Single fiber EMG and repetitive stimulation of the same muscle in myasthenia gravis

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. © 1994 John Wiley & Sons, Inc.     

Single‐fiber EMG with concentric electrodes in lambert‐eaton myasthenia

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     

Dysfunction at the motor end-plate and axon membrane in Guillain-Barré syndrome: a single-fiber EMG study

In nine patients with Guillain-Barré syndrome (GBS), stimulation single-fiber electromyography (SFEMG) and serological studies were performed in the acute stage of the illness. Increased jitter and intermittent blocking of muscle fiber action potentials occurred to a varying degree in all patients. Five patients had elevated titers of antiganglioside antibodies. The most remarkable EMG phenomenon was the occurrence in all patients of impulse blocking at normal or slightly increased jitter. The assumption that this phenomenon was due to an axolemmal dysfunction was confirmed by the occurrence in two patients of concomitant blocking of two muscle fiber action potentials at strictly normal jitter values. In one patient this sign of axonal dysfunction was demonstrated with SFEMG at voluntary activation. In another patient, concomitant blocking was associated with greatly increased but completely independent jitter of both components. The results of this study show that both a disorder of neuromuscular transmission and an axolemmal dysfunction play a role in the pathophysiology of GBS.     

Stimulated jitter in the masseter muscle: normative values

Nineteen healthy volunteers (median age, 25; range, 18-51 years) were enrolled in a study to obtain normative values for stimulated jitter in the masseter muscle. Axonal microstimulation was performed via a monopolar needle electrode introduced in the masseter 2-2.5 cm above the mandibular angle on the line connecting it with the lateral canthus. The recording single-fiber electromyography (SFEMG) electrode was inserted anteriorly in the twitching area of the muscle. The mean consecutive difference (MCD) values for the 426 endplates studied followed a distribution skewed to the left, with a minimum value of 4.3 micros, maximal 44.7 micros, and a maximum of distribution at 11 micros. Mean pooled MCD measured 16.0 micros, and the mean of mean MCD per study was 13.6 micros. The value of the 95th upper percentile for an individual fiber was 29.3 micros. We suggest an upper normal limit for mean MCD per study of 21 micros and upper normal limit of MCD for individual fibers of 30 micros. The stimulated jitter study of masseter muscle is easy and reliable.     

Concentric needle jitter on voluntary activated frontalis in 20 healthy subjects

Introduction: Normative data for jitter parameters using a disposable concentric needle have been described in a few studies. Methods: Jitter, expressed as the mean consecutive difference (MCD), was measured in the frontalis muscle in 20 subjects by voluntary contraction. Results: Mean MCD for individual studies (20, Gaussian), all potentials (400, non‐Gaussian), and 18th highest value (20, Gaussian) were 19.9 ± 2.9 μs, 19.9 ± 6.6 μs, and 26.9 ± 4.4 μs, respectively. Conclusion: The suggested upper normal limit for mean MCD is 26 μs and for outliers is 36 μs. Muscle Nerve 47:440‐442, 2013     

Single‐fiber EMG and clinical correlation in Lambert‐Eaton myasthenic syndrome

Objectives: We analyzed 82 single‐fiber EMG (SFEMG) tests in the extensor digitorum communis muscle in 30 Lambert‐Eaton myasthenic syndrome (LEMS) patients to study the relationship between electrodiagnostic findings and clinical severity. Methods: The repetitive nerve stimulation test was performed in the abductor digiti quinti and flexor carpi ulnaris muscles. SFEMG was performed in the extensor digitorum communis muscle using the conventional method. Results: Fiber density was normal in all patients. Jitter was abnormal in all patients at the first evaluation regardless of clinical severity. The jitter was increasingly abnormal with worsening disease severity. Mean MCD correlated well with clinical and electrophysiological severity. In 5 potential pairs in 3 patients, MCD analysis in relation to firing rate showed improvement with increasing firing rates, which is consistent with presynaptic neuromuscular transmission disorders. Conclusions: In all LEMS studies, SFEMG was abnormal on the first evaluation. The mean MCD correlated well with clinical and electrophysiological disease severity on the repetitive nerve stimulation test. Muscle Nerve 47: 664–667, 2013     

Single-fiber electromyography in sporadic inclusion body myopathy.

OBJECTIVE: To report the SFEMG findings in sporadic inclusion body myopathy (S-IBM). METHODS: We have analyzed the SFEMG data in 25 patients (mean age: 63; 16 males) with S-IBM which was diagnosed by the presence of classical rimmed vacuoles in the muscle biopsy together with clinical, laboratory, and electrophysiological findings. RESULTS: All patients had fibrillations, positive sharp waves, and small-amplitude short-duration motor unit potentials (MUPs) in the needle EMG. High-amplitude MUPs were observed in eight (32%) patients, two of whom had long-duration MUPs. SFEMG was abnormal in 17 (68%) cases: mean "mean consecutive difference (MCD)" was increased beyond the age-adjusted normal limit in 16 cases, and more than 10% of potential pairs (PP) had MCD longer than the upper normal limit of an individual MCD in one case. Mean fiber density (FD) was 2.16, with maximum FD being 4.15. Increased FD was noted in 11 (44%) cases. In four cases, more than 10% of PP had blocking, but there was no neurogenic blocking in any PP. As expected, MCD increased linearly (r=0.85) with the percentage of PP beyond the normal upper limit. CONCLUSIONS: The SFEMG findings in S-IBM are typical of the classical pattern of myopathy. SIGNIFICANCE: Our findings support the consensus that S-IBM is a myopathy.     

AAEM minimonograph #25: Single-fiber electromyography

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 diseases, 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. © 1996 American Association of Electrodiagnostic Medicine. Published by John Wiley & Sons, Inc.     

Single fiber electromyography of extraocular muscles: A sensitive method for the diagnosis of ocular myasthenia gravis

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.     

Jitter of the stimulated motor axon.

Electrical microstimulation of motor axons in conjunction with single fiber EMG (SFEMG) is increasingly used to measure the jitter of the motor endplates. This study examines the jitter of the stimulation site on the axon when stimulus strength is at threshold. In the absence of spurious blocking, this was found to be 5 microseconds on the average. With intermittent blocking, however, a mean additional jitter of 40 microseconds was obtained. The latter is considered to result from changing propagation velocity in the muscle fiber due to irregularity of activation rate. In clinical jitter studies, inadvertent threshold stimulation can result in significant error when associated with intermittent blocking.     

Stimulated single-fiber EMG of the frontalis and orbicularis oculi muscles in ocular myasthenia gravis

We performed single-fiber electromyography by axonal stimulation (stimulated SFEMG) of the frontalis and orbicularis oculi muscles of 20 patients with ocular myasthenia gravis (OM) and 46 controls. In controls, mean consecutive differences (MCD) ranged from 5 to 55 micros (average, 14.7 +/- 2.8 micros) in the frontalis and from 4 to 56 micros (average, 12.56 +/- 2.19 micros) in orbicularis oculi. The mean MCD of individual muscle potentials (MPs) was 14.6 +/- 6.8 micros in frontalis and 12.68 +/- 6.10 micros in orbicularis oculi. In the OM patients, the mean MCD was 43.85 +/- 25.18 micros in the frontalis and 69.85 +/- 29.55 micros in orbicularis oculi (P < 0.0001), and the number of MPs with altered MCD was 7.15 +/- 4.66 (range, 1-18) and 12.65 +/- 4.90 (range, 6-21), respectively (P < 0.0001). We conclude that stimulated SFEMG of the orbicularis oculi muscle is more sensitive for the diagnosis of OM than of the frontalis muscle.     

单纤维肌电图在肌萎缩侧索硬化和颈椎病鉴别诊断中的价值

目的 探讨单纤维肌电图(SFEMG)技术在肌萎缩侧索硬化(ALS)与神经根型和脊髓型颈椎病鉴别诊断中的价值.方法 对61例ALS伴有MRI颈椎病表现、59例ALS不伴MRI颈椎病表现、55例神经根型和脊髓型颈椎病患者进行伸指总肌SFEMG测定,分析不同组之间SFEMG改变的特点.结果 在3组患者中,平均颤抖(jitter)值分别为(81.2±25.9)、(91.6±32.4)、(40.9±11.8) μs,jitter>55 μs的百分比M50分别为73%、80%、5%,阻滞所占百分比M50分别为10%、20%、0,纤维密度分别为2.9±0.5、2.9±0.6、2.4±0.6.ALS伴和不伴MRI颈椎病变2组之间各参数比较差异无统计学意义.两组ALS患者合并后[平均jitter值(86.3±29.6)μs,jitter>55μs的百分比M50为80%,阻滞所占百分比M50为14%,纤维密度2.9±0.5]再与颈椎病组比较,各参数均明显高于颈椎病组(分别为t=14.49,Z=8.96、7.68,t=5.83,均P=0.000).在经随诊而确诊的18例ALS患者中,初诊时肌电图仅有1个节段的神经源性损害,在伸指总肌肌力和常规肌电图均正常情况下,有16例SFEMG可见纤维密度增高,13例jitter增宽,6例可见阻滞.结论 ALS伴或不伴MRI颈椎病变的SFEMG均表现为jitter明显增宽,可伴有阻滞,纤维密度增高,与神经根型和(或)脊髓型颈椎病患者明显不同.SFEMG测定有助于ALS与颈椎病的鉴别诊断.     

Single fiber EMG in a congenital myasthenic syndrome associated with facial malformations

Six patients with a newly described genetic syndrome in Iraqi and Iranian Jews of congenital myasthenia associated with facial malformations were studied with voluntary and stimulation single fiber EMG (SFEMG). Voluntary SFEMG revealed abnormal jitter in all patients in both extensor digitorum communis (EDC) and orbicularis oculi (OOC) muscles, though much smaller in the clinically unaffected EDC. SFEMG study of OOC muscle by axonal stimulation at rates from 1 to 48 Hz showed the most increased jitter at the highest stimulation frequencies in the majority of end-plates, one-third of which showed maximal jitter at intermediate rates. These results may suggest a postsynaptic abnormality as the underlying cause for the neuromuscular transmission defect, and demonstrate the usefulness of SFEMG in the diagnosis of congenital myasthenia. © 1993 John Wiley & Sons, Inc.     

Single fiber EMG as an outcome measure in myasthenia gravis: results from a double-blind, placebo-controlled trial.

In a placebo-controlled, therapeutic, pilot trial of mycophenolate mofetil (MM) in autoimmune myasthenia gravis (MG), the authors compared pretreatment and posttreatment single fiber electromyography (SFEMG) jitter measurements performed on the same muscle in a total of 11 patients. The mean jitter value decreased (improved) by an average of 15.4 micros in patients receiving MM (n = 6), compared to an increase (worsening) in mean jitter of 4.0 micros in patients receiving placebo (n = 5). This difference was statistically significant (P = 0.030). In most patients, the change in SFEMG measurements correlated with the change in clinical state as measured by quantitative testing of muscle function. The authors conclude that immunomodulation by MM improves neuromuscular junction function in MG and that SFEMG may be a useful marker of early response in future therapeutic trials in autoimmune MG.     

Stimulation SFEMG in myasthenia gravis

The diagnostic usefulness of single-fiber electromyography (SFEMG) in the diagnosis of neuromuscular transmission disorders is well established. Increased jitter is one of the earliest indications of abnormality. In patients with severe weakness, tremor, or altered consciousness, performance of the study is difficult because of the degree of cooperation needed. We studied five patients and eight normal subjects with voluntary and stimulation SFEMG techniques. Our results, in search of normal values and changes with pathology, revealed differences in the values of jitter and the percentage of abnormal fibers between both techniques. The mean consecutive difference (MCD) is smaller (on average 30% less), and the percentage of abnormal fibers is lower (on average 10% less) with the stimulation technique. These differences are largely explained by the jitter measurement of one endplate with the stimulation technique versus two endplates with the voluntary. They may also be related, however, to the difference in motor unit populations sampled with each technique.     

单纤维肌电图在肌萎缩侧索硬化鉴别诊断中的价值

目的 探讨单纤维肌电图(SFEMG)技术在肌萎缩侧索硬化(ALS)鉴别诊断中的价值.方法 对我院收治的165例ALS患者和145例下运动神经元受累为主的非ALS疾病患者进行伸指总肌SFEMG测定,并测定伸指总肌肌力,按照伸指总肌肌力进行分组,分析不同组之间SFEMG改变的特点.结果 伸指总肌肌力正常者,ALS和非ALS组的平均颤抖(jitter)值分别为(66.1±20.1)、(38.0±9.2)μs(t=9.05),jitter＞55μs的百分比中位数分别为55%、0(Z=-7.81),阻滞所占百分比中位数分别为6.7%、0(Z=-6.93),ALS组各参数均明显高于非ALS组(均P＜0.01).伸指总肌肌力医学研究委员会(MRC)评分≤4者,ALS和非ALS组平均jitter值分别为(93.5±31.2)、(52.8±25.9)μs(t=9.37),jitter＞55μs的百分比中位数分别为86%、20%(Z=-8.46),阻滞所占百分比中位数分别为20%、0(Z=-7.25),ALS组各参数均明显高于非ALS组(均P＜0.01).在MRC评分＞4者,采用平均jitter＞55μ s诊断ALS的敏感性和特异性分别为70.2%和92.7%.结论 当采用SFEMG测定协助ALS的诊断和鉴别时,应尽量选择肌力正常的肌肉.平均jitter、jitter＞55μs的百分比和阻滞在ALS与其他下运动神经元疾病的鉴别诊断中具有重要价值.     

Concentric needle jitter in stimulated frontalis in 20 healthy subjects

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 μs and 16.05 ± 5.96 μs, respectively. The suggested limit for mean MCD is 22 μs and for outliers is 28 μs.     

Subclinical impairment of neuromuscular transmission in transient global amnesia.

OBJECTIVE: To investigate the neuromuscular transmission (NMT) of the patients with transient global amnesia (TGA) using single fiber electromyography (SFEMG). BACKGROUND: The pathophysiology of TGA remains unknown and several elements support the hypothesis of a shared background with migraine. Recent studies showed that some migraineurs have subclinical abnormalities of NMT by using SFEMG. We aimed to test the patients with TGA using SFEMG. METHODS: We investigated 6 patients diagnosed with TGA according to published criteria and 5 healthy volunteers with similar ages. SFEMG during voluntary contraction of the extensor digitorum communis muscle, nerve conduction studies and concentric needle electromyography were performed and 20 single fiber potential pairs were recorded from each subject and individual and mean jitter values were calculated. RESULTS: Three patients with TGA showed pronounced NMT failure by SFEMG, whereas none of the controls disclosed this abnormality. The mean jitter value of TGA patients (35+/-33) was greater than that of the control subjects (25+/-15) (P=0.006). Seventeen of the 120 individual jitter values of the TGA group and only 3 (from 3 different volunteers) of the 100 individual jitter values of the control group exceeded upper normal limit (P=0.004). CONCLUSIONS: These results suggest that TGA shares the same type of subclinical abnormality of NMT observed in migraine patients in recent studies.     

单纤维肌电图对糖尿病周围神经病变的应用价值

目的探讨单纤维肌电图(SFEMG)对糖尿病周围神经病变(DPN)的应用价值。方法应用SFEMG检测129例DPN患者的优势侧指总伸肌颤抖(jitter)和纤维密度(FD),按常规方法行神经传导速度(NCS)检测。比较SFEMG和NCS的异常检出率,并分析jitter值与血糖化血红蛋白(HbA1C)和预后的关系。结果 SFEMG异常检出率(91.5%)显著高于NCS(78.3%)(P<0.01)。HbA1C轻度升高组SFEMG异常检出率(86.4%)显著高于NCS异常检出率(69.7%)(χ2=7.69,P<0.01),而HbA1C重度升高组差异无统计学意义。jitter值与HbA1C水平呈正相关(r=0.3132,P<0.05)。jitter值正常及轻度异常患者治疗有效率(82.3%)及治愈率(30.6%)均显著高于明显异常者(54.2%,11.9%)(χ2=11.02,P<0.01;χ2=6.32,P<0.05)。结论 SFEMG对DPN的诊断意义显著,并且可用于DPN的预后判断。     

Evaluation of neuromuscular transmission by using monopolar needle electrode

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.