Needle EMG of abductor hallucis and peroneus tertius in normal subjects

Normal values for standard concentric-needle electromyography (EMG) of the abductor hallucis (AH) and peroneus tertius (PT) muscles have not been established to date, yet both are potentially useful muscles in the diagnosis of length-dependent peripheral nerve disorders. Forty-three normal asymptomatic subjects stratified by age underwent a standard set of nerve conduction studies and concentric-needle examination to exclude asymptomatic disease and develop normal values for the AH and the PT for various EMG parameters. Fibrillation potentials were observed in the AH in 21% of normal subjects (10% < 60 years old, 30% > 60 years old); 19% of subjects were unable to voluntarily activate the AH. All subjects could activate the PT regardless of age. No fibrillation potentials were observed in subjects < 60 years of age, whereas 9% of those older than 60 years had mild fibrillation potentials in the PT. The PT is a useful muscle in the evaluation of length-dependent peripheral neuropathy and other peripheral nerve disorders of the lower extremities, on the basis of ease of motor unit potential activation and analysis, and relative infrequency of fibrillation potentials in normal subjects.     

Decrement in area of muscle responses to repetitive nerve stimulation

Measurement of the decremental muscle response to repetitive nerve stimulation (RNS) has low yields for the diagnosis of neuromuscular transmission defects compared with single fiber electromyography (SFEMG). We compared area and amplitude of muscle responses to RNS in 87 patients and 30 controls, using SFEMG as the reference standard. Decrement of response area provided additional diagnostic yields of 5.3% to 30% depending on the muscle examined and disease severity, and is recommended as a diagnostic adjunct to measurement of amplitude decrement during RNS.     

Electromyography of the anal sphincter: Which muscle to examine?

Electromyographic examination of the deeper external anal sphincter (EAS) muscle is far more uncomfortable than of the subcutaneous muscle, so we tested the need for its examination. We compared the findings in 85 paired examinations of ipsilateral subcutaneous and deeper EAS muscles in 67 patients with a cauda equina lesion. When the other muscle was normal, the deeper or subcutaneous muscle was pathological in 18% or 13% of pairs, respectively. In addition, the subcutaneous EAS muscle was usually more severely affected than the deeper EAS muscle. Thus, examination of the deeper EAS muscle did not increase the sensitivity of MUP analysis significantly, and did not seem clinically necessary.     

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.     

Prevalence and progression of mitochondrial diseases: a study of 50 patients

We report 50 patients with various clinical phenotypes of mitochondrial disease studied over the past 10 years in a large urban area (Madrid Health Area 5). The clinical phenotypes showed a large variety of abnormalities in molecular biology and biochemistry. The prevalence of mitochondrial diseases was found to be 5.7 per 100,000 in the population over 14 years of age. Clinical and electrophysiological assessment reveal signs of neuropathy in 10 patients. Electromyographic findings consistent with myopathy were obtained in 37 cases. Six patients died of medical complications. Disease phenotype influenced survival to some degree (P < 0.01). Age of onset and gender were not associated with differences in survival. Mitochondrial disease is thus far more common than expected and a common cause of chronic morbidity.     

Small-amplitude cortical myoclonus in Parkinson's disease: physiology and clinical observations.

We studied the occurrence of small-amplitude myo- clonus in 20 idiopathic Parkinson's disease patients who had no evidence of dementia as defined by criteria in the Diagnostic and Statistical Manual of Mental Disorders, fourth edition. Parkinson's disease was diagnosed by United Kingdom Brain Bank criteria, and clinical assessment was performed with the Unified Parkinson's Disease Rating Scale motor score, Hoehn and Yahr staging, and the Mini-Mental State Examination. Clinical assessment showed a range of mild-to-moderate disease severity. All patients underwent polygraphic electro-encephalographic-electromyographic (EMG) recording with back-averaging, somatosensory evoked potential testing, and attempted elicitation of long-latency EMG responses. Multichannel surface EMG recording during muscle activation showed irregular, multifocal, brief (<50 msec) myoclonus EMG discharges. Back-averaging consistently showed a focal, short-latency, electroencephalographic transient prior to the myoclonus EMG discharge. Cortical somatosensory evoked potential waves were not enlarged, and long-latency EMG responses at rest were not present. The small-amplitude myoclonus in such cases arises from an abnormal discharge from the sensorimotor cortex. The mechanism of this cortical myoclonus in Parkinson's disease has differences from the more common "cortical reflex myoclonus" physiology. Advanced parkinsonism is not a requirement for manifestation of this myoclonus type. Although the myoclonus occurred without dementia in these cases, its relationship to the subsequent development of cognitive impairment remains to be defined.     

Predictive power of motor unit potential parameters in anal sphincter electromyography

The diagnostic utility of motor unit potential (MUP) parameters is usually based exclusively on their diagnostic sensitivity, disregarding specificity. In the present study, advanced statistical methods were used to determine MUP parameters with the highest predictive power for the separation of neuropathic and normal external anal sphincter (EAS) muscles. Using multi-MUP analysis, 3,720 MUPs from 138 muscles of 52 patients with cauda equina lesion and 2,526 from 112 muscles of 64 controls were obtained. Only two principal components (PCs), which put weight on the MUP area and amplitude, were needed to explain all the data variability. On logistic and probit regression analyses, MUP area, duration, and number of turns gave results identical to all MUP parameters. Our results suggest that only these three MUP parameters are needed, and that they are as effective as PCs, in MUP analysis of chronic neuropathic EAS muscles. Reduced number of MUP parameters is expected to simplify MUP analysis and increase its specificity.     

Within-train neuromuscular propagation varies with torque in paralyzed human muscle

Electromyographic (EMG) recordings may serve an important role in predicting torque during repetitive activation of paralyzed muscle. We compared the initial M-wave to the subsequent M-waves of the same train under fatigued and recovered conditions in the paralyzed human soleus muscle. Sixteen individuals with chronic (n = 13) or acute paralysis (n = 3) had the tibial nerve activated before and after a repetitive supramaximal stimulation protocol. The mean within-train M-wave amplitude and median frequency increased approximately 20%, whereas the duration decreased approximately 15% compared with the initial M-wave of each train. During fatigue, there was a linear decrease in the difference between the initial M-wave amplitude and subsequent train ( approximately 20% to 8%). Following fatigue, this difference recovered to approximately 12%. The difference between the M-wave train average and the initial M-wave for amplitude, duration, and median frequency closely followed torque (Pearson correlations = 0.99, 0.94, and 0.98, respectively) during fatigue. We conclude that the difference between the later-occurring M-waves (average of the train) and initial M-wave is large when muscle torque is high and less when torque is low and, therefore, predicts torque during activation of paralyzed muscle. This difference in the within-train M-wave amplitude, duration, and median frequency may reflect a mechanical change, such as muscle shortening and increased muscle cross-sectional area during isometric contractions. Electromyographic feedback may assist in the optimization of neuromuscular electrical stimulation of paralyzed muscle.     

Surface EMG crosstalk between knee extensor muscles: experimental and model results

Surface electromyographic (EMG) crosstalk between vastus lateralis, vastus medialis, and rectus femoris muscles was evaluated by selective electrical stimulation of one muscle and recording from the stimulated and another muscle with linear surface arrays of eight electrodes. The ratio between the amplitude of the signals recorded over nonstimulated and stimulated muscles and their correlation coefficient were used as indices to quantify crosstalk. Single-differential and double-differential detection systems were used with interelectrode distances in the range 10-40 mm. The multichannel EMG signals clearly showed that crosstalk is largely due to nonpropagating potentials that correspond in time to the end of the propagation of the action potentials generated by the stimulated muscle. The crosstalk signal increased with increasing interelectrode distance and was statistically higher for single- than for double-differential recordings. The correlation-based indices of crosstalk were poorly correlated with the amplitude-based indices. Moreover, the characteristic spectral frequencies of the signals detected over the nonstimulated muscles were statistically higher than those from the stimulated muscles. A mathematical model of signal generation was used to explain the experimental findings. This study clarifies many controversial findings of past investigations and creates the basis for crosstalk interpretation, simulation, and reduction.     

单纤维肌电图在糖尿病周围神经病变中的变化和意义探讨

目的观察单纤维肌电图(SFEMG)在糖尿病周围神经病变(DPN)中的变化,探讨DPN的发病机制。方法36例已作常规神经传导检测(NCS)的2型糖尿病患者,测定指总伸肌的颤抖和纤维密度(FD),并测量空腹血糖(FBG)、糖化血红蛋白(HbA1c)、总甘油三酯(TG)、总胆固醇(TC)、高密度脂蛋白胆固醇(HDL-C)、低密度脂蛋白胆固醇(LDL-C)、脂蛋白a[Lp(a)]、载脂蛋白A(Apo-A)、载脂蛋白B(Apo-B)及血压。结果在18例NCS异常者中,颤抖值均超出正常范围(11例伴阻滞),14例FD增加;18例NCS正常者中,有7例颤抖值增大(3例伴阻滞),5例FD增加。颤抖和FD呈正相关(r=0.7621,P<0.01),颤抖和FD均与糖化血红蛋白、TG、LDL-C、Lp(a)及舒张压呈正相关。结论SFEMG是DPN早期诊断的敏感手段,可发现亚临床神经病变。血糖、血压、血脂控制不良在DPN的发生和发展中起重要作用。