Adult-onset centronuclear myopathy: evidence against a neurogenic pathology

A case of sporadic adult-onset centronuclear myopathy is presented. EMG was myopathic and nerve conduction study entirely normal. Single-fiber electromyography showed a normal percentage of potential pairs with abnormal jitter, slightly increased mean jitter value, no blocking and normal fiber density. Somatosensory and motor evoked potentials were within the normal limits. While it is still a subject of debate whether centronuclear myopathy is neuropathic or myopathic in origin, our findings are against peripheral nerve and CNS involvement.     

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.     

Electrophysiological spectrum of inclusion body myositis

We present electrodiagnostic data on 30 patients with inclusion body myositis (IBM) in order to better delineate its electrophysiological features. Comprehensive electromyography (EMG) and nerve conduction studies (NCS) were performed in all cases. Twelve patients had single fiber electromyography (SFEMG). EMG showed abundant short-small motor unit potentials (MUP) with fibrillations and positive sharp waves in 56.6% of patients, and a mixed pattern of large and small MUP in 36.7%. In 6.7%, only "neurogenic" features were seen. NCS were slow in 33.3%. SFEMG revealed a mildly abnormal jitter and a slightly increased fiber density. IBM demonstrates a heterogeneous EMG profile. A pattern of large and small MUP is highly suggestive of IBM but is seen in only about one third of cases.     

Causes of the increased fiber density in muscular dystrophies studied with single fiber EMG during electrical stimulation

The impulse transmission in motor end-plates and along muscle fibers was studied with single fiber EMG in 13 patients with muscular dystrophy during intramuscular nerve stimulation and direct muscle fiber stimulation. For comparison, three patients with spinal muscular atrophy (SMA) and five normal subjects were studied. At nerve stimulation, 25% of the recordings in the patients with muscular dystrophy showed "increased" jitter (> 55 microsec), 48% "normal" (10-55 microsec), and 27% "abnormally low" jitter (< 5 microsec). At direct muscle fiber stimulation, the jitter was "abnormally low" in 91% of the recordings; 9% of the recordings had normal jitter. In SMA, no abnormally low jitter values were found. Increased jitter is a sign of impaired impulse transmission in immature intramuscular nerves and motor end-plates. "Abnormally low jitter" suggests the presence of branched muscle fibers and ephaptic transmission between hyperexcitable fibers.     

Electrophysiologic study in benign human botulism type B

Conventional electromyography (EMG) and single fiber EMG (SFEMG) were performed in a 64-year-old diabetic woman with mild type B botulism. The main clinical signs were autonomic dysfunction and cranial nerves paresis. Conventional EMG was normal, except for small changes that were consistent with mild mixed peripheral neuropathy in the lower limbs and were related to diabetes. Repetitive stimulation and results of single stimulus before and after full effort were normal. SFEMG showed increased jitter and impulse blocking in clinically normal muscles. The jitter was frequency dependent and improved at a higher innervation rate. Impulse blocking in potentials with only slightly increased jitter was found. The follow-up showed improvement of the jitter in agreement with clinical recovery. Jitter abnormalities were recorded after 16 weeks, when clinical signs of botulism had been reversed to normal. Motor unit fiber density increased progressively, and on examination at 8 weeks, some potentials showed very high jitter values. Both findings might suggest new endplate formation, perhaps due to ultraterminal sprouting development.     

Single fiber electromyography in chronic progressive external ophthalmoplegia

We have reviewed the electromyographic (EMG) studies of 17 patients with chronic progressive external ophthalmoplegia (CPEO). In 13 of 17 patients, conventional concentric needle EMG demonstrated a "myopathic" pattern, usually predominating in the shoulder muscles. Single-fiber EMG showed increased jitter and/or blocking in at least one muscle in 13 of 16 patients. Jitter was increased in the frontalis muscle in 10 of 13 patients and in an arm muscle in 5 of 12. When both muscles were tested, jitter was greater in the frontalis muscle in 5 patients and in the arm muscle in 2. These observations demonstrate that it may be difficult to distinguish myasthenia gravis from CPEO by EMG. The frequency with which abnormal jitter is found in CPEO suggests that, in addition to a mild generalized myopathy, a primary defect in neuromuscular transmission may be present.     

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.     

Single-fiber electromyography, examination technic and findings

Single-fibre electromyography has become much easier because of the advantages offered by modern computerised EMG equipment. Fibre density, jitter and the frequency of blockings can thus be examined with relative reliability. The technique allows a sensitive diagnosis of disturbances of neuromuscular stimulus transmission. Furthermore, different pathological results obtained in patients suffering from neuropathies or myopathies (12 controls, 65 patients) proved the diagnostic value of single-fibre EMG. The method is a valuable addition to conventional EMG. The examination technique is described and illustrated by various examples.     

Electromyographic evidence of subclinical myopathy in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is due to a number of mutations of contractile protein genes such as beta-cardiac myosin, myosin binding protein-C, and troponin-T. Unlike troponin-T, beta-myosin is a constituent of slow skeletal muscle and its mutations generally have a better prognosis. In order to investigate the usefulness of electromyography in detecting skeletal muscle involvement in HCM, 46 patients were examined using both conventional electromyography (EMG) and quantitative electromyography (QEMG) methods. The QEMG involved motor unit potential (MUP) analysis, turns/amplitude (TAA) analysis, and power spectrum analysis of the interference pattern. Using conventional EMG, myopathic findings were demonstrated in 13 patients (28%). Receiver operating characteristic (ROC) analysis of the results of a discriminant function extracted using QEMG values, identified correctly 10 out of 11 normal controls and all 9 myopathic control patients, and displayed a 15% presence of myopathy (7 patients) among the cardiomyopathy group. The duration of MUPs was the most sensitive among the quantitative parameters in differentiating normal from myopathic subjects. Since skeletal muscle involvement may be due to distinct gene mutations, normal and myopathic EMG findings may reflect HCM subpopulations with a different genetic substrate.     

Single fiber electromyography in the differential diagnosis of myopathic limb girdle syndromes and chronic spinal muscular atrophy

Single fiber electromyography (SFEMG) of the extensor digitorum communis muscle was performed on 20 patients with either myopathic limb girdle syndromes (LGS) or chronic spinal muscular atrophy (CSMA) to assess its value in the differential diagnosis of these disorders. Neurologic examinations (muscle biopsies, standard electromyography, or both) were reviewed in 16 patients and resulted in diagnosing LGS in 11 patients and CSMA in 5 patients. In four patients, discordance between EMG and biopsy, or mixed features of myopathy and neuropathy in either test, resulted in an indeterminate diagnosis. Two groups were discerned from SFEMG, one with higher fiber density, jitter, and percentage of abnormal pairs consistent with neuropathy and another with lower values consistent with myopathy. In all 16 patiets, SFEMG confirmed the initial diagnosis, and in the four patients with indeterminate diagnoses, SFEMG suggested diagnoses of LGS in two patients and CSMA in two patients. Single fiber electromyography may be a useful diagnostic aid in the differential diagnosis of myopathic LGS and CSMA.     

Reinnervation of anal sphincter muscle by low and high-threshold motor neurones.

The external anal sphincter (EAS) has continuously active low-threshold and recruitable high-threshold motor units (MUs), the latter being 'larger'. On performing concentric needle electromyography (EMG) of the EAS, the high-threshold MUs seemed to reveal more neuropathic changes than the low-threshold MUs. To verify this hypothesis, low- and high-threshold motor unit potentials (MUPs) were compared in patients with neuropathic EAS and controls. Fifteen subjects without pelvic disorders and 29 patients with sequela after cauda equina lesions were studied. In patients, only muscles ipsilateral to severe perianal sensory loss were included. MUPs were sampled using multi-MUP analysis during relaxation ('low-threshold'), and on activation ('high-threshold' MUs). MUP parameters of low- and high-threshold MUs from controls and patients were compared, as was the sensitivity and specificity with which MUPs were classified as normal or pathological (using discriminant analysis). MUP changes due to reinnervation, and the sensitivity and specificity in classifying MUPs as normal or pathological were not significantly different between the low- and high-threshold MUPs. Stronger activation of EAS does not improve discrimination between neuropathic and normal MUPs. New EMG techniques for sampling sphincter MUPs at higher activation levels would seem not to yield additional information.     

Which patients need referral for anal sphincter electromyography?

Needle electromyography (EMG) of lower sacral myotomes is useful in certain patients with urinary, bowel, or sexual dysfunction. The aim of the study was to identify the clinical profile of patients who require such testing. Medical records were retrospectively reviewed, and findings evaluated using bivariate and multivariate statistics. A neuropathic condition affecting the lower sacral segments was diagnosed by quantitative concentric needle EMG of the external anal sphincter (EAS) muscle. Neuropathic changes in the EAS were found in 85 (44%) of 193 patients studied. On ordinal logistic regression analysis, bladder-emptying difficulties and perineal sensory loss were significantly related to the presence of a neuropathic EMG. No guidelines for referral for anal sphincter EMG could be defined that would include all patients with neuropathic abnormalities in the lower sacral segments. However, patients with bladder-emptying difficulties and perineal sensory loss seem to be the most suitable candidates for testing.     

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.     

Single-fiber EMG in familial hemiplegic migraine

Twelve familial hemiplegic migraine (FHM) patients (6 with the I1811L mutation in CACNA1A, 3 with M731T mutation in ATP1A2, and 3 without known mutations) and 10 control subjects underwent single-fiber EMG. Mean jitter did not differ significantly between patients and control subjects or among patients. No blocking was found. The results suggest that neuromuscular function is normal in FHM.     

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.     

Neurourologic findings in conus medullaris and cauda equina injury

Fifty-seven patients with documented conus medullaris and cauda equina injury underwent neurourologic evaluation consisting of cystometrography (CMG), perineal floor electromyography (EMG), and bethanechol chloride supersensitivity testing (BST). The bulbocavernosus reflex was normal in only 16% of the patients, and perineal sensation and muscle stretch reflexes were absent or significantly diminished in 77%. The predominant CMG finding was detrusor areflexia (93%). Neuropathic EMG changes were noted in 67% and a positive BST response in 95% of the cases. Statistical analysis showed significant correlations between (1) a compromised bulbocavernosus reflex and perineal floor neuropathy (.01 less than P less than .05) and (2) sex of the patient and incidence of urinary incontinence among subjects with perineal floor neuropathy (P less than .01). The major neurourologic features in these patients (1) An absent or substantially diminished bulbocavernosus reflex, (2) detrusor areflexia on CMG, (3) neuropathic perineal EMG changes, and (4) a positive BST response.     

Neuromuscular transmission as a function of motor unit size in patients with prior poliomyelitis.

We studied neuromuscular transmission in 16 patients with prior poliomyelitis by measuring single fiber electromyographic (SFEMG) jitter. This was compared with 3 indirect methods of assessing reinnervation: SFEMG fiber density, macro EMG, and the presence of fiber type grouping on muscle biopsy. In patients with acute poliomyelitis before the age of 10, there was a positive correlation between the extent of neuromuscular transmission impairment, demonstrated by increased SFEMG jitter, and the enlargement of the motor unit, as indicated by increased fiber density, increased macro EMG signals, and fiber type grouping on muscle biopsy. However, there was no correlation between any of these parameters and the presence or absence of new symptoms of weakness. These findings suggest that impaired neuromuscular transmission is most common in patients with prior poliomyelitis whose motor units have been maximally enlarged by axonal sprouting, but is independent of the presence or absence of new symptoms of weakness.     

Relation between the clinical manifestations and electromyographic findings in motor neurone disease]

343 cases of motor neurone disease (MND) were examined with electromyography. The result showed EMG examination was of much vale in helping to ascertain an accurate diagnosis which clinically could be made in only about 1/4 of the series of cases. The ages of onset ranged from 4 months to 10 years with an average of 36.8 years. 56.8% under 40 years. There was a higher male preponderance, the male/female ratio being 3.2:1. It was 1.6:1 in a report from a western country. 123 cases showed only one limb involvement clinically while the EMG findings were also abnormal in the other three limbs. Fibrillation potentials were found to be at more than two sites in one muscle in 84.5% in this series, where as they occurred in 95-100% of the infantile and juvenile cases. Abundant fibrillation potentials were found in 37.1% of the cases within 3 years after the onset and in 13.6% in those with a longer duration. The increment of the mean duration of motor unit potential was 94.5% and that of the mean amplitude 91%. It seemed not necessary to emphasize giant potentials. The motor nerve conduction velocities (NCV) were normal in 95% while the sensory NCV were almost always normal (98%). All of the 3 cases tested with single fiber EMG showed an increment of jitter of 95-100% and a muscle fiber density of 2.95-3.65.     

Abnormalities of neuromuscular transmission in patients with Miller–Fisher syndrome

The mechanism of motor weakness in patients with Miller–Fisher syndrome (MFS) remains to be fully elucidated. We performed stimulated single fibre electromyography (sSFEMG) in a clinically weak frontalis muscle in a patient with MFS. Stimulate single fiber EMG revealed increased jitter in over 50% of the apparent single fibre action potentials from the frontalis muscle in addition to increased mean jitter. The findings in the present study suggest dysfunction of neuromuscular transmission in patients with MFS.     

Lambert-Eaton肌无力综合征6例临床与电生理特点分析

目的探讨Lambert-Eaton肌无力综合征(LEMS)的临床及电生理特点。方法分析2002-2011年作者医院诊断的6例LEMS患者的临床资料及神经电生理检查结果。结果 6例患者起病年龄34～65岁(中位数53岁),病程0.5～35个月(中位数4个月)。4例患者最初诊断为重症肌无力。5例患者伴恶性肿瘤。6例患者均以肢体近端无力起病。5例患者腱反射减低或消失。3例患者伴口干、眼干等自主神经症状。5例患者行新斯的明试验,其中4例阳性。6例患者均行神经电生理检查,共9次。5例行针极肌电图检查共6次,其中结果显示肌源性改变3次,神经源性改变2次,正常1次。5例行7次神经传导速度检查,全部提示复合肌肉动作电位明显减低。6例共行9次重复神经电刺激(RNS)检查,全部提示高频刺激波幅递增。结论掌握LEMS的临床及电生理特征有助于及时正确诊断。