Motor unit size estimation: confrontation of surface EMG with macro EMG

Surface EMG (SEMG) is little used for diagnostic purposes in clinical neurophysiology, mainly because it provides little direct information on individual motor units (MUs). One of the techniques to estimate the MU size is intra-muscular Macro EMG. The present study compares SEMG with Macro EMG. Fifty-eight channel SEMG was recorded simultaneously with Macro EMG. Individual MUPs were obtained by single fiber triggered averaging. All recordings were made from the biceps brachii of healthy subjects during voluntary contraction at low force. High positive correlations were found between all Macro and Surface motor unit potential (MUP) parameters: area, peak-to-peak amplitude, negative peak amplitude and positive peak amplitude. The MUPs recorded with SEMG were dependent on the distance between the MU and the skin surface. Normalizing the SEMG parameters for MU location did not improve the correlation coefficient between the parameters of both techniques. The two measurement techniques had almost the same relative range in MUP parameters in any individual subject compared to the others, especially after normalizing the surface MUP parameters for MU location. MUPs recorded with this type of SEMG provide useful information about the MU size.     

Macro EMG in neuromuscular diseases]

The aim of this study is the introducing of macro-emg method as electrophysiological test used in diagnosis of neuromuscular diseases. The macro motor unit potentials (macro MUPs) obtained by recording macroelectrode (modified single-fibre electrode) represents temporal and spatial summation of individual single fiber action potentials belonging to whole motor unit territory--so the uptake area is larger for macroelectrode than for the concentric electrode, commonly used in emg routine work, when central main complex is generated only from less than 15 muscle fibers [10, 12, 13]. Additional information obtained by macro-emg method is spatial organisation of muscle fibers within the motor unit, so-called fiber density (F.D) In our study macro-emg examinations were performed in 20 healthy subjects, aged 21-55, without signs and symptoms of neuromuscular disorders. Macro MUPs were recorded using special programme for macro-emg and performed on electromyograph Counterpoint. 37 muscles (20 BB and 17 RF) were examined, and median values of amplitude, area of macro MUPs and F.D. in healthy subjects of different age were analyzed. Mean values of median for amplitude and area of macro MUPs in BB and RF muscles show respectively--148 microV, 382 microV x ms, and 319 microV, 763 microV x ms. Parameters of macro MUPs obtained in healthy subjects were compared to results obtained in 10 patients with myopathy and lower motor neuron lesion. Our results have confirmed the value of macro-emg method for investigating of the pathophysiological changes in motor units in neurogenic disorders, in myopathy the study should be continued.     

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.     

Voluntary activation and fiber density of fasciculations in motor neuron disease.

Two hundred voluntarily activated motor units and 211 fasciculations were recorded in the biceps of 10 patients with motor neuron disease with the Macro EMG technique. Twenty-two fasciculations, in nine of 10 muscles, had a potential of closely similar shape, amplitude, and area to that of a voluntary unit. Fasciculating units that could not be activated voluntarily had a higher mean number of spikes in their triggering single fiber potentials than units that could only be activated voluntarily, but statistically similar Macro EMG parameters. The mean number of single fiber spikes, and Macro EMG parameters, of fasciculations activated voluntarily, were similar to those of units that were only activated voluntarily. A positive correlation between fiber density and Macro EMG median amplitude and area in individual patients, and between number of single fiber spikes and Macro EMG amplitudes and areas in the pooled data, was found for fasciculations but not for voluntary units. At least 10% of fasciculations in patients with motor neuron disease may originate near or above the point of axonal branching and a proportion of those without evidence of voluntary activation may have a higher number of smaller muscle fibers, or more closely packed muscle fibers, of similar or greater size, than voluntarily activated motor units. Differences in the peripheral microanatomy of a number of fasciculation units not activated voluntarily may underlie ectopic impulse generation in the terminal axonal arborization, endplate zone, or muscle fibers of these units.     

Macro EMG follow-up study in post-poliomyelitis patients

We investigated the muscle strength and motor unit (MU) territory of five patients with postpolio syndrome (PPS), six stable patients with prior poliomyelitis, and five healthy volunteers. The MU territory was assessed by measuring amplitudes of motor unit potentials (MUPs) recorded by the macro EMG technique. The investigations were repeated after 11–20 months (mean 15.6). The macro MUP amplitudes in both patient groups were markedly increased (P = 0.02). However, no statistical difference was found between the two groups in the initial amplitude values. Macro MUP amplitudes obtained on repeated examinations did not differ significantly from the initial macro MUP amplitudes in any of the three groups. In three individual PPS patients, a decline in muscle strength on the follow-up study was documented, providing the diagnosis of post-poliomyelitis muscular atrophy (PPMA). The three PPMA patients had the highest initial macro MUPs. Two of them showed a decrease in macro MUP amplitudes on follow-up. These findings suggest that a later breakdown of oversized MUs may play a role in the pathogenesis of PPMA.     

Discriminant analysis of various concentric needle EMG and macro-EMG parameters in detecting myopathic abnormality.

OBJECTIVES: The aim of the study was to evaluate the effectiveness of various concentric needle electromyography (EMG) motor unit action potentials (cnMUPs) and macro-EMG motor unit potentials (mMUPs) parameters for differentiation between myopathic motor unit action potentials (MUPs) and normal MUPs. METHODS: We have analyzed 112 cnMUPs and 84 mMUPs recorded from 7 patients with myopathy and 256 cnMUPs, 256 mMUPs from 14 healthy subjects. Biceps brachii muscle was investigated. Evaluated variables were duration, amplitude, area, number of phases, area/amplitude ratio, size index and area/number of phases ratio for cnMUPs, area and amplitude for mMUPs. Univariate statistical analysis and discriminant analysis for each parameter were performed. RESULTS: The variable 'area ' gave rather good discrimination than duration, amplitude, number of phases, area/amplitude ratio, and size index. As demonstrated by discriminant analysis, area/phase ratio is more useful than area alone if myopathic MUPs had to be discriminated from normal MUPs. Discriminant efficiency of mMUP parameters were lower than all cnMUP parameters except number of phases. CONCLUSIONS: The new parameter area/number of phases ratio seemed to be promising, since it produced a better yield in detecting of myopathic abnormality than other investigated parameters in discriminant analysis. Discriminating ability of macro-EMG was lower than that of cnEMG.     

Acquired neuromyotonia in childhood: case report and review

Recently characterized as an immune-mediated channelopaty, Isaacs' syndrome (also known as acquired neuromyotonia) was first described in 1961 in two men with persistent, generalized muscle stiffness, in addition to spontaneous, rapid discharges of motor-unit potentials on electromyography. In the peripheral nervous system, antibodies targeted to voltage-gated potassium channels induce hyperexcitability of motor axons, resulting in signs of muscle stiffness or of pseudomyotonia. A spontaneous burst of single motor-unit activity, and myokymic and neuromyotonic discharges, are the most characteristic features found in electromyography studies. This report describes Isaacs' syndrome in a child, in whom the diagnosis was made by clinical features of acquired, spontaneous muscle overactivity and typical electromyographic findings.     

Clinical electrophysiological characterization of the acquired neuromyotonia phenotype of autoimmune peripheral nerve hyperexcitability

Acquired autoimmune neuromyotonia is regarded as part of the spectrum of peripheral nerve hyperexcitability disorders. We aimed to use clinical neurophysiological measurements to study the extent, distribution, and characteristics of spontaneous motor unit potentials in 11 patients with acquired neuromyotonia. Investigations revealed that most spontaneous discharges recorded were motor unit, or partial motor unit potentials of normal size. Bursts of motor unit potentials arose more commonly from distal portions of the peripheral nerve and had abnormal absolute and relative refractory periods. Spontaneous discharges in some patients occurred in semirhythmic bursts in certain muscles. No patient had neurophysiological abnormalities detectable in first-order neurons of the central nervous system when using transcranial magnetic stimulation to estimate the threshold for corticomotor excitation and determine central motor conduction time. Only patients with coexistent myasthenia gravis had neurophysiologically detectable defects in neuromuscular transmission. The pathogenic region of abnormality in peripheral nerve hyperexcitability disorders therefore seems to lie within the terminal branches of peripheral motor nerves.     

The standard concentric needle cannula cannot replace the Macro EMG electrode

ObjectiveTo establish the usefulness of the single use and affordable standard concentric EMG electrode as a substitute for the expensive standard macro electrode.MethodsMacro EMG performed with macro electrode is compared with recordings from the uninsulated cannula of a standard EMG electrode at two different recording depths in the tibialis anterior muscle. This was performed both in muscles with signs of collateral reinnervation and without.ResultsThe amplitude of the motor units recorded with the uninsulated concentric needle cannula were lower for the deeply recorded motor units compared to motor unit potential (MUP) amplitudes recorded with the standard macro electrode. The deeply recorded concentric needle (CN) cannula recorded MUPs amplitudes were also lower than superficially recorded CN cannula MUPs. The standard Macro EMG signals show no difference between deeply and superficially recorded motor units.ConclusionThe uninsulated cannula of the concentric needle electrode cannot replace the standard Macro EMG electrode due to technical reasons, probably from different effects of shunting of the bare cannula in deep vs. superficially recorded motor units.SignificanceThe standard CN electrode could not be used as substitute for the standard Macro EMG needle.     

Fiber density of the motor units recruited at high and low force output

Motor units (MUs) are recruited according to the size principle. At low force output, macro‐motor unit potentials (macro‐MUPs) with small amplitude and area are recorded; MUs with large electrical size fire at high force output. Our objective was to elucidate whether this difference is caused by a higher fiber density (FD) of the MUs recruited at high force output. We measured the FD and respectively the amplitude and the area of the macro‐MUPs via single‐fiber macro electromyography (EMG) recorded at low and high force output in 48 healthy subjects. The macro‐MUPs were significantly larger at high force output than at low force. The FD did not differ at the two force levels. Our findings suggest that the larger electrical size of the high recruitment threshold MUs is due not to a higher FD, but to a larger territory. FD is a robust EMG parameter, independent of the level of the force output. Muscle Nerve 40: 112–114, 2009     

Generator sites for spontaneous activity in neuromyotonia. An EMG study

A 16-year-old female patient with symptoms and signs compatible with neuromyotonia was studied with various neurophysiological tests and with muscle biopsy. Nerve conduction studies revealed signs of axonal motor neuropathy. EMG showed denervation in distal muscles, and moderate neurogenic changes in other muscles. Abundant spontaneous motor unit activity was recorded in all muscles. This activity did not disappear upon proximal nerve blockade with local anaesthetics. Based on the shape of spontaneous discharges and their behaviour on nerve stimulation and during voluntary effort, the site of generation was suggested. This varied for different discharges, from proximally in the nerve, to various sites along the intramuscular nerve tree. In some axons there were signs of conduction block proximal to the generation site for the spontaneous discharges. Different axons showed various degrees of abnormality; local hyperexcitability triggering new impulses only after the passage of a preceding impulse, increased hyperexcitability generating spontaneous activity, total impulse blocking, and finally axonal degeneration.Treatment with dihydantoin reduced the spontaneous activity with concomitant clinical improvement.     

Can the size principle be detected in conventional emg recordings?

According to Henneman's size principle, small motor units are recruited before large ones. It is commonly believed that this can be detected in routine conventional EMG recordings even among the earliest recruited motor units. That is, the MUP amplitude, area, and thickness should increase with recruitment order. We studied the first four motor unit potentials (MUPs) recruited within the pickup area of the electrodes. Data were obtained from 179 different sites in monopolar recordings and in 153 concentric recordings from 5 health subjects. In the pooled material, amplitude, area, and thickness increased slightly between consecutively recruited MUPs. However, at individual recording sites the size of consecutively recruited MUPs varied considerably. At some recording sites the first recruited MUP had the largest amplitude and the later MUPs has successively smaller amplitudes. We conclude that, at individual recording sites, the size principle cannot be detected in low threshold motor units with monopolar or concentric EMG electrodes. The reason for this is the small uptake area of these electrodes in relation to the motor unit territory. © 1995 John Wiley & Sons, Inc.     

Neuromyotonia in idiopathic hypoparathyroidism

Α 62-year-old man was presented with bilateral cataract, proximal muscle weakness and difficulty in relaxing the hands after voluntary contraction. Idiopathic hypoparathyroidism was diagnosed. Electrophysiological study showed spontaneous motor unit action potentials, occurring and disappearing abruptly, as duplets, triplets and multiplets, with an intra-burst frequency of up to 100 Hz and some of them waning in amplitude, findings consistent with neuromyotonia.     

Standardisation of anal sphincter EMG: high and low threshold motor units.

OBJECTIVE: The anal sphincter muscle has a proportion of low threshold motor units (MUs) that are continuously active and other, recruitable high threshold MUs. In standard EMG recordings, motor unit potentials (MUPs) of the later seem to be of higher amplitudes. A quantitative EMG study was performed to assess possible consequences of sampling MUPs at different levels of sphincter activation. METHODS: Fifteen females without uroneurological disorders were studied. After insertion, standard concentric EMG needle was left in the anal sphincter muscle undisturbed for 1 min; then 30 s of the remaining continuous, and 1 min of voluntarily increased EMG activity were recorded on a DAT recorder. MUPs were collected and analysed by 'Multi-MUP' analysis. MUPs analysed during relaxation constituted the 'low threshold MUP pool'. MUPs sampled on activation were checked for those, already sampled during relaxation, (which were discarded), and the remaining MUPs constituted the 'high threshold MUP pool'. Parameters of both MUP pools were compared. RESULTS: High threshold MUPs were found to be significantly larger than low threshold MUPs. CONCLUSIONS: EMG investigator should be aware of the differences of MUPs sampled at various anal sphincter activity levels. For the technique of 'Multi-MUP' analysis sampling at an activity level which provides 3-5 MUPs per detection site would seem practical, providing a standardised approach suitable for comparing normative data with individual findings from most patients.     

Simulation and analysis of the electromyographic interference pattern in normal muscle. Part II: Activity, upper centile amplitude, and number of small segments

We have defined three new features of the electromyographic (EMG) interference pattern (IP): activity, upper centile amplitude (UCA), and number of small segments (NSS). These parameters were measured in simulated IPs constructed by adding together motor unit action potentials (MUAPs) recorded with a concentric needle EMG electrode. The activity increases linearly with the number of MUAP discharges to approximately 80% of its theoretical maximum value. The UCA correlates strongly with the peak-to-peak amplitude of the largest MUAP in the IP and the mean segment amplitude and does not depend on the discharge rate of the largest MUAPs. We infer that the UCA defines the upper limit of the peak-to-peak amplitude of the MUAPs contained in the IP. The NSS increases with the number of MUAP discharges, but reaches a constant value at higher MUAP discharge rates, probably because small amplitude MUAPs are masked by the large amplitude MUAPs. The potential value of these parameters in automated IP analysis is discussed.     

不同阶段肌萎缩侧索硬化患者肌电图的研究

目的研究不同阶段肌萎缩侧索硬化(ALS)患者的定量肌电图(EMG)表现,寻找早期诊断ALS的敏感电生理指标。方法对60例ALS患者进行定量EMG检查,分析不同阶段运动单位动作电位(MUPs)多相参数、自发电位和大力收缩募集相变化,并与健康对照组进行比较。结果不同阶段ALS EMG表现不同,从最早期阶段到最后阶段可分为N0~N56个连续的电生理阶段。N2期MUPs的时限、波幅、面积、运动单位指数(SI)、多相波数值均较健康对照组显著升高(均P<0·001),N0、N4期MUPs部分多相参数数值明显升高(P<0·05);自发电位在病变的各个阶段均可见到,以N2~N5多见,分别为63·6%、83·0%、91·2%、100%。结论ALS患者早期阶段如出现自发电位,即为下运动神经元受累的特征表现;定量EMG检查中运动单位面积和波幅增大是其显著特点。     

Ocular neuromyotonia: a case report

Ocular neuromyotonia is a rare clinical entity, which is characterized by spontaneous spasm of ocular muscles resulting in paroxysmal diplopia and strabismus. Inappropriate discharges from ocular motor neurons or axons with unstable cell membranes may cause the sustained contraction of their respective ocular muscles. In most cases, ocular neuromyotonia resulted from radiation therapy to the parasellar and sellar regions or compressive lesions on ocular motor nerves. Among 30 patients reported in the literatür only six patients were accepted as idiopathic. Here, we reported a patient with third nerve myotonia representing with spells of diplopia. No lesion was found and she was accepted as idiopathic ocular neuromyotonia.     

The spectrum of concentric macro EMG correlations. Part I. Normal subjects.

Using a concentric macro electrode, both the concentric and macro action potentials of a motor unit were analyzed for duration, area, and amplitude. Eighty-six different motor units were analyzed from the tibialis anterior muscle in 10 normal subjects. The aim of this work was to compare concentric and macro action potential measurements of the same motor unit. The study revealed significant correlations between concentric and macro samples, with the concentric potential's area correlating better with the macro potential than its amplitude. This shows that the 10 to 15 muscle fibers studied by the concentric electrode serve as a good sample of the motor unit as a whole. We briefly review the technique used in concentric macro EMG, as well as describe the methods used for collecting and comparing both concentric and macro action potentials.     

Epileptic discharges triggered by eye convergence

A 27-year-old man with major motor and minor seizures showed focal epileptic discharges and electrical seizures triggered by eye convergence. Other voluntary ocular movements failed to evoke reflex epileptic discharges. Eye convergence triggered discharges even after the eyelids were strapped open with tapes and the pupillary and accommodation reflexes were temporarily paralyzed. This patient also showed pattern-sensitive focal epileptic discharges arising from the same area of the brain as those induced by eye convergence, but he was not photosensitive.     

肛门括约肌肌电图在鉴别诊断多系统萎缩、帕金森病及晚发型脊髓小脑共济失调中的作用

目的 分析多系统萎缩(multipe system atrophy,MSA)、帕金森病(Parkinson's disease,PD)、晚发型脊髓小脑共济失调(1ate-onset spinocerebellar ataxia,LOSCA)患者的肛门括约肌肌电图(external anal sphincter electromyography,EAS-EMG)的差异等电生理改变特点,为临床鉴别诊断提供依据.方法 分别对88例MSA、69例原发性PD、18例LOSCA患者的电生理检查结果进行回顾性分析.结果 EAS-EMG检查中MSA组有84例(95.5%)患者存在不同程度的神经源性受损,表现为运动单位电位(MUPs)平均时限[(12.92±2.59)ms]显著延长、平均波幅[(648.6±251.0)μV]增高、多相波百分比(42.6%±21.2%)增加、异常自发电位与卫星电位多见,与PD[(8.99±0.47)ms、(470.0±91.9)μV、24.2%±11.0%]及LOSCA组[(9.04±0.62)ms、(493.1±113.7)μV、22.0%±12.1%]相比差异有统计学意义(Welch值分别为:94.240、18.093、26.710,均P=0.000).PD及LOSCA组EAS-EMG检查未发现有神经源性受损,也未见自发电位与卫星电位.结论 MSA临床表现可与PD及LOSCA相似,有时容易相互误诊,EAS-EMG检查可提高MSA的正确诊断率,尤其与PD、LOSCA进行鉴别诊断时有较大价值.

Abstract：

Objective To observe the electrophysiological changes, especially in the examination of external anal sphincter electromyography ( EAS-EMG), with those patients diagnosed as multiple system atrophy ( MSA), Parkinson's disease (PD) and late-onset spinocerebellar ataxia (LOSCA) and explore its clinical diagnostic value as well as differential diagnostic value for the three diseases. Methods The clinical data, cranial magnetic resonance imaging (MRI) data as well as results of EAS-EMG for 3 groups patients, including 88-cases MSA, 69-cases PD and 18-cases LOSCA, were analyzed retrospectively.Results EAS-EMG showed that 84 cases (95.5%) in MSA group had varying degrees of neurogenic injury. Meanwhile, mean motor unit potentials (MUPs) duration (( 12.92 ± 2.59)ms), mean MUPs amplitude ( ( 648.6 ± 251.0 ) μV ), and MUPs polyphasicity ( percentage of polyphasic MUPs; 42. 6% ±21.2% ) in MSA group were significantly different from those in PD ( ( 8. 99 ± 0. 47 ) ms, (470. 0 ±91.9) μV, 24.2% ±11.0%) and LOSCA groups ((9.04 ±0.62)ms, (493.1 ± 113.7)μV,22.0% ±12. 1%; Welch:94. 240,18. 093,26. 710,all P =0. 000). The spontaneous potentials and satellite potentials showed more common in MSA group, but not in other groups. Conclusions MSA and PD and LOSCA are easily mutually misdiagnosed because of some similar syndromes, but the method of EAS-EMG could be effective and helpful to enhance accurate diagnostic rate of MSA and its differential diagnosis with PD and LOSCA.