Single fiber electromyography in normal subjects: reproducibility, variability, and technical considerations.

We performed 59 single fiber electromyography (SFEMG) examinations on 33 patients with spasmodic torticollis, but no other medical or neurological disorder. 14 patients were studied serially (3 examinations over 12 weeks). There was excessive jitter (greater than 55 microseconds) in 14 of 1180 fiber pairs (1.1%). 7 of the 14 abnormal fiber pairs were found at single sites (1 in 20 sites studied). Abnormal jitter occurred at more than 2 of 20 sites in only two patients, both of whom head increased fiber density and were more than 70 years of age. Of the 14 abnormal fibers, subtle technical problems were discovered in 4: bimodal jitter (1); borderline amplitude of single fiber potential (1); and borderline rise time (2). 6 of the 14 jittering potentials were part of a triplet or quadruplet. 4 fibers with increased jitter occurred in pairs and these were seen only in patients over 70. One patient with quiescent non-tropical sprue was excluded from consideration because of increased mean jitter before injection and confirmed during 2 subsequent studies. Therefore, SFEMG is a valid and reliable technique that must be strictly interpreted according to existing guidelines, with special consideration to studies in older patients. Abnormal jitter is rarely found in normal muscle, however, when found, it usually occurs as part of a triplet or multiplet.     

A comparative study of single fiber electromyography and repetitive nerve stimulation in consecutive patients with myasthenia gravis

AIM: To compare the diagnostic yield of single fiber electromyography (SFEMG) and repetitive nerve stimulation (RNS) in consecutive patients with myasthenia gravis (MG). METHODS: Consecutive 33 patients with MG diagnosed on the basis of clinical features, positive neostigmine test and/or acetylcholine receptor antibody assay were categorized into stage 1 (3), 2A (10), 2B (12) and 2C (8 patients). Low rate repetitive nerve stimulation (3Hz) was performed in distal muscles (abductor digiti minimi, anconeus, flexor carpi ulnaris, tibialis anterior) and proximal muscles (deltoid, serratus anterior, trapezius and nasalis). Decrement exceeding 10% was considered abnormal. Single fiber EMG was performed in extensor digitorum communis (EDC), recording 20 potential pairs. The abnormality was defined as mean jitter exceeding 40 micros or 10% of potential pairs having block or jitter exceeding 54 micros. The abnormality in RNS and SFEMG was compared and correlated with severity of MG. RESULTS: RNS study was carried out in 33 and SFEMG in 30 patients. In 2 patients SFEMG was not possible due to lack of cooperation and in one due to severe weakness. The RNS study was normal in 6 (2 in stage 1, 3 in 2A and 1 in 2B) patients and in all of them SFEMG was abnormal. The abnormality in RNS and SFEMG correlated with severity of MG. CONCLUSION: SFEMG is indicated in the patients with MG in whom RNS test is negative.     

甲状腺机能亢进伴发重症肌无力患者电生理研究

目的：探讨甲状腺机能亢进（甲亢）伴发重症肌无力（MG）患者的电生理检测特点，和与慢性甲状腺机能亢进性肌病（CTM）的关系。方法：对7例甲亢伴发MG患者进行神经传导速度（NCV）、重复电刺激（RNS）、针极肌电图（EMG）和单纤维肌电图（SFEMG）检测。结果：7例NCV均正常，RNS5例异常。EMG2例发现有肌病的表现，SFEMG均出现jitter增宽。结论：甲亢病人可伴发MG，还可能同时伴发CTM，进行RNS、EMG、SFEMG检测是有必要的。     

Fiber density in congenital muscle fiber type disproportion. I. Congenital myopathies

In 15 cases with congenital muscle fiber type disproportion, concentric needle EMG (CNEMG) and single fiber EMG (SFEMG) with fiber density (FD) estimation was performed. The aim of the work was to establish the nature of congenital muscle fiber type disproportion. In 11 cases CNEMG revealed interference pattern on maximal effort and low, polyphasic motor unit action potentials (MUAPs) of short duration indicating a myopathic lesion. In four other cases electromyographic changes were less evident. The FD values were slightly increased in 9 cases. This finding could be explained by pronounced muscle fiber splitting with subsequent ephaptic transmission or even secondary denervation and reinnervation. The most important conclusion from our pilot study is the confirmation of the fact that reinnervation with excessive sprouting is not the only mechanism responsible for muscle fiber type disproportion.     

单纤维肌电图(SFEMG)的研究进展

单纤维肌电图(single fiber electromyogram,SFEMG)研究的主要内容是骨骼肌同一运动单位相邻两条肌纤维在重复兴奋过程中,电位对时间间隔的变异,即颤抖(jitter)。两根肌纤维的放电间在2—20mS之间,而人体骨骼正常jitter值一般为5-55uS,因此在引导、测量、分析方面难度较大。随着科学技术的发展,SFEMG已在生理学科的研究和临床医学诊断等领域中占有重要地位。本文阐述了单纤维肌电图jitter的产生、引导、测量、分析的方法及应用价值。     

Facioscapulohumeral muscular dystrophy. A quantitative electromyographic study

BACKGROUND: Quantitative electromyography (EMG) using different needle techniques has not been performed or reported on a relatively large group of patients with facioscapulohumeral muscular dystrophy (FSHD). Purpose: To establish statistically: (1) correlations between clinical features of patients (age, disease duration and degree of weakness) and quantitative needle EMG/SFEMG,; (2) correlations between different EMG parameters in the patient group, and (3) quantitative EMG differences comparing patients with a healthy control group. METHODS: Nerve conduction studies, and needle EMG (motorunit analysis, MacroEMG, SFEMG) were performed on Mm. triceps brachii and Mm. tibialis anterior according to standard techniques on 20 patients with FSHD. RESULTS: Nerve conduction studies were normal. In Mm. triceps brachii and, to a lesser extent, Mm. tibialis anterior motorunit analysis and MacroEMG showed myopathic changes, that correlated with patient clinical parameters. In Mm. triceps brachii (but not in Mm. tibialis anterior) EMG results were statistically different in patients compared to control group data. The most sensitive indicators of a myopathy were MUP duration (motorunit analysis) and MUP area (MacroEMG). In the Mm. triceps brachii SFEMG revealed correlations between worsening pooled MCD data and patient clinical parameters. Pooled MCD results did not correlate with other MUP parameters. SFEMG showed abnormal jitter only in 2 patients with the longest disease duration. CONCLUSION: Quantitative EMG results are compatible with a mild, slowly progressive myopathy. The most sensitive indicators of early muscle disease were MUP duration (motorunit analysis) and MUP area (MacroEMG) that would not be detected on "routine" EMG SFEMG showed subtle, progressive worsening of neuromuscular junction physiology. However, quantitative EMG and SFEMG showed that muscle fiber degeneration and loss followed a course independent of muscle fiber regeneration and reinnervation.     

Fiber density in congenital muscle fiber type disproportion. II. Congenital muscle hypotonia and hip dislocation

Our previous paper presenting electromyographic findings in patients with congenital fiber type disproportion myopathy, confirmed the myogenic character of the disease process. That group of patients was however fairly heterogenous regarding both the clinical features and the morphological changes in muscle fibers (e.g. cases with central cores). In the present study we have examined 13 children with hypotonia and muscle fiber type disproportion operated on in childhood for congenital hip dislocation. In all cases CNEMG and SFEMG with FD estimation was performed in biceps brachii and quadriceps femoris muscles. In all muscles examined either slight EMG changes indicative of myopathy or a normal EMG pattern was found. None of the patients demonstrated an evident increase in FD values. Normal FD and the recruitment pattern proportional to the force of contractures indicate that the normal number of motoneurons is preserved. Accordingly, our present findings confirm the conclusions of our previous paper.     

Disintegration of the motor unit in post-polio syndrome. Part II. Electrophysiological findings in patients with post-polio syndrome

The aim of the study is to investigate the motor unit abnormalities in late postpolio muscular atrophy (PPMA) as compared to those found in patients who had polio 20-30 years prior to examination without any new clinical signs. The quantitative concentric needle EMG and a single fiber EMG techniques were employed. Spontaneous activity, the parameters of individual motor units potentials (MUP), number of complex potentials and their stability, jitter and blocking as well as fiber density (FD) have been evaluated. In PPMA patients (5 subjects) we found in newly weakened muscles: spontaneous activity, high percentage of complex potentials, increased jitter, increased FD. The EMG findings in muscles previously affected but without any signs of progression have been similar. In the patients with stable nonprogressing postpolio muscle atrophy (12) all MUP-s parameters indicated changes similar to PPMA but less marked in initially affected muscle with complete or incomplete recovery as well as sometimes in initially clinically unaffected muscles. These findings suggest that the signs of ongoing reinnervation processes persist many years after polio and that PPMA occurring later in life represents disintegration of the previously reinnervated motor units. It is still unclear whether this disintegration depends on decompensation by different factors of fully reinnervated motor units or whether most of the motor units after polio never regained a stable reinnervation.     

基于遗传算法的sEMG至SFAP的分解算法

本研究提出了一种表面肌电信号(Surface Electromyogram，sEMG)至单纤维动作电位(Single Fiber Action Potential，SFAP)新的分解算法。由于sEMG分解的复杂性，本研究将sEMG分解问题转化为SFAP三基函数参数的优化问题和同一SFAP参数的聚类问题。在算法中，运用改进的遗传算法(Genetic Algorithm，GA)进行参数的优化，运用无监督学习的Kohonen神经网络进行参数的聚类。遗传算法的运用加强了算法的搜索能力，提高了分解的正确率，加快了算法的收敛速度。本分解算法的运用使得医疗诊断和假肢控制等领域可以通过非侵入式测量得到SFAP随时间的变化规律。     

Anal sphincter EMG in anorectal disorders

In 26 patients with different anorectal disorders electromyography was performed in combination with anal manometry. EMG was carried out with a concentric needle electrode as well as with a single fibre electrode. Also the pudendal nerve terminal motor latency (PNTML) was assessed. A relationship was found between maximal squeeze pressure in anal manometry and maximal voluntary contraction pattern in concentric needle EMG. Mean fibre density (FD) was increased while mean PNTML was not increased. However a relationship was found between PNTML and FD. This discrepancy, increased FD with normal PNTML could mean that a myogenic factor plays an important role in our patients.     

Motor unit remodelling in Duchenne muscular dystrophy. Electrophysiological assessment.

Conventional EMG, motor and sensory conduction velocities, averaging analysis of MUPs, SFEMG, and muscle fiber conduction velocity in situ were performed in 14 boys with Duchenne muscular dystrophy (DD) aged 5 to 11 years. MUPs parameters study showed a striking increment of long duration MUPs followed by satellites and increase of polyphasic potentials of variable duration. The main findings in SFEMG examination were increment in fiber density of the motor unit, large MISI and presence of complex potentials of long duration in all patients. Muscle fiber conduction velocity in situ was significantly slower than in controls, with significant decrease in minimum conduction and increased variability (large SD) in propagation velocity values. Low conduction velocity of muscle fibers, long duration of polyphasics and MUPs followed by satellites, and large MISI were significantly related. These findings support the hypotheses which have suggested that the motor unit remodelling in DD is mainly myogenic. The abnormalities in muscle fiber conduction velocity in situ reflect an increased diameter variation of muscle fibers consistent with splitting fibers, small groups of regenerating and necrotic fibers, and fiber diameter variation found in histological studies. Thus, increased variability in fiber diameter may be the cause of complex and long duration MUPs in DD.     

Rigid spine syndrome (vacuolar variant). A quantitative electromyograhic study

BACKGROUND: Quantitative electromyography (EMG) using different needle techniques was performed as part of a complete systems review on 9 patients diagnosed with the vacuolar variant of rigid spine syndrome (RSS). Purpose: To establish statistically: (1) correlations between clinical features (patient age, disease duration, degree of weakness) and quantitative EMG; (2) correlation between different EMG parameters; (3) differences in quantitative EMG comparing patients with a healthy control group; and (4) correlate EMG with muscle pathology findings. METHODS: Nerve conduction studies and needle EMG (motorunit analysis, MacroEMG, SFEMG) were performed on Mm. triceps brachii and tibialis anterior according to standard techniques on 9 RSS patients. RESULTS: Nerve conduction studies were normal. Overall, clinical parameters did not correlate well with motorunit analysis and MacroEMG results. Motorunit analysis and MacroEMG results were significantly different comparing patients with controls. Motorunit analysis and MacroEMG correlated well with muscle biopsy findings. SFEMG results were within normal limits. CONCLUSION: Comprehensive EMG study results were compatible with a benign myopathic process. Results were consistent amongst patients within the study group, but differed significantly from the control group. Stable neuromuscular junction physiology did not accurately reflect evidence of muscle fiber degeneration and regeneration observed on muscle biopsies.     

Follow-up study after replantation of the forearm and nerves resuture

OBJECTIVE: Clinical and electrophysiological evolution after total section of the forearm and nerves resuture. MATERIAL AND METHODS: A young boy aged 14 years with accidental amputation of the right forearm. The forearm was replanted within the first 6 hours after accident. Electromyography, nerve conduction, estimated number of the motor units, single fiber EMG and motor complex reflex responses were studied until 4 years after surgery. RESULTS: Functional recovery was reached in muscles innervated by median and ulnar nerves. After 4 years of evolution EMG showed signs of chronic neuropathy. Nerve conduction did not reach normal values. Single fiber EMG showed increased fiber density and jitter, and intermittent impulse blocking The estimated number of the motor units was severely reduced with high mean amplitude. Motor reflex responses were elicited by cutaneous stimulation consistent with axon reflexes or ephatic responses. CONCLUSIONS: Replanted limbs in selected cases and nerve's resuture may reach a functional recovery for daily activities.     

Neurological manifestations of the post-polio syndrome

Patients with late effects of poliomyelitis, i.e., PPS, are being seen at an ever increasing frequency by general physicians, neurologists, and orthopedists. An appropriate time interval for the onset of late manifestations has elapsed since the major epidemics of poliomyelitis in the 1940s and 1950s. Post-polio neurological manifestations primarily include new weakness, atrophy, muscle pain, and fasciculations. Fortunately, the weakness is of a very slow, progressive nature. Abnormal laboratory studies include routine EMG, demonstrating chronic denervation; SFEMG, demonstrating increased fiber density, increased jitter, and blocking; and muscle biopsy most often revealing fiber-type grouping of chronic denervation and small isolated angular (or angulated) fibers and group atrophy in some series, both suggestive of active denervation. Unfortunately, both EMG and muscle biopsy studies suffer from a lack of specificity as they do not appear to distinguish asymptomatic from symptomatic (new weakness, PPMA) patients with prior poliomyelitis. Although the cause of PPMA is unknown, electrophysiological (SFEMG) and muscle biopsy studies suggest that the process involves a loss or dropout of axon terminals of reinnervated motor units. The axons terminal dropout could be due to dysfunction in the cell soma, the axon, or the terminals themselves. Whether motor neuron exhaustion, a persistent viral infection, or immune-mediated mechanisms play a role in the pathogenesis of the late weakness is unclear at present and will require further investigation. Treatment at this time is of a supportive nature. A major controversy involves the role of strengthening exercises in these patients since experimental animal studies suggest that excessive exercise of denervated muscles leads to increased weakness. Clearly, a better understanding of PPS and PPMA will allow more effective management of these patients' problems and might also provide insight into other motor neuron and neuromuscular junction diseases.     

耻骨直肠肌综合征的常规肌电图与单纤维肌电图比较

本文对１０２例耻骨直肠肌综合征的患者均检查耻骨直肠肌及肛门内、外括约肌共３０６块肌肉，检测６１２０个运动单位。结果表明：常规肌电图（ＥＭＧ）和单纤维肌电图（ＳＦＥＭＧ）在耻骨直肠肌肥厚组和耻骨直肠肌痉挛组异常率分别为９２．２％（５９／６４）、９５．３％（６１／６４）和８６．３％（３３／３８）、６３．２％（２４／３８）。提示ＥＭＧ和ＳＦＥＭＧ对耻骨直肠肌肥厚症和痉挛症具有重要诊断价值。     

Shape Variability of Potentials Recorded by a Single-Fiber Electrode and its Effect on Jitter Estimation

Technical problems accompanying the recording of fiber pair potentials introduce certain instability in the peak-to-peak interval (rise-time, RT) of these potentials. This study aims (1) to measure the variability observed in RT of a large number of sets of consecutive potentials recorded by a single-fiber (SF) electrode and (2) to evaluate the effect of such variability on the jitter estimation. Using a SF electrode, 140 sets of consecutive potentials were recorded from the m. tibialis anterior of four healthy subjects. For each set, the rise-time variability (RTV) was calculated as the standard deviation of the RTs of the discharges within that set. The effect of RTV in the estimation of jitter from simulated fiber pairs with controlled values of neuromuscular jitter was analyzed. The RTVs of sets visually assessed as produced by a “single-fiber” were always less than 20 μs, whereas those of “composite” sets were normally higher than 20 μs. We found that the RTV always increased the estimated jitter of fiber pairs. Such increment depended on the amount of neuromuscular jitter. The RTV provides an estimate of the possible error introduced in jitter assessment. This could be important for the diagnosis of mild clinical manifestations of myasthenia gravis, myopathies, and Duchenne dystrophies.     

The influence of air temperature on the EMG/force relationship of the quadriceps

Summary Surface electromyography (EMG) in the past has been used to estimate the intensity of muscle contraction. These estimates were derived from the EMG/force relationship measured at room temperature. How the surface EMG signal is influenced by varying air temperature as it relates to the EMG/force relationship has yet to be investigated. Thus, this study evaluated the influence of different air temperatures (10, 23 and 40° C) on surface EMG during contractions of the quadriceps muscle. Ten subjects [mean (SD) age 29 (7) years and weight 78.3 (7.8) kg] performed a criterion task of five contractions ranging from 10 to 100% of a maximal voluntary contraction, five times over a 1.5-h period in all conditions. The EMG signals generated from the rectus femoris, and the forces associated with the contractions, were captured on FM tape and subsequently digitized at a sampling rate of 2000 Hz. The relationship between EMG and force was different under the different conditions; EMG was reduced at a given force as temperature increased, and the EMG increased in the 10° C environment over time. The differences that occurred at the various temperatures were believed to be related to fluid distribution in the muscle, muscle conduction velocity and sweating. The data imply that the EMG/force relationship measured using surface electrodes is influenced by ambient temperature.     

The eccentric mechanotransduction,neuro-muscular transmission,and structural reversibility of muscle fatty infiltration. An experimental advanced disuse muscle-wasting model of rabbit supraspinatus

IntroductionFull-thickness rotator cuff tear is present in almost 50% of patients over age 65 years, and its degree is known to be a good predictor of the severity of muscle-wasting (MW) sarcopaenia, also known as fatty degeneration (FD). A FD CT grade > 2° is recognized as a borderline of its reversibility. A disuse model of supraspinatus FD (grade 2) in rabbits provides clinically relevant data. Therefore, the present study evaluates the correlation between eccentric mechanotransduction, neuromuscular transmission (NT), and reversibility of muscle fatty infiltration (MFI) in rabbit supraspinatus FD > 2°.Material and methodsThe supraspinatus tendon was detached from the greater tubercle, infraspinatus, and subscapularis in 16 rabbits. The tendon was reinserted after 12 weeks, and the animals were euthanized 24 weeks after reconstruction. MFI was measured in the middle part of the supraspinatus. Single-fibre EMG (SFEMG) examination of the supraspinatus NT was performed on 4 animals.ResultsThe power of analysis was 99%. Significant differences in MFI volume were found between the operated (4.6 ±1.1%) and the opposite control sides (2.91 ±0.61%) (p < 0.001). SFEMG revealed no significant differences between the disuse and the control supraspinatus muscles (p > 0.05); however, 6.5% of the examined muscle fibres exhibited NT disorders combined with blockade of conduction in 2.5% of muscle fibres.ConclusionsCritical MFI in a disuse model of rabbit supraspinatus FD, CT grade > 2°, is substantially reversible by eccentric training despite subclinical impairment of neuromuscular transmission. In addition, 0.63% reversal of MFI is correlated with 1% hypertrophy of type I and II muscle fibre diameter.     

Digital archiving of biomedical recordings for off-line computer analysis

This article describes a new procedure for archiving biomedical recordings on industry standard digital magnetic tape. Familiar computer methodology is employed for data-banking heartbeat patterns in a format which has been optimized for later analysis. Recordings are made through an encoder-controller unit coupled to a four channel FM cassette data recorder. This unit produces FM analog magnetic tape with square wave identification and calibration code preceding each sample of biomedical data. Code bits and data sample are timed out sequentially in repetitive standardized format. Digital images of these specially formatted analog tape cassettes are then processed by an edit program on an IBM $\text{370}\text{145}$. Here, the identifiers are decoded and data sections located. Identification, calibration, and biomedical recordings are then archived on a directory tape which may be efficiently and repeatedly accessed for future computations.     

Single fiber electromyography (SFEMG) in mitochondrial diseases (MD)

Conventional EMG, nerve conduction studies and SFEMG were performed in 18 patients with various phenotypes of MD. 14 cases showed findings consistent with mild myopathy, 2 patients signs of sensory-motor axonal neuropathy and 2 cases a mixture of myopathy and axonal neuropathy. Motor unit fiber density was mild increased in 8 out of 13 tested cases. Jitter was abnormal in 10 out of 18 tested patients. Jitter abnormalities were not related to myopathic or neurogenic features in the EMG study, and may be observed in muscles without clinical weakness. The results suggest the existence of neuromuscular transmission disturbances in patients with MD.