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.     

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.     

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.     

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

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

Motor unit sound in needle electromyography: assessing normal and neuropathic units

Motor unit action potentials (MUPs) recorded by a monopolar needle electrode in normal and neuropathic muscles were computer-simulated. Five experienced electromyographers acted as examiners and assessed the firing sounds of these MUPs without seeing them on a display monitor. They judged whether the sounds were crisp or close enough to accept for the evaluation of MUP parameters and whether, when judged acceptable, they were neuropathic-polyphasic. The examiners recognized motor unit (MU) sound as crisp or polyphasic when the MUP obtained was 0.15-0.2 mm from the edge of the MU territory. When the intensity of the sound decreased, they were unable to perceive it as crisp. When the intensity exceeded the saturation level of loudspeaker output, the sound was perceived as polyphasic, but the wave form of the MUP was not. When the frequency of the neuropathic MUP was lowered, the examiners were unable to determine whether the MUP was polyphasic. MUPs recognized as acceptable for evaluation can be distinguished by listening to MU sounds. The audio amplifier gain must be appropriately adjusted for each MUP amplitude in order to assess whether an individual MU sound is crisp or polyphasic before MUP parameters are measured on a display monitor.Copyright 2000 John Wiley & Sons, Inc.     

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.     

The origin of spontaneous discharges in acquired neuromyotonia. A Macro EMG study.

OBJECTIVE: To study the generator sites of spontaneous discharges in patients with immune-mediated neuromyotonia. METHODS: Macro EMGs triggered by both spontaneously and voluntarily activated single action potentials were recorded and the mean peak-to-peak amplitude and area of the macro motor unit potentials were compared in two patients with typical acquired neuromyotonia having positive antibodies against voltage-gated potassium channels. RESULTS: Mean peak-to-peak amplitude and area of Macro EMG motor unit potentials (macro MUPs) triggered by spontaneous discharges were significantly smaller than those triggered by voluntary activation in both patients. However, a few macro MUPs triggered by spontaneous discharges resembled those triggered by voluntary activation. CONCLUSIONS: Spontaneous discharges in two patients with immune-mediated neuromyotonia seem to be mostly generated at sites distal to the terminal axon branching points. SIGNIFICANCE: This finding may provide a new insight in the understanding of spontaneous discharges in immune-mediated neuromyotonia.     

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.     

Quantitative anal sphincter EMG in multisystem atrophy and 100 controls

OBJECTIVE: To evaluate data of quantitative anal sphincter EMG in normal controls and to compare them with patients with multiple system atrophy (MSA). METHODS: Quantitative anal sphincter EMG were performed on 100 normal controls and 11 patients with MSA to characterise EMG data in these two groups. RESULTS: In the normal controls, there was a trend for increased motor unit potential (MUP) amplitude, duration, area, and polyphasicity with advancing age. Patients with MSA exhibited similar MUP size and fibre density. Significant differences were found only in parameters of the recruitment pattern, which were reduced in MSA, with a diminution in the number of active MUPs during rest. CONCLUSIONS: These results may reflect either decreased number of motor cells in Onuf's nucleus without significant consequential reinnervation, or upper motor neuron involvement affecting the anal sphincter in MSA. They further underline the importance of comparative data for age matched controls.     

Multichannel surface EMG: basic aspects and clinical utility

The generation of the surface electromyogram (sEMG) is described with regard to the properties of the single muscle fiber action potential as source, the physical aspects of volume conduction and recording configuration, and the properties and firing pattern of motor units (MUs). The spatial aspect of the motor unit action potential (MUP) is emphasized in relation to the results of high-density, multichannel sEMG measurements. The endplate zone, depth, size, and position of MUs can be estimated. The use of muscle fiber conduction velocity measurements in channelopathies and the changes in pathological fatigue are described. Using the unique patterns of spatial spread of MUPs over the skin (MU fingerprint), MU classification and the determination of firing moments is done noninvasively. Clinical applications of high-density sEMG measurements are reviewed. Emerging possibilities provided by MUP size and fingerprint measurements in neuromuscular disease and motor control are discussed. We conclude that multichannel sEMG adds unique, and sometimes indispensable, spatial information to our knowledge of the motor unit.     

Reliability of quantitative EMG analysis of the extensor carpi radialis muscle

This study investigated the within-subject, intra- and inter-operator reliability of quantitative electromyographic (EMG) analysis using decomposition-based quantitative electromyography (DQEMG). Needle and surface-detected EMG signals were collected during low-level isometric contractions of the extensor carpi radialis (ECR) muscle. DQEMG was used to extract needle-detected motor unit potential (MUP) trains and surface-detected MUPs (SMUPs) associated with each train. Two independent experienced operators re-decomposed and processed the MUP data on two separate occasions. One-way analyses of variance (ANOVA) were performed to identify within-subject differences (test-retest, n=6), and operator and trial differences (intra- and inter-operator, n=20) for the MUP morphological variables. The within-subject reliability, as well as the intra- and inter-operator reliability were estimated using intraclass correlation coefficients (ICCs). The 95% limits of agreement were calculated to measure within-subject and between operator agreements. MUP durations were found to be significantly different between days (p<0.05). For intra- and inter-operator reliability, a significant difference was found within and between the operators for MUP duration, and between the operators for MUP number of turns (p<0.05). SMUP morphological parameters yielded higher ICC values for both intra (0.96-0.99) and inter (0.96-0.99) operator scores when compared to MUP morphological parameters (intra-operator: 0.81-0.99; and inter-operator: 0.67-0.98). Mean motor unit (MU) firing rate was found to be a highly reliable measure for both intra- and inter-operators (0.99-0.97, respectively). The between-operator agreement was above 95% for all morphological parameters. These results concerning within-subject, intra- and inter-operator reliability and levels of agreement for quantitative motor unit analysis suggest that DQEMG provides sufficiently consistent results to allow it to be effectively used for QEMG analysis. Needle-detected MUP morphology although clinically useful in the diagnosis and monitoring of neuropathies, was not as reliable as surface MUP QEMG measures.     

EMGLAB: an interactive EMG decomposition program

This paper describes an interactive computer program for decomposing EMG signals into their component motor-unit potential (MUP) trains and for averaging MUP waveforms. The program is able to handle single- or multi-channel signals recorded by needle or fine-wire electrodes during low and moderate levels of muscular contraction. It includes advanced algorithms for template matching, resolving superimpositions, and waveform averaging, as well as a convenient user interface for manually editing and verifying the results. The program also provides the ability to inspect the discharges of individual motor units more closely by subtracting out interfering activity from other MUP trains. Decomposition accuracy was assessed by cross-checking pairs of signals recorded by nearby electrodes during the same contraction. The results show that 100% accuracy can be achieved for MUPs with peak-to-peak amplitudes greater than 2.5 times the rms signal amplitude. Examples are presented to show how decomposition can be used to investigate motor-unit recruitment and discharge behavior, to study motor-unit architecture, and to detect action potential blocking in doubly innervated muscle fibers.     

Tracking motor unit action potentials in the tibialis anterior during fatigue

New surface electromyogram (SEMG) techniques offer the potential to advance knowledge of healthy and diseased motor units. Conduction velocity (CV) estimates, obtained from indwelling electrodes, may provide diagnostic information, but the standard method of CV estimation from SEMG may be of only limited value. We developed a motor unit (MU) tracking algorithm to extract motor unit conduction velocity (MUCV) and motor unit action potential (MUAP) amplitude estimates from SEMG. The technique is designed to provide a noninvasive means of accessing fatigue and recruitment behavior of individual MUs. We have applied this MU tracking algorithm to SEMG data recorded during isometric fatiguing contractions of the tibialis anterior (TA) muscle in nine healthy subjects, at 30%-40% maximum voluntary contraction (MVC). The results reveal that MUCVs and MUAP amplitudes of individual MUs can be estimated and tracked across time. Time-related changes in the MU population may also be monitored. Thus, the SEMG technique employed provides insight into the behavior of the underlying muscle at the MU level by noninvasive means.     

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

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

Size of motor unit potential sample

In quantitative electromyography (EMG), a sample size of 20 motor unit potentials (MUPs) is standard. The effect of increase in the number of MUPs above 20 is not known, although advanced MUP analysis techniques make such samples practical. In the present study, using multi-MUP analysis, pools of 3,720 neuropathic and 2,526 control MUPs were obtained from external anal sphincter muscles. From each pool, 10,000 random samples of 5, 10, 15, 20, 30, 40, 50, and 100 MUPs were obtained by a computer. For each sample size, 95% normative limits for mean values, SDs, and "outliers," and sensitivities were calculated for eight MUP parameters. As the magnitude of MUP samples increased, normative limits narrowed and sensitivities increased (at 5: 20-30%; at 20: 30-55%; at 100: 80-100%) for all statistics of all MUP parameters. Our results demonstrated a substantial increase in sensitivity by increasing the MUP sample to more than 20. This option deserves consideration in an attempt to improve the usefulness of quantitative EMG.     

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.     

Reinnervation of anal sphincter muscle by low and high-threshold motor neurones.

The external anal sphincter (EAS) has continuously active low-threshold and recruitable high-threshold motor units (MUs), the latter being 'larger'. On performing concentric needle electromyography (EMG) of the EAS, the high-threshold MUs seemed to reveal more neuropathic changes than the low-threshold MUs. To verify this hypothesis, low- and high-threshold motor unit potentials (MUPs) were compared in patients with neuropathic EAS and controls. Fifteen subjects without pelvic disorders and 29 patients with sequela after cauda equina lesions were studied. In patients, only muscles ipsilateral to severe perianal sensory loss were included. MUPs were sampled using multi-MUP analysis during relaxation ('low-threshold'), and on activation ('high-threshold' MUs). MUP parameters of low- and high-threshold MUs from controls and patients were compared, as was the sensitivity and specificity with which MUPs were classified as normal or pathological (using discriminant analysis). MUP changes due to reinnervation, and the sensitivity and specificity in classifying MUPs as normal or pathological were not significantly different between the low- and high-threshold MUPs. Stronger activation of EAS does not improve discrimination between neuropathic and normal MUPs. New EMG techniques for sampling sphincter MUPs at higher activation levels would seem not to yield additional information.     

Anal sphincter EMG does not distinguish between multiple system atrophy and Parkinson's disease

Clinical distinction of multiple system atrophy (MSA) from Parkinson's disease (PD) is often difficult. Several recent reports indicate that objective classification may be accomplished using electromyographic (EMG) testing of the anal or urethral sphincters, but some authors have found that these tests are not reliable for this purpose. We studied 13 patients with PD and 10 with probable MSA, as diagnosed by consensus of four movement disorders specialists, according to accepted clinical criteria. Anal sphincter EMG was performed blind to the clinical diagnosis. We found no significant differences in the mean duration of motor unit potentials (MUPs), mean MUP amplitude, or prevalence of polyphasic potentials, satellite potentials, very long duration MUPs, or spontaneous activity between the two groups. Thus, anal sphincter EMG does not differentiate between PD and MSA.     

Comparison of quantitative techniques in anal sphincter electromyography.

Data comparing results and utility of different quantitative electromyographic (EMG) techniques are limited. In the present study, we analyzed the EMG signal from the external anal sphincter (EAS) muscle using three techniques of motor unit potential (MUP) analysis, and a technique of interference pattern (IP) analysis. We examined 56 patients with damage to the cauda equina or conus medullaris, and 64 control subjects. Using manual-MUP and multi-MUP analysis about 20 MUPs, using a single-MUP technique about 10 MUPs, and using turn/amplitude (T/A) analysis about 20 IP samples were obtained. The sensitivities of these techniques in distinguishing neuropathic from control muscles were calculated. The single-MUP technique detected 63%, manual-MUP 57%, and multi-MUP analysis 62% of neuropathic muscles, and MUP parameters obtained by each of these differed significantly from the other. The sensitivity of T/A analysis of IP was 29%. Our results confirm the need for separate MUP normative data for each of the MUP analysis techniques, and favor them over the IP analysis technique. The normative data presented for the EAS muscle should improve and promote quantitative EMG in patients.     

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.