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This review aims to comprehensively summarize the application of electrophysiological methods, specifically repetitive nerve stimulation (RNS) and single fiber electromyography (SFEMG), in the diagnosis of neuromuscular junction (NMJ) disorders, including myasthenia gravis, Lambert-Eaton syndrome, and sarcopenia in the elderly. Both RNS and SFEMG have demonstrated high sensitivity and specificity in detecting NMJ abnormalities. RNS aids in distinguishing presynaptic from postsynaptic lesions, while SFEMG provides direct evidence of NMJ function by assessing single motor unit action potentials. Key parameters in SFEMG, such as fiber density, jitter, and pulse blocking, are crucial for evaluating NMJ function. Increased fiber density and jitter value, along with pulse blocking, are often observed in patients with NMJ disorders. However, despite the extensive application of these techniques in various NMJ-related diseases, their role in aging, particularly in sarcopenic patients, remains underexplored, highlighting the need for future research. [ABSTRACT FROM AUTHOR]

Difficulty relaxing the genioglossus muscle makes the evaluation of spontaneous activity problematic in patients with motor neuron disease (MND). We performed jitter analysis using conventional disposable concentric needle electrodes (CNEs) of the voluntarily activated genioglossus muscle in patients with and without MND to detect the denervation-reinnervation process. CNE jitter analysis was performed at the genioglossus muscle in 21 MND(+) patients and 22 MND(–) subjects. The jitter analysis was considered abnormal if the jitter values exceeded these limits for the mean consecutive difference (MCD) or the individual MCD in more than 10% of readings. Seventeen MND(+) patients (81%) had at least three abnormal individual jitter values whereas denervation findings were obtained in eleven of them during the needle electromyographic examination at genioglossus muscle. None of the MND(–) subjects showed CNE jitter abnormality. CNE jitter analysis of genioglossus muscle may provide an useful information that may be suggestive of a diagnosis of MND/ALS. [ABSTRACT FROM AUTHOR]

Introduction: The aim of this study is to demonstrate the conduction disturbance at the neuromuscular junction in a cranial muscle by measuring jitter with a concentric needle (CN) electrode in the diagnosis of Amyotrophic Lateral Sclerosis (ALS) and to investigate the utility of evaluating the peak number as an ongoing reinnervation marker. Method: Twelve patients diagnosed with ALS were included in this study. Single fiber electromyography (SFEMG) was performed using a CN electrode during the voluntary contraction of the right extensor digitorum communis (EDC) and left frontalis muscles. Results: In SFEMG from the right EDC muscle, the mean jitter value was high in all of them. The average jitter calculated in EDC muscles was 57.76±24.17 µs. The mean jitter value in the frontal muscles was 28.91±10.21 µs. In all patients, the number of CN electrode peaks was more than 4 in the EDC muscle and above 4 in 91.67% of the frontal muscle. Conclusion: Detection of high jitter in SFEMG examination indicates that the examined muscle undergoes a denervation-reinnervation process in the case of increased peak number values. When such a determination is made in the extremity muscles, it becomes important for the diagnosis of ALS. [ABSTRACT FROM AUTHOR]

Objective: The present study reports single fiber electromyography (SFEMG) findings in patients with ocular symptoms referred to the electromyography (EMG) laboratory with a presumed diagnosis of myasthenia gravis (MG). This study also examines repetitive nerve stimulation and serologic and clinical findings. Method: We reviewed the medical records of 45 consecutive patients from January 2019 to September 2021 retrospectively. SFEMG was performed on the frontalis muscle (Front) during voluntary contraction using a disposable concentric needle electrode (CNE) (25 mm, 30 G). The number of single fiber-like action potential (SFLAP) pairs, the mean consecutive difference (MCD), the mean sorted difference (MSD), and the percentage of abnormally high individual jitters were noted. Results: SFEMG results were normal for 16 patients, abnormal for 15, and borderline for 14. The mean jitters for the normal, borderline, and abnormal SFEMG groups were 19.75±3.84 µs, 27.21±4.89 µs, and 74.4±38.74 µs, respectively. A minimum of 20 SFLAP pairs were acquired in the normal or borderline SFEMG groups, whereas an analysis of fewer than 20 SFLAP pairs sufficed for 53% of the patients in the abnormal SFEMG group (p=0.001). SFEMG revealed diagnostic high jitter in 79% of patients with MG. The acetylcholine receptor (AchR) antibody titer correlated positively with mean MCD and MSD (p<0.01) but not with the percentage of high jitter. Conclusion: CNE SFEMG of the Front is beneficial for diagnosing ocular and mild MG. The correlation of absolute AChR antibody titers with mean MCD and MSD, but not with the percentage of high jitter, is notable. [ABSTRACT FROM AUTHOR]

• Myopathic changes in qEMG and/or increased jitter in sfEMG were seen in 63% of 84 patients with Long COVID neuromuscular symptoms. • Low quality of life score correlated with higher mean jitter values in sfEMG but not with qEMG measures. • Electron microscopy showed damage of terminal nerves and motor endplate. To describe neurophysiological abnormalities in Long COVID and correlate quantitative electromyography (qEMG) and single fiber EMG (sfEMG) results to clinical scores and histopathology. 84 patients with non-improving musculoskeletal Long COVID symptoms were examined with qEMG and sfEMG. Muscle biopsies were taken in a subgroup. Mean motor unit potential (MUP) duration was decreased in ≥ 1 muscles in 52 % of the patients. Mean jitter was increased in 17 % of the patients in tibialis anterior and 25 % in extensor digitorum communis. Increased jitter was seen with or without myopathic qEMG. Low quality of life score correlated with higher jitter values but not with qEMG measures. In addition to our previously published mitochondrial changes, inflammation, and capillary injury, we show now in muscle biopsies damage of terminal nerves and motor endplate with abundant basal lamina material. At the endplate, axons were present but no vesicle containing terminals. The post-synaptic cleft in areas appeared atrophic with short clefts and coarse crests. Myopathic changes are common in Long COVID. sfEMG abnormality is less common but may correlate with clinical scores. sfEMG changes may be due to motor endplate pathology. These findings may indicate a muscle pathophysiology behind fatigue in Long COVID. [ABSTRACT FROM AUTHOR]

The aim of this simulation study was to evaluate the resulting value of jitter measured from a simulated examination recording and to analyze its dependence on both the number of SFPs contributing either to the triggering peak or the non-triggered peak, and time shifting (delays of triggering at the end-plate) of individual SFPs in these paired potentials. We simulated potentials recorded using a concentric needle electrode with two well separated peaks, and performed a simulated examination (consisting of 50 trains of 100 discharges) with an assumed number of fibers forming peaks. For each train, fiber diameters were chosen at random within the allowed ranges. For each discharge the delay of triggering for each fiber at the end-plate was selected at random from an assumed range. The mean jitter values were calculated, together with the median and 95% quantile. The results suggest that jitter is related to the mean of the individual SFP shifts. These findings extend the understanding of reduced jitter measurements using a concentric needle electrode. If more than one fiber forms the peak, then jitter decreases due to averaging of individual time shifts of potentials constituting the peak, rather than due to detection of the SFP with the earliest peak. [ABSTRACT FROM AUTHOR]

Aim The diagnostic workup in patients with delayed motor milestones suspected of having either myopathy or a congenital myasthenic syndrome is complex. Our hypothesis was that performance of a muscle biopsy and neurophysiology including stimulated single-fiber electromyography during an anesthetic procedure, combined with genetic testing has a high diagnostic quality. Materials and Methods Clinical and paraclinical data were retrospectively collected from 24 patients aged from 1 month to 10 years (median: 5.2 years). Results Neurophysiology examination was performed in all patients and was abnormal in 11 of 24. No patients had findings suggestive of a myasthenic syndrome. Muscle biopsy was performed in 21 of 24 and was normal in 16. Diagnostic findings included nemaline rods, inclusion bodies, fiber size variability, and type-II fiber atrophy. Genetic testing with either a gene panel or exome sequencing was performed in 18 of 24 patients, with pathogenic variants detected in ACTA1 , NEB , SELENON , GRIN2B , SCN8A , and COMP genes. Conclusion Results supporting a neuromuscular abnormality were found in 15 of 24. In six patients (25%), we confirmed a genetic diagnosis and 12 had a clinical neuromuscular diagnosis. The study suggests that combined use of neurophysiology and muscle biopsy in cases where genetic testing does not provide a diagnosis can be useful in children with delayed motor milestones and clinical evidence of a neuromuscular disease. [ABSTRACT FROM AUTHOR]

The aim was to improve the identification of potentials recorded using single fiber electromyography (SFEMG) contaminated by potentials from other muscle fibers, which might affect measured jitter value, by defining more selective criteria of single fiber potential (SFP) discrimination. We were looking for solutions suitable for automatization. Standard parameters characterizing SFP and their combinations were analyzed to define an analytical discriminating function able to verify if potentials recorded using SFEMG are due to single fiber or due to two (or more) fibers. The discriminating function is based on combination of standard SFP parameters. The procedure was tested on a set of simulated i.e., known data and on samples of clinical data. The tests on simulated data confirmed assumed properties of discriminating function. Preliminary results of pilot studies using patient data suggest its ability for differentiation between potentials of one fiber and contaminated ones. The procedure is suitable for automatization. Results suggest that proposed discriminating function when supplementing standard criteria would help to promote SFP recordings and enable to improve relevancy of jitter measurements and of jitter value norms. [ABSTRACT FROM AUTHOR]

• Follistatin overexpression was studied in aged mice between 24 to 27 months of age. • Follistatin increased muscle size and absolute torque production in aged mice. • Normalized twitch torque, but not tetanic torque, was reduced with follistatin. • Follistatin improved neuromuscular junction transmission but not motor unit loss. • Endogenous mouse follistatin but not myostatin was increased in aged mice. Sarcopenia, or age-related loss of muscle mass and strength, is an important contributor to loss of physical function in older adults. The pathogenesis of sarcopenia is likely multifactorial, but recently the role of neurological degeneration, such as motor unit loss, has received increased attention. Here, we investigated the longitudinal effects of muscle hypertrophy (via overexpression of human follistatin, a myostatin antagonist) on neuromuscular integrity in C57BL/6J mice between the ages of 24 and 27 months. Following follistatin overexpression (delivered via self-complementary adeno-associated virus subtype 9 injection), muscle weight and torque production were significantly improved. Follistatin treatment resulted in improvements of neuromuscular junction innervation and transmission but had no impact on age-related losses of motor units. These studies demonstrate that follistatin overexpression-induced muscle hypertrophy not only increased muscle weight and torque production but also countered age-related degeneration at the neuromuscular junction in mice. [ABSTRACT FROM AUTHOR]

Background: Little is known about how different outlier estimation methods affect cutoff limits for outliers in single fiber electromyography. Methods: We compared in a prospective fashion the established 18th jitter value (18thjv) method to three, whole‐distribution based, outlier detection methods: the interquartile range (IQR), the log‐normal, and the Z‐score method. The reference limits were probed in a normal cohort and in myasthenia gravis (MG) patients. Results: Differences in outlier cutoff values between the different methods were in the range of 2 μs. The number of abnormal muscles according to the computed criteria was similar for all four methods in the control group. Classification metrics (sensitivity, specificity, Youden's statistic, and predictive values) were also similar among the different methods. In the MG group, however, the Z‐score method failed to identify the abnormal jitter values. Accordingly, Kappa agreement was substantial to perfect (0.658 to 1) between the three methods (18thjv, IQR, and log‐normal), but was equivalent to chance between the three methods and the Z‐score in the MG group. Conclusions: The established 18thjv method proved largely robust when compared to whole‐distribution based methods, and its use in clinical practice is justified. Simple estimation of outlier limits by adding two SDs to the mean of the data, leads to unacceptable deviations from the true cutoff values. Moreover, in a clinical scenario in which the final electrodiagnosis depends only on the number of outliers, it is meaningful to accept a tolerance zone of about 2 μs, which is the approximate variation range among the different methods. [ABSTRACT FROM AUTHOR]

Summary Objectives The aim of our study was to verify the effectiveness of single fiber potential (SFP) criteria in cases when the potential recorded using single fiber electrode (SFE) or concentric needle electrode (CNE) is contaminated by distant fibers. Methods Morphological counterparts of SFP were studied using computer simulations. In this study, we examined triphasic potentials using a model of a linear source of SFP. The criteria defining SFP in the case of SFP contaminated by distant fibers were analyzed, and the effect of second fiber contamination on jitter and fiber diameter determination evaluated. Results We found that SFP criteria prevent detection of SFP from fibers smaller than about 30 μm in diameter, but do not prevent classification of a potential as an SFP even though it is formed by two or more fibers. This suggests that the presently used criteria may lead to incorrect interpretation of SFP potentials. SFPs contaminated by fibers of diameters differing by a few percent fulfill the criteria but a negative peak may be shifted in time and therefore impact jitter and diameter measurements. This contamination generally tends to decrease both the jitter and the determined diameter. A new approach to the identification of SFP is presented, determining fiber diameter and distance from the electrode to enable maximum sensitivity to potential contamination by the effect of a second fiber. Conclusion A new parameter characterizing SFP shape changes is introduced. This parameter is used in the method by which additional fibers affecting the SFP may be detected. [ABSTRACT FROM AUTHOR]

Highlights • Jitter determination is feasible with monopolar or concentric needle electrodes. • The more discriminant high-pass filter (1 vs 3 KHz) is uncertain. • Both electrode types, with either 1 or 3 KHz high-pass filters, are of equivalent sensitivity. Abstract Objectives To investigate if monopolar (MN) and concentric (CN) electrodes are equivalent for volitional contraction jitter estimation in orbicularis oculi (OO), and to study the effect of selecting a specific high-pass filter. Methods We studied neuromuscular jitter in OO on both sides in 100 consecutive patients with a clinical diagnosis of ocular myasthenia gravis (MG). We used either MN (50 patients) or CN (50 patients) electrodes in individual patients, according to a randomised protocol, with a 1kH high pass filter on one side and a 3kH filter on the other. Ten or more potential pairs were studied on each side. Results 48 patients had a definite clinical diagnosis of ocular MG, and 52 of mimicking-disorders, who were analysed as controls. In controls, jitter (MCD) showed a normal distribution independent of the electrode type or filter settings. The mean jitter value and the number of abnormal pairs (>10%) was similar in MN and CN recordings, with both 1 kHz and 3 kHz filters. Sensitivity was 73% for mean jitter and 94% for number of abnormal pairs. Specificity was 100%. Conclusions The jitter in OO using MN or CN was similar in controls and the diagnostic sensitivity was similar using either electrode in patients with ocular MG. The use of high-pass filters of 1 or 3 kHz did not influence these results. Significance MN and CN are both suitable for determining volitional jitter in OO. [ABSTRACT FROM AUTHOR]

Introduction: We analyzed jitter recordings made with concentric needle electrode (CNE) single-fiber electromyography (SFEMG) in Lambert-Eaton myasthenia (LEM).Methods: Fifteen subjects diagnosed with LEM were studied using CNE-SFEMG in the extensor digitorum (ED) and tibialis anterior (TA) muscles. CNE-SFEMG in the ED and TA was also used to evaluate 12 and 10 healthy controls (HCs), respectively.Results: Ten men and 5 women were diagnosed with LEM based on an increase of 100% in compound muscle action potential amplitude during 50 Hz repetitive nerve stimulation. All patients exhibited markedly greater jitter in the ED (88.8 ± 23.2 µs) and TA (92.2 ± 30.2 µs) than HCs (28.3 ± 3.4 µs and 30.9 ± 5.1 µs, respectively).Conclusions: CNE-SFEMG is sensitive for discovering abnormalities in neuromuscular transmission in LEM. Muscle Nerve 56: 253-257, 2017. [ABSTRACT FROM AUTHOR]

Background Myasthenia gravis (MG) is a chronic autoimmune neuromuscular disease characterized by weakness of bodily skeletal muscles. Office-based diagnostic tests such as repetitive nerve stimulation (RNS), single fiber electromyography (SFEMG), and the ice test, are used to refine the differential clinical diagnosis of this disease. Evaluating the clinical sensitivity and specificity of these tests, however, may be confounded by lack of a gold standard, non-blinding, incorporation bias, use of non-representative populations and retrospective data. Objective In this study comprising a large Asian cohort of 127 patients recruited from a Neuro-ophthalmology clinic, we minimized aforementioned confounders and tested the diagnostic value of 3 office-based tests against 2 reference standards of MG by virtue of clinical features, antibody assay and response to treatment. Results Regardless of the reference standard used, the ice and SFEMG tests displayed a higher sensitivity (86.0 to 97.3%) compared to the RNS test (21.3 to 30.6%). Conversely, the specificity of the ice (31.3%) and SFEMG (21.7% and 17.2%) tests were reduced compared to the RNS test (82.6% and 84.4%). The combined use of the ice test and SFEMG, improved the specificity of MG diagnosis to 63.6% and 64.3%, without affecting the sensitivity of those tests. Conclusion Our findings indicate, in an Asian population, high sensitivity of the SFEMG test and suggest the ice test as a valid, affordable and less technically demanding approach to diagnose MG with ocular involvement. Both ice test and SFEMG alone, however, yielded poor specificity. We suggest that the combination of SFEMG and ice test provides a more reliable diagnosis of MG. [ABSTRACT FROM AUTHOR]

Single fiber electromyography (SFEMG) is the most sensitive clinical neurophysiological test for neuromuscular junction disorders, particularly myasthenia gravis. Normal values for jitter obtained with SFEMG electrode have been published, but there are few publications for concentric needle electrode (CNE). The aim of this study was to discuss the possibilities to analyse the jitter in CNE recordings and to get normal values of jitter for voluntary activated Extensor Digitorum Communis using disposable CNE. Fifty normal subjects were studied, 16 male and 34 female with a mean age of 37.1±10.3 years (19-55). The jitter values of action potentials pairs of isolated muscular fibers were expressed as the mean consecutive difference (MCD) after 20 analysed potential pairs. The mean MCD (n=50) obtained was 24.2±2.8 µs (range of mean values in each subject was 18-31). Upper 95% confidence limit is 29.8 µs. The mean jitter of all potential pairs (n=1000) obtained was 24.07±7.30 µs (range 9-57). A practical upper limit for individual data is set to 46 µs. The mean interpotential interval (MIPI) was 779±177 µs (range of individual mean values was 530-1412); there were no potentials with impulse blocking. The present study confirms that CNE is suitable for jitter analysis although certain precautions must be mentioned. Our findings of jitter values with CNE were similar to some other few reports in literature.Eletromiografia de fibra única (SFEMG) é o método eletrofisiológico mais sensível para diagnóstico das desordens de junção neuromuscular, particularmente miastenia gravis. Jitter obtido por meio de eletrodo de SFEMG já foi padronizado, porém há poucas publicações com uso de eletrodo de agulha concêntrica (CNE). O objetivo deste estudo é discutir as possibilidades de analisar o jitter por registro com CNE e obter valores normativos para o músculo Extensor Digitorum Communis por ativação muscular mínima. Foram estudados 50 indivíduos normais, 34 do sexo feminino e 16 do sexo masculino, com média de idade de 37,1±10,3 anos (19-55). Os valores do jitter para pares de potenciais de fibras musculares isoladas foram medidos por meio da média das diferenças consecutivas (MCD) em 20 análises de pares de potenciais. A média de MCD (n=50) foi 24,2±2,8 µs (variação de 18 a 31). O limite superior (95%) foi 29,8 µs. O jitter médio de todos os pares de potenciais obtidos (n=1000) foi 24,07±7,30 µs (variação de 9 a 57). O limite superior de normalidade prático para os dados individuais foi 46 µs. O valor médio dos intervalos interpotenciais (MIPI) foi 779±177 µs (variação de 530 a 1412); não foram obtidos potenciais com bloqueio. O presente estudo confirma a viabilidade da análise do jitter por CNE embora certas precauções devam ser mencionadas. Nossos valores de jitter obtidos por CNE são parecidos com os poucos relatos da literatura.

Isolated respiratory muscles weakness is an unusual presentation of Myasthenia Gravis (MG). We present a case of 49-year-old male with undiagnosed MG who presented with fluctuating dyspnea on exertion and at rest. There was no peripheral muscle involvement, diagnostic tests and standard electromyography was normal, and the serologic tests were negative. The repetitive nerve stimulation and Single Fiber Electromyography revealed the diagnosis of MG. Interestingly the patient did not have sufficient therapeutic response on first line agents and required immunoglobulins and corticosteroids due to respiratory muscle involvement. Since skeletal muscle weakness is a cardinal feature of MG, dyspnea may be fluctuating as in our patient causing further difficulty in diagnosis as the pulmonary function tests performed during remission may be normal. This presentation highlights the need to consider MG in the differential diagnosis of unexplained dyspnea on exertion/rest.

Introduction: Single fiber electromyography (SFEMG) is the most sensitive diagnostic tool for diagnosis of myasthenia gravis (MG). Its prognostic value is not known.Methods: We retrospectively analyzed the clinical course of 232 MG patients who presented with only mild symptoms and had SFEMG of the orbicularis oculi muscle. We correlated their SFEMG results with the severity of their later clinical course.Results: During the observation period 39 patients (17%) developed severe disease exacerbations, and 193 (83%) remained stable. Patients with severe disease exacerbation had a significantly higher mean jitter value (P < 0.0001), a greater percentage of fibers with increased jitter (P < 0.0001), and/or impulse blocking (P < 0.0001) on SFEMG.Conclusions: The extent of the SFEMG abnormalities in this study correlated with the later clinical course of MG. Muscle Nerve 54: 1034-1040, 2016. [ABSTRACT FROM AUTHOR]

Objectives To explore the increased diagnostic yield of repetitive nerve stimulation (RNS) following activation for myasthenia gravis (MG) diagnosis, and compare with testing an additional muscle at rest only. Methods We performed a retrospective chart review of patients diagnosed with MG attending the neuromuscular clinic from 2013 to 2015 and extracted data on electrophysiological studies, including frequency of decrement of 10% or above, with facial RNS at rest, and following activation. Results The total cohort included 102 patients with MG, 65 with generalized, and 37 with ocular MG. Facial RNS sensitivities for diagnosing MG were 32–46% and 14–19% respectively. The increase in RNS sensitivity following muscle activation was 6–8% for frontalis muscle recordings, and 0–2% for nasalis muscle recordings. Recording from both muscles at rest only, increased the sensitivity by 9–15%. Conclusion RNS is a valid method for confirming a clinical diagnosis of MG. The increased diagnostic yield of RNS following activation is controversial. Our study shows that the increased diagnostic yield of facial RNS following activation is modest, and is less than performing facial RNS in a second muscle. Significance Performing facial RNS in an additional muscle at rest appears to be more sensitive than facial RNS in a single muscle after activation. [ABSTRACT FROM AUTHOR]

ABSTRACT Introduction: Congenital myasthenic syndromes are a heterogeneous group of inherited neuromuscular disorders. Neurophysiological testing has a major role in screening suspected cases and guiding genetic testing. We performed a systematic literature review to ascertain whether sufficient age-specific normative data exist for these techniques. Methods: We searched Ovid Medline (1948 to October 2012) for citations on repetitive nerve stimulation (RNS) or single fiber electromyography (SFEMG) in children. Results: We identified 5 articles containing data on 48 normal children studied with RNS and 1 article containing data on SFEMG in 20 normal children. A variety of techniques were used, including a variety of stimulation frequencies. Nevertheless, the data identify significant differences in the response to RNS in children as compared with adults, emphasizing the need for adequate age-appropriate normal values. Conclusions: We found a paucity of published normal data for pediatric neuromuscular transmission studies. Further studies using standardized techniques are needed to expand the currently limited pool of available data. Muscle Nerve 48:711-715, 2013 [ABSTRACT FROM AUTHOR]

Abstract: Objective: The aim of this study is to develop a novel method to assess activity-dependent hyperpolarization in human single motor axons at a constant stimulus frequency by using intra-muscular axonal stimulating single fiber electromyography (s-SFEMG). Methods: We performed s-SFEMG in the extensor digitorum communis (EDC) muscle of 10 normal subjects, and measured changes in latencies for single muscle fiber action potentials (MAPs) during 500 stimuli delivered at 5, 10 and 20Hz. The data were analyzed with a repeated measurement analysis, and multiple comparisons were performed. Results: A total of 585 MAPs were examined at 5Hz (n =190), 10Hz (n =210), and 20Hz (n =185) steady stimulation. There was a progressive linear prolongation of latencies, as the stimulus rate increased (F =95.6, p <0.001); the least square means (SEM) of latency change were 100.7 (0.28)% at 5Hz, 102.3 (0.27)% at 10Hz and 105.3 (0.28)% at 20Hz. There were statistically significant differences between frequencies by Tukey–Kramer’s method. Despite the significant latency prolongation, no activity-dependent conduction block developed. A 20Hz electric stimulation to intramuscular axons was well-tolerated in all the subjects. Conclusions: Tetanic stimulation at a constant rate results in significant latency increase in single human motor axons, the extent of which depends on the stimulus frequency. The findings imply that physiological discharge rates will activate the Na+/K+ pump and thereby produce axonal hyperpolarization in single motor axons. Significance: This technique may detect activity-dependent conduction block if the safety margin of impulse transmission is significantly reduced by demyelination or increased branching due to collateral sprouting in a variety of neuromuscular disorders. [Copyright &y& Elsevier]

Abstract: Objectives: The aim of this study was to estimate the jitter parameters in healthy controls in stimulated Orbicularis Oculi (OOc) muscle using concentric needle electrode (CNE). Methods: Fifty healthy subjects, 13 males and 37 females (21–56years, mean age of 38±9.2years) were studied. The zygomatic branch of facial nerve was stimulated with a bar electrode. Jitter was expressed as the mean consecutive difference (MCD). Filter settings 1000Hz–10kHz. Results: The mean MCD from individual studies (n =50, Gaussian distribution) was 21.5±1.99μs (median=21μs), ranging from 17.8 to 26μs (upper limit, 97.5%, 25.5μs). The mean and median MCD from all potentials (n =1500, non-Gaussian distribution) were 21.6 and 21μs, ranging from 7.1 to 39μs (upper limit, 97.5%, 33.4μs). Conclusions: Suggested practical limits in the OOc for mean MCD was 26μs and for outliers 34μs. Significance: Stimulation jitter recordings with CNE could be used in practice but borderline findings should be judged with great caution until larger database obtained with uniform setting available. [ABSTRACT FROM AUTHOR]

Abstract: Objective: Double-step nerve stimulation test (DSST) is a repetitive nerve stimulation (RNS) technique that is performed under exercise and ischemic conditions. We tested the diagnostic significance of DSST at a distal muscle in 17 control subjects and 10 myasthenic patients who had normal conventional RNS test. Methods: Myasthenia Gravis was diagnosed by SFEMG test and acetylcholine receptor antibody titers. During DSST decremental responses were noted. Sensitivity/specificity of DSST were evaluated by receiver operating characteristics (ROC) analysis and best variable in discrimination of myasthenic patients from control subjects with its optimal cutoff-point was selected. Results: At a selected cutoff-point, sensitivity and specificity of DSST reached up to 100%. Also DSST response patterns, especially during the resolution of ischemia, showed significant differences in MG patients. There was a delayed recovery in the ischemia–exercise aggravated decremental response after the resolution of ischemia in the patients when compared with rapid recovery in controls. Conclusions: By using ROC derived cutoff-points, DSST could accurately discriminate MG patients from control subjects. Quantitative results of our study are limited by small series of patients and can vary with larger series. However we think that the difference between the decremental response patterns of patients and controls is a valuable finding. Significance: DSST can be a sensitive, specific and non-invasive choice in the patients who have high suspicion for MG but normal conventional RNS. [Copyright &y& Elsevier]

Background and purpose: The F wave, a late response of low amplitude, is widely used in the study of peripheral nerve lesions, and its persistence and latencies are the main parameters that are usually considered. The analysis of repeater F-waves, which are commonly observed in association with focal or generalized motor neuropathy, is not always performed as a standard electrodiagnostic protocol. Methods: We recorded and quantified the F waves from 13 healthy subjects and 22 patients with unilateral lumbosacral radiculopathy (ULSR) affecting the L5 or S1 roots. Results: We found differences between the injured and normal sides of patients with ULSR in several F-wave parameters. Taking into consideration the normalized and pooled values of tibial and peroneal nerves in the injured side of patients with ULSR, the minimum and mean latencies were higher (1.05 and 1.04 with respect to 1.00; P < 0.01), the relative amplitude of the F waves was higher (1.95 with respect to 1.00; P < 0.001), and the percentage of repeater F-waves was also higher (4.19 with respect to 1.00; P < 0.001). This latter parameter was the most sensitive to detect lateral differences as indicated by the percentage of change and its high z score. Conclusions: Our results show that the use of F-waves may improve the electrodiagnosis of the ULSR if the number of repeater waves is evaluated given the clear and consistent increase of this variable in patients with lumbosacral root injury. [ABSTRACT FROM AUTHOR]

[Purpose] Joint contracture and disuse-induced muscle atrophy were created in rats by fixing their knee joints in the maximum flexion position for four weeks. [Methods] After removing the fixation, the rats were either trained by prolonged stretching exercise of the joints for four or eight weeks (4S and 8S groups), or were not trained (NS group). The angle of extension range of restricted knee joint, the average diameter of hamstring muscles, and the temporal profile of the hamstring single fiber electromyography (SFEMG) were examined. [Results] A significant electrophysiological improvement was found as an effect of the prolonged stretching exercise in the 4S and 8S groups. However, a significant improvement in knee extension angle and average diameter of the hamstring muscle was only found in the 8S group. [ABSTRACT FROM AUTHOR]

Abstract: Objective: To compare the jitter values in voluntarily activated (v-CNE) and stimulated (s-CNE) techniques for Extensor Digitorum Communis muscle using a disposable concentric needle electrode (CNE). Quantifying jitter using a CNE in conjunction with a stimulated technique has not been reported previously. Methods: Forty-one normal subjects were studied, 15 male and 26 female with a mean age of 34.1±10.7 years (19–55). The jitter values were expressed as the mean consecutive difference (MCD) of 20 analyzed potential pairs using v-CNE and 30 isolated potentials using s-CNE. Results: The mean MCD (n =41) was 23.0±2.8μs for v-CNE and 18.2±2.2μs for s-CNE. The mean jitter of all recorded potentials was 22.9±6.7μs for v-CNE (n =820) and 18.3±5.2μs for s-CNE (n =1230). Upper limits for the 18th (v-CNE) and 27th highest (s-CNE) MCD were 38.9 and 30μs, respectively (95% confidence limit). The jitter decrease in s-CNE compared to v-CNE was 1:0.79. Conclusions: Our findings of the jitter values using CNE were similar to other published reports using the voluntarily activated technique; however, these are the first described for the stimulated technique using CNE. Significance: The present study confirms that CNE can be used for the stimulated jitter acquisition and measurement, although certain precautions must be taken regarding signal quality, e.g., observing minimal summation. [Copyright &y& Elsevier]

To examine if the effect of temperature on neuromuscular jitter differs in myasthenics and normals, we performed single fiber electromyography (SFEMG) in 10 myasthenics and 10 healthy controls after heating the upper extremity to 37 and 42°C. In each case, 10–24 mean consecutive difference (jitter) values were obtained at both temperatures. All jitters were pooled appropriately and the groups were compared with each other. The mean jitter was 33.4 ± 10.4 μs at 37°C and 28.2 ± 11.4 μs at 42°C in controls, and 48.3 ± 18.3 μs at 37°C and 54.8 ± 24.9 μs at 42°C in patients. Seven out of 10 patients showed SFEMG abnormalities at 37°C. The number of patients with SFEMG abnormalities rose to 9 after heating to 42°C. Heating decreases neuromuscular jitter in controls and increases it in myasthenics. SFEMG performed at higher temperatures may increase the diagnostic sensitivity of the method in myasthenia gravis. The change of jitter with temperature in opposite directions in myasthenics and normals could be helpful to detect neuromuscular dysfunction. Copyright © 2008 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: Anti-ganglioside GQ1b antibody induces neuromuscular blocking on mouse phrenic nerve–diaphragm preparations. Several reports suggest that patients with this antibody show abnormal neuromuscular transmission in the facial or limb muscles, but limb muscle weakness is unusual in Miller Fisher syndrome that is often associated with anti-GQ1b antibody. To determine whether anti-GQ1b sera affect neuromuscular transmission in human limb muscles, axonal-stimulating single fiber electromyography was performed in the forearm muscle of seven patients with anti-GQ1b antibody. All showed normal jitter and no blocking. Anti-GQ1b antibody does not affect neuromuscular transmission in human limb muscles. The different findings in mouse and human may be explained by the extent of expression of GQ1b on the motor nerve terminals in the muscle examined. [Copyright &y& Elsevier]

Abstract: Objective: Calcium channel blockers are commonly used in some cardiovascular disorders. These drugs can act at neuromuscular transmission, at both pre- and postsynaptic levels and may produce neuromuscular dysfunction. Therefore, they may result in misdiagnosis in electrophysiological testing of healthy subjects. This study aimed to investigate the influence of calcium channel blockers on neuromuscular transmission, using single fiber electromyography, in subjects who were healthy excepting controlled arterial hypertension condition. Methods: Single fiber electromyography during voluntary contraction of the extensor digitorum communis muscle, nerve conduction studies of upper and lower extremities, and concentric needle electromyography of the extensor digitorum communis were performed on 16 verapamil users, 16 amlodipine users, and 16 age-matched normal controls. Twenty potential pairs were recorded from each subject. Twenty individual jitter values and a mean jitter value were calculated for each subject. Both mean jitter values and numbers of abnormal individual jitter values were compared in verapamil and amlodipine users versus normal controls. Results: Eight of 16 verapamil users and 7 of amlodipine users showed evident neuromuscular transmission abnormalities by single fiber electromyography. Two subjects from verapamil and one subjects from amlodipine users group had borderline dysfunction of neuromuscular transmission. Conclusions: These results suggest that both verapamil and amlodipine impair neuromuscular transmission in subjects without neuromuscular disease. Significance: The effects of verapamil and amlodipine are at a level, which may cause misinterpretation of single fiber electromyography studies carried out to investigate neuromuscular junction disorders. [Copyright &y& Elsevier]

Abstract: Objective: To examine the clinical manifestations and patterns of electromyographic abnormalities in MuSK-Ab positive myasthenia gravis. Methods: The clinical evaluations and electrodiagnostic testing results of 20 MuSK-Ab positive myasthenia gravis patients were retrospectively reviewed and compared with matched AChR-Ab positive (N=72) and MuSK-Ab negative/AChR-Ab negative (N=24) patients. Results: MuSK-Ab positive patients were younger and more frequently female and African-American, and compared to the AChR-Ab positive patients, were more likely to present with respiratory symptoms or neck extension weakness. MuSK-Ab positive patients were less likely to have abnormal jitter in a limb muscle: only 59% had abnormal jitter in the extensor digitorum communis muscle, compared to 80% of the AChR-Ab negative/MuSK-negative patients and 91% of the AChR-Ab positive patients. Conclusions: Our MuSK-Ab positive patients not only differ demographically from our MuSK-Ab negative cohort, but they also appear to have a more limited distribution of SFEMG abnormalities. Significance: The possibility that electrophysiologic abnormalities may not be widely distributed should be considered during electrodiagnostic evaluation of suspected MuSK-Ab positive MG and in selecting muscles for molecular, morphologic, or microphysiologic studies in this condition. [Copyright &y& Elsevier]

Objective To assess the significance of single fiber electromyography (SFEMG) in diagnosis of inflammatory myopathies and the correlation with other assistant examination findings. Methods SFEMG were recorded from the extensor digitorum communis of 34 patients with polymyositis or dermatomyositis and compared with the findings of routine electromyography (EMG), serum creatine kinase (CK) determination, and muscle biopsy. Results SFEMG recordings in 34 patients were all abnormal. The prominent feature was markedly increased fiber density (FD) with normally or mildly increased jitter. FD ranged from 1.0 to 6.0 (2.34 ±0.43). Jitter ranged from 5 to 78 p.s (41.6±10.3 jis). The potential pairs with jitter values greater than 55 p.s ranged from 0% to 55% (7.7% ± 11.8%). Block was detected at one recording site in only one patient. Routine EMO demonstrated myogenic lesions in only 24 patients (70.6%). FD was a little higher in the normal-EMG subgroup or the neurogenic-EMU subgroup than myogenic-EMG subgroup but without statistical significance. Elevated CK levels were found in 75% patients (24/32). FD in the normal CK subgroup was significantly higher than that in the elevated CK subgroup (2.62±0.40 vs. 2.28±0.40, P < 0.05). Muscle pathologies were consistent with the diagnosis of myositis in 75% (15/20). Conclusion SFEMG is of great value in the diagnosis and disease process understanding of inflammatory myopathies for the clinically suspected patients with normal routine EMQ, CK levels, and muscle biopsies. [ABSTRACT FROM AUTHOR]

Objectives: Approximately 50% of patients treated with thymectomy have a chance for symptom-free life. However, immunological and neurophysiological abnormalities may be detected in patients with clinical remission. Although improvement usually parallels decrease in acetylcholine receptor antibody (AChRAb) levels and jitter values, there is a question what factors influence immunological and electrophysiological remission in a population of myasthenia gravis (MG) patients.Methods: We analyzed retrospectively clinical data of 32 MG patients operated for generalized MG, followed-up at our department for 17.2 (4–31) years. They were in clinical remission for 12.8 (2–25) years. All of them had single fiber electromyograhy (SFEMG) of extensor digitorum communis muscle (EDC) muscle and estimation of AChRAb level at the end of follow-up. Their age at onset of MG was 17 years (6–48) and at thymectomy 19 (6.4–58) years. Tensilon test was positive in 30, repetitive nerve stimulation in 29 cases.Results: Clinical remission was reached on average 4.2 years after thymectomy. SFEMG jitter value normalized in 60% of cases. AChRAb were negative only in 34% of patients. Jitter values correlated with AChRAb levels (P=0.006, r=0.5) but were not related to clinical factors. Only time to thymectomy correlated with time from thymectomy to clinical remission (P=0.001, r=0.5).Conclusions: Clinical remission is not always accompanied by normalization of SFEMG and AChRAb. Although normalization of neuromuscular transmission in patients with remission of MG is individual, short duration of MG before thymectomy increases the chance of early remission. [Copyright &y& Elsevier]

Objective: One of the important characteristics of myfascial trigger point [MTrP] is spontaneous electrical activity [SEA]. Spontaneous electrical activity is recorded from an active locus [a basic unit] of MTrP and has been considered as an abnormal endplate potential, which might be due to excessive acetylcholine release in neuromuscular junction. This study is designed to test the hypothesis that active loci in MTrPs are related to neuromuscular tranmission disorder. Methods: Twenty-one adult New Zealand rabbits were anesthetized and their biceps femoris were exposed to localize myofascial trigger spot [MTrS, equivalent to MTrP in human]. A monopolar needle electrode was first used for searching SEA in an MTrS region. Then, a single fiber electromyography [SFEMG] electrode was used to collect the neuromuscular jitter at the site where SEA was recorded. The same procedure was performed at the normal muscle site [no SEA recorded] in contralateral limb to collect the neuromuscular jitter as a control. Mean value of consecutive differences [MCD] of 100 successive interpotential intervals was calculated to express the neuromuscular jitter. Results: There was no statistically significant difference [P > 0.05] in MCD of MTrS between the active loci and control sites. Conclusion: It appears that the neuromuscular transmission of endplate in MTrS in rabbits is not impaired based on this SFEMG study using jitter as the sole criteria. Spontaneous electrical activity is not related to neuromuscular transmission abnormality. Further studies are required to clarify the mechanism of dysfunctional endplates in relation to MTrP. [ABSTRACT FROM PUBLISHER]

Isolated respiratory muscles weakness is an unusual presentation of Myasthenia Gravis (MG). We present a case of 49-year-old male with undiagnosed MG who presented with fluctuating dyspnea on exertion and at rest. There was no peripheral muscle involvement, diagnostic tests and standard electromyography was normal, and the serologic tests were negative. The repetitive nerve stimulation and Single Fiber Electromyography revealed the diagnosis of MG. Interestingly the patient did not have sufficient therapeutic response on first line agents and required immunoglobulins and corticosteroids due to respiratory muscle involvement. Since skeletal muscle weakness is a cardinal feature of MG, dyspnea may be fluctuating as in our patient causing further difficulty in diagnosis as the pulmonary function tests performed during remission may be normal. This presentation highlights the need to consider MG in the differential diagnosis of unexplained dyspnea on exertion/rest. [ABSTRACT FROM AUTHOR]