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.     

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。     

Single fiber EMG in the frontalis muscle in ocular myasthenia: specificity and sensitivity.

Patients (n = 41) with isolated weakness of the eyelids or extraocular muscles, who had been referred for single fiber electromyography (SFEMG), were followed up after 4 to 24 months, At follow-up the patients were classified as "definite ocular myasthenia gravis" (MG), "definite other diagnosis," or "no definite diagnosis" on the basis of the completed investigations and subsequent course. The original SFEMG findings in the frontalis muscle were then reviewed. The specificity and sensitivity of SFEMG for "definite ocular MG" could be maximized by using as criteria for abnormality greater than 8/20 pairs with jitter greater than 45 microseconds, or a mean jitter of 20 pairs of greater than 50 microseconds. Patients with abnormal SFEMG according to these criteria have MG, and are likely to require treatment in the immediate future. Patients who have normal SFEMG according to these criteria (and no other demonstrated disorder) may have MG, but it is so mild that they are unlikely to require treatment. Two patients whose final diagnosis was progressive external ophthalmoplegia had normal SFEMG according to these criteria.     

Jitter of Corticospinal Neurons During Repetitive Transcranial Magnetic Stimulation. Method and Possible Clinical Implications

BackgroundRepetitive transcranial magnetic stimulation (rTMS) of the motor cortex activates corticospinal neurons mainly through the depolarization of cortico-cortical axons belonging to interneurons of superficial layers.ObjectiveWe used single-fiber electromyography (SFEMG) to estimate the “central jitter” of activation latency of interneural pools from one pulse of TMS to another.MethodsWe evaluated 10 healthy subjects and one patient with multiple sclerosis. By recording SFEMG evoked activity from the left first dorsal interosseous (FDI), we first used a standard repetitive electrical 3 Hz stimulation of the ulnar nerve at the wrist to calculate the mean consecutive difference from at least 10 different potentials. The same procedure was applied during 3 Hz repetitive TMS of the contralateral motor cortex. The corticospinal monosynaptic connection of the FDI and the selectivity of SFEMG recording physiologically justified the subtraction of the “peripheral jitter” from the whole cortico-muscular jitter, obtaining an estimation of the actual “central jitter.”ResultsAll subjects completed the study. The peripheral jitter was 28 μs ± 6 and the cortico-muscular jitter was 344 μs ± 97. The estimated central jitter was 343 ± 97 μs. In the patient the central jitter was 846 μs, a value more than twice the central jitter in healthy subjects.ConclusionCurrent results demonstrate that the evaluation of the central component of the cumulative cortico-muscular latency variability in healthy subjects is feasible with a minimally invasive approach. We present and discuss this methodology and provide a “proof of concept” of its potential clinical applicability in a patient with multiple sclerosis.     

RNS与SFEMG在检测ALS患者神经肌肉接头功能紊乱的比较研究

目的探讨重复神经电刺激(RNS)与单纤维肌电图(SFEMG)在检测肌萎缩侧索硬化(ALS)患者神经肌肉接头功能紊乱中的吻合率及RNS低频递减阳性率与SFEMG指标纤维密度(FD)、颤抖(jitter)、阻滞(block)的关系。方法收集2008-5—2009-4在北京协和医院神经科门诊或病房确诊或拟诊的ALS患者43例,同时行RNS及SFEMG检查。比较RNS与SFEMG在判断ALS患者神经肌肉接头紊乱的敏感性和特异性,并分析RNS低频递减与SFEMG参数指标jitter、block、FD的相关性。结果(1)43例患者中26例RNS(+),占60.5%,17例RNS(-),占39.5%。SFEMG(+)34例,占79.1%,SFEMG(-)9例,占20.9%。其中SFEMG(+)+RNS(+)者共25例,SFEMG(-)+RNS(-)者8例。RNS在判断ALS存在神经肌肉接头受累方面与SFEMG比较有一定的吻合性(Kappa=0.47,P0.01)。(2)RNS阴性和阳性组FD间比较无统计学差异(t=-0.1405,P0.05)。RNS阳性组Block程度明显高于RNS阴性组(χ~2=11.432,P0.01),jitter值也明显高于RNS阴性组(t=2.906,P0.01)。桡神经RNS波幅递减程度与jitter值呈正相关(r=0.626,P0.05)。结论 RNS与SFEMG比较有一定的吻合率。RNS检查灵敏度较高,具有操作简单,费用低,耗时短,无创,不需患者特殊配合,近远端肌肉均可操作,易于推广的特点,对ALS患者的辅助诊断具有意义。     

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.     

Electrophysiological studies in the post-viral fatigue syndrome.

Single fibre electromyography (SFEMG) was studied in 40 patients with the post-viral fatigue syndrome. These patients were also assessed clinically, serologically, virologically and immunologically. About 75% of the patients had definitely abnormal SFEMG results. This was regarded as evidence of abnormality in the peripheral part of the motor unit. The muscle fibre was the likely site of involvement.     

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.     

Chronic inflammatory demyelinating polyradiculoneuropathy associated with central nervous system involvement--as compared to multiple sclerosis

Chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) with central nervous system (CNS) demyelinating lesions has recently been reported to mimic multiple sclerosis (MS). In this paper, a series of patients with CIDP were examined to see if they had CNS involvement. CIDP patients with CNS lesions were then compared to patients with MS with peripheral nervous system (PNS) involvement for similarities. CNS and PNS involvement were detected by clinical symptoms, neurological findings, neuro-otological and neuro-ophthalmological tests, electrophysiological examinations such as electroencephalography, evoked potentials, blink reflex, conventional peripheral nerve conduction studies and electromyography, as well as computed tomography and magnetic resonance imaging (MRI). There were 7 of 17 CIDP patients with CNS involvement, but only 2 of 59 MS patients with PNS lesions were found. The rate of CIDP with CNS involvement (41.2%) was higher than that of MS with PNS lesions (3.4%). The CNS signs and symptoms of 7 CIDP patients were not so constant as their PNS symptoms, and consisted of 1 case with optic neuritis, 4 cases with cerebellar atxia and/or nystagmus, and 3 cases with spinal symptoms. These signs and symptoms are all well known in MS. Prolonged latencies on evoked potentials and high signal white matter lesions on T2 weighted MRI, indicating demyelinating CNS lesions were also similar to those found in MS. The CNS involvement in those patients with CIDP was therefore similar in character to those found in MS, but was far less severe than the PNS finding.(ABSTRACT TRUNCATED AT 250 WORDS)     

Anti-MuSK-positive myasthenia gravis: neuromuscular transmission failure in facial and limb muscles

The presence of antibodies against muscle-specific receptor tyrosine kinase (MuSK) appears to define a subgroup of patients with myasthenia gravis (MG) characterized by weakness predominant in bulbar, facial and neck muscles compared with anti-acetylcholine receptor (AChR) antibody-positive MG. To investigate the patterns and severity of neuromuscular transmission failure in different muscles in MuSK-positive MG, we performed single fiber electromyography (SFEMG) in the facial (frontalis) and limb (extensor digitorum communis, EDC) muscles in three anti-Musk-positive patients, and compared results with those of 11 anti-AChR-positive patients. Only one of the three MuSK-positive patients had abnormal jitter in EDC, but all the three showed clearly increased jitter in the frontalis. By contrast, the AChR-positive patients showed similarly abnormal jitter for the two muscles. These results suggest that when the diagnosis of anti-MuSK-positive MG is suspected, SFEMG should be performed in most prominently affected muscles.     

Application of futility analysis to refine jitter recordings in myasthenia gravis

Introduction: The current practice of single‐fiber electromyography (SFEMG) requires that 20 fiber pairs with normal jitter be collected to exclude myasthenia gravis (MG). We applied principles of futility analysis from clinical trials in an attempt to reduce that requirement. Methods: We utilized conditional power futility analysis to assess the probability of an abnormal 20‐pair SFEMG based on ongoing analysis of jitter as each pair is collected. Rules for early test termination in the presence of 0, 1, or 2 abnormal pairs were identified. These rules were then applied to previously collected SFEMG data. Results: SFEMG could be stopped at just 12 pairs if all are normal and at 17 pairs if 1 is abnormal. The rules successfully determined when SFEMG could be stopped in 104 of 106 (98%) studies originally reported to be normal. Conclusions: If the first 12 SFEMG pairs have normal jitter, the study can be terminated and interpreted as normal. Muscle Nerve, 2012     

Single-fiber electromyography,nerve conduction studies,and conventional electromyography in patients with critical-illness polyneuropathy: Evidence for a lesion of terminal motor axons

Nine patients at risk for critical illness polyneuropathy (CIP) were included in a prospective study. We performed nerve conduction studies, electromyography, and a stimulation single-fiber electromyography (SFEMG). Five of 9 patients were diagnosed as CIP because they developed abnormal spontaneous activity during the follow-up period. Their SFEMG revealed a significant increase in mean jitter (25%, P < 0.005). In 4 patients without abnormal spontaneous activity there was no significant increase in the mean jitter, although 1 of the latter 4 patients showed an increased jitter, indicating that abnormal SFEMG may precede abnormal spontaneous activity. Nerve conduction studies did not show any significant changes in both patient groups. Our findings suggest that CIP is a primarily axonal motor neuropathy. The increased jitter in patients with CIP indicates that CIP is a primarily axonal neuropathy with a lesion of terminal motor axons. © 1997 John Wiley & Sons, Inc. Muscle Nerve, 20, 696–701, 1997.     

Electrophysiological study of neuromuscular system involvement in mitochondrial cytopathy.

OBJECTIVES: To define the neuromuscular involvement in 'mitochondrial' patients with clinical evidence of a neuromuscular disorder, and to evaluate if the proposed electrophysiological protocol was suitable to reveal a subclinical neuropathy or myopathy in 'mitochondrial' patients with no clinical sign of a neuromuscular disturbance. METHODS: Quantitative concentric needle electromyography (CNEMG), single fiber electromyography (SFEMG) and nerve conduction studies (NCS) were performed in 33 patients with mitochondrial cytopathies. Lastly, we studied 9 clinically unaffected relatives. RESULTS: NCS were abnormal in 18% of patients, with CNEMG and SFEMG in 58% of cases, but there was not a complete overlapping of the positivity of the different techniques. No asymptomatic relatives showed abnormalities of the electrophysiological studies. CONCLUSIONS: Electrophysiological findings did not correlate with any specific biochemical or genetic defect, but were consistent with clinical diagnosis in almost all of the patients with clinical signs of myopathy and/or neuropathy. Increase of both SFEMG jitter and fiber density was significantly tied to a neuropathic process. CNEMG and SFEMG were altered in about 30% of subjects without clinical signs of myopathy or neuropathy and were therefore able to reveal a subclinical involvement of neuromuscular system in some patients who had external ophthalmoplegia or retinitis only.     

The effect of cholinesterase inhibitors of SFEMG in myasthenia gravis

We report four patients with myasthenia gravis (MG) in whom single-fiber electromyography (SFEMG) jitter measurements were normal in some muslces while they were taking pyridostigmine and became abnormal 2-14 days after the medication was discontinued. When the abnormality of neuromuscular transmission in MG is mild, cholinesterase inhibitors may mask the findings of increased jitter on SFEMG.     

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.     

AAEE minimonograph #25: Single-fiber electromyography in myasthenia gravis

Single-fiber electromyography (SFEMG) demonstrates abnormal jitter in virtually all (99%) patients with myasthenia gravis (MG). One muscle, the extensor digitorum communis, is abnormal in most patients with this disease, but to obtain the maximum diagnostic sensitivity, it may be necessary to examine other muscles, especially ones that are more involved clinically. There is no one muscle that will be more abnormal in every patient with MG. The muscle(s) to be tested must be selected based on the distribution of weakness in the individual patient. Abnormal jitter is also seen in diseases of nerve and muscle; these diseases must be excluded by other electrophysiologic and clinical examinations before diagnosing MG. If neuronal or myopathic disease is present, increased jitter does not indicate that MG is also present. However, if jitter is normal in a muscle with definite weakness, the weakness is not due to MG. When abnormal neuromuscular transmission has been demonstrated by repetitive nerve stimulation, the finding of abnormal jitter does not add to the diagnosis, though it may be useful in providing baseline values for comparison with the results of subsequent studies. SFEMG is most valuable clinically in the patient with suspected MG in whom other tests of neuromuscular transmission and antiacetylcholine receptor antibody titers are normal. Serial measurements of jitter can be useful in following the course of disease and in assessing the effect of treatment, but the results from these studies must always be interpreted in light of the overall clinical picture.     

Single fibre EMG in 6 cases of botulism

ABSTRACT- In 6 cases of mild botulinum intoxication, conventional EMG and single fibre EMG (SFEMG) were performed on admission to our ward (about 15 days after ingestion of the toxin) and 4, 8 and 14 weeks after admission.
In 4 cases, conventional EMG resulted in abnormal findings; and they normalized 4 weeks later. On the first examination, SFEMG revealed in all cases but one the occurrence of potential pairs with abnormal jitter (above 50 μs). The % of the potential pairs with abnormal jitter ranged in different cases from 17% to 44%. Some of the potential pairs with abnormal jitter showed blockings; the occurrence of blockings was not strictly related to jitter value. Mean jitter value and % of potential pairs with abnormal jitter became progressively reduced with increasing time after intoxication. Nevertheless, in 4 cases slightly abnormal findings were still present after 4 months.
The data obtained in the basal condition are in agreement with those reported by others. SFEMG findings relate fairly well to conventional EMG data and clinical status. SFEMG has proved to be a very sensitive method for studying the neuromuscular transmission defect in botulism and in obtaining further information on the course of the syndrome.     

The single-fiber EMG in chronic demyelinating neuropathy

Various parameters of single- fiber electromyography (SFEMG) were studied in 19 patients with electrophysiologically and histologically proven chronic demyelinating neuropathy. The mean duration of disease at the time of testing was four years. Motor nerve conduction in the median nerve was abnormal in all patients, whereas sensory nerve conduction was abnormal in all but one. Needle EMG in the extensor digitorum communis (EDC) muscle showed rare fibrillations and fasciculations and some abnormal motor unit potentials in most of patients. SFEMG in the EDC muscle showed an increased fiber density in seven cases (37%) and minimally abnormal jitter in 14 cases (74%). Single-fiber action potentials were stable, whereas blocking was rare. Fiber density was significantly increased in patients with fibrillation in the conventional needle EMG. Our study showed that the SFEMG is mildly abnormal in many patients with demyelinating neuropathy and that this test is useful in detecting and quantitating axonal degeneration in demyelinating neuropathy.     

Ocular myastyenia gravis: The diagnostic yield of repetitive nerve stimulation and stimulated single fiber EMG of orbicularis oculi muscle and infrared reflection oculography

For the diagnosis of ocular myasthenia gravis (ocular MG), testing of the muscles close to the affected ones may be important. The relative importance of several methods: stimulated single fiber EMG (stimulated SFEMG), repetitive nerve stimulation test (RNS) of orbicularis oculi muscle, and infrared reflection oculography (IROG) was investigated. Thirty-two patients in whom a diagnosis of ocular MG was considered on clinical grounds were admitted to the study. Based on the results of the three neurophysiological tests, the patients could be divided in three groups: a first group with an abnormal stimulated SFEMG, and an abnormal RNS and/or abnormal IROG; a second group with only a slightly abnormal stimulated SFEMG; and a third group with normal tests in all three tests. The clinical diagnosis of ocular MG was made in all 11 patients of the first group; in 86% (6 of 7) of the patients of the second group; and in 7% (1 of 14) of the patients of the third groups. This study demonstrates that the orbicularis oculi muscle is a suitable muscle for stimulated SFEMG in patients with ocular MG, and that the results obtained with this technique showed a better relation with the clinical diagnosis than those of the two other techniques. We also demonstrate that there is no additional value in studying the jitter with different stimulation rates in patients with suspected ocular MG. © 1993 John Wiley & Sons, Inc.