Simulation of concentric needle EMG motor unit action potentials

Computer simulations of motor unit action potentials (MUAPs) as measured by a concentric needle (CN) electromyography (EMG) electrode in normal motor units (MUs) indicated that the MUAP amplitude is determined mainly by the proximity of the electrode to the closest muscle fiber. The area and duration of the simulated MUAPs were affected by all muscle fibers in front of the active recording surface but mainly by those that were less than 2 and 2.5 mm, respectively, from the active recording surface. The MUAP area was also affected by the proximity of the electrode to the closest muscle fiber. The number of phases of the simulated MUAPs increased when the dispersion of the arrival times of individual muscle fiber APs at the electrode was increased. Increased temporal dispersion of APs decreased the MUAP amplitude and area slightly but did not affect the MUAP duration. It is inferred that different features of the CN MUAP are determined by the distribution of muscle fibers within different portions of the MU territory and thus provide complementary information about the MU architecture.     

Analysis of amplitude and area of concentric needle EMG motor unit action potentials

Computer simulations indicate that measurements of the area of motor unit action potentials (MUAPs) recorded with a concentric needle electrode could be useful in differentiating between neuropathy and myopathy. However, MUAP area varies markedly when the position of the recording electrode is changed only slightly within the motor unit territory, mainly because of the changes in the MUAP amplitude produced by only slight electrode movements. The ratio of MUAP area to amplitude is much less affected by changes in electrode position and measures the 'thickness' of the MUAP wave form. We found that the MUAP area:amplitude ratio was reduced in myopathy even when the MUAP amplitude was normal or increased. In patients with neuropathy, the MUAP amplitude and area both tend to be increased while their ratio is normal or increased. The diagnostic yield obtained from MUAP area, amplitude and their ratio in combination was similar to that obtained using measurements of MUAP duration. Unlike the MUAP duration, the MUAP area, amplitude and area:amplitude ratio are robust features of the MUAP in that they are less sensitive to the signal-to-noise ratio and inter-operator differences in signal selection.     

Single-fiber EMG with a concentric needle electrode: validation in myasthenia gravis

We performed a retrospective study to validate whether a disposable concentric needle electrode (CNE) can be used in place of a single-fiber (SF) electrode for jitter measurements in myasthenia gravis (MG). Normal values for voluntary contraction of orbicularis oculi (OO) and extensor digitorum communis (EDC) were collected from 20 healthy subjects. The method was validated by a retrospective analysis of 56 consecutive MG patients, the "gold standard" being a positive acetylcholine receptor (AChR) antibody titer at the time of the electrophysiological (electromyography) study and the clinical diagnosis. Receiver operating characteristic (ROC) curves were constructed to define maximal sensitivity and specificity of the technique. The sensitivity was 96.4% (95% confidence interval 87.5%-99.6%), with no false-positive results, similar to traditional SF EMG and confirming that the disposable CNE is a justifiable alternative.     

Principal component analysis of the features of concentric needle EMG motor unit action potentials

Motor unit action potentials (MUAPs) were recorded from the biceps muscle of normal subjects and of patients with nerve or muscle diseases. Principal component analysis of the MUAP amplitude, area, area/amplitude ratio, duration, and the number of turns and phases produced three components that among them contained 90% of the variance of the data set. Thus the dimensionality of data was reduced from six to three. The first component reflected changes in the size of the MU, whereas the second reflected variations in the arrival time at the recording electrode of the action potentials of muscle fibers in the motor unit. The third factor reflected local loss of muscle fibers within the MU territory. Patterns of variations in the three components were different in patients with neuropathy and myopathy.     

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.     

Comparison between concentric needle EMG and macro EMG in patients with a history of polio.

OBJECTIVES: Acute poliomyelitis causes degeneration of anterior horn cells, followed by denervation. Reinnervation and muscle fibre hypertrophy are mechanisms that compensate this loss of neurones. Concentric needle EMG (CNEMG) and macro EMG are two methods to assess the magnitude of initial involvement and the compensatory reinnervation. The aim of this study is to explore the difference between CNEMG and macro EMG describing the status of the motor unit in patients previously affected by polio. METHODS: Macro and concentric needle EMG investigations were performed in 261 muscles in 121 patients with a remote history of polio. RESULTS: CNEMG was abnormal in 211 muscles, macro EMG was abnormal in 246 muscles. The macro amplitude was 3-4 times 'more abnormal' than CNEMG amplitude relative to the reference values. CNEMG duration was less abnormal and showed only weak correlation with macro amplitudes. The most likely explanation for the difference in magnitude of deviation from reference values for CNEMG and macro EMG, is a more pronounced 'phase cancellation' between single fibre action potentials in CNEMG. This is supported by simulation studies reported here. CONCLUSIONS: In conclusion macro EMG better reflects the size of the motor unit than the CNEMG. For detection of concomitant disorders, CNEMG is the method of choice.     

同心轴针极肌电图运动单位电位多项参数定量分析

目的研究运动单位电位（ＭＵＰ）多项参数的特征、相互关系、正常值及其神经生理意义。方法１１６名健康成人和４５例神经原性疾病患者的拇短展肌、胫前肌和股四头肌的２６５８个ＭＵＰ，通过棘波触发平均技术得到记录。对ＭＵＰ大小指数（ＳＩ）等９项参数及其９５％或９９％可信限区间进行ＭＵＰ水平统计和显著性检验。结果在相互独立的参数中，以时限和波幅的相关性最为明显，这２种参数从不同角度反映了ＭＵＰ的特征。面积与波幅比值和波幅为相互独立的参数。在ＭＵＰ所有的参数中，以波幅／面积和波幅／ＳＩ比值的相关性最为明显，面积和ＳＩ同为波幅依赖性参数。经９５％或９９％可信限显著性检验证明，面积、ＳＩ、波幅和时限具有较其他参数更高的诊断敏感性。结论ＭＵＰ时限低于面积、ＳＩ的诊断作用，仍为一项重要参数。此种结果与传统肌电图和新近模式匹配肌电图均有所不同。     

Quantitative comparison of motor unit potential parameters between monopolar and concentric needles

This study quantitatively compared the simultaneous recording of the "same" motor unit potentials recorded by closely positioned concentric and monopolar needles. The motor unit potentials from the anterior tibialis of 12 young subjects were analyzed independently by both needles being connected to 2 sets of EMG-computer combinations. Recordings of the same motor unit potentials were confirmed by triggering and averaging of the 2 sets of motor unit potentials with identical firing patterns on both EMG screens. Automatic analysis disclosed the monopolar recordings had a significantly higher mean amplitude (2.05 times), larger surface area (2.64 times), and longer duration (1.86 times) than the concentric recordings, while the mean number of phases (1.58 times) and turns (1.35 times) revealed no statistical differences. Both active recording and reference electrodes contributed to these differences.     

Properties of motor unit action potentials recorded with concentric and monopolar needle electrodes: ADEMG analysis

We compared the configurational and firing properties of 7270 motor unit action potentials (MUAPs) recorded with either concentric (CNE) or monopolar (MNE) needle electrodes from the brachial biceps and anterior tibial muscles of 10 healthy young adults (mean age 27 +/- 4.5 years) using automatic decomposition electromyography (ADEMG). In both muscles, mean MUAP amplitude, rise rate, and number of turns were significantly greater when recorded with MNE (paired t-test, P less than 0.001 in each case). Similar findings were observed at all three tested levels of isometric contractile force: threshold, 10% of maximum voluntary contraction (MVC), and 30% MVC. In contrast, there was no significant difference between electrode types on measurements of mean MUAP duration or firing rate (P greater than 0.05 in each case). These findings indicate that it is acceptable to generalize normative data on MUAP duration and firing rate from one electrode type to another, but that measures of MUAP amplitude and complexity require independent normative databases.     

Recording and physical characteristics of disposable concentric needle EMG electrodes

There is currently considerable interest in using disposable concentric needle (CN) electrodes for clinical electromyography (EMG). To determine how these electrodes compare with reusable CN electrodes, we have compared signals recorded by these two electrode types from the same muscle in normal subjects. We also made similar recordings with two groups of reusable electrodes. There was no difference in the features of motor unit action potentials (MUAPs) recorded by the two groups of reusable electrodes. Disposable electrodes performed satisfactorily in conventional EMG examination. However, compared to reusable electrodes, the disposable electrodes recorded MUAPs with smaller amplitude and area but with the same area:amplitude ratio and MUAP duration. The physical and electrical properties of the CNE groups were also investigated. Disposable electrodes had lower electrical resistance and greater capacitance than reusable electrodes when measurements were made in saline. Photomicrographs showed that the disposable electrodes had smaller recording surfaces and that the central wire was frequently eccentric in the cannula. The differences in electrical recording characteristics could be due to differences in the size of the recording surface, eccentric placement of the central wire in the cannula or differences in the metal used for the central wire. We conclude that electrical and physical testing may not predict the recording characteristics of needle electrodes. Electrophysiologic testing is necessary to determine how EMG signals recorded by new types of electrodes compare with those recorded by currently used electrodes.     

Reference values for voluntary and stimulated single-fibre EMG using concentric needle electrodes: a multicentre prospective study

ObjectiveThe aim of this study is to establish reference values for single-fibre electromyography (SFEMG) using concentric needles in a prospective, multicentre study.MethodsVoluntary or stimulated SFEMG at the extensor digitorum communis (EDC) or frontalis (FRO) muscles was conducted in 56–63 of a total of 69 normal subjects below the age of 60 years at six Japanese institutes. The cut-off values for mean consecutive difference (MCD) of individual potentials were calculated using +2.5 SD or 95% prediction limit (one-tail) of the upper 10th percentile MCD value for individual subjects.ResultsThe cut-off values for individual MCD (+2.5 SD) were 56.8 μs for EDC-V (voluntary SFEMG for EDC), 58.8 μs for EDC-S (stimulated SFEMG for EDC), 56.8 μs for FRO-V (voluntary SFEMG for FRO) and 51.0 μs for FRO-S (stimulated SFEMG for FRO). The false positive rates using these cut-off values were around 2%.ConclusionsThe +2.5 SD and 95% prediction limit might be two optimal cut-off values, depending on the clinical question. The obtained reference values were larger than those reported previously using concentric needles, but might better coincide with conventional values.SignificanceThis is the first multicentre study reporting reference values for SFEMG using concentric needles. The way to determine cut-off values and the statistically correct definition of the percentile were discussed.     

Comparison of sensitivities of macro EMG and concentric needle EMG in L4 radiculopathy

Abstract. The purpose of this study was to compare the sensitivities of macro EMG (mEMG) and concentric needle EMG (cnEMG) in showing abnormality in L4 radiculopathy. We evaluated 23 patients with clinically and radiologically proven L4 root lesions. Among these patients, 21 (92%) had cnEMG abnormalities. Out of 21 patients with cnEMG abnormality, 3 (14%) had fibrillations and positive sharp waves, 8 (38%) had interference pattern abnormality and all of them had motor unit potential (MUP) abnormality on quantitative MUP analysis. Seventeen patients (74%) had mEMG abnormality. Diagnostic yield of cnEMG is higher than mEMG in L4 radiculopathy. mEMG may not contribute much to the diagnosis of lumbar radiculopathy.Presented in part at the 18th Annual Meeting of the Turkish Clinical Neurophysiology EEG-EMG Society, June 2002, Turkey.     

Effects of fatigue on motor unit firing rate versus recruitment threshold relationships

Introduction: The purpose of this study was to examine the influence of fatigue on the average firing rate versus recruitment threshold relationships for the vastus lateralis (VL) and vastus medialis. Methods: Nineteen subjects performed ten maximum voluntary contractions of the dominant leg extensors. Before and after this fatiguing protocol, the subjects performed a trapezoid isometric muscle action of the leg extensors, and bipolar surface electromyographic signals were detected from both muscles. These signals were then decomposed into individual motor unit action potential trains. For each subject and muscle, the relationship between average firing rate and recruitment threshold was examined using linear regression analyses. Results: For the VL, the linear slope coefficients and y‐intercepts for these relationships increased and decreased, respectively, after fatigue. For both muscles, many of the motor units decreased their firing rates. Conclusion: With fatigue, recruitment of higher threshold motor units resulted in an increase in slope for the VL. Muscle Nerve 45: 100–109, 2012     

Comparison of standard and pediatric size concentric needle EMG electrodes.

OBJECTIVE: To compare motor unit action potential (MUAP) metrics recorded by standard and pediatric size concentric EMG electrodes. METHODS: Commercial electrodes were used to record MUAPs from biceps brachii, first dorsal interosseous and tibialis anterior muscles in normal subjects and those with amyotrophic lateral sclerosis (ALS). RESULTS: In normal subjects, peak amplitude and area were significantly higher when recorded by the pediatric size electrode in tibialis anterior muscles and peak amplitude recorded in first dorsal interosseous muscles. In ALS subjects, peak amplitude was higher recorded by the pediatric size electrode in tibialis muscle but lower when recorded in first dorsal interosseous muscles. CONCLUSIONS: Differences of MUAP metrics when recording with standard and pediatric size electrodes do not seem to have a clinical relevance. SIGNIFICANCE: Pediatric and standard concentric electrodes record similar MUAP metrics.     

Influence of needle electrode depth on DE‐STA motor unit number estimation

Introduction: To assess a potential source of technique‐associated error, we evaluated the influence of needle electrode depth on decomposition‐enhanced spike‐triggered averaging (DE‐STA) motor unit number estimation (MUNE) and quantitative motor unit analysis in the upper trapezius (UT). Methods: The DE‐STA MUNE protocol was performed at superficial, intermediate, and deep needle electrode depths in 18 control subjects. Results: Mean surface‐detected motor unit potential amplitudes were significantly smaller for intermediate versus superficial (P < 0.05), deep versus superficial (P < 0.001), and deep versus intermediate (P < 0.05). MUNE was significantly larger for deep versus superficial (P < 0.001), with statistical trends toward larger MUNE values at greater depths for the remaining comparisons. No significant differences were found among needle electrode depths for quantitative motor unit potential parameters. Conclusions: These results demonstrate the important influence of needle electrode depth on DE‐STA MUNE in the UT. Suggestions are made for improved standardization of the protocol. Muscle Nerve 50: 587–592, 2014     

The motor unit in muscular dystrophy, a single fibre EMG and scanning EMG study.

Dystrophic muscle shows increase in fibre density, abnormally low jitter in some recordings and more often increased jitter. The cross section of the motor unit has normal length. There are no signs of abnormal volume conduction characteristics. The increased fibre density is believed to be due to localised increase in the number of muscle action potential generators. The findings are compatible with a remodeling of the motor unit due to fibre loss and a reparative process with fibre regeneration and reinnervation.     

A novel approach to the measurement of motor conduction velocity using a single fibre EMG electrode.

OBJECTIVE: To evaluate whether, for patients with suspected myelin impairment, the sensitivity of motor nerve conduction studies can be increased by using an SFEMG electrode which makes it possible to study conduction velocity in a small number of axons (SF-CV). METHODS: We studied 22 consecutive patients with suspected neuropathy through conventional motor conduction study and through SF-CV. For each patient we selected a nerve that was normal at conventional neurography and studied it through SF-CV. Also, we performed SF-CV in 15 healthy subjects. We considered 36 m/s as the low limit of normal SF-CV (the normal value commonly accepted in the literature for the slowest alpha motor axons). RESULTS: In the healthy subjects we never observed abnormal SF-CV values. Of the 22 patients, in 18 the conventional tests showed abnormal findings suggestive of neuropathy. The remaining 4 patients were completely normal at the conventional tests. Through SF-CV we studied 22 nerves that were normal at the conventional tests. Fourteen of 22 (64%) nerves presented pathological SF-CV test. Half of the patients with normal findings at the conventional tests showed pathological SF-CV test. CONCLUSIONS: SF-CV evaluation may be useful in detecting early, mild, or partial myelin damage, because it makes it possible to detect nerve conduction slowing when conventional tests are normal. SIGNIFICANCE: Increasing sensitivity of motor conduction evaluation.     

Novel information on peripheral tactile mechanisms in man acquired with concentric needle electrode microneurography

Microneurography with tungsten electrodes has provided a wealth of new data on peripheral nerve fibre function in man. Yet, some lingering controversies pertaining to the technique and its results have not been resolved. In particular, the working principles of microneurography allowing single unit sampling in man are not fully understood. Additionally debated, especially during recent years, was the validity of some neurographic data which supported the long standing conventional concept that myelinated fibres are randomly distributed intraneurally. A novel approach to address these issues was provided by microneurography with concentric needle electrodes. Data obtained with the latter technique suggested that these electrodes record activity extraaxonally from single myelinated fibres in man, possibly at or close to a node of Ranvier. The mechanisms described, which allow single unit resolution in humans, might well also be valid when performing microneurography with tungsten electrodes. Other sets of data indicated that Ranvier nodes tend to occur in clusters within certain regions of a nerve fascicle. Interestingly, the nerve fibres belonging to these clustering nodes were of the same modality and tended to innervate the same skin area in the hand. The discovered nerve fibre segregation involved all the four main classes of myelinated low threshold skin afferents in the hand (RA, PC, SAI and SAII units). The fact that sensory nerve fibres with clustering nodes and of the same modality tend to run together suggests at least a partially ordered intrafascicular nerve fibre organisation. The demonstrated intraneural fibre systematisation could be of profound functional significance both under normal conditions and in disease     

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.