Motor unit size in muscular dystrophy, a macro EMG and scanning EMG study

Patients with muscular dystrophy were investigated with Macro EMG to study activity from whole individual motor units, and with Scanning EMG to study the distribution of activity within the motor unit. Macro motor unit potentials were normal or only slightly reduced in amplitude. In Scanning EMG the units had unchanged mean length compared with normal, but an uneven distribution of the activity. This was also seen in severely weak muscles. The findings are interpreted to be the result of degenerative and regenerative processes, giving rise to remodelling of the motor unit.     

Multielectrode surface EMG for noninvasive estimation of motor unit size.

To noninvasively estimate the motor unit size, we present a novel surface electromyographic (EMG) measurement system consisting of a surface multielectrode with four-pin electrodes and a pair of surface-disk electrodes. Surface motor unit action potentials (MUAPs) were recorded with the multielectrode, in the so-called multielectrode surface EMG (MSEMG), which was spatially filtered to localize the sensing area and reduce the noise. In addition, a modified decomposition algorithm, considering the geometrical configuration of the multielectrode, was designed to identify the individual MUAPs in the measured MSEMG. The identified MUAP was subsequently used as the triggering source for the EMG signals recorded by the surface-disk electrodes. From a pool of 34 subjects with neuromuscular diseases and 14 normal subjects, the median amplitudes of surface-disk EMG after spike-triggered averaging, called MSEMG-MUAP, correlated well (r = 0.82, P < 0.0001) with those of macro EMG. Moreover, the MSEMG-MUAP recording during a ramp force contraction exhibited the common size principle phenomenon during motor unit recruitment. The results of this study demonstrate that the MSEMG-MUAP measurement is a feasible approach for estimating the motor unit size from the skin surface.     

Motor unit size estimation of enlarged motor units with surface electromyography

Surface EMG is hardly used to estimate motor unit (MU) characteristics, while its non-invasiveness is less stressful for patients and allows multi-electrode recordings to investigate different sites of the muscle and MU. The present study compares motor unit potentials (MUPs) obtained with surface EMG and macro EMG during voluntary contraction of the biceps brachii muscle of patients with enlarged MUs caused by prior poliomyelitis. Averaged surface MUPs were obtained by means of needle EMG (SMUP1) and surface EMG (SMUP2) triggering. The MUPs area and peak amplitudes correlated well when comparing the macro MUP and SMUP1 of the same MUs. When MU populations of different patients were compared, the SMUP1s and SMUP2s were equally sensitive to pathology as macro MUPs. In this, the late non-propagating positive wave (only present in unipolar recordings) is more robust than the triphasic propagating wave. Therefore, surface EMG can be used for detecting enlarged MUs. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:878–886, 1998.     

Motor unit number estimation: Sample size considerations

A computer model of the motor unit number estimation procedure was developed to evaluate the sampling error associated with estimates of the number of motor units in muscles. Two different distributions were used to model the motor unit amplitude distribution and were chosen in such a manner that they qualitatively matched the distributions observed under both normal and neurogenic conditions. As expected, the results indicated that estimation error decreases as a function of sample size. However, the relationship between these two variables was nonlinear in the sense that successive increases in sample size lead to progressively smaller decreases in estimation error. The results also indicated that the shape of the motor unit amplitude distribution plays an important role. Specifically, estimates obtained using the distribution modeling normal muscle were generally higher than the actual number of motor units in the muscle, which was not the case for the distribution modeling neurogenic muscle. In addition, the neurogenic distribution was associated with much smaller estimation error, suggesting that motor unit number estimation is well suited to the analysis of neurogenic disease processes. © 1997 John Wiley & Sons, Inc.     

A new approach to motor unit estimation with surface EMG triggered averaging technique

A new method for estimating the number of motor units using a surface EMG triggered averaging technique is described. This method provides an estimation of mean motor unit potential (MUP) amplitude at different leveles of contraction, which can be utilized to estimate the number of motor units in a given muscle. Motor unit count estimated in abductor pollicis brevis (APB) muscle of 11 normal healthy subjects ranged from 131 to 371 with a mean of 246 ± 68. In our preliminary study of patients with lower motor neuron lesions, there was a significant reduction in the number of motor units. We believe our new noninvasive method of motor unit counting is a relatively simple and reproducible physiological technique.© 1995 John Wiley &Sons, Inc.     

Motor unit number estimation using high-density surface electromyography.

OBJECTIVE: To present a motor unit number estimation (MUNE) technique that resolves alternation by means of high-density surface EMG. METHODS: High-density surface EMG, using 120 EMG channels simultaneously, is combined with elements of the increment counting technique (ICT) and the multiple-point stimulation technique. Alternation is a major drawback in the ICT. The spatial and temporal information provided by high-density surface EMG support identification and elimination of the effects of alternation. We determined the MUNE and its reproducibility in 14 healthy subjects, using a grid of 8 x 15 small electrodes on the thenar muscles. RESULTS: Mean MUNE was 271+/-103 (retest: 290+/-109), with a coefficient of variation of 22% and an intra-class correlation of 0.88. On average, 22 motor unit potentials (MUPs) were collected per subject. The representativity of this MUP sample was quantitatively assessed using the spatiotemporal information provided by high-density recordings. CONCLUSIONS: MUNE values are relatively high, because we were able to detect many small MUPs. Reproducibility was similar to that of other MUNE techniques. SIGNIFICANCE: Our technique allows collection of a large MUP sample non-invasively by resolving alternation to a large extent and provides insight into the representativity of this sample. The large sample size is expected to increase MUNE accuracy.     

Motor unit characteristics in healthy subjects and those with postpoliomyelitis syndrome: a high-density surface EMG study

The purpose of this study was to identify optimal ways to detect neurogenic changes with high-density surface electromyography (HD-sEMG). For this purpose, we searched for the variables that most clearly discriminated between postpoliomyelitis and healthy subjects. We obtained HD-sEMG from the quadriceps muscle at different force levels in nine subjects with postpoliomyelitis syndrome and in matched healthy controls. Single motor unit action potentials (MUAPs), extracted from the HD-sEMG signal and the raw signal itself, were analyzed. Areas under the curve of the extracted MUAP waveform, indicating motor unit size, perfectly separated both groups. Raw signal analysis showed significant differences between groups for the monopolarly recorded amplitude up to 60% of maximal force and for the level of interference at higher force levels (40-100% force). We conclude that with HD-sEMG it is possible to detect neurogenic motor unit changes noninvasively, both by analysis of the raw signal itself and by analysis of extracted single MUAPs. The diagnostic yield of the single MUAP analysis is clearly higher. These findings point toward applications for clinical practice and invite further studies exploring the diagnostic value of HD-sEMG.     

Motor unit potential change with contraction level: A concentric macro electromyography study

Introduction: Motor unit action potential (MUAP) reference values are usually given per muscle and age group. Our aim was to evaluate the change in MUAP size at different contraction levels using the concentric macro (ConMac) EMG technique. Methods: ConMac needles were used to record the electrode cannula MUAP and measure its amplitude and area during weak, moderate, and strong muscle contractions. Results: MUAP area and amplitude gradually increased from weak to strong contraction levels in all muscles studied. MUAP amplitudes were larger in distal than in proximal muscles, likely because of a higher fiber density distally. Conclusions: MUAP normal values in the literature per muscle do not take into account the contraction level at which they were recorded and can misrepresent the interpretation of normal. Concentric macro EMG is a simple and useful complement to routine EMG studies and yields additional information on MUAP neurophysiology. Muscle Nerve 48 : 551–556, 2013     

Motor unit properties of biceps brachii in chronic stroke patients assessed with high‐density surface EMG

The aim of this study was to investigate motor unit (MU) characteristics of the biceps brachii in poststroke patients using high‐density surface electromyography (sEMG). Eighteen chronic hemiparetic stroke patients took part. The Fugl‐Meyer score for the upper extremity was assessed. Subjects performed an isometric step contraction consisting of force levels from 5%–50% maximal voluntary contraction while sEMG of the biceps brachii was recorded with a two‐dimensional 16‐channel electrode array. This was repeated for both sides. Motor unit action potentials (MUAPs) were extracted from the EMG signals, and their root‐mean‐square value (RMS_MUAP, reflecting MU size) and mean frequency of the power spectrum (FMEAN_MUAP, reflecting recruitment threshold) were calculated. FMEAN_MUAP was smaller on the affected than on the unaffected side, indicating an increased contribution of low‐threshold MUs, possibly related to degeneration of high‐threshold MUs. The ratio of RMS_MUAP on the affected side divided by that on the unaffected side correlated significantly with the Fugl‐Meyer score. This ratio may reflect the extent to which reinnervation has occurred on the affected side. © 2008 Wiley Periodicals, Inc. Muscle Nerve 2008     

Short-term stability of single motor unit recordings in motor neuron disease: a macro EMG study.

Thirty five individual macro EMG motor unit potentials in 13 patients with motor neuron disease were recorded every 15 minutes during a 2 hour period. No significant change in amplitude or area was seen in 15 control units in nine patients or in 20 units in 11 patients receiving RX77368 0.2-0.3 mg/kg. The findings provide no evidence for an action of this long acting TRH analogue on the peripheral territory of motor units in motor neuron disease.     

Motor control after spinal cord injury: Assessment using surface EMG

The brain motor control assessment (BMCA) protocol is a comprehensive multichannel surface EMG recording used to characterize motor control features in persons with upper motor neuron dysfunction. Key information is contained in the overall temporal pattern of motor unit activity, observed in the EMG (RMS) envelope. In paralysis, a rudimentary form of suprasegmental control of tonic and phasic reflexes can be demonstrated. EMG patterns evoked by voluntary and passive maneuvers and by volitional modulation of reflex responses reveal features of motor control not apparent in the clinical examination. Such subclinical findings may explain paradoxically different responses in apparently similar SCI subjects, and may be used to monitor spontaneous or induced changes. The recording protocol, examples of EMG patterns, and their prevalence in 40 spinal cord injured (SCI) subjects are presented, and compared with 5 healthy subjects. © 1996 John Wiley & Sons, Inc.     

帕金森病患者的运动单位数目评价

目的对帕金森病患者的运动单位数目进行检测,观察有无运动单位数目的下降。方法采用半自动递增刺激法对20例帕金森病患者的大鱼际肌（Thenar）和趾短伸肌（EDB）进行运动单位数目估计（MUNE）,并与对照组12名健康受试进行比较。结果帕金森病患者的大鱼际肌运动单位数目与对照组比较无差异,趾短伸肌的运动单位数目与对照组相比虽有降低趋势,但差异无统计学意义（P〉0．05）。帕金森病患者的全部运动单位面积及单个运动单位面积与正常对照比较差异无统计学意义（P〉0．05）。结论帕金森病患者运动单位数目与正常对照相比差异无统计学意义,提示锥体外系病变对运动神经元数目影响可能并不显著。     

Motor unit number estimation in neuromuscular disease

Motor unit number estimation (MUNE) is an electrophysiological method designed to quantify motor unit loss in target muscles of interest. Most of the techniques are noninvasive and are therefore well suited for longitudinal monitoring. In this brief review, we describe the more commonly used techniques and their applications in amyotrophic lateral sclerosis, poliomyelitis, spinal muscular atrophy and hereditary sensorimotor neuropathies. Findings in some of these studies offer important pathophysiological insights. Since conventional electrophysiologic methods are not sensible measures of motor neuronal loss, MUNE could play a potentially important role in the diagnosis, monitoring of disease progression and response to treatment in neuromuscular diseases in which motor unit loss is a major feature.     

Motor unit number estimation in facial paralysis

The value of motor unit number estimation (MUNE) in determining the prognosis of acute peripheral facial paralysis (PFP) was evaluated in 89 patients with PFP on days 6, 8, 11, 14, 20, and 30 of PFP and repeated once per month until complete recovery or the end of the first year. The symptomatic/asymptomatic side ratios of the compound muscle action potential (CMAP) amplitudes recorded from nasalis muscles and MUNEs studied using the incremental method by recording from the same muscle were assessed with regard to three outcome groups (Group I, complete recovery; Group II, mild dysfunction; Group III, moderate-moderately severe dysfunction). CMAP and MUNE ratios were parallel to each other in all patient groups throughout the observation period with lower values in the more severe groups. However, CMAP amplitude loss was significantly greater than the MUNE loss in the first 3 weeks of PFP. The MUNE method is not superior to CMAP size in determining prognosis in PFP. However, the significant disparity between the CMAP and MUNE ratios in the early period may have some physiological relevance with regard to the pathophysiology of the Wallerian degeneration process and deserves further research into its potential sources.     

Single fiber macro versus concentric trigger macro EMG: a comparison of methods.

The values obtained from two different macro EMG methods were compared, and found to be different. Normally, macro electromyography (EMG) is performed with a modified single fiber (SF) needle using the SF potential as a trigger; a new method recommends a modified concentric needle and triggers on the concentric EMG signal. The concentric macro EMG has a 40% to 50% smaller amplitude and area values than data obtained with a SF macro EMG needle. The different values are the result of variant spatial relationships of the respective needles to the motor unit under study, and may be due to a recruitment-dependent bias resulting from different trigger properties of the two methods. The concentric macro EMG needle can be used to estimate motor unit size, to scan the unit, and to investigate its different concentric EMG signals.     

糖尿病感觉神经病患者的运动单位数目估计

目的 通过运动单位数目估计技术检测糖尿病感觉神经病患者运动单位,以期评估其下运动神经功能状态.方法 纳入54例符合世界卫生组织糖尿病周围神经病国际协作研究诊断标准的糖尿病周围神经病(DPN)住院患者,并根据尺神经传导异常结果分组:感觉异常组(即仅有感觉传导异常而运动传导正常)33例,其中男20例,女13例;感觉运动异常组(即感觉传导和运动传导均异常)21例,其中男13例,女8例,并与42名健康人对照.应用Keypoint4肌电诱发电位仪,计数各组小鱼际肌运动单位数目,同时记录54例DPN患者入院后糖尿病病程和空腹血糖.结果 感觉异常组、感觉运动异常组和健康对照组的小鱼际肌运动单位数目分别为97.1±47.6、63.3±22.3、173.0±75.5(F=21.259,P=0.000);54例DPN患者小鱼际肌运动单位数目(84.0±42.8)与糖尿病病程(1个月至26年)呈负相关(r=0.414,P=0.002),与空腹血糖水平(5.0～20.4 mmol/L)无明显相关.结论 糖尿病感觉神经病存在着临床下运动神经损害,运动单位的丢失程度受糖尿病病程的影响.     

Motor unit number estimation in cases with Carpal Tunnel Syndrome

Degenerative or destructive processes result in the loss of whole motor neurons or in the peripheral axon portion. Loss of motor axons or neurons, and conduction blocks, are the basis of the weakness seen in most patients with neurogenic disease. The severity of the clinical deficit is directly associated with the number of the motor neurons or/and axons lost or blocked. So, it is important to find out the number of the functional motor units while evaluating neuromuscular disease. In neurological practice, motor unit number estimation studies are made in many diseases, especially in anterior horn disease. Entrapment neuropathies are one of these diseases. This study utilized motor unit number estimate testing in 50 patients with carpal tunnel syndrome and 34 controls without any systemic disease. The authors compared the results of these two groups and found statistical significance ( p < .0001).     

Motor unit number estimation: A technology and literature review

Introduction: Numerous methods for motor unit number estimation (MUNE) have been developed. The objective of this article is to summarize and compare the major methods and the available data regarding their reproducibility, validity, application, refinement, and utility. Methods: Using specified search criteria, a systematic review of the literature was performed. Reproducibility, normative data, application to specific diseases and conditions, technical refinements, and practicality were compiled into a comprehensive database and analyzed. Results: The most commonly reported MUNE methods are the incremental, multiple‐point stimulation, spike‐triggered averaging, and statistical methods. All have established normative data sets and high reproducibility. MUNE provides quantitative assessments of motor neuron loss and has been applied successfully to the study of many clinical conditions, including amyotrophic lateral sclerosis and normal aging. Conclusions: MUNE is an important research technique in human subjects, providing important data regarding motor unit populations and motor unit loss over time. Muscle Nerve 50 : 884–893, 2014