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.     

Diagnostic approach to peripheral neuropathy

Peripheral neuropathy refers to disorders of the peripheral nervous system. They have numerous causes and diverse presentations; hence, a systematic and logical approach is needed for cost-effective diagnosis, especially of treatable neuropathies. A detailed history of symptoms, family and occupational history should be obtained. General and systemic examinations provide valuable clues. Neurological examinations investigating sensory, motor and autonomic signs help to define the topography and nature of neuropathy. Large fiber neuropathy manifests with the loss of joint position and vibration sense and sensory ataxia, whereas small fiber neuropathy manifests with the impairment of pain, temperature and autonomic functions. Electrodiagnostic (EDx) tests include sensory, motor nerve conduction, F response, H reflex and needle electromyography (EMG). EDx helps in documenting the extent of sensory motor deficits, categorizing demyelinating (prolonged terminal latency, slowing of nerve conduction velocity, dispersion and conduction block) and axonal (marginal slowing of nerve conduction and small compound muscle or sensory action potential and dennervation on EMG). Uniform demyelinating features are suggestive of hereditary demyelination, whereas difference between nerves and segments of the same nerve favor acquired demyelination. Finally, neuropathy is classified into mononeuropathy commonly due to entrapment or trauma; mononeuropathy multiplex commonly due to leprosy and vasculitis; and polyneuropathy due to systemic, metabolic or toxic etiology. Laboratory investigations are carried out as indicated and specialized tests such as biochemical, immunological, genetic studies, cerebrospinal fluid (CSF) examination and nerve biopsy are carried out in selected patients. Approximately 20% patients with neuropathy remain undiagnosed but the prognosis is not bad in them.     

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.     

A useful electrophysiological test for diagnosis of minimal conduction block.

OBJECTIVE: To evaluate the usefulness, sensitivity and specificity of a new neurophysiological test for partial conduction block. METHODS. In 17 patients (17 nerves) with clinical pictures strongly suggesting the presence of motor conduction block and 20 healthy subjects (40 nerves), motor nerve conduction studies were performed with the conventional surface technique and with a new technique developed by us: the single fiber EMG (SFEMG) conduction block test. Moreover, we also evaluated patients with other neurological diseases. The recent American Association of Electrodiagnostic Medicine (AAEM) consensus criteria for partial conduction block were used for the standard conduction block tests. RESULTS: According to AAEM consensus criteria, 5/17 cases presented 'definite' partial conduction block and 6 presented 'probable' partial conduction block. In contrast, 16/17 cases (94%) presented evidence of conduction block at the SFEMG conduction block test. The 5/6 cases that did not fulfill in the AAEM criteria and that presented abnormal findings at SFEMG nerve conduction test could be considered affected by minimal conduction block. The sensitivity of this new test was greater than conventional test. The specificity was 100% (no abnormal findings in healthy subjects or patients with diseases other than neuropathy). CONCLUSIONS: The SFEMG conduction block test is a sensitive, complementary, technique for diagnosis of minimal conduction block in patients with normal findings in standard nerve conduction studies.     

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 in diabetic peripheral polyneuropathy

In this study we examined the value of single-fiber electromyography (SFEMG) in assessing the degree of reinnervation in diabetic patients with clinical neuropathy. Relationships between reinnervation and the degree of metabolic control, and/or duration of diabetes were examined. Thirty-six insulin-dependent diabetics and 54 non-insulin-dependent diabetics underwent SFEMG examination of the tibialis anterior muscle, as well as conventional nerve conduction studies of the upper and lower limbs. All patients examined exhibited some abnormality of SFEMG even in the presence of normal nerve conduction studies found in 18% of patients. In diabetic patients, the jitter in the tibialis anterior muscle correlated positively with glycosylated hemoglobin; whereas lower limb nerve conduction studies did not correlate with this measure of diabetic control. These data suggest that SFEMG is a sensitive measure of nerve function and reinnervation and that it may reflect the dynamic changes in metabolic status in diabetic patients. © 1996 John Wiley & Sons, Inc.     

The effects of chronic muscular activity on age-related changes in single fiber electromyography

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.     

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.     

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.     

Peripheral neuropathy in Tangier disease: A literature review and assessment

Tangier disease (TD) (OMIM#205400) is a rare cause of inherited metabolic neuropathies characterized by marked deficiency of high‐density lipoproteins and accumulation of cholesterol esters in various tissue resulting from reverse cholesterol transport deficiency. We report a case of a patient with TD with multifocal demyelinating neuropathy with conduction block who presents with winging scapula, tongue, and asymmetric extremity weakness. We also present a review of all studies published from 1960 to 2017 regarding peripheral neuropathy in TD. Our search identified 54 patients with TD with peripheral neuropathy. Syringomyelia‐like neuropathy subtype (52.4%) was more frequent than multifocal sensorial and motor neuropathy subtype (26.2%), focal neuropathy subtype (19.1%), and distal symmetric polyneuropathy subtype (2.4%). Splenomegaly was the most common (40.7%) clinical manifestation in these patients. The pattern of electrodiagnostic abnormalities are: (1) demyelinating abnormalities were more predominant in the upper extremities than in the lower extremities and (2) slowing of motor nerve conduction was more prominent in the intermediate segment than in distal nerve segments. The sural‐sparing pattern was present in 34.6% and conduction block was present in 11.5% of the patients. Our literature review and our case showed the clinical spectrum of TD neuropathy is quite wide and that it should be considered in the differential diagnosis of non‐uniform demyelinating neuropathies.     

Fiber density in acute and chronic inflammatory demyelinating polyneuropathy.

The fiber density in the deltoid, extensor digitorum communis, and first dorsal interosseous muscles was measured using SFEMG in 11 patients with acute and chronic inflammatory demyelinating polyneuropathy. The fiber density was increased in 58% of the muscles studied. The deltoid muscle was the most abnormal of the 3 muscles studied. There was no correlation with the clinical syndrome, with conduction block or slowed motor conduction, or with the distribution of weakness. Changes were noted even in patients studied within 3 weeks of presentation, suggesting that reinnervation begins soon after the onset of the disease.     

Pain related potentials by electrical stimulation of skin for detection of small-fiber neuropathy in HIV

We compared the sensitivity of pain related evoked potentials (PREP), a novel electrophysiological technique, with standard nerve conduction (SNC) testing in the diagnosis of small fiber neuropathy in 47 patients with HIV infection and 31 age matched controls. SNC testing revealed a neuropathy in only 31%, whereas PREP was abnormal in 74% of symptomatic patients. This result hints that PREP is more sensitive in the detection of HIV-associated small fiber neuropathy than standard neurography. Received in revised form: 28 March 2006     

What is the best diagnostic index of conduction block and temporal dispersion?

In order to find the best diagnostic index of conduction block and abnormal temporal dispersion, the amplitude, duration, and area of the compound muscle action potentials (CMAP) were studied in 40 normal controls and 28 patients with acquired demyelinating neuropathies. In the normal subjects, there was a substantial difference among the various nerves in the degree of CMAP amplitude reduction and CMAP duration prolongation with proximal stimulation, and thus different criteria should be used for conduction block or abnormal temporal dispersion for a given nerve. In 28 patients with demyelinating neuropathy, 58 of 207 (28%) tested nerve segments showed nerve conduction velocity (NCV) evidence of demyelination. To identify “demyelination” in these segments, conduction block was best detected by the total area method in 71% of cases, and abnormal temporal dispersion was bast by the negative-peak duration method. This study showed that the best diagnostic index for conduction block is the total area method and for abnormal temporal dispersion, the negative-peak duration method. © 1994 John & Sons, Inc.     

系统性红斑狼疮合并周围神经病的临床特点和肌电图改变

分析２２例临床有或疑有神经系统损害的系统性红斑狼疮（ＳＬＥ）患者，其中仅３例被临床诊断为ＳＬＥ合并周围神经病，然神经电生理检查证实１３例为周围神经损害。主要临床特点为对称性和非对称性四肢远端麻木、疼痛，深浅感觉障碍，肌力减退，肌萎缩等。神经电生理检查显示神经传导速度减慢，波幅降低，异常自发电位（纤颤电位和正锐波），运动单元多相电位增加。电生理检查与病理改变相符：ＳＬＥ合并周围神经病既有轴索损害，又有脱髓鞘改变。提示神经电生理检查可以为ＳＬＥ患者提供早期或亚临床周围神经损害的依据。     

Utility of somatosensory evoked potentials in chronic acquired demyelinating neuropathy

Chronic acquired demyelinating polyneuropathy (CADP) is a heterogeneous syndrome that may be classified into a number of subtypes. Somatosensory evoked potentials (SSEPs) assess proximal segments of sensory nerves, inadequately assessed by routine nerve conduction studies (NCSs). The aim of the present study was to determine the utility of SSEPs in diagnosing and classifying different CADP subtypes. Forty-seven patients with CADP were studied and classified in five groups based on conventional NCSs and SSEPs. Some patients in Group 1 were initially misdiagnosed as having either motor neuron disease or multifocal motor neuropathy due to normal sensory NCSs, but they exhibited abnormal tibial and median nerve SSEPs, as evidenced by marked prolongation or absence of peripheral potentials (N9-median nerve, and N20-tibial nerve). These were reclassified as having chronic inflammatory demyelinating neuropathy (CIDP). In CIDP patients (Group 2), SSEPs were abnormal, thereby confirming the presence of demyelination in the proximal peripheral nerves. Patients with distal acquired demyelinating neuropathy (DADS) (Group 3), as defined by conventional NCS, exhibited abnormal SSEPs when anti-MAG antibodies were present. Anti-MAG-negative DADS patients (Group 3) had normal SSEPs. In the pure sensory ataxic group (Group 4), SSEP studies disclosed poorly formed and delayed cortical potentials with absent lumbar (N20) potentials, thereby suggesting the presence of proximal demyelination. SSEPs were normal in the pure motor CIDP and multifocal motor neuropathy patients (MMN) (Group 5), thereby differentiating asymmetric forms of CIDP from MMN. These findings suggest that SSEPs may be an important complementary investigation to conventional NCSs in the diagnosis of CADP.     

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 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     

Inclusion body myositis: peripheral nerve involvement. Combined morphological and electrophysiological studies on peripheral nerves

The occurrence of neuropathy in 5 cases of inclusion body myositis (IBM) was studied. The intramuscular nerve branches showed variable ultrastructural changes in all cases. The observed changes were loss of axons, wallerian degeneration and axon terminal atrophy. EMG with concentric needles showed myopathic motor unit potentials in all cases. A reduced interference pattern due to loss of motor units was found in all cases. All but one patient showed fibrillation potentials in several muscle groups. Motor nerve conduction velocities and F-wave latencies were pathological in two of the cases, in which there were motor unit potentials with increased amplitude and duration as evidence of reinnervation. Sural nerve biopsy in one of these cases revealed slight neuropathy of the axonal type. These findings support the concept of peripheral nerve involvement in many cases of IBM.     

Steroid-responsive multifocal demyelinating neuropathy with central involvement

We describe 2 patients with associated central and peripheral demyelination. Electrophysiological studies revealed a demyelinating polyneuropathy with sensory and motor conduction blocks. Visual evoked potentials were abnormal. Motor evoked potentials showed abnormal central conduction time in 1 patient. Magnetic resonance imaging revealed regions of abnormal high signal in the spinal cord and brain; sural nerve biopsy disclosed a demyelinating neuropathy. Both patients showed clinical and electrophysiological improvement after steroid therapy.     

Electrophysiological findings including single fibre EMG in a family with mitochondrial myopathy

Nerve conduction studies, conventional and quantitative concentric needle EMG and single fibre EMG were performed on 5 clinically affected and 7 clinically asymptomatic membres of a family with a mitochondrial myopathy manifesting as a facioscapulohumeral syndrome. Abnormalities of nerve conduction present in 3 clinically affected cases were attributed to co-existent diabetes mellitus. Quantitative CNEMG showed a reduction of the mean motor unit potential duration and increased incidence of polyphasic potentials in all 5 clinically manifest cases consistent with a primary myopathic disorder. Similar but less marked changes were found in 6 of the clinically asymptomatic individuals revealing the presence of a subclinical myopathy. Abnormalities on SFEMG consisting of increases in fibre density and/or jitter were present in all the clinically affected and in 5 clinically normal cases. These changes indicate local reorganization of the spatial arrangement of muscle fibres of the motor unit and a disturbance of neuromuscular transmission. The CNEMG and SFEMG findings are discussed in relation to the histopathological changes in 4 cases.