Surface detected potentials of normal and reinnervated motor units: a simulation study for muscles consisted of short fibres

We aimed to check whether the characteristics used up to now in macro EMG to distinguish between normal and reinnervated motor unit potentials (MUPs), were suitable for surface detected MUPs. MUPs produced by normal and reinnervated MUs were simulated with a fast and precise convolution model. An increased number of fibres in the MU territory enhanced the amplitude, area and RMS of the MUP proportionally irrespective of the MU-electrode distance. An increased scatter of the end-plates and greater desynchronization in the fibres' activation decreased the MUP amplitude and affected the temporal characteristics of the MUP (duration of the negative phase and its area to amplitude ratio). The effects were more pronounced at shorter distances. At larger distances, the effect of the MU-electrode distance on temporal and amplitude characteristics of MUPs was much stronger than that of the parameters changed with reinnervation. We conclude that reinnervated MUs consisting of short fibres can not be distinguished from the normal ones by means of characteristics of MUP used in macro EMG. To discriminate reinnervated MUs non-invasively, the MUP amplitude should be normalized in respect of the MU-electrode distance or other MUP characteristics (independent of MU-electrode distance and sensitive to reinnervation) should be used.     

The reorganisation of motor units in different motor neuron disorders

A study was made of the degree and sequence of neurophysiological changes during motor unit reorganisation in motor neuron disease (MND), spinal muscular atrophy (SMA), and prior polio. Concentric needle EMG was used in conjunction with our own computerized EMG-LAB system. Motor unit action potential (MUAP) parameters were measured in 543 muscles on weak and maximum effort. MUAP amplitude and area were found to increase in the early stages of damage, declining to normal or subnormal values in the course of the disease. It was concluded that in MND there is a pathological sequence: denervation--reinnervation--terminal denervation. The increase in MUAP amplitude and area in the early stages of lesion, reflecting reinnervation, was much greater in SMA than MND and most marked in prior polio. The eventual decrease is an expression of terminal decompensation.     

The presence of unknown layer of skin and fat is an obstacle to a correct estimation of the motor unit size from surface detected potentials

To overcome problems with a strong distance-dependence of the motor unit potentials (MUPs), different methods to estimate the MU location and size have been proposed. Distance-independence of the exponent of the power function, that describes the MUP distance decline, and homogeneity of the volume conductor, are assumed in all methods. Some of them consider the exponent value as unique, irrespective of persons, muscles and their functional state. One method estimates the current exponent value. We evaluate this method by computer simulation of MUPs in infinite and semi-infinite volume conductor. Our results show that although the first assumption is not fulfilled, it does not affect considerably the estimate of the MU location and size obtained for infinite or semi-infinite homogeneous volume conductor. The errors of the MU location can be insignificant even in inhomogeneous volume conductor with a layer of lower conductivity (skin and fat) between the muscle tissue and electrode. The accurate location of the MU electrical axis is, however, not a sufficient condition for a correct MU size estimation that depends considerably on actual parameters of the layer. Thus, the surface EMG could hardly be considered as non-invasive alternative to macro EMG for detection of the enlarged MUs.     

肌营养不良征的肌电图分析

目的：探讨肌营养不良肌患的神经电生理改变。方法：对16例肌营养不良患进行常规肌电图(EMG)、神经电图(ENOG)检测，EMG检测四肢近端肌肉及腓肠肌等，观察静息状态时自发电位，测定运动单位电位(MUP)的时限、波幅、大力收缩时的募集相。测定运动、感觉神经的传导速度(MCV、SCV)及动作电位的末端潜伏期(ML)诱发电位波幅。结果：本组资料显示所检肌时限异常率占82％，波幅降低率占72％，大力收缩早募集占60％。结论：肌电图检测可以对肌营养不良和脊肌萎缩症提供很好的诊断和鉴别诊断依据。     

运动神经元病患者咬肌肌电图研究及临床意义的探讨

目的：探讨咬肌EMG检测在运动神经元病（MND）诊断中的价值。方法：对30例MND患者均进行常规EMG检测，包括上肢、下肢、胸锁乳突肌及咬肌，测定自发电位，轻收缩时运动单位电位（MUP）的多相波、时限及波幅，募集相。比较患者咬肌EMG与胸锁乳突肌EMG相关性及差异。结果：咬肌EMG病变程度与胸锁乳突肌EMG比较，自发电位、运动单位电位（MUP）时限和波幅异常表现均无显著差异（P〉0．05）；但多相波、募集相比较有显著差异（P〈0．05）。时限增宽幅度分别为66．44％、58．88％无显著差异（P〉0．05）。结论：MND患者咬肌EMG检查所见异常表现与胸锁乳突肌EMG检测的异常表现具有可比性，在MND患者伴有颈椎病，尤其是患有高颈段颈椎病时，进行咬肌EMG的检查更具有鉴别诊断的积极意义。     

Motor unit changes in inflammatory myopathy and progressive muscular dystrophy

The aim of present study was to analyse the motor unit (MU) changes in progressive muscle dystrophy (PMD) and in inflammatory myopathy (IM) and to evaluate eventual neurogenic factors in MU reorganisation. The material consisted of 20 patients with (PMD), 20 patients with (IM) and 20 healthy age-matched volunteers. The shape of concentric needle motor unit potentials (cn MUPs), including their duration, amplitude, area, size index and number of phases, the interference pattern and the amplitude and area of macro MUPs were evaluated. The cn emg data satisfied the classical criteria for myopathy in all examined patients, at least in one of the tested muscles. A decreased amplitude and/or area of macro MUPs, compatible with myopathy, were observed in 32 of the 40 patients. In some cases of chronic IM and PDM the long duration polyphasic potentials were recorded. The size index (SI) value of long polyphasic MUPs was usually decreased or normal. This feature indicated that desynchronisation of "myopathic" MUPs results from a reduced number of muscle fibers and their degeneration and regeneration. The results indicated no difference in MU reorganization between PMD and IM and no evidence of neurogenic factors in MU changes.     

Motor unit remodelling in Duchenne muscular dystrophy. Electrophysiological assessment.

Conventional EMG, motor and sensory conduction velocities, averaging analysis of MUPs, SFEMG, and muscle fiber conduction velocity in situ were performed in 14 boys with Duchenne muscular dystrophy (DD) aged 5 to 11 years. MUPs parameters study showed a striking increment of long duration MUPs followed by satellites and increase of polyphasic potentials of variable duration. The main findings in SFEMG examination were increment in fiber density of the motor unit, large MISI and presence of complex potentials of long duration in all patients. Muscle fiber conduction velocity in situ was significantly slower than in controls, with significant decrease in minimum conduction and increased variability (large SD) in propagation velocity values. Low conduction velocity of muscle fibers, long duration of polyphasics and MUPs followed by satellites, and large MISI were significantly related. These findings support the hypotheses which have suggested that the motor unit remodelling in DD is mainly myogenic. The abnormalities in muscle fiber conduction velocity in situ reflect an increased diameter variation of muscle fibers consistent with splitting fibers, small groups of regenerating and necrotic fibers, and fiber diameter variation found in histological studies. Thus, increased variability in fiber diameter may be the cause of complex and long duration MUPs in DD.     

Effects of muscle fibre shortening on the characteristics of surface motor unit potentials

Traditionally, studies dealing with muscle shortening have concentrated on assessing its impact on conduction velocity, and to this end, electrodes have been located between the end-plate and tendon regions. Possible morphologic changes in surface motor unit potentials (MUPs) as a result of muscle shortening have not, as yet, been evaluated or characterized. Using a convolutional MUP model, we investigated the effects of muscle shortening on the shape, amplitude, and duration characteristics of MUPs for different electrode positions relative to the fibre–tendon junction and for different depths of the MU in the muscle (MU-to-electrode distance). It was found that the effects of muscle shortening on MUP morphology depended not only on whether the electrodes were between the end-plate and the tendon junction or beyond the tendon junction, but also on the specific distance to this junction. When the electrodes lie between the end-plate and tendon junction, it was found that (1) the muscle shortening effect is not important for superficial MUs, (2) the sensitivity of MUP amplitude to muscle shortening increases with MU-to-electrode distance, and (3) the amplitude of the MUP negative phase is not affected by muscle shortening. This study provides a basis for the interpretation of the changes in MUP characteristics in experiments where both physiological and geometrical aspects of the muscle are varied.     

Adaptive fuzzy k-NN classifier for EMG signal decomposition

An adaptive fuzzy k-nearest neighbour classifier (AFNNC) for EMG signal decomposition is presented and evaluated. The developed classifier uses an adaptive assertion-based classification approach for setting a minimum classification threshold. The similarity criterion used for grouping motor unit potentials (MUPs) is based on a combination of MUP shapes and two modes of use of motor unit firing pattern information: passive and active. The performance of the developed classifier was evaluated using synthetic signals with specific properties and experimental signals and compared with the performance of an adaptive template matching classifier, the adaptive certainty classifier (ACC). Across the sets of simulated and experimental EMG signals used for comparison, the AFNNC had better average classification performance overall, but due to the assignment of higher numbers of MUPs it made relatively more errors. Nonetheless, these increased error rates would still be acceptable for most clinical uses of decomposed EMG data. An independent and a related set of simulated signals were used for testing. For the independent simulated signals of varying intensity, the AFNNC had on average an improved correct classification rate (CCr) (8.1%) but an increased error rate (Er) (1.5%) compared to ACC. For the related simulated signals with varying amounts of shape and/or firing pattern variability, the AFNNC on average had an improved CCr (5%) but a slightly increased Er (0.3%) compared to ACC. For experimental signals, the AFNNC on average had improved CCr (6%) but an increased Er (2.1%) compared to ACC. The greatest gains in AFNNC performance relative to that of the ACC occurred when the variability of MUP shapes within motor unit potential trains was high suggesting that compared to a template matching assignment strategy the NN assignment paradigm is better able to ameliorate the classification problems caused by MUP instability.     

运动神经元病的临床及神经电生理分析

目的:探讨本地区运动神经元病(MND)患者的临床表现及神经电生理特点。方法:对入选的21例MND患者进行肌电图(EMG)及神经传导检测(NCS),分析其临床特征及神经电生理特点。结果:在21例患者中,运动神经传导检测异常率为55.2%,主要表现为M波波幅降低;感觉神经传导正常率为98.85%。静息时发现纤颤电位18例(85.71%),正锐波16例(76.19%),束颤电位6例(28.57%),运动单位电位时限延长18例(85.71%),平均波幅增高10例(47.62%),大力收缩时表现为单纯相9例(42.86%)。其中上下肢肌肉的异常率为71.08%,胸锁乳突肌的异常率为92.31%,胸椎旁肌的异常率为33.33%。结论:神经电生理检查对MND的诊断非常重要,其中EMG检测是MND诊断的重要手段。EMG呈广泛性的运动神经元损害是MND的特征性改变,束颤电位在诊断中有重要价值。胸锁乳突肌阳性率高,可作为检查延髓节段下运动神经元受累的首选肌肉。     

肌萎缩侧索硬化患者的腹直肌肌电图检测

目的：探讨腹直肌针极肌电图（EMG）在肌萎缩侧索硬化（ALS）中的诊断价值。方法：对ALS组58例患者进行常规EMG检测,包括上、下肢肌肉、胸锁乳突肌、下胸段脊旁肌及腹直肌,测定自发电位、募集相、运动单位电位（MUP）时限、波幅及多相波,对健康对照组36例健康志愿者进行腹直肌EMG的检测,比较ALS组与对照组腹直肌EMG的差异,以及ALS组中腹直肌EMG与下胸段脊旁肌EMG的差异。结果：健康对照组腹直肌EMG的MUP参数分别为波幅（389±35．7）μV,时限（9．78±1．23）ms,多相波（16．2±5．2）％;ALS组腹直肌EMG的MUP参数分别为波幅（675±135）μV,时限（12．78±1．03）ms,多相波（36．2±7．2）％,ALS组腹直肌EMG各参数与健康对照组比较差异有统计学意义;ALS组腹直肌EMG神经原性改变（43／58,74％）与下胸段脊旁肌EMG（39／58,67％）比较差异无统计学意义。结论：腹直肌EMG各参数均能可靠、稳定地测出,可作为诊断ALS患者胸段下运动神经元病变的辅助手段。     

Facioscapulohumeral muscular dystrophy. A quantitative electromyographic study

BACKGROUND: Quantitative electromyography (EMG) using different needle techniques has not been performed or reported on a relatively large group of patients with facioscapulohumeral muscular dystrophy (FSHD). Purpose: To establish statistically: (1) correlations between clinical features of patients (age, disease duration and degree of weakness) and quantitative needle EMG/SFEMG,; (2) correlations between different EMG parameters in the patient group, and (3) quantitative EMG differences comparing patients with a healthy control group. METHODS: Nerve conduction studies, and needle EMG (motorunit analysis, MacroEMG, SFEMG) were performed on Mm. triceps brachii and Mm. tibialis anterior according to standard techniques on 20 patients with FSHD. RESULTS: Nerve conduction studies were normal. In Mm. triceps brachii and, to a lesser extent, Mm. tibialis anterior motorunit analysis and MacroEMG showed myopathic changes, that correlated with patient clinical parameters. In Mm. triceps brachii (but not in Mm. tibialis anterior) EMG results were statistically different in patients compared to control group data. The most sensitive indicators of a myopathy were MUP duration (motorunit analysis) and MUP area (MacroEMG). In the Mm. triceps brachii SFEMG revealed correlations between worsening pooled MCD data and patient clinical parameters. Pooled MCD results did not correlate with other MUP parameters. SFEMG showed abnormal jitter only in 2 patients with the longest disease duration. CONCLUSION: Quantitative EMG results are compatible with a mild, slowly progressive myopathy. The most sensitive indicators of early muscle disease were MUP duration (motorunit analysis) and MUP area (MacroEMG) that would not be detected on "routine" EMG SFEMG showed subtle, progressive worsening of neuromuscular junction physiology. However, quantitative EMG and SFEMG showed that muscle fiber degeneration and loss followed a course independent of muscle fiber regeneration and reinnervation.     

Adaptive motor unit potential train validation using MUP shape information

A decomposed electromyographic (EMG) signal provides information that can be used clinically or for physiological investigation. However, in all instances the validity of the extracted motor unit potential trains (MUPTs) must first be determined because, as with all pattern recognition applications, errors will occur during decomposition. Moreover, detecting invalid MUPTs during EMG signal decomposition can enhance decompositions results. Eight methods to validate an extracted MUPT using its motor unit potential (MUP) shape information were studied. These MUPT validation methods are based on existing cluster analysis algorithms, four were newly developed adaptive methods and four were classical cluster validation methods. The methods evaluate the shapes of the MUPs of a MUPT to determine whether the MUPT represents the activity of a single motor unit (i.e. it is a valid MUPT) or not. Evaluation results using both simulated and real data show that the newly developed adaptive methods are sufficiently fast and accurate to be used during or after the decomposition of EMG signals. The adaptive gap-based Duda and Hart (AGDH) method had significantly better accuracies in correctly categorizing the MUPTs extracted during decomposition (91.3% and 94.7% for simulated and real data, respectively; assuming 12.7% of the extracted MUPTs are on average invalid). The accuracy with which invalid MUPTs can be detected is dependent on the similarity of the MUP templates of the MUPTs merged to create the invalid train and suggests the need, in some cases, for the combined use of motor unit firing pattern and MUP shape information.     

Comparison of amplitudes of surface macro motor unit potentials recorded from various muscle sites

Peak-to-peak amplitudes and total areas of surface macro motor unit potentials (S-MMUPs) were measured in 19 healthy volunteers. While participants maintained minimal isometric muscle contraction of the left biceps brachii, motor unit potentials (MUPs) were recorded from a needle and surface electrodes. The largest MUP recorded by the needle electrode was designated the trigger source. Electrical activities from the surface electrodes, which emerged synchronously with the trigger-potential, were averaged by the spike-triggered averaging (STA) technique. When the surface electrodes were placed over the muscle belly at a right angle to the muscle fibers, the S-MMUP amplitude and area decreased gradually with the distance of the electrodes from the point of insertion of the needle electrode. In contrast, when the surface electrodes were arranged parallel to the muscle fibers, the S-MMUP amplitude and area did not always decrease. In addition, negative peak positions in individual S-MMUPs showed a time delay along the muscle fibers. The placement and size of the surface electrodes, as well as the depth of the needle electrode, must be carefully considered when MUPs are analyzed by the STA technique. Muscle fiber conduction velocity (MFCV) is measurable by the STA technique combined with surface electrodes.     

多发性肌炎和皮肌炎患者的临床与肌电图分析

目的 :探讨多发性肌炎 (PM)和皮肌炎 (DM)病人的临床与肌电图特征。方法 :对 74例PM和DM临床与肌电图特征进行分析。结果 :首发症状以肌肉无力为最多见 (占 3 4% ) ,其他依次为皮肤损害 (占 3 1% ) ,发热 (占 13 % )。肌电图检查示肌原性损害 64例 ,神经原性损害 2例 ,异常率为 89%。主要表现为插入电位延长 (9% )、出现自发电位 (5 2 % ) ;MUP时限缩短 (74% )、MUP波幅降低 (6% ) ,多相波增多 (3 4% ) ;重收缩时波型异常 (4 5 % )及峰值波幅降低 (3 7% )。股四头肌、胫前肌及肱二头肌组阳性率显著高于外展拇短肌组 (P <0 0 5 ) ,胫前肌组MUP时限缩短阳性率最高 ,多相波增多阳性率胫前肌组最高。结论 :肌电图检查是诊断PM和DM的重要手段 ,选择股四头肌、胫前肌及肱二头肌进行EMG检查阳性率最高     

A review of clinical quantitative electromyography

Information regarding the morphology of motor unit potentials (MUPs) and motor unit firing patterns can be used to help diagnose, treat, and manage neuromuscular disorders. In a conventional electromyographic (EMG) examination, a clinician manually assesses the characteristics of needle-detected EMG signals across a number of distinct needle positions and forms an overall impression of the condition of the muscle. Such a subjective assessment is highly dependent on the skills and level of experience of the clinician, and is prone to a high error rate and operator bias. Quantitative methods have been developed to characterize MUP waveforms using statistical and probabilistic techniques that allow for greater objectivity and reproducibility in supporting the diagnostic process. In this review, quantitative EMG (QEMG) techniques ranging from simple reporting of numeric MUP values to interpreted muscle characterizations are presented and reviewed in terms of their clinical potential to improve status quo methods. QEMG techniques are also evaluated in terms of their suitability for use in a clinical decision support system based on previously established criteria. Aspects of prototype clinical decision support systems are then presented to illustrate some of the concepts of QEMG-based decision making.     

神经电生理检测对肌萎缩侧索硬化症患者的早期诊断价值

目的：探讨肌萎缩侧索硬化症(ALS)与脊髓型颈椎病(CSM)的神经电生理改变的差异。方法：对60例ALS与CSM患者进行常规肌电图(EMG)、神经电图(ENoG)检测。EMG检测包括三肢体肌、胸锁乳突肌、胸段棘旁肌等肌肉，观察静息状态时自发电位，测定运动单位电位(MUP)的时限、波幅，大力收缩时的募集相。测定运动、感觉神经的传导速度(MCV，SCV)及动作电位的末端潜伏期(ML)、波幅(Amp)。结果：ALS与CSM中自发电位的异常率分别为：胸锁乳突肌39％和17．5％，胸段棘旁肌分别为93．3％和3．3％，肢体肌分别为88．1％和75％，ALS患者MUP时限、波幅的增高不同于CSM患者，差异均有显著意义。结论：胸段棘旁肌EMG阳性率高、简便易行，为早期鉴别诊断ALS与CSM提供了更敏感的依据。同时表明电生理检测可作为ALS可疑或ALS与CSM两病并存患者的随访观察及判定病情和预后的客观指标。     

Adaptive certainty-based classification for decomposition of EMG signals

An adaptive certainty-based supervised classification approach for electromyographic (EMG) signal decomposition is presented and evaluated. Similarity criterion used for grouping motor unit potentials (MUPs) is based on a combination of MUP shapes and two modes of use of motor unit (MU) firing pattern information: passive and active. Performance of the developed classifier was evaluated using synthetic signals of known properties and real signals and compared with the performance of the certainty classifier (CC). Across the sets of simulated and real EMG signals used for comparison, the adaptive certainty classifier (ACC) had both better average performance and lower performance variability. For simulated signals of varying intensity, the ACC had an average correct classification rate (CC _r ) of 83.7% with a mean absolute deviation (MAD) of 5.8% compared to 78.3 and 8.7%, respectively, for the CC. For simulated signals with varying amounts of shape and/or firing pattern variability, the ACC had a CC _r of 79.7% with a MAD of 4.7% compared to 76.6 and 6.9%, respectively, for the CC. For real signals, the ACC had a CC _r of 70.0% with a MAD of 6.3% compared to 64.9 and 6.4%, respectively, for the CC. The test results demonstrate that the ACC can manage both MUP shape variability as well as MU firing pattern variability. The ACC adapts to EMG signal characteristics to create dynamic data driven classification criteria so that the number of MUP assignments made reflects the signal complexity and the number of erroneous assignments is kept sufficiently low. The ability of the ACC to adjust to specific signal characteristics suggests that it can be successfully applied to a wide variety of EMG signals.     

Motor unit potential characterization using "pattern discovery"

Typically in clinical practice, electromyographers use qualitative auditory and visual analysis of electromyographic (EMG) signals to help infer if a neuromuscular disorder is present and if it is neuropathic or myopathic. Quantitative EMG methods exist that can more accurately measure feature values but require qualitative interpretation of a large number of statistics. Electrophysiological characterization of a neuromuscular system can be improved through the quantitative interpretation of EMG statistics. The aim of the present study was to compare the accuracy of pattern discovery (PD) characterization of motor unit potentials (MUPs) to other classifiers commonly used in the medical field. In addition, a demonstration of PD's transparency is provided. The transparency of PD characterization is a result of observing statistically significant events known as patterns. Using clinical MUP data from normal subjects and patients with known neuropathic disorders, PD achieved an error rate of 30.3% versus 29.8% for a Na?ve Bayes classifier, 30.1% for a Decision Tree and 29% for discriminant analysis. Similar results were found for simulated EMG data. PD characterization succeeded in interpreting the information extracted from MUPs and transforming it into knowledge that is consistent with the literature and that can be valuable for the capture and transparent expression of clinically useful knowledge.     

Distribution of motor unit potential velocities in short static and prolonged dynamic contractions at low forces: use of the within-subject’s skewness and standard deviation variables

Behaviour of motor unit potential (MUP) velocities in relation to (low) force and duration was investigated in biceps brachii muscle using a surface electrode array. Short static tests of 3.8 s (41 subjects) and prolonged dynamic tests (prolonged tests) of 4 min (30 subjects) were performed as position tasks, applying forces up to 20% of maximal voluntary contraction (MVC). Four variables, derived from the inter-peak latency technique, were used to describe changes in the surface electromyography signal: the mean muscle fibre conduction velocity (CV), the proportion between slow and fast MUPs expressed as the within-subject skewness of MUP velocities, the within-subject standard deviation of MUP velocities [SD-peak velocity (PV)], and the amount of MUPs per second (peak frequency = PF). In short static tests and the initial phase of prolonged tests, larger forces induced an increase of the CV and PF, accompanied with the shift of MUP velocities towards higher values, whereas the SD-PV did not change. During the first 1.5–2 min of the prolonged lower force levels tests (unloaded, and loaded 5 and 10% MVC) the CV and SD-PV slightly decreased and the MUP velocities shifted towards lower values; then the three variables stabilized. The PF values did not change in these tests. However, during the prolonged higher force (20% MVC) test, the CV decreased and MUP velocities shifted towards lower values without stabilization, while the SD-PV broadened and the PF decreased progressively. It is argued that these combined results reflect changes in both neural regulatory strategies and muscle membrane state.