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 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.     

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.     

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.     

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.     

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.     

Patterns and severity of neuromuscular transmission failure in seronegative myasthenia gravis

OBJECTIVES: To compare the clinical and electrophysiological features of myasthenia gravis (MG) patients with (seropositive) or without (seronegative) antibodies to acetylcholine receptor. To investigate whether antibodies to muscle specific kinase (MuSK) and ryanodine receptor (RyR) are associated with particular features. METHODS: Clinical profiles and single fibre electromyography (SFEMG) in the extensor digitorum communis (EDC) were reviewed in consecutive 57 seropositive and 13 seronegative patients. Antibodies to MuSK and RyR were measured by immunoassays. RESULTS: Of the 13 seronegative patients, four (31%) were positive for MuSK antibodies and seven (54%) were positive for RyR antibodies, including all four MuSK positive patients. Clinical features were similar at presentation for seropositive and seronegative patients, but MuSK positive patients frequently developed myasthenic crises. Despite the similar clinical severities at the time of examination, the proportion with positive jitter (93% of seropositive patients, 50% of MuSK positive patients, and 44% of MuSK negative patients) and the extent of jitter (mean consecutive difference: 76 micros in seropositive patients, 36 micros in MuSK positive patients, and 30 micros in MuSK negative patients) were less in seronegative MG patients compared with seropositive MG patients. CONCLUSIONS: Seronegative MG is heterogeneous with respect to the presence of antibodies to MuSK. Impairment of neuromuscular synaptic transmission in EDC is less marked in seronegative than seropositive MG despite the similar clinical severity. This discrepancy may partly reflect the distribution of affected muscles in seronegative patients, but it is possible that other factors, such as impaired excitation-contraction coupling resulting from RyR antibodies, contribute to the clinical phenotype.     

Single-fiber electromyography in limb and facial muscles in muscle-specific kinase antibody and acetylcholine receptor antibody myasthenia gravis

We examined the findings from single-fiber electromyography in extensor digitorum communis (EDC) and orbicularis oculi (OOc) in 13 myasthenia gravis (MG) patients with muscle-specific kinase antibodies (MuSK-MG) and 12 MG patients with acetylcholine receptor antibodies (AChR-MG) with similar clinical scores. More than 70% of AChR-MG patients had abnormal jitter in both EDC and OOc, but the majority of MuSK-MG patients had normal jitter in EDC despite abnormal jitter in OOc. These findings demonstrate clear differences between the neurophysiology of MuSK-MG and AChR-MG.     

胸腺切除术对重症肌无力患者电生理学指标和临床评分的影响

目的评价胸腺切除术对重症肌无力(MG)的近期疗效。方法对15例MG在胸腺切除术前(平均9天)及术后(平均11天)依次进行了临床绝对评分、右侧腋神经低频重复电刺激(RNS)和右侧伸指总肌单纤维肌电图(SFEMG)检查。结果手术后SFEMG和RNS异常率分别为100%和73%,手术后平均颤抖(jitter)值、异常电位对比例、阻滞电位对比例和临床绝对评分都较手术前有显著的降低;病理为胸腺瘤5例,手术前后平均jitter值、阻滞电位对比例和临床绝对评分均无显著差异,胸腺增生9例,手术后阻滞电位对比例和临床绝对评分较术前显著减低。结论MG患者胸腺切除术后在临床表现和电生理学指标上都有一定程度的改善,但此时大多数患者仍有临床症状和电生理学指标的异常,需要进一步的免疫调节治疗;MG并发胸腺瘤者可能手术后近期疗效差,并发胸腺增生者可能疗效相对较好。     

Jitter analysis with concentric needle electrode in the masseter muscle for the diagnosis of generalised myasthenia gravis

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.     

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.     

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.     

Repetitive nerve stimulation of facial muscles in MuSK antibody-positive myasthenia gravis

To better define electrophysiological abnormalities in myasthenia gravis (MG) patients with muscle-specific tyrosine kinase (MuSK) antibodies (Ab), we compared electrophysiological features of 14 MuSK Ab-positive, 73 acetylcholine receptor antibody (AChR Ab)-positive, and 22 MuSK and AChR Ab-negative (seronegative) patients with generalized disease. Repetitive nerve stimulation (RNS) abnormalities were observed in 86% of MuSK Ab-positive and 82% of AChR Ab-positive patients but in only 55% of seronegative patients. RNS decrements in the orbicularis oculi were more common and severe in the MuSK Ab-positive patients than the other two groups. Single-fiber electromyography (SFEMG) of the extensor digitorum communis was abnormal in 90% of MuSK Ab-positive patients. The high frequency of RNS abnormalities in facial muscles in the MuSK Ab-positive population reflects the propensity for facial muscle involvement in this form of MG and emphasizes the importance of including facial muscles in RNS protocols when evaluating these patients.     

HTLV‐1–associated myelopathy/tropical spastic paraparesis and peripheral neuropathy following live‐donor renal transplantation

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     

Electrophysiological profile of the patients with MuSK positive myasthenia gravis

Abstract

Objectives:

To determine the electrophysiological profile of our cohort of patients with muscle-specific tyrosine kinase (MuSK) positive myasthenia gravis (MG).

Methods:

Repetitive nerve stimulation test (RNS) and jitter analysis using concentric needle electrode were performed in 31 MuSK and in 28 acetylcholine receptor (AChR) positive MG patients.

Results:

Pathological RNS was verified in 16 (51·6%) MuSK and 26 (92·9%) AChR MG patients (P < 0·01). Pathological jitter analysis was registered in 28 (90·3%) MuSK and 26 (92·9%) AChR MG patients (P > 0·05). Increased jitter was present in extensor digitorum communis (EDC) in 23 (74·2%) MuSK and in 25 (89·3%) AChR MG patients (P > 0·05) as well as in orbicularis oculi (OO) muscle in 24 (85·7%) MuSK and 22 (81·5%) AChR MG patients (P > 0·05). Lower mean value of mean consecutive difference (MCD) and fewer potential pairs with increased jitter were registered in MuSK MG compared to AChR MG patients only in EDC muscle (P < 0·05). In MuSK MG patients, increased jitter was observed to be more frequent in patients with longer disease duration (P < 0·05) and also in those patients exhibiting more severe disease forms (P < 0·01) only in EDC muscle.

Discussion:

Repetitive nerve stimulation test has low sensitivity in MuSK MG patients, while jitter analysis shows high sensitivity, especially in facial muscles. The EDC muscle in MuSK MG patients usually shows increased jitter in more severe disease forms and later in the course of the disease.     

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.     

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.     

Repetitive nerve stimulation in myasthenia gravis—relative sensitivity of different muscles

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.     

Clinical, electrophysiological and immunological remissions after thymectomy in myasthenia gravis.

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

Diagnostic sensitivity of the laboratory tests in myasthenia gravis.

The diagnostic sensitivity of three laboratory tests [serum antiacetylcholine receptor antibody (AChR-ab) assay, the repetitive nerve stimulation (RNS) test, and, the single fiber EMG (SFEMG)] for myasthenia gravis (MG) was compared in 120 patients. In all cases, at least one of the tests was abnormal. SFEMG was the most sensitive test, being abnormal in 92% of cases, followed by the RNS test (77%) and the AChR-ab assay (73%). SFEMG was abnormal in all cases with negative AChR-ab and RNS tests, in 97% of cases with negative AChR-ab assay, in 89% of cases with negative RNS test, and in 89% of cases with mild MG. We conclude that one of these three tests is abnormal in all cases of MG, and that the SFEMG is most sensitive in the diagnosis of MG.