular serum creatine kinase; (3) necrosis and regeneration of myofibers; and (4) molecular neurogenetic assessment particularly utilizing next-generation sequencing of the genome of the likeliest candidates genes in an index case or family proband. A number of different animal models of therapeutic strategies have been developed for gene transfer therapy, but so far these techniques have not yet entered clinical practice. Treatment remains for the most part symptomatic with the goal of ameliorating locomotor and cardiorespiratory manifestations of the disease.

On the establishment of reference values of clouds of electromyography interference pattern by linear regression method and percentile method and comparison of sensitivity and specificity of both methods

Objective

Turn-amplitude clouds were widely used in automatic electromyography (EMG) interference pattern analysis. Earlier works employed the intercept ± 2SD (standard deviation) of the linear regression equation as the upper and lower boundaries of the clouds. The goal of this study was to employ the linear regression method and percentile method to calculate the reference value of turn-amplitude clouds, identify the determining criteria in accordance with the receiver operator characteristic curve (ROC), and analyze the sensitivity and specificity of the linear regression cloud, percentile cloud, and quantitative assessment of the motor unit potential (QMUP).

Methods

First, we explore what factors affect the number of turns per second and the mean amplitude. Then, their logarithms were taken for the normal test. All muscle data were used to calculate the reference values of percentile clouds. However, the reference values of the linear regression clouds were obtained for the muscles with a bivariate normal distribution, homogeneous variances and a linear correlation. We calculated the prediction interval with the standard errors of the intercept and slope of the linear regression equation, which can determine the upper and lower boundaries of the linear regression clouds. Furthermore, we obtained ROCs of these clouds, which were used as the determining criteria to determine the optimum cut-off values. Finally, our study analyzed the sensitivity and specificity of the linear regression cloud, percentile cloud, and QMUP.

Results

We here presented the reference values and ROCs of the linear regression clouds and percentile clouds. We suggest the determining criteria be based on ROCs. The areas under the curve (AUC) of both clouds are larger than 0.8, revealing that they have significant diagnostic value. Our results display that the specificities of the linear regression clouds, percentile clouds, and QMUP are almost identical to each other, whereas the sensitivity of percentile cloud is higher than those of QMUP and linear regression clouds.

Conclusion

According to ROCs, the researchers determine the determining criteria of the linear regression clouds and percentile clouds. Our findings suggest that the percentile clouds possess a wide application range and significant diagnostic value, therefore it may be the optimum for automatic EMG interference pattern analysis.

Masked least-squares averaging in processing of scanning-EMG recordings with multiple discharges

Removing artifacts from nearby motor units is one of the main objectives when processing scanning-EMG recordings. Methods such as median filtering or masked least-squares smoothing (MLSS) can be used to eliminate artifacts in recordings with just one discharge of the motor unit potential (MUP) at each location. However, more effective artifact removal can be achieved if several discharges per position are recorded. In this case, processing usually involves averaging the discharges available at each position and then applying a median filter in the spatial dimension. The main drawback of this approach is that the median filter tends to distort the signal waveform. In this paper, we present a new algorithm that operates on multiple discharges simultaneously and in the spatial dimension. We refer to this algorithm as the multi-masked least-squares smoothing (MMLSS) algorithm: an extension of the MLSS algorithm for the case of multiple discharges. The algorithm is tested using simulated scanning-EMG signals in different recording conditions, i.e., at different levels of muscle contraction and for different numbers of discharges per position. The results demonstrate that the algorithm eliminates artifacts more effectively than any previously available method and does so without distorting the waveform of the signal. Graphical abstract The raw scanning-EMG signal, which can be composed by several discharges of the MU, is processed by the MMLSS algorithm so as to eliminate the artifact interference. Firstly, artifacts are detected for each discharge from the raw signal, obtaining a multi-discharge validity mask that indicates the samples that have been corrupted by artifacts. Secondly, a least-squares smoothing procedure simultaneously operating in the spatial dimension and among the discharges is applied to the raw signal. This second step is performed using only the not contaminated samples according to the validity mask. The resulting MMLSS-processed scanning-EMG signal is clean of artifact interference.

Sensitivity and specificity of single and combined clouds analyses compared with quantitative motor unit potential analysis

INTRODUCTION

Turns-amplitude, number of small segments (NSS)-activity, and envelope-activity clouds are three methods of electromyography (EMG) interference pattern analysis. Our objective was to evaluate the sensitivity and specificity of each individual cloud analysis and combined clouds analysis to compare with that of quantitative motor unit potential (QMUP) analysis.

METHODS

A total of 379 muscles from 100 patients were analyzed by both QMUP and clouds analyses. Calculation of sensitivity and specificity was based on the clinical diagnosis as the "gold standard."

RESULTS

For discrimination of abnormal vs normal and neuropathic vs non-neuropathic, combined clouds analysis had greater sensitivity than QMUP analysis and any single cloud analysis, but there were no differences in specificity. For discrimination of myopathic vs non-myopathic, combined clouds analysis and single cloud analysis had greater sensitivity than QMUP analysis, but there were no differences in specificity.

DISCUSSION

Combined clouds analysis was superior to QMUP and each single cloud analysis for distinguishing normal, myopathic, and neuropathic muscles.

Updated size index valid for both neurogenic and myogenic changes

BACKGROUND

Size index (SI) is a motor unit potential (MUP) parameter in concentric needle electromyography calculated from amplitude and area/amplitude, which can sensitively discriminate between control and neurogenic MUPs. In this study, we investigated the application of SI to myogenic MUPs based on expanded data.

METHODS

MUPs were collected from the biceps brachii (BB) and tibialis anterior (TA) muscles. Muscles showing unequivocal neurogenic or myogenic changes by visual inspection were selected for patients. In addition to the original SI, a revised SI (rSI) was defined using the logarithmic scale for area/amplitude. The coefficient for area/amplitude was varied and that achieving the best sensitivity both for BB and TA was selected.

RESULTS

Analyzed were 1619, 340, and 498 MUPs from the BB of 26, 10, and 14 subjects (control, neurogenic, and myogenic), respectively, and 1245, 536, and 473 MUPs from the TA of 23, 18, and 13 subjects (control, neurogenic, and myogenic), respectively. For neurogenic MUPs, the original SI and the newly defined rSIn were similarly sensitive (82.1% and 81.8% sensitivity for SI and rSIn, respectively, for BB, and 68.1% and 69.6% for TA), and were more sensitive than area (72.6% for BB and 57.6% for TA), the most sensitive parameter among conventional ones. For myogenic MUPs, the sensitivity of rSIm was 9.0% for BB and 24.5% for TA, which was not significantly different from duration (7.4% for BB and 21.8% for TA), the most sensitive parameter among conventional ones.

CONCLUSIONS

SI, rSIn, and rSIm are promising as new MUP parameters.

Developing normal number of small segments-activity clouds of the electromyography interference pattern

BACKGROUND

Number of small segments (NSS) and activity analysis is a mature method for electromyographic automatic interference pattern analysis (IPA), but there are few reports on the application of this technique. Our objective was to establish normal reference values of NSS-activity clouds.

METHODS

The NSS and activity data of the sternocleidomastoid, deltoid, biceps brachii (long head), extensor digitorum communis, abductor digiti minimi, vastus medialis, tibialis anterior, and gastrocnemius (lateral head) muscles were obtained from 34 men and 25 women, aged 15-80 years, using concentric needle electrodes. A linear regression of log(NSS) vs log(activity) was performed and the slope, intercept and standard deviation were calculated for each muscle. These variables were transformed back to the original parameters to yield clouds.

RESULTS

Normal NSS-activity clouds for the above eight muscles were obtained.

CONCLUSIONS

Normal reference values of NSS-activity may facilitate detection of early and mild neurogenic and myogenic abnormalities.

Developing Normal Turns-Amplitude Clouds for Upper and Lower Limbs

PURPOSE

Turns and amplitude analysis (T&A) is a frequently used method for automatic EMG interference pattern analysis. The T&A normal values have only been developed for a limited number of muscles. Our objective was to obtain normal T&A clouds for upper and lower extremity muscles for which no normal values exist in the literature.

METHODS

The T&A normative data using concentric needle electrodes were obtained from 68 men and 56 women aged 20 to 60 years.

RESULTS

Normal upper and lower extremity T&A clouds were obtained and presented in this article.

CONCLUSION

The T&A normal values collected in this study maybe used to detect neurogenic and myopathic abnormalities in men and women at low-to-moderate muscle contractions. The effect of turns-amplitude data obtained at high force level of muscle contraction and its potential to falsely show neurogenic abnormalities are discussed.

Between genetics and biology. Is ENMG useful in peripheral neuropathy diagnosis and management?

Neurography and EMG are complementary techniques used in the diagnosis and monitoring of neuropathies. Both assess function of the peripheral nervous system and provide clinically useful information regarding the functional status of peripheral nerves. This information is not readily obtainable using biochemical, genetic or imaging techniques. I will discuss the role of these techniques in the diagnosis and management of neuropathies and some limitations of these techniques. These methods are routinely used in an EMG lab. These are most useful when used in conjunction with clinical examination to answer a well-defined clinical question. Reference values are required for interpretation of the data.

A critical overview of the current myofascial pain literature - March 2016

The worldwide interest in myofascial pain syndrome (MPS) and trigger points (TrPs) is reflected in the increasing number of publications. In this overview of the literature, we included 26 studies, case reports and review articles by authors from 18 different countries. Several research groups are exploring the characteristic of TrPs such as Chen and colleagues, who continued their work on the quantification of the taut bands. Meng and colleagues studied the relationships between TrPs and central sensitization, while Yu and colleagues examined the electrophysiological characteristics that occur as a result of active TrPs. Several researchers used objective measurements to determine clinical outcomes, such as Koppenhaver and colleagues who measured objective changes in the function and nociceptive sensitivity of lumbar multifidus muscle subjects with low back pain. Turo and colleagues quantified muscle tissue changes after dry needling in chronic myofascial pain using elastography. Multiple studies explored various treatment options for TrPs, such as dry needling, injections with lidocaine or granisetron, traditional Thai massage, self-myofascial release, kinesiotaping, and monochromatic infrared photo energy, among others.

Myopathic changes detected by quantitative electromyography in patients with MuSK and AChR positive myasthenia gravis

Myopathic changes are frequent a electrophysiological finding in patients with muscle specific tyrosine kinase (MuSK) positive myasthenia gravis (MG). The aim of this study was to explore the importance of quantitative electromyography (EMG) in the detection of myopathic changes in MuSK MG patients. Classical and quantitative EMG were performed in 31 MuSK and 28 acetylcholine receptor (AChR) positive MG patients, matched by sex, age, disease duration and severity. Classical EMG revealed the presence of myopathic changes more frequently in MuSK MG compared to AChR MG patients, especially in the facial muscles. Quantitative EMG registered myopathic lesions more frequently than classical EMG, but the frequency was similar between MuSK and AChR MG patients. Quantitative EMG revealed myopathic changes in the majority of both MuSK and AChR positive MG patients. This examination is sensitive, but it cannot be used to differentiate between MG patients belonging to the different disease groups. It should not be used in isolation. Rather, it should complement classical EMG in the detection of myopathic changes.

Estimating the tendency of motor unit recruitment during steady-hold and rapid contractions using surface EMG and Turns-amplitude analysis

PURPOSE

The purpose of this study was to investigate changes in the interference pattern in surface electromyography (EMG), and its relationship with the tendency of motor unit (MU) recruitment during steady-hold and rapid muscle contractions.

METHODS

Fifteen healthy adults (eight females and seven males, 22.6 ± 1.5 years old) performed steady-hold and rapid isometric contractions of the bicep brachii, adductor pollicis, and tibialis anterior muscles at various force levels. Surface EMG recordings were analyzed using Turns-Amplitude Analysis (TAA).

RESULTS

During steady-hold contractions, the number of turns per second (T/s) increased exponentially with force during submaximal contractions, and plateaued after force levels of 66, 70 and 57 % MVC for the tibialis anterior, bicep brachii and adductor pollicis muscles, respectively. These force levels were proximate to the maximal recruitment threshold (MaxRT) reported previously. The slopes of the T/s-force relationships before the MaxRT were significantly greater than the slopes after the MaxRT for all three muscles tested. During rapid contraction, the slopes of the T/s-force relationships were significantly lower than the slopes of the steady-hold contraction at 20-40 % MVC in all three muscles, and for 40-60 % MVC in TA muscles.

CONCLUSIONS

Our results suggested that the changes in the number of turns in surface EMG with respect to muscle force can be used to estimate the force levels at which the majority of the MUs to be recruited, and completion of MU recruitment was observed at lower force levels during rapid muscle contraction.

Motor unit

Movement is accomplished by the controlled activation of motor unit populations. Our understanding of motor unit physiology has been derived from experimental work on the properties of single motor units and from computational studies that have integrated the experimental observations into the function of motor unit populations. The article provides brief descriptions of motor unit anatomy and muscle unit properties, with more substantial reviews of motoneuron properties, motor unit recruitment and rate modulation when humans perform voluntary contractions, and the function of an entire motor unit pool. The article emphasizes the advances in knowledge on the cellular and molecular mechanisms underlying the neuromodulation of motoneuron activity and attempts to explain the discharge characteristics of human motor units in terms of these principles. A major finding from this work has been the critical role of descending pathways from the brainstem in modulating the properties and activity of spinal motoneurons. Progress has been substantial, but significant gaps in knowledge remain.

Evaluation of spinal and bulbar muscular atrophy by the clustering index method

INTRODUCTION

A reliable electrophysiological marker for clinical trials is increasingly needed in spinal and bulbar muscular atrophy (SBMA). We previously developed a quantitative analysis method for surface electromyography (SEMG), the clustering index (CI) method. Our purpose was to test the utility of the CI method for evaluating lower motor neuron involvement in SBMA patients.

METHODS

Subjects included 29 SBMA patients and 27 healthy controls. The recording electrode was placed over the abductor digiti minimi (ADM) muscle with a proximal reference. The Z-score, based on the CI method, was compared with compound muscle action potential (CMAP) amplitude and motor unit number estimation (MUNE), with regard to sensitivity.

RESULTS

The Z-scores of the CI method, CMAP amplitude, and MUNE were abnormal in 100%, 72%, and 93% of the patients, respectively. Interrater reliability of the CI method was sufficiently high.

CONCLUSION

The CI method is promising as a non-invasive electrophysiological marker in SBMA.

Nerve and muscle involvement in mitochondrial disorders: an electrophysiological study

Involvement of the peripheral nervous system in mitochondrial disorders (MD) has been previously reported. However, the exact prevalence of peripheral neuropathy and/or myopathy in MD is still unclear. In order to evaluate the prevalence of neuropathy and myopathy in MD, we performed sensory and motor nerve conduction studies (NCS) and concentric needle electromyography (EMG) in 44 unselected MD patients. NCS were abnormal in 36.4% of cases, and were consistent with a sensori-motor axonal multineuropathy (multifocal neuropathy), mainly affecting the lower limbs. EMG evidence of myopathy was present in 54.5% of patients, again mainly affecting the lower limbs. Nerve and muscle involvement was frequently subclinical. Peripheral nerve and muscle involvement is common in MD patients. Our study supports the variability of the clinical expression of MD. Further studies are needed to better understand the molecular basis underlying the phenotypic variability among MD patients.

"Clustering Index method": a new technique for differentiation between neurogenic and myopathic changes using surface EMG

OBJECTIVE

To establish a non-invasive and quantitative analysis method using single-channel surface EMG (SEMG) for diagnosing neurogenic and myopathic changes.

METHODS

The subjects consisted of 66 healthy controls, 12 patients with neurogenic diseases, and 18 patients with myopathic diseases. The tibialis anterior muscle was examined using a belly to the adjacent bone lead. From each subject, 20-40 signals of 1 s length were collected of various strengths. A new parameter, the "Clustering Index (CI)", was developed to quantify the uneven distribution of the SEMG signal, and was plotted against the SEMG area. The results were expressed as the Z-score of each subject calculated using linear regression from the normative data.

RESULTS

When ±2.5 was used as the cut-off value of the Z-score, the specificity was 95%, whereas the sensitivity was 92% (11/12) and 61% (11/18) for the neurogenic and myopathic patients, respectively. There was no overlap of the Z-score values between the neurogenic and myopathic groups.

CONCLUSIONS

The CI method achieved a reasonably high diagnostic yield in detecting neurogenic or myopathic changes.

SIGNIFICANCE

This is a new simple and quantitative analysis method using SEMG with good reproducibility, and is promising as a non-invasive complement to needle EMG.

Turns-amplitude analysis in normal and myopathic facial muscles

The purpose of this study was to assess turns/amplitude analysis (TAA) as an objective alternative to conventional qualitative electromyography (EMG) for detection of myopathy in facial muscles. Normal values of TAA parameters were calculated in the frontalis and mentalis muscles of 26 control subjects. We estimated the slope of the regression line of mean amplitude/turn values (MA) plotted against the number of turns/second (NT) and the resulting clouds. The 95% confidence limits of the cloud data were drawn as an ellipse. The sensitivity of TAA was determined from a group of 35 myopathic patients and specificity from a second group of 25 control subjects. Significant differences for every TAA parameter were found between frontalis and mentalis. Cumulative sensitivity and specificity of TAA for frontalis and mentalis were 74.6%, 56.5%, and 73.3%, 70.8%, respectively. With at least two of the aforementioned criteria abnormal, the sensitivity and specificity for frontalis and mentalis were 61.3%, 82.6%, and 56.7%, 100.0%, respectively.

Quantitative measurements and analysis in electrodiagnostic studies: present and future

Electrodiagnostic studies (nerve conduction and needle electromyography) are powerful methods to study diseases of nerves and muscles. Conduction studies are performed to assess the continuity, anatomic course, excitability, number of axons and their synaptic connections, while needle electromyography examination is performed to assess the ‘electrical stability’ of the muscle fiber membrane, and the study of motor units (architecture, activation and number). We have reviewed the relationship between the quantitative measurements and the generators of the recorded potentials. Based on these relationships, the expected patterns of abnormalities for different pathologies are tabulated. This gives us a better appreciation of the sensitivity, specificity and usefulness of different tests when planning and conducting an electrodiagnostic examination. The limitations of current methods are indicated to suggest the need for future development.

Changes in intracellular action potential profile affect parameters used in turns/amplitude analysis

The influence of changes in the intracellular action potential (IAP) spatial profile on motor unit potentials (MUPs), number of turns per second (NTs), and mean turn amplitude were simulated and analyzed. We show why measurement of NTs was "the best indicator of neurogenic affection" and why the lower diagnostic yield of turns/amplitude analysis in myopathy could be due to changes in IAP shape caused by elevated free calcium concentration. The results explain the complications observed when interference electromyographic signals obtained during high levels of isometric contractions were analyzed. We show that, in contrast to earlier assumptions, the effect of increased IAP spike duration on NTs was stronger than that of a decrease in muscle fiber propagation velocity (MFPV). The decrease in the NTs could occur without a drop-out of MUs and/or a decrease in their firing rates, and without a change in MFPV and synchronous firing.

Determining the shape of the turns-amplitude cloud during anal sphincter quantitative EMG

We aimed to compare our normative data for quantitative interference pattern (IP) analysis of the anal sphincter to previously published data. In 28 nulliparous women, we performed IP analysis during quantitative concentric needle electromyography (QEMG) of the anal sphincter. At each sampling site, a 500-ms epoch was analyzed. The data were log transformed. Linear regression lines (with 95% confidence intervals) were calculated from the log transformed variables "turns-second" and "amplitude-turn." These confidence intervals were then transformed back into the original parameters to yield scatterplots with confidence curves. The mean turns-second were 203 (SD 174). The mean amplitude (mcv)-turn was 266 (SD 87). The regression coefficients for the log-transformed variables are constant = 1.5, slope = 0.3, and resultant cloud of raw data has a convex upper boundary. These appear slightly different than previously published reports, potentially influencing the determination of normal and abnormal studies.

The electromyographer's guide to the motor unit

This article's purpose is to explain the anatomicophysiologic basis for observations and measurements made by the electromyographer. An electromyographer may be trained in the techniques of electromyography without understanding the anatomicophysiology, and valuable interpretive subtleties may be missed. This article is an attempt to provide that background (ie, the link among anatomy, physiology, and electrodiagnostic findings). It is hoped that with a fuller understanding of the anatomicophysiologic basis of clinical electromyography, subtle observations can be made which will allow a more sophisticated level of interpretation of electromyography results. Such interpretations should improve the electromyographer's capacity to provide useful information to a referring physician and hence, improve the management of a patient.

Dysphonia and dysphagia after anterior cervical decompression

OBJECT

In this paper, the authors investigate the effects of anterior cervical decompression (ACD) on swallowing and vocal function.

METHODS

The study comprised 114 patients who underwent ACD. The early group (50 patients) was examined immediately pre- and postoperatively, and the late group (64 patients) was examined at only 3 to 9 months postoperatively. Fifty age- and sex-matched patients from the Department of Otorhinolaryngology-Head and Neck Surgery who had not been intubated in the previous 5 years were used as a control group. All patients in the early and control groups were examined by a laryngologist; patients in the late group were examined by a laryngologist and a neurosurgeon. Videolaryngostroboscopy was performed in all members of the patient and control groups, and the function of the ninth through 12th cranial nerves were clinically evaluated. Data were collected concerning swallowing, voice quality, surgery results, and health-related quality of life. Patients with persistent dysphonia were referred for phoniatric evaluation and laryngeal electromyography (EMG). Those with persistent dysphagia underwent transoral endoscopic evaluation of swallowing function and videofluorography.

RESULTS

Sixty percent of patients in the early group reported dysphonia and 69% reported dysphagia at the immediate postoperative visit. Unilateral vocal fold paresis occurred in 12%. The prevalence of both dysphonia and dysphagia decreased in both groups 3 to 9 months postoperatively. All six patients with vocal fold paresis in the early group recovered, and in the late group there were two cases of vocal fold paresis. The results of laryngeal EMG were abnormal in 14 of 16 patients with persistent dysphonia. Neither intraoperative factors nor age or sex had any effect on the occurrence of dysphonia, dysphagia, or vocal fold paresis. Most patients were satisfied with the surgical outcome.

CONCLUSIONS

Dysphonia, dysphagia, and vocal fold paresis are common but usually transient complications of ACD. Recurrent laryngeal nerve damage detected by EMG is not rare. Pre-and postoperative laryngeal examination of ACD patients should be considered.

Quantitative EMG of facial muscles in myasthenia patients with MuSK antibodies

OBJECTIVE

Our aim was to study the pathophysiological process leading to facial muscle atrophy in 13 patients with MuSK antibody positive myasthenia gravis (MuSK-MG), and to compare with findings from 12 acetylcholine receptor antibody positive myasthenia patients (AChR-MG), selected because they suffered from the same degree of disease severity and required similar treatment.

METHODS

Motor unit action potential (MUAP) and interference pattern analysis from orbicularis oculi (O oculi) and orbicularis oris (O oris) muscles were studied using a concentric needle electrode, and compared with findings in 20 normal subjects, 6 patients receiving botulinum toxin injections (representing a neurogenic model) and 6 patients with a muscle dystrophy (representing a myopathic model). The techniques and control data have been reported previously.

RESULTS

The mean MUAP durations for O oculi and O oris were significantly reduced (p<0.001) in both MG cohorts when compared with healthy subjects, and were similar to those in the myopathic control group. They were significantly different from those obtained from the neurogenic control group (p<0.001 for both O oculi and O oris). The MUAP findings in O oculi occurred independently from neuromuscular blocking on single fibre EMG (SFEMG) in the same muscle. On turns amplitude analysis (TAA), 50% of MuSK-MG patients and 42% of AChR-MG patients had a pattern in O oculi which was similar to that in the myopathic control group, and 62% of MuSK-MG patients and 50% of AChR-MG patients had a pattern in O oris that was also similar to that in the myopathic control group. The TAA findings for O oculi and O oris in both MG cohorts were different from those obtained from the neurogenic control group.

CONCLUSIONS

Facial muscle atrophy in MuSK-MG patients is not neurogenic and the pathophysiological changes are akin to a myopathic process. The selected AChR-MG patients also show evidence of a similar pathophysiological process in the facial muscles albeit to a lesser degree.

SIGNIFICANCE

We propose that muscle atrophy in MuSK-MG is a myopathic process consisting of either muscle fibre shrinkage or loss of muscle fibres from motor units. The duration of disease and long-term steroid treatment may be further contributory factors.

The role of different EMG methods in evaluating myopathy

For the diagnosis of myopathy, EMG may have an important role along with blood tests, muscle biopsies and genetic testing. This review evaluates different EMG methods in the diagnosis of myopathy. These include manual analysis of individual motor unit potentials and multi-motor unit potential analysis sampled at weak effort. At high effort, turns-amplitude analyses such as the cloud analysis and the peak ratio analysis have a high diagnostic yield. The EMG can seldom be used to differentiate between different types of myopathy. In the channelopathies, myotonia, exercise test and cooling of the muscle are helpful. Macro-EMG, single-fibre EMG and muscle fibre conduction velocity analysis have a limited role in myopathy, but provide information about the changes seen. Analysis of the firing rate of motor units, power spectrum analysis, as well as multichannel surface EMG may have diagnostic potential in the future. EMG is of great importance in the diagnosing of patients with myopathy, preferably a needle electrode and quantitative analyses should be used. A combination of a method at weak effort as well as a method at stronger effort seems optimal.

Singularity Characteristics of Needle EMG IP Signals

Clinical electromyography (EMG) interference pattern (IP) signals can reveal more diagnostic information than their constituents, the motor unit action potentials (MUAPs). Singularities and irregular structures typically characterize the mathematically defined content of information in signals. In this paper, a wavelet transform method is used to detect and quantify the singularity characteristics of EMG IP signals using the Lipschitz exponent (LE) and measures derived from it. The performance of the method is assessed in terms of its ability to discriminate healthy, myopathic and neuropathic subjects and how it compares with traditionally used Turns Analysis (TA) methods and a method recently developed by the authors, interscale wavelet maximum (ISWM). Highly significant intergroup differences were found using the LE method. Most of the singularity measures have a performance similar to that of ISWM and considerably better than that of TA. Some measures such as the ratio of the mean LE value to the number of singular points in the signal have considerably superior performance to both methods. These findings add weight to the view that wavelet analysis methods offer an effective way forward in the quantitative analysis of EMG IP signal to assist the clinician in the diagnosis of neuromuscular disorders.

Autosomal dominant congenital fibre type disproportion: a clinicopathological and imaging study of a large family

Congenital fibre type disproportion (CFTD) is considered a non-progressive or slowly progressive muscle disease with relative smallness of type 1 fibres on pathological examination. Although generally benign, CFTD has a variable natural course and severe progression has been observed in some patients. The pathogenesis of the disorder is unknown and many authors consider CFTD a syndrome with multiple aetiologies rather than a separate clinical entity. A positive family history has been reported in about 40% of cases, but the inheritance pattern is not clear. Both autosomal recessive and dominant modes of inheritance have been suggested. The present paper describes a large, multigenerational kindred that has an inherited myopathy fulfilling the histological criteria of CFTD, with autosomal dominant transmission and high penetrance. The clinical picture, remarkably similar in all affected family members, started in early infancy with mild limb muscle weakness. There was slow progression of symptoms into adulthood, with moderate to severe, mainly proximal, muscle weakness without loss of ambulation. Muscle biopsy from two affected individuals demonstrated predominance of small type 1 muscle fibres without other significant findings. Nerve conduction studies were normal and needle electromyography showed a myopathic pattern. MRI examination performed on three patients from successive generations showed involvement of proximal limb and paraspinal muscles. The clinical and pathological homogeneity in the present family, together with the lack of additional histological abnormalities after decades of disease progression in two affected individuals, supports this being a distinct myopathy with fibre type disproportion. Whether the disease in this family can be regarded as a form of the congenital myopathy known as CFTD or rather a unique condition sharing histological features with CFTD needs further investigation. This is, to our knowledge, the largest kindred with muscle fibre type disproportion reported to date. Our data confirm autosomal dominant inheritance, and this is the first MRI document of this disorder.

Turns-amplitude analysis of the electromyographic recruitment pattern following upper motor neuron lesions

OBJECTIVE

To assess the pattern of motor unit recruitment of weak muscles in upper motor neuron (UMN) lesions.

MATERIALS AND METHODS

Ten patients underwent turns-amplitude analysis (TAA) on the paretic and healthy brachial biceps muscles, in the acute and subacute stages of hemiparesis. The control group comprised 10 age- and sex-matched subjects.

RESULTS

Although absent in the acute stage, five patients developed a myogenic cloud pattern in their paretic extremities in the subacute stage; which was statistically significant when compared with controls (P = 0.033). Mean amplitude was reduced in both acute and subacute stages of the hemiparesis compared with controls (P = 0.000). The turns/mean amplitude ratio in the subacute stage was increased compared with both the paretic limbs examined in the acute stage (P = 0.000) and to controls (P = 0.000).

CONCLUSION

Abnormalities in the recruitment of motor units in UMN lesions give rise to a myogenic cloud pattern in the TAA, which is prominent in the third month after the initial insult. This may result from the increase in motor unit activity, while the recruitment of bigger motor units is still defective.