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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., (© 2020 Wiley Periodicals LLC.)

Fatigability is the hallmark of myasthenia gravis (MG). It is not clear, however, whether there is an analogous increase in jitter during the course of a single fiber electromyography (SFEMG) session. The individual jitter values of all potentials of 76 normal and 44 myasthenic orbicularis oculi muscles were assigned a rank number according to their temporal order in which they were collected and linear regression was performed to determine if the slope of the regression line was significantly different from zero. Control and MG subjects displayed rather flat linear regression lines with non-significant positive or negative slopes. Accordingly, ROC analysis yielded areas under the curve near 0.5. We conclude that there is no systematic jitter increase during the collection of 20 potential pairs in a typical SFEMG session.

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., (Copyright © 2018 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. All rights reserved.)

Competing Interests: Competing interests: None declared.

Introduction: Electrophysiological studies play an important role in the diagnosis of myasthenia gravis (MG). The objectives of this study was to explore the correlation of jitter and decrement with various clinical symptoms and signs and disease severity., Methods: We performed a retrospective chart review of 75 MG patients who attended the neuromuscular clinic from April 2013 to May 2014. We compared clinical characteristics between patients with high jitter (>100 µs) and decrement (>10%), and patients with lower values to explore the correlations and optimal thresholds of jitter and decrement for different clinical features., Results: High jitter and decrement values were associated with more severe disease, manifested by more frequent symptomatic bulbar and limb muscle weakness, more frequent ocular and limb muscle weakness on examination, higher quantitative MG score, and generalized disease., Conclusions: The yield of the electrophysiological assessment in MG extends beyond disease diagnosis and correlates with disease severity and the presence of generalized disease. Muscle Nerve 56: 445-448, 2017., (© 2017 Wiley Periodicals, Inc.)

Purpose: Our aim in the current study was to determine the minimum number of SFEMG potential pairs required to confirm neuromuscular junction impairment and relate this number to disease severity., Methods: Ninety-four patients with myasthenia gravis (MG) attending the neuromuscular clinic from February 2013 to November 2015 were included. The SFEMG sensitivity was determined for each number of recorded pairs up to 20. In addition, we compared clinical and electrophysiologic characteristics between patients with abnormality within the first 3, 4 to 7, and ≥8 recorded pairs to determine whether this number is associated with disease severity., Results: Ninety-eight percent of patients had abnormal SFEMG, within 17 pairs in ocular MG, and within 15 pairs in generalized MG. All patients with generalized MG had at least one abnormal pair in the first five recorded pairs. Patients with three abnormal pairs apparent earlier during the test had more frequent bulbar, respiratory, and limb muscle weakness, and had higher mean jitter values and decrement values., Conclusions: In most cases, an abnormal SFEMG examination can be demonstrated in the first 15 recorded potential pairs in patients with generalized MG, and in the first 17 pairs in patients with ocular MG, thus shortening the test time and decreasing patient discomfort while preserving test sensitivity.

Introduction: The literature lacks data on accuracy of single fiber electromyography (SFEMG) for myasthenia gravis (MG) patients followed longitudinally., Methods: We included patients with a clinical suspicion of MG who received SFEMG and follow-up at our institution between 2003 and 2013. Data collected included demographics, symptom details, clinical deficits, other diagnostic testing results, MG medication regimen, duration on treatment, response to therapy, and ultimate diagnosis after follow-up. When available, information was also extracted from the MG-specific Activities of Daily Living, MG Quality of Life, and European Quality of Life assessments before and after SFEMG., Results: Three hundred forty eight SFEMG patients met inclusion criteria. Myasthenia gravis was ultimately diagnosed in 31% (19% ocular, 12% generalized). A sensitivity of 78% was seen for MG regardless of subtype, 73% for ocular MG, and 85% for generalized MG. A specificity of 91% was obtained for MG of either ocular or generalized subtype., Conclusions: The diagnostic accuracy of SFEMG using this methodology minimizing incorporation bias is more reliable than that usually described in previous studies. There is utility in increasing diagnostic yield when SFEMG results are combined with clinical data and those from other diagnostic tests, particularly serology.

Background: Single-fiber electromyography (SFEMG) abnormality in the extensor digitorum communis (EDC) was reported in ocular myasthenia gravis (OMG), which indicated subclinical involvement beyond extraocular muscles in OMG patients. The relationship between the abnormal findings of SFEMG in EDC and the probability for OMG to develop generalized myasthenia gravis (GMG) is unknown. This retrospective study aimed to determine the predictive value of abnormality of SFEMG in EDC of OMG patients., Methods: One-hundred and two OMG patients underwent standard clinical diagnosis process and SFEMG test in EDC muscle when diagnosed and were clinically followed up for 5 years. The SFEMG data were compared between different clinical groups according to thymus status, onset age, and different outcome of OMG developing. Chances of progressing to GMG were compared between two different groups according to SFEMG and repetitive nerve stimulation (RNS) results, acetylcholine receptor antibody (AchRAb) titer, thymus status, and onset age., Results: Abnormal SFEMG results were observed in 84 (82.4%) patients. The mean jitter, percentage of jitter >55 μs (%), and blocking were higher in OMG patients than in healthy volunteers. There were no statistical differences in jitter analysis between thymoma group and non-thymoma group (P = 0.65), or between the later OMG group and the later GMG group (P = 0.31), including mean jitter, percentage of jitter >55 μs (%), and blocking. Elderly group (≥45 years old) had a higher mean jitter than younger group (t = 2.235, P = 0.028). Total 55 OMG developed GMG, including 47 in abnormal SFEMG group while 8 in normal SFEMG group. There was no statistical difference in the conversion rates between the two groups (χ2 = 0.790, P = 0.140). RNS abnormality, AchRab titer, or onset age had no correlation with OMG prognosis (P = 0.150, 0.070, 0.120, respectively) while thymoma did (χ2 = 0.510, P = 0.020)., Conclusion: SFEMG test in the EDC showed high abnormality in OMG, suggesting subclinical involvement other than extraocular muscles. Nevertheless, the abnormal jitter analysis did not predict the prognosis of OMG according to clinical follow-up.

Purpose of Review: It is easy to forget the contribution of electromyography (EMG) to the investigation of paediatric peripheral neuromuscular disease, and this review highlights its continued importance., Recent Findings: The discovery that Brown-Vialetto-van Leare disease, when associated with disorder of riboflavin metabolism, may be treatable has raised awareness of the importance of EMG for its early detection. Unexpected discovery of motor neuronopathy, which may be useful for the definition of the phenotype of several conditions, now has an added significance. The investigation of disorders of peripheral nerve cannot proceed without nerve conduction studies but particular interest has been shown in its role in the management of obstetric brachial plexus palsy, with investigation within 1 month now recommended. The key role of neurophysiology in identifying abnormalities of the neuromuscular junction, and therefore leading investigators to a diagnosis of myasthenia, is once again highlighted. EMG in muscle disease continues to have a role, particularly when identifying myotonia., Summary: Paediatric EMG, while a daunting technical challenge to some practitioners, remains a valuable investigative tool for the specialists in paediatric neuromuscular disorders and will continue to deliver important diagnostic information, often as quickly and accurately as other more recent innovations.

Objectives: The purpose of our study was to show neuromuscular transmission abnormality in the masseter muscle of generalised myasthenia gravis (MG) patients and to compare motor end-plate failure of the masseter with the extensor digitorum communis (EDC) and periocular muscles., Methods: Motor end-plate function was evaluated during voluntary contraction of the masseter muscle of 20 generalised MG patients aged between 16 and 63 years, as well as 20 age-matched healthy volunteers. The mean jitter value was calculated for each group and compared. The upper limit of normal jitter was also calculated and the number of jitters exceeding this cut-off value was counted for each group for comparison. In MG patients, jitter analysis was also performed in periocular and EDC muscles along with the masseter and the number of single fibre-like potentials with abnormal jitter was counted for each muscle. All tests were performed during the same session with a concentric needle electrode (CNE)., Results: For the masseter muscle, the mean jitter of all potential pairs was significantly higher in the patient group (24.7 ± 9.6 μs in healthy volunteers, 71.9 ± 41 μs in patients). The calculated mean jitter for the 18th highest value in healthy volunteers was 33.8 ± 5.9 μs (upper 95% confidence limit was 45.6 μs). The number of abnormal jitters (≥ 46 μs) was significantly higher in the patient group (276 out of 402 jitters) compared to healthy volunteers (10 out of 400 jitters). In the patient group, the number of single fibre-like potentials with abnormal jitter was found to be similar for the masseter, periocular and EDC muscles., Conclusion: The masseter muscle has diagnostic importance in generalised MG. The ratio of high jitters to all of the calculated jitters in a particular muscle was similar for masseter, periocular and EDC muscles., Significance: Jitter analysis of the masseter muscle during voluntary contraction is easy to perform and it was found as informative as other muscles in patients with generalised MG., (Copyright © 2013 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Objective: To estimate jitter parameters in myasthenia gravis in stimulated frontalis and extensor digitorum muscles using the concentric needle electrode., Methods: Forty-two confirmed myasthenia gravis patients, being 22 males (aged 45.6±17.2 years-old) were studied. Jitter was expressed as the mean consecutive difference (MCD)., Results: MCD in extensor digitorum was 61.6 µs (abnormal in 85.7%) and in frontalis 57.3 µs (abnormal in 88.1%). Outliers represented 90.5% for extensor digitorum and 88.1% for frontalis. At least one jitter parameter was abnormal in 90.5% of the combined studies. Acetylcholine receptor antibody was abnormal in 85.7% of the cases., Conclusions: Stimulated jitter recordings measured from muscles using concentric needle electrode can be used for myasthenia gravis diagnosis with high sensitivity. Extensive normative studies are still lacking and, therefore, borderline findings should be judged with great caution.

Because of certain restrictions in medical praxis, reusable materials are only allowed in some countries. This also applies to electrodes for electromyography; the special single-fiber electromyography electrode must be replaced. This article gives some details of the possibilities of using an alternative-a small concentric needle electrode. Practical hints, reference values, and the application in diagnostic work for myasthenia gravis are summarized., (© 2012 New York Academy of Sciences.)

Objective: To explore the value of low-frequency repetitive nerve stimulation (RNS) in the diagnosis of myasthenia gravis (MG)., Methods: A total of 436 MG patients admitted during the period of July 2008 and August 2010 and undergoing the repetitive nerve stimulation test were reviewed retrospectively. We analyzed the positive rates of RNS in MG patients and compared the abnormalities in different nerves including facial, accessory, axillary and ulnar nerves., Results: Among them, 73.85% had abnormal recordings on low-frequency RNS test. The highest abnormality was in facial nerves (82.30%), then axillary nerves (52.17%) and the lowest in ulnar nerves (27.64%). The positive rates of RNS in ocular MG were significant lower than those in general MG patients. And there were no significant statistical differences of RNS abnormal rates in types IIa, IIb, III and IV MG patients with 89.66%, 82.56%, 91.67% and 83.33%, respectively. In ocular MG, 16.34% patients were positive in RNS test under the stimulation of accessory, axillary and ulnar nerves. And 79.50% patients with general MG had two or more nerves with abnormal results., Conclusion: The low-frequency RNS test is of great value in the diagnosis of MG. And it shows a higher sensitivity in general MG patients than that in ocular ones. The stimulation of facial and axillary nerves increases the positive rates of RNS in MG patients.

In seronegative myasthenia gravis repetitive nerve stimulation and single-fibre EMG have a crucial diagnostic value but they may be negative, particularly in repetitive nerve stimulation studies. We report the case of a 43-year-old patient with generalized seronegative myasthenia gravis with negative 3 Hz repetitive nerve stimulation at Erb's point and voluntary single-fibre EMG in the orbicularis oculi. We also performed 6 and 12 Hz repetitive nerve stimulation at Erb and stimulated single-fibre EMG in the extensor digitorum communis and our findings were pathological. Our data suggest that, for individual patients with an atypical picture characterised by dissociation between a severe clinical pattern and no definite neurophysiological findings on conventional tests, repetitive nerve stimulation with a stimulation rate higher than 3 Hz and/or stimulated single-fibre EMG with an increasing stimulation rate may be helpful.

The single fiber needle electrode (SFNE), which is designed to isolate single muscle fiber action potentials, has played an important role in the diagnosis of myasthenia gravis (MG). However, the concentric needle electrode (CNE) has been recently adopted by some workers to study neuromuscular instability in MG, and reference data have also been obtained in healthy subjects. In this study we wanted to establish whether data acquired using the SFNE is comparable to that obtained using the CNE when studying patients with MG. We established reference data for our laboratory using the CNE for orbicularis oculi (OO) and extensor digitorum communis (EDC). We compared data from 24 MG patients using both SFNE and CNE and found no significant differences in mean jitter values for either muscles. We correlated the neurophysiological data obtained by either electrode with various clinical assessments, the ice pack test, OO and EDC strength measurement, and MGFA classification of disease, and we found no significant relation. We compared discomfort scores for the two needle electrodes for each muscle and found that the discomfort scores for CNE are significantly lower (P = 0.0004). We conclude that the CNE is a useful alternative electrode for studying single fiber potentials, but more reference data from normal control subjects is desirable. Muscle Nerve, 2008.

The diagnosis of myasthenia gravis is above all clinical, however electroneuromyography (ENMG) and laboratory tests can be helpful. ENMG testing is readily available and with immediate results. Useful with emergent symptoms, it is equally so in the event of more acute pictures found in generalized motor deficit and bulbar findings of respiratory failure. It can be performed in out-patient clinics or at the bedside. ENMG is based on an assessment of repetitive nerve stimulations (RNS), which can be sensitized, and more rarely on jiter studies using single-fiber electromyography (SFEMG). RNS recordings from multiple sites, depending on symptoms, are preferable. The usefulness of these tests varies depending on the clinical situation, not only for diagnosis but also during follow-up, in order to obtain objective evidence of the effects of treatment.

Jitter after axonal microstimulation in the masseter muscle was studied in 30 consecutive patients (12 women) with myasthenia gravis (MG). Patients' mean age was 42.3 (12-75), median disease duration was 3 months (1-72), and onset was ocular (15 cases), oculobulbar (7), bulbar (6), or generalized (2). There were 23 newly-diagnosed patients. Nine cases developed purely ocular MG and 21 cases developed generalized MG. In the latter group, five subjects had a rapidly progressive course and 16 subjects had stable or well-controlled disease (MGFA grade 2-3). Six patients did not have circulating anti-acetylcholine receptor antibodies. Masseter single-fiber electromyography (SFEMG) was abnormal in 6 of 9 ocular MG patients and in all generalized cases (overall sensitivity 27 of 30 cases or 90%; confidence interval 79.3%-100.0% at P = 0.95). Masseter should be considered for SFEMG in diagnosis of MG, especially in cases with bulbar onset.

Objective: Our aim was to study the pathophysiological process leading to facial muscle atrophy in 13 patients with MuSK antibody positive myasthenia gravis (MuSK-MG), and to compare with findings from 12 acetylcholine receptor antibody positive myasthenia patients (AChR-MG), selected because they suffered from the same degree of disease severity and required similar treatment., Methods: Motor unit action potential (MUAP) and interference pattern analysis from orbicularis oculi (O oculi) and orbicularis oris (O oris) muscles were studied using a concentric needle electrode, and compared with findings in 20 normal subjects, 6 patients receiving botulinum toxin injections (representing a neurogenic model) and 6 patients with a muscle dystrophy (representing a myopathic model). The techniques and control data have been reported previously., Results: The mean MUAP durations for O oculi and O oris were significantly reduced (p<0.001) in both MG cohorts when compared with healthy subjects, and were similar to those in the myopathic control group. They were significantly different from those obtained from the neurogenic control group (p<0.001 for both O oculi and O oris). The MUAP findings in O oculi occurred independently from neuromuscular blocking on single fibre EMG (SFEMG) in the same muscle. On turns amplitude analysis (TAA), 50% of MuSK-MG patients and 42% of AChR-MG patients had a pattern in O oculi which was similar to that in the myopathic control group, and 62% of MuSK-MG patients and 50% of AChR-MG patients had a pattern in O oris that was also similar to that in the myopathic control group. The TAA findings for O oculi and O oris in both MG cohorts were different from those obtained from the neurogenic control group., Conclusions: Facial muscle atrophy in MuSK-MG patients is not neurogenic and the pathophysiological changes are akin to a myopathic process. The selected AChR-MG patients also show evidence of a similar pathophysiological process in the facial muscles albeit to a lesser degree., Significance: We propose that muscle atrophy in MuSK-MG is a myopathic process consisting of either muscle fibre shrinkage or loss of muscle fibres from motor units. The duration of disease and long-term steroid treatment may be further contributory factors.

Objective: To evaluate the value of single-fibre electromyography (SFEMG) with monopolar electrode (MNPE) in revealing neuromuscular transmission dysfunction., Material and Methods: We examined the extensor digitorum communis muscle by using single-fibre electrode (SFE) and MNPE sequentially, in randomly assigned 20 healthy volunteers and in 17 patients with known myasthenia gravis (MG). The high-pass filter setting was 3 kHz for MNPE. Ten individual jitter values were calculated for each electrode in every muscle. Repetitive nerve stimulation (RNS) test on trapezius muscle was performed on 15 patients., Results: In controls, the mean jitter values were 27 +/- 9 (10-59) micro s with SFE, and 21 +/- 7.2 (9-56) micro s with MNPE (P = 0.001). In the MG group, the mean jitter values were 52.4 +/- 38 (12-221) micro s with SFE, and 51.8 +/- 34.7 (12-179) micro s with MNPE. Both electrodes identified junction dysfunction in 14 patients. RNS revealed decrement in four patients but 11., Conclusion: SFEMG with SFE is still the gold standard; however, SFEMG with MNPE is superior to RNS like SFEMG with SFE.

The decrement pattern at low rates of repetitive nerve stimulation in myasthenia gravis (MG) is characterized by a decrease of compound muscle action potential size within the first 4-5 responses. With subsequent stimuli, compound muscle action potential size either increases or does not change. Following an observation that the pattern of decrement might be different in patients with Lambert-Eaton myasthenic syndrome (LEMS), we retrospectively studied traces from eight LEMS patients and 14 patients with seropositive generalized MG, calculating decrement percent from first to fourth and from first to ninth compound muscle action potential. In the LEMS patients, compound muscle action potential amplitude decreased progressively from first to ninth stimulus at 2, 3 or 5Hz in all traces but one. In contrast, MG patients demonstrated the expected improvement after the initial decrement in all traces except one. In the evaluation of patients suspected of having myasthenia gravis, the finding of progressive decrement pattern at low rates of repetitive nerve stimulation may alert the electromyographer to the possibility of Lambert-Eaton syndrome and prompt the performance of further electrodiagnostic tests.

Introduction: The role played by neurophysiological studies (NPS) in the diagnosis of diseases affecting neuromuscular transmission (NMT) is based on the study of the failure of muscle fibres to achieve a sufficient degree of depolarisation for the junction potential to reach the appropriate threshold and attain a muscular action potential. This totally or partially blocked impulse will give rise to different types of responses in neurophysiological tests., Aims: To analyse the different NPS as diagnostic methods in diseases that affect NMT., Development: The article offers a review of the concept of the safety margin at the neuromuscular junction and a description of the most common neurophysiological techniques currently in use--repetitive stimulation, as well as conventional or single fibre electromyography (EMG) with voluntary activation or axonal electrical activation. The most frequent findings in diseases affecting NMT are also discussed., Conclusions: NPS will be useful to confirm or reject the clinical diagnosis, to exclude other concomitant neuromuscular diseases, to establish whether the process is pre- or post-synaptic, to monitor the clinical course of the disease (when it is both natural or in response to the medical or surgical treatment) and also to enable the physician to determine the status of NMT in cases of clinical remission, as well as to detect subclinical disorders. Single fibre EMG studies are the most sensitive method of neurophysiological diagnosis when dealing with these diseases.

Objective: To correlate repetitive nerve stimulation (RNS) decrement in different muscles with the predominant clinical presentation in myasthenia gravis (MG), and to study single fibre EMG (SFEMG) sensitivity in ocular MG., Methods: Sixty-nine, untreated, consecutive patients suspected for MG were observed prospectively for a minimum of 6 months. Those who improved on medical treatment were diagnosed as MG. The others, in whom the neurophysiological studies were normal and that did not improve on medical treatment served as a control group, from which normative data for RNS and SFEMG was obtained. The MG patients were further classified in 3 subgroups according to the predominant clinical presentation: group I (ocular); group b (bulbar); and group a (axial). We performed RNS in nasalis, trapezius, anconeus, and abductor digiti minimi. All patients with ocular MG underwent jitter determination of the orbicularis oculi muscle., Results: Thirty-seven patients were diagnosed as MG (group I, 15; group b, 13; group a, 9). In group I, RNS was abnormal in 33% of the patients. RNS studies disclosed at least one abnormal muscle response in every patient in groups a and b. Trapezius was significantly more sensitive in group a, and anconeus and nasalis in group b (P < 0.01). Jitter was abnormal in all patients in group I, and the most sensitive parameter was an increased number of unstable pairs, 100%., Conclusions: Based on these observations, we recommend that a shoulder muscle, as the trapezius, should be studied first in the limb-axial presentation of MG, and the anconeus-nasalis muscles in predominant bulbar MG. In ocular MG, RNS is not sensitive and jitter should be performed in facial muscles., Significance: This paper shows the unequal sensitivity of several muscles to RNS in different forms of MG.

Single-fibre electromyography (SF-EMG) is the most sensitive electrophysiological test for myasthenia gravis and other neuromuscular junction pathology. It is also useful in the assessment of motor unit morphology in some neuromuscular diseases. A special needle with a 25 microm recording surface is used to record the time-locked potentials of 2 muscle fibers belonging to the same motor unit. Jitter is the variability in the arrival time of action potentials to the recording surface between consecutive discharges. The junctional part of the jitter depends on the amount of Ach released and on the sensitivity of the postsynaptic membrane and is related to the safety margin of neuromuscular transmission. Thus, SF-EMG can detect subclinical impairment of neuromuscular transmission, which cause an increased jitter. However, an increased jitter is not specific of neuromuscular transmission disorders, because it may be due to unstable conduction in motor nerves and muscle fibers. It is the extrajunctional part of the jitter. SFEMG is performed either during slight voluntary contraction (volitional SFEMG) or by axonal stimulation (stimulated SFEMG). Jitter is expressed as the mean of the absolute consecutive differences (MCD) of the latency between the time-locked potentials (volitional SFEMG) or from the stimulus to the negative peak of the potential (stimulated SFEMG). Recording is judged abnormal when more than 10% of the collected pairs are abnormal. On the other hand, single use coaxial needle electrodes which are cheaper could be an alternative for neuromuscular transmission analysis, because the jitter analysed with this type of needle was found highly comparable to that analysed with SF electrode. Moreover, jitter measurements coupled with fiber density estimates provide valuable information on the pathophysiology of the motor units in various neuromuscular disorders.

Objective: To clarify the optimum trace count for jitter calculation., Materials and Methods: Single-fiber electromyography was performed during voluntary contraction (VC-SFEMG) of extensor digitorum muscle in six healthy and five myasthenic subjects. Twenty single-fiber action potential (SFAP) pairs were recorded from each subject. For each pair, 100 consecutive traces were recorded and stored for off-line analysis. Ten different jitters were calculated in 10 consecutive steps for each SFAP pair by increasing the number of traces included to analysis (from 10 to 100). The jitter calculated in each step was compared with that calculated from 100 traces., Results: Sixty was the optimum number of trace count for both myasthenics and normal controls. Using less than 60 traces for jitter calculation revealed lower values., Conclusion: Jitter calculation should be performed from at least 60 traces in VC-SFEMG. Less numbers yield lower jitter and may cause diagnostic error.

Jitter values are calculated in reference to a triggering potential during single-fiber electromyography (SFEMG) performed during voluntary contraction. When there are more than two single-fiber action potentials (SFAP) and the selected triggering potential is from an abnormal end-plate, all the jitters calculated from the same trace will be affected. In this study, the effect of triggering potential on calculated jitter was investigated in myasthenic and healthy volunteers by switching the triggering potential and recalculating the jitter off-line. Selecting a triggering potential from an abnormal end-plate increased the number of abnormal individual jitters as well as the mean jitter. Therefore, if the equipment software has the capacity to change the trigger potential, the triggering potential should not be from an abnormal end-plate if all possible jitter values are to be calculated for traces having three or more single-fiber potentials. Otherwise, only one jitter value should be included from any one trace to prevent false-positive results., (Copyright 2002 Wiley Periodicals, Inc.)

Surface stimulation for single-fiber electromyography has been proposed previously as a novel technique based on a study performed on healthy subjects. The current study was designed to determine the diagnostic value of surface stimulation single-fiber electromyography in patients with myasthenia gravis. Ten patients with myasthenia gravis were recruited for the study. Surface stimulation of the facial nerve trunk, as well as extramuscular needle stimulation of its zygomatic branch was performed. Twenty single-fiber potentials were recorded from the orbicularis oculi muscle for each stimulation type in each patient. For both stimulation techniques, mean jitter values and the total number of abnormal individual junctions were found to be abnormally high. Jitter values obtained by surface stimulation were comparable with those obtained by needle stimulation.

Mastication was evaluated in patients with bulbar myasthenia gravis and compared with that of patients with ocular myasthenia gravis, patients in remission who previously suffered from bulbar symptoms, and healthy controls. Bulbar myasthenia gravis may impair mastication due to weakness of the masticatory muscles. The aim of the study was to objectively evaluate the influence of myasthenia gravis on mastication. The subjects chewed a piece of breakfast cake and chewed 1 min on a piece of chewing gum. Surface EMG of the masseter muscle, temporalis muscle and jaw opener muscles was recorded. Statistical analysis revealed that bulbar patients produced significantly less EMG activity in the closing phase of a chewing cycle in both experiments. The EMG of the masseter muscle expressed as percentage of the maximum EMG during maximal clenching showed significantly higher values in the bulbar group than in the other groups. This was not found for the temporalis muscle. It was suggested that bulbar patients use a strategy of limited effort to produce a bolus that can be swallowed. The ocular patients and the patients in remission showed no subclinical impairments in muscle function during chewing.

Objective: To compare voluntary single fiber electromyography (v-SFEMG) and repetitive nerve stimulation (RNS) at the same extensor digitorum communis (EDC) muscle in myasthenia gravis (MG)., Methods: We examined v-SFEMG and RNS successively on the same day in the same EDC muscle. We studied 45 examinations of both v-SFEMG and RNS in 29 patients suffering from MG, together with examinations of RNS in 30 control subjects., Results: Forty-one of 45 (91%) v-SFEMGs showed abnormal results, whereas only 18/45 (40%) RNSs showed an abnormal decrement. The percentage of decrement showed similar correlations with 3 v-SFEMG parameters: percentage of abnormal pairs, percentage of blocking pairs, and the mean MCD value. Examinations showing a significant decrement in RNS had at least 60%, and usually no less than 90%, abnormal pairs, and 10-80% blocking pairs. Some muscles without a decrement had up to 50% blocking pairs., Conclusions: These results suggest that the blocking phenomenon observed in v-SFEMG is not a direct counterpart of the decrement in RNS. This must be partly because fibers contributing to the decrement are continuously blocked during voluntary contraction, and partly, because smaller motor units explored by v-SFEMG are probably more abnormal in MG than larger motor units mainly contributing to a decrement. Both factors make v-SFEMG much more sensitive than RNS.

Masticatory muscle strength was quantified in patients with bulbar myasthenia gravis and compared with that of patients with ocular myasthenia gravis, patients in clinical remission (whether or not pharmacological) who previously suffered from bulbar myasthenia gravis, and healthy subjects. Maximal bite force and maximal activity of the masseter and temporalis muscles and of the submental muscle complex were measured. Bite force was decreased in the patients with bulbar myasthenia gravis, but was normal in the patients in the clinical remission group and in the ocular group. These findings were consistent with the results of electromyographic data. Although subjective reports of masticatory muscle weakness provide valuable information, quantitative measurements provide more information about the degree of muscle weakness of individual muscles. This is especially important for longitudinal evaluation of therapy in individual patients and for pharmacotherapeutic research., (Copyright 2000 John Wiley & Sons, Inc.)

Background and Objective: In typical cases, the patient's history and clinical examination make it possible to diagnose ocular myasthenia gravis (OMG). But, in many cases a clear clinical picture is not present and OMG diagnosis is very difficult because gold diagnostic standard tests are not available. The diagnostic tests for OMG are usually unable to display a good sensitivity and specificity simultaneously. In this paper, we studied 86 cases submitted for suspected OMG., Methods: The patients were studied clinically and with various other tests used in OMG diagnosis (SFEMG, repetitive nerve stimulation, Ab anti AChR titration, tensilon test)., Results and Conclusion: SFEMG showed the highest sensitivity (100%) while Ab anti AChR showed the highest specificity (100%). To our knowledge this is the largest population of suspected OMG studied using most of the diagnostic parameters, reported in the literature.

We performed single fiber electromyography by axonal stimulation (SFEMG-AS) of the frontalis muscle of 16 patients with ocular myasthenia gravis (OM) and 33 controls. In the controls, values of mean consecutive differences (MCD) ranged from 5 to 55 micros (average, 14.7 +/- 2.8 micros) and mean MCD of individual MPs was 14. 6 +/- 6.8 micros. All the OM patients showed abnormal SFEMG-AS jitter before prostigmine was administered (mean MCD: 49.19 +/- 21. 82 micros, percentage of blocks: 20.97 +/- 18.53). Twenty or 30 min after prostigmine had been administered, we saw a significant improvement in jitter: mean MCD was 36.38 +/- 22.49 micros (P = 0. 005), and percentage of blocks was 10.16 +/- 18.87 (P = 0.008). The method was well tolerated. We conclude that SFEMG-AS of the frontalis muscle is a sensitive technique for the diagnosis of OM and is easy to carry out., (Copyright 2000 John Wiley & Sons, Inc.)

Introduction: Electrophysiological studies are of recognized use in the confirmation of alterations of neuromuscular transmission in further determining their physiopathological characteristics, helping to differentiate them from other conditions with secondary effects on their function., Development and Conclusions: In our study we review the physiopathology of these disorders which compromise the safety factor of the neuromuscular junction, by presynaptic or postsynaptic alterations, and forms the basis of the results of electrophysiological studies. We describe the techniques currently most used: repetitive stimulation and single fibre electromyography complemented by conventional electromyography. Their application and findings in the commonest syndromes are discussed. Finally, their sensitivity, specificity and difficulties are considered.

Voluntary and stimulation single-fiber electromyography were performed in the extensor digitorum communis muscle of 15 myasthenic patients. The increase in mean and individual mean consecutive difference as well as the proportion of blocking in the volitional activation were greater than in the stimulation method. These differences may be explained in part by the different degree of alteration in large as compared with small motor units in patients with myasthenia gravis.

Twenty patients with generalized myasthenia gravis (MG) were studied to assess firing rate-dependent changes in end-plate jitter. Stimulated single-fiber electromyography (EMG) was performed in the extensor digitorum communis muscles at stimulation frequencies of 1, 2, 5, and 10 Hz for all the sampled fibers and at 20 Hz for a few ones. In all 137 end-plates were obtained, of which 43 showed blocking. Statistical analysis demonstrated significant increases in jitter and the blocking rate from 1 to 2 and 2 to 5 Hz, whereas there were decreases from 5 to 10 and 10 to 20 Hz. Further analysis showed that the decrement in jitter from 5 to 10 Hz was greater in end-plates with preexisting low safety factors. In contrast, even though the safety factor of long-duration MG end-plates was lower than that of the short-duration group, the decrement in jitter was insignificant in the long-duration MG end-plates. These results suggest that the intratetanic facilitation effect begins at 10 Hz and is more prominent in end-plates with a preexisting low safety factor. Long-lasting MG, however, eliminates this effect.

Single-fiber electromyography (SFEMG) is a selective recording technique in which a needle electrode with a small recording surface in the side is used to identify action potentials from individual muscle fibers. The SFEMG parameters of greatest clinical use are fiber density (FD) and neuromuscular jitter. FD reflects the local organization of muscle fibers within the motor unit; jitter reflects the safety factor of neuromuscular transmission at individual neuromuscular junctions. SFEMG can be of great value in demonstrating or excluding abnormalities in mild or questionable disease of nerve, muscle, or the neuromuscular junction. The neuromuscular jitter may be measured during nerve stimulation, which is particularly useful in uncooperative patients or when it is desirable to control the firing rate precisely, or during voluntary muscle activation, which is less subject to technical artifact. The SFEMG findings may not be specific to a particular disease, but they frequently increase understanding of the disease process by demonstrating abnormal neuromuscular transmission or rearrangement of muscle fibers within the motor unit, which complements information from more conventional EMG examinations.

We performed single fiber electromyography (SFEMG) in the superior rectus and levator palpebralis (SR-LP) muscles of 17 patients with pure ocular myasthenia gravis (MG) and 9 controls. Thirteen patients were also assessed with SFEMG in the orbicularis oculi (OO) muscle. All the MG patients but none of the control subjects showed abnormal SFEMG jitter in the SR-LP muscles. On the other hand, only 62% of the MG patients had abnormal SFEMG jitter in the OO muscle. The procedure was well tolerated by the patients, and complications were minor. We conclude that SFEMG of the SR-LP muscles is a safe and highly sensitive technique for the diagnosis of ocular MG.

Consecutive patients (n = 114), who had single fiber electromyography of the frontalis muscles for symptoms suggestive of ocular myasthenia gravis, were followed up for a mean of 14 months (3-64 mos). At follow up, based on strict criteria, 23 patients were classified as having ocular myasthenia gravis, 8 patients were diagnosed as having mitochondrial myopathy or oculopharyngeal dystrophy, 18 patients were found to have other diseases and 65 patients remained without a definite diagnosis. The single fiber electromyography data of these patients were then reviewed. The patients with ocular myasthenia gravis had, on average, more than 7/20 single fiber pairs with jitter > 45 microseconds and mean jitter of 56 microseconds. The 8 patients with mitochondrial myopathy or oculopharyngeal dystrophy had an average of 5/20 single fiber pairs with jitter > 45 microseconds and a mean jitter of 52 microseconds and could not be separated from the group with ocular myasthenia gravis on the basis of the single fiber electromyography results. The 18 patients with definite other diagnosis had an average of less than 1/20 single fiber pair with jitter > 45 microseconds and a mean jitter of 25 microseconds. This group could be clearly separated from the group with ocular myasthenia gravis. We conclude that single fiber electromyelography is useful in the separation of ocular myasthenia gravis from other causes of oculomotor weakness except mitochondrial myopathy and oculopharyngeal dystrophy.

Electrodiagnostic studies are valuable in confirming the diagnosis of a disorder of neuromuscular transmission. They are used to distinguish presynaptic and postsynaptic abnormalities. These studies provide an objective measure of the severity of the illness and may be useful in assessing the response to therapy. This article reviews the electrodiagnostic techniques that are commonly used today and highlights their specificity, sensitivity, and pitfalls.

We performed RNS and SFEMG studies of the same muscle in 46 patients with myasthenia gravis. Maximum decrement to 3-5-Hz stimulation before and after maximum voluntary exercise, percentage of action potential pairs with increased jitter and blocking, and mean MCD in each study were compared. A significant decrement (> 10% decrease in CMAP area or amplitude between the first and fourth response) was never found without increased jitter and impulse blocking on SFEMG. Increased jitter, blocking, and mean MCD were each correlated with maximum decrement (r > 0.61, P < 0.0001). We conclude that decrement to RNS and impulse blocking on SFEMG result from the same physiologic phenomenon, and that SFEMG is more sensitive at detecting disordered neuromuscular transmission given its ability to detect impulse blocking at levels below the resolution of RNS and increased neuromuscular jitter when there is not blocking.

Quantitative electromyography, comprising manual motor unit potential analysis at weak effort and turns/amplitude analysis at 30% of maximum force were performed in the brachial biceps muscle of 17 patients with myasthenia gravis (MG). Findings simulating myopathic and less often neurogenic changes were observed in seven out of 17 patients, suggesting that the myasthenic muscle may have random block of muscle fibres, functional block of the main part or whole motor units or a changed recruitment pattern. In addition, turns/amplitude analysis was performed at low force levels (10% of maximum force) both before and after a provocative manoeuvre consisting of a maximum effort sustained for 1 min, and at maximum force at the beginning and at the end of the provocation itself. Turns/amplitude analysis at low force failed to differentiate MG patients from controls. The relative change of ratio of turns to mean amplitude calculated from 10% to maximum force (at the beginning of the provocative manoeuvre) was increased in seven out of eight patients compared to the controls. This last finding seems to be useful in differentiating MG patients from patients with myopathy.

We report the use of single fiber electromyography (SFEMG) to demonstrate changes in the physiologic abnormality of myasthenia gravis (MG) during pregnancy. A 23-year-old became pregnant 15 months after the onset of mild ocular weakness. On initial evaluation, SFEMG jitter measurements demonstrated a slight abnormality of neuromuscular transmission. There was no change in severity of clinical disease or jitter measurements until the third trimester, when she improved. Jitter measurements at that time were normal. Labor was normal and she delivered a normal male. Three days postpartum, myasthenic weakness recurred temporarily and jitter measurements showed worsening. At 16 days and 6 weeks postpartum, she had only minimal medial rectus weakness and jitter studies were normal. Three months postpartum, ocular symptoms recurred and jitter measurements were slightly abnormal. She continued to worsen, developing limb muscle and severe ocular muscle weakness at 4 months postpartum. She was treated with plasma exchange and thymectomy. Prednisone was added 2 months after thymectomy due to continued worsening and development of oropharyngeal weakness. Three years postpartum she was taking prednisone 10 mg every other day and had only slight weakness of neck flexors, and jitter studies were again normal.

Most infants whose mothers have myasthenia gravis are healthy at birth, but 10% to 15% have a transient neonatal form of myasthenia gravis. In this study, the muscular function and neuromuscular transmission were examined in 31 children, aged 3 months to 31 years (median, 10 years), of 15 myasthenic mothers. Eleven of these children had had the neonatal form of myasthenia gravis. The children were examined clinically and with neurophysiologic methods. Blood samples were taken for HLA typing, creatine kinase levels, and myoglobin and acetylcholine receptor antibody studies. Twenty-nine of the 31 children had no signs of neuromuscular disease. Two children (who had had neonatal myasthenia gravis) had a moderate stationary myopathy, probably unrelated to the myasthenia gravis of their mother. Creatine kinase levels were normal for all subjects. Acetylcholine receptor antibody levels were similar to those of a control population. The HLA type B8 antigen was not significantly more prevalent in the children who had had neonatal myasthenia gravis than in the healthy children. Neonatal myasthenia gravis in a previous sibling was the only factor in the material that predicted the occurrence of myasthenic symptoms in the neonatal period.

A 12-month-old girl with ocular myasthenia gravis was reported. Electromyograms (EMG) of the orbicularis oculi muscle were studied during a period of 16 months. The degree of the waning phenomenon on EMG correlated well with that of her clinical symptoms. The study of post-tetanic exhaustion after repetitive electrical stimulation at 20 Hz for 4 seconds, was the most sensitive technique in the evaluation of the function of neuromuscular junction. EMG showed the waning phenomenon in the initial worsening after a high dose methylprednisolone therapy, and at the symptom-free stage without medication after the steroid therapy. In our patient, orbicularis oculi EMG was useful in the estimation of the severity of ocular myasthenia gravis and the effect of its treatment.

We performed repetitive nerve stimulation on 38 adult patients with generalised myasthenia to compare the relative diagnostic yield from deltoid and trapezius. The decrement was consistently greater in deltoid, both before and after maximum voluntary contraction. In 12 patients the test was negative in trapezius but diagnostic in deltoid, whereas the converse occurred in only one. The yield from facial muscles was comparable to that from trapezius while that from hand muscles was very low. Post-tetanic exhaustion often enhanced the decrement but the use of stimulus frequencies greater than 2-3 Hz did not. We conclude that deltoid provides the highest diagnostic yield in myasthenia when doing decremental studies.

Single fibre electromyography (SFEMG) has been used to study neuromuscular transmission and the degree of reinnervation in patients with myasthenia gravis (MG) (n = 70); Lambert-Eaton syndrome (n = 3); myopathies (n = 8); motor neuron disease (n = 4) and peripheral neuropathies (n = 3) (Table 1). An automatic method was used to calculate neuromuscular jitter by means of a PC computer, a TECA TD 20 electromyograph and a jittermeter. Twenty pairs of potentials were selected from the extensor digitorum communis muscle for analysis using a trigger unit and a delay line. Mean jitter and percentage of pairs with normal and abnormal jitter were calculated (Figs. 1 and 2). MG patients showed pairs with normal (Fig. 3) and other with abnormal jitter and intermittent blocking (Fig. 4). Abnormalities were found in 72% of patients with ocular MG, in 95% with mild generalized MG, in 93% with moderate generalized MG and in 100% of severe MG cases (Table 2), (Fig. 5). There was a significant correlation between patient disability and jitter values (Fig. 6). The method was useful for the follow-up during immunosuppressant treatment (Fig. 7). Patients with other myopathies showed normal or mildly increased jitter and increased fibre density. The most common abnormality in patients with neurogenic conditions was increased fibre density, which ranged from 2.1 to 4.3 (Figs. 8 and 9). The method used showed high sensitivity for the detection of neuromuscular transmission defects. In some cases an abnormal jitter was found even before the appearance of transmission block and therefore it was possible to find abnormalities in clinically normal muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

We studied juvenile ocular myasthenia gravis (MG) with special reference to evoked EMG in orbicularis oculi muscle. The subjects consisted of 5 cases aged 1-4 years and 3 cases over 10 years. Young children were examined during drug-induced sleep. Stimulation was delivered to preauricular facial nerve, and M waves were recorded from ipsilateral orbicularis oculi muscle. Examinations were also carried out in thenar or hypothenar muscles by stimulating the median or ulnar nerves respectively. On Harvey-Masland test, 6 out of 8 cases showed waning of more than 10%. On M-wave recovery cycle, 3 out of 6 cases examined showed decrement during stimulation interval of 100 msec to 500 msec. In 2 of these, the peak of recovery cycle curve rose over 100% during stimulation interval of 30 to 60 msec on a usual dose treatment of anti-cholinesterase, while on prednisolone treatment this peak did not increase over 100% and the pattern of recovery cycle changed to almost normal. On post-tetanic cycle study, only 1 out of 4 cases examined showed post-tetanic facilitation and exhaustion. The response of the belly-tendon in the hand showed no abnormality. Although there still remains technical difficulty in the examination of evoked EMG in orbicularis oculi muscle, this examination is very useful in diagnosis, evaluation and understanding of pathophysiology of MG.