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INTRODUCTION In this study we aimed to investigate the dispersion of mean consecutive difference (MCD) of concentric needle jitter studies of patients with myasthenia gravis (MG) and its effect on diagnostic sensitivity for MG. METHODS One hundred fifty-three patients, including 76 patients with MG and 77 controls with possible MG who later received another diagnosis, underwent stimulated concentric needle jitter studies of the frontalis muscle. MCD mean, standard deviation (SD), and coefficient of variation (CV) were calculated. Diagnostic sensitivity and specificity were determined using receiver operating characteristic (ROC) analyses. RESULTS MG patients showed a significantly greater MCD mean (MG: control, 26.3 μs; 13.5 μs [median]; P

Introduction: Our aim in this study was to provide an updated literature review of electrodiagnostic testing in myasthenia gravis and Lambert–Eaton myasthenic syndrome. Methods: A systematic review of the recent literature was performed using the following key words: myasthenia gravis (MG); Lambert–Eaton myasthenic syndrome (LEMS); electromyography (EMG); repetitive nerve stimulation (RNS); single-fiber electromyography (SFEMG); nerve conduction study; and normative values. Results: Several articles supported testing of facial, bulbar, and respiratory muscles in the diagnosis of neuromuscular junction (NMJ) disorders, including muscle-specific kinase antibody (MuSK)-seropositive MG. Several articles supported use of concentric needle EMG as an alternative to SFEMG jitter in disorders of neuromuscular transmission. A limited number of articles addressed measurement of area (vs. amplitude) decrement in RNS and decreasing the threshold of post-exercise facilitation. Conclusions: Electrodiagnostic testing continues to be useful for diagnosis of MG and LEMS, although the quality of the evidence is not great. This literature review summarizes RNS and jitter measurement of facial and respiratory muscles and use of concentric needle EMG for SFEMG. Muscle Nerve 52:455–462, 2015

INTRODUCTION Our objective was to compare the effect of different low-frequency filters on jitter parameters when stimulating the orbicularis oculi. METHODS Ten healthy volunteers were studied. Jitter was expressed as the mean consecutive difference (MCD). The low filter settings compared were 1, 2, and 3 kHz. RESULTS No significant difference in mean MCD or outliers was found with the different filter settings. No significant difference in mean MCD was seen when the number of potentials analyzed was reduced. CONCLUSION Different low-frequency settings do not influence the mean MCD when using a peak detection system. Muscle Nerve 54: 317-319, 2016.

The purpose of this study was to perform a careful neurophysiological examination to identify subclinical signs of botulinum toxin spread distant to the injection site following intragastric injection for obesity treatment. Single-fiber electromyography of extensor digitorum communis and repetitive stimulation of abductor digiti minimi were performed before and 8 days after multiple intragastric injections of botulinum toxin A (Botox, 200 U per patient) or placebo. The study was performed in a randomized double-blind fashion. No patient in either group displayed results indicative of neuromuscular dysfunction either before or after the treatment. No significant change in muscle jitter was observed when comparing baseline with the after-treatment evaluation in either group, and no significant differences between groups were observed. After intragastric botulinum toxin injection no subclinical sign of distant spread was observed.

The aim of this study was to estimate normal jitter in voluntarily activated extensor digitorum communis (EDC) and orbicularis oculi (OOc) muscles using a disposable concentric needle electrode (CNE). The EDC of 67 normal subjects (22 males and 45 females, mean age 35.5 +/- 10.2 years) and the OOc of 50 normal subjects (13 males and 37 females, mean age 37.9 +/- 9.6 years) were studied. Jitter values were expressed as the mean consecutive difference (MCD) of 20 potential pairs. The mean MCD for EDC was 23.6 +/- 3.1 micros (upper 95% confidence limit [CL]: 29.7 micros). The mean MCD of all potential pairs (n = 1340) was 23.5 +/- 7.3 micros (95% CL: 38.2 micros). The mean MCD for the 18th highest value was 31.4 +/- 4.9 micros (95% CL: 41.2 micros). The mean MCD for OOc was 24.7 +/- 3.1 micros (95% CL: 31.0 micros). The mean MCD of all potential pairs (n = 1000) was 24.7 +/- 7.1 micros (95% CL: 39.0 micros). The mean MCD for the 18th highest value was 32.7 +/- 4.1 micros (95% CL: 40.9 micros). Our reported CNE jitter values obtained during voluntary activation represent the largest series currently available. The suggested practical limit in the EDC for mean MCD was 30 mus and for outliers was 42 micros, and in the OOc for mean MCD was 31 micros and 41 micros for outliers. The present study confirms that CNE can be used to assess jitter values, although certain precautions must be taken.

We report a patient with muscle-specific tyrosine kinase (MuSK) antibody-positive myasthenia gravis who experienced worsening of myasthenic weakness associated with alterations in estrogen and progesterone levels during the administration of oral contraceptive therapy. Single-fiber electromyography was performed to document changes in neuromuscular transmission associated with the clinical exacerbation and subsequent resolution of the menstrual exacerbation and clinical improvement experienced with continuous monophasic oral contraceptive therapy. The potential long-term benefit of ovulatory suppression in MuSK antibody-positive myasthenia gravis is discussed.

The goal of this study was to estimate the accuracy of concentric-needle single-fiber electromyography (CN-SFEMG) for the diagnosis of myasthenia gravis (MG). A consecutive series of patients referred for CN-SFEMG was evaluated by an investigator blinded to the results of CN-SFEMG in order to determine the presence or absence of MG using an independent reference standard. Sensitivity, specificity, predictive values, and likelihood ratios were calculated. The study population included 51 patients (21 with MG). CN-SFEMG was normal in 34 patients (67%) and abnormal in 17 (33%). The sensitivity of CN-SFEMG for the diagnosis of MG was 0.67 and the specificity was 0.96. The positive likelihood ratio was 16.8 and the negative likelihood ratio was 0.34. The positive and negative predictive values were 0.93 and 0.76, respectively. These results indicate that CN-SFEMG showing abnormal jiggle is extremely useful for confirming the diagnosis of MG, but that CN-SFEMG showing normal jiggle has limited utility in excluding the diagnosis.

Stimulated single-fiber electromyography (SSF-EMG) is useful to assess neuromuscular junction (NMJ) abnormalities in children. Conventionally mean consecutive difference (MCD) analysis measures the jitter for each muscle-fiber potential. We present a new algorithm that analyzes the entire SSF-EMG waveform. Cross-correlational coefficients (between 0-1.0) are calculated for consecutive pairs of 100 SSF-EMG waveforms obtained at each needle position in orbicularis oculi, and averaged. A lower normal limit (0.722, mean -3 SD) was established from 123 SSF-EMG samples in 10 adult control subjects, and applied to SSF-EMG data from 23 children referred for a suspected myasthenic syndrome. Results were compared with MCD analysis and related to the final clinical diagnosis. Our results showed that compared with conventional MCD measurement, the new algorithm had better specificity (87% vs. 53%) but similar sensitivity (88% for both). These findings indicate that the cross-correlational method is a useful predictor of NMJ dysfunction in children.

Introduction Cervical spondylosis (CS) is a common disease in adults and may coexist with amyotrophic lateral sclerosis (ALS). It is important to detect ALS coexisting with CS (ALS-cs) at an early stage, especially when surgical treatment of CS is planned. Methods Single-fiber electromyography was performed in 26 patients with ALS, 19 with ALS-cs, and 22 with CS. Results Mean jitter, percentage of jitter >55 μs, and percentage of impulse blocking were not statistically different between ALS and ALS-cs cases, but they were significantly lower in CS. Mean fiber density was not statistically different among the 3 groups. The percentage of pairs with jitter >55 μs exceeding 40% and mean jitter exceeding 55 μs had high sensitivity and specificity in the diagnosis of ALS. Conclusions Single-fiber electromyography can supply valuable information in helping to differentiate ALS from CS. Muscle Nerve, 2013

Normative data for jitter parameters using a disposable concentric needle have been presented in a few studies. Jitter, expressed as the mean consecutive difference (MCD), was measured in the frontalis muscle in 20 subjects by percutaneous bar stimulation of the temporal nerve branch. The mean MCD for individual studies (20) and for all potentials (600) were 16.05 +/- 2.73 mu s and 16.05 +/- 5.96 mu s, respectively. The suggested limit for mean MCD is 22 mu s and for outliers is 28 mu s.

Stimulated single-fiber electromyography (SSFEMG) is a valuable diagnostic tool in cases of myasthenia gravis with limited disease. From 1990 to 2008 SSFEMG in the orbicularis oculi muscle (OO) was performed in a cohort of 456 patients referred with clinical suspicion of myasthenia gravis (MG) and exclusively ocular symptoms. A diagnosis of MG was made on clinical grounds in 103 patients. In this patient cohort, the specificity of SSFEMG for myasthenia was 97%, and the sensitivity was 80%. MG patients with a normal SSFEMG had a benign clinical course. This study confirms a high specificity and sensitivity of SSFEMG when it is performed on patients suspected to have ocular MG. In such patients, a normal SSFEMG of the OO predicts a benign clinical course.

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 μs (average, 14.7 ± 2.8 μs) and mean MCD of individual MPs was 14.6 ± 6.8 μs. All the OM patients showed abnormal SFEMG-AS jitter before prostigmine was administered (mean MCD: 49.19 ± 21.82 μs, 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 μs (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. © 2000 John Wiley & Sons, Inc. Muscle Nerve 23: 779–783, 2000

Motor units (MUs) are recruited according to the size principle. At low force output, macro-motor unit potentials (macro-MUPs) with small amplitude and area are recorded; MUs with large electrical size fire at high force output. Our objective was to elucidate whether this difference is caused by a higher fiber density (FD) of the MUs recruited at high force output. We measured the FD and respectively the amplitude and the area of the macro-MUPs via single-fiber macro electromyography (EMG) recorded at low and high force output in 48 healthy subjects. The macro-MUPs were significantly larger at high force output than at low force. The FD did not differ at the two force levels. Our findings suggest that the larger electrical size of the high recruitment threshold MUs is due not to a higher FD, but to a larger territory. FD is a robust EMG parameter, independent of the level of the force output.

Extraocular muscle weakness is the most common presenting sign of myasthenia gravis (MG). More than half of patients presenting with symptoms isolated to these muscles (OMG) develop generalized myasthenia gravis (GMG) over the course of their illness. No clinical, laboratory, or electrophysiological features are recognized that identify these high-risk patients. We have therefore assessed the ability of single-fiber electromyography (SFEMG) to predict the development of GMG in patients presenting with OMG. Thirty-nine consecutive patients presenting with OMG underwent SFEMG of the extensor digitorum communis muscle as well as a battery of other laboratory and imaging studies at the time of diagnosis. All patients were followed prospectively for a minimum of 24 months or until they developed GMG. Two patients were excluded, leaving 37 for assessment. Twenty remained with pure OMG for the entire follow-up period (mean, 55 months). Twenty-six of the 37 had abnormal SFEMG studies at presentation. Eleven of these remained with OMG and 15 developed GMG. Fifty-eight percent of patients with an abnormal SFEMG developed GMG, whereas 82% of those with a normal study remained with OMG. Thus, a normal SFEMG was associated with MG remaining restricted to the extraocular muscles. (P = 0.036, Fisher's exact test), but an abnormal SFEMG was not predictive of subsequent development of GMG.

The ability to detect muscle fiber action potential (MFAP) contributions to motor unit action potentials (MUAPs) measured using single fiber (SF) and concentric needle (CN) electrodes was studied using simulated MUAPs. Various MFAP-acceleration thresholds were used to define significant fiber contributions. Attempts to detect the significant MFAP contributions, by locating peaks in filtered MUAPs or MUAP accelerations using various MUAP-based thresholds, were then made. Considering filtered MUAPs and a significant contribution threshold of 7.5 kV/s 2 , and using fiber-density peak-detection criteria, at best 46% and 50% of significant MFAP contributions were detected for the SF and CN MUAPs, respectively. Considering MUAP accelerations and a significant contribution threshold of 7.5 kV/s 2 , 80% and 84% of significant MFAP contributions could be detected, respectively. Most significant contributions were created from fibers located within approximately 350 μm of the electrode. The results suggest that significant peaks, defined using MUAP-based thresholds, within the acceleration of CN MUAPs can strongly correspond to individual fiber activity and may be useful for measuring fiber density and neuromuscular jitter.

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. © 1995 John Wiley & Sons, Inc. . ophthalmoparesis MUSCLE & NERVE 18 :943-9471995

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

The author recounts the lessons taught by single-fiber electromyography that reached him through the medium of low-frequency attenuation and a small concentric needle electrode. He concludes that it is difficult to imagine practicing electromyography today without the benefits that have flowed from the work of Erik Stålberg and his colleagues.

Neuromuscular jitter was determined in the extensor digitorum communis (EDC) of 41 healthy control subjects and 8 patients with myasthenia gravis (MG). Standard single-fiber electromyographic (SFEMG) techniques were used, except that a monopolar electrode (MPE) was substituted for a single-fiber electrode (SFE). In normals, mean jitter for 20 pairs was 22.4 +/- 2.8 microseconds and the mean jitter for an individual pair was 22 +/- 5.6 microseconds. In the age range tested (18 to 49 years), jitter did not change with increasing age. When MPE jitter studies were repeated in 16 normals, mean jitter usually varied by less than 10% (mean 7.4% +/- 6.2%) and remained normal. Jitter was significantly increased in MG compared to normals 73 +/- 56 microseconds versus 22 +/- 5.6 microseconds (F = 149.4, P less than 0.0001). Using an analog pain scale, the discomfort during electromyography using MPE and SFE was compared between the left and right arms in 35 normals. MPEs caused less discomfort than SFEs (P = 0.0031), and were preferred (71% versus 20%) to SFEs (chi 2 = 9.21, P = 0.01). Based on these results, we conclude that MPE determined jitter studies are reproducible, can distinguish between normals and MG, and are associated with less discomfort than SFE.

Single fiber electromyography (SFEMG) measurements of fiber density and jitter are used in the diagnosis of a variety of peripheral nervous system disorders. However, the normal values of these measurements for most muscles and age groups are not well documented in the literature. We present a retrospective and prospective multicenter collection of SFEMG jitter and fiber density data from control subjects obtained for the purpose of defining reference values for many muscles and different ages. The data and calculated upper limits for fiber density, individual pair jitter, and mean jitter are presented for each muscle in tabular and graphical format, for different age groups.

Stimulation single-fiber electromyography (S-SFEMG) is an alternative method to SFEMG during voluntary contraction (VC-SFEMG). S-SFEMG is preferred to VC-SFEMG in uncooperating patients, children, and patients having severe weakness. Surface stimulation is a viable alternative to needle stimulation in S-SFEMG. In the present study, surface versus needle stimulation of facial nerve has been tested by recording from the orbicularis oculi and frontalis muscles. Jitter values obtained by both methods have been found to be nearly equal.

Changes of the terminal innervation pattern in polymyositis were studied in nine patients using single fiber electromyography (SFEMG) and histochemical investigations of muscle biopsies. In all patients, and in 16 out of 18 muscles studied, reinnervation was found. The preceding denervation could be caused either by segmental necrosis of the muscle fiber that disconnects one part of the fiber from the end-plate region or by direct intramuscular nerve involvement.

Single fiber electromyography ( SFEMG ) of the extensor digitorum communis (EDC) muscle and nerve conduction studies were performed on healthy, active elderly men (66-77 years old) to assess age-related changes in neuromuscular physiology and the effect of long-term increased muscular activity on these changes. The following two groups were studied: a control group and a group composed of men with occupationally greater usage of hand extensors. Fiber density and mean jitter were essentially the same in both groups; however, in the hand-user group there was greater variability in mean jitter and a significant increase in the prevalence of potential pairs with increased jitter or blocking. In both groups, slower nerve conduction velocities and lower amplitudes of sensory and motor evoked potentials tended to correlate with increased jitter and fiber density. These electrophysiological changes in healthy aged men are consistent with an extremely mild process of nerve terminal denervation and reinnervation. Although long-term increased synaptic activity did not greatly alter the rate or extent of this process, it did produce a higher incidence of abnormal potential pairs and greater variability in mean jitter.

The double-step technique of repetitive nerve stimulation was compared with repetitive nerve stimulation to a distal and a proximal muscle and with single fiber needle electromyography in 10 patients with myasthenia gravis. We conclude that the double-step technique is slightly more sensitive than repetitive nerve stimulation to a proximal muscle but only 60% as sensitive as single fiber electromyography in demonstrating abnormal neuromuscular transmission in myasthenia gravis.

A new EMG recording technique called macro EMG is described. The recording electrode is the cannula of the modified single fiber electromyography (SFEMG) electrode. By means of spike triggered averaging, the contribution from all muscle fibers in a motor unit is extracted. The resulting signal reflects the number and size of muscle fibers in one motor unit. This paper presents the details of the technique, the neurophysiological basis for generation of the macro EMG signal, and the typical findings in normal and diseased muscles. Finally, examples are given of the additional information that can be obtained by combining investigations with SFEMG, conventional EMG, and macro EMG in the same muscles.

Nineteen patients with chronic renal failure receiving intermittent hemodialysis had single fiber electromyography studies of their extensor digitorum communis muscles. Jitter values were abnormal, more so in men than in women. The jitter abnormalities tended to improve after intermittent hemodialysis treatments lasting longer than 1 year.

The case of a 7-year-old girl, the only descendant of non-con-sanguineous parents, who presented typical features of the Schwartz-Jampel syndrome and electrophysiological evidence of bilateral carpal tunnel is reported. Conventional electromyogram (EMG) showed persistent and continuous electrical activity and high frequency discharges elicited spontaneously by movement of the needle or after voluntary activation. Electrical silence after phenytoin therapy was sometimes seen. Single fiber electromyography (SFEMG) showed that high frequency discharges had a complex configuration and multiple components. Occasionally the discharges showed a progressive decrease in amplitude. Increased jitter was also found in some potential pairs that had been isolated under voluntary contraction after phenytion therapy. Motor and sensory conduction velocities on the median nerve were slowed bilaterally across the carpal tunnel. Bilateral carpal tunnel syndrome is an unusual condition in children and its clinical picture differs from that in adults. Carpal tunnel syndrome was not clinically suspected in the patient reported in this article and the diagnosis was confirmed by the conduction velocity study.