Power spectrum analysis of the EMG pattern in normal and diseased muscles

The diagnostic value of analogue frequency analysis of EMG from patients with neuromuscular disorders has not been convincing. Using fast Fourier transformation it is today possible to obtain the EMG power spectrum on-line and with a better resolution. We examined the power spectrum of the EMG pattern of the brachial biceps muscle in 20 control subjects, 20 patients with myopathy, and 12 with neurogenic disorders. The electrical activity was sampled with a concentric needle electrode from 10 sites in each muscle. From each spectrum, mean power frequency, the power at 140 Hz, 1400 Hz, 2800 Hz and 4200 Hz relative to total power and the high/low ratio (1400/140) were obtained. The mean power frequency was higher at 10% than at 30% of maximal force. At a force of 30% of maximum the power spectrum analysis identified 55% and 64% of the patients with myopathy and neurogenic disorders, respectively. Although the diagnostic yield of the power spectrum analysis at a force of 10% of maximum was less than that at 30%, additional patients were identified at 10% increasing the diagnostic yield to 65% and 73% for patients with myopathy and neurogenic disorders, respectively. The best diagnostic parameters were the mean power frequency and the relative power at 1400 Hz.     

Oculopharyngodistal myopathy

Some clinical variants of oculopharyngeal dystrophy are known; a rare form is described in this article: the early-adult form of oculopharyngodistal myopathy. The diagnosis was made in 2 patients (brother and sister) on the grounds of extensive clinical, biochemical and morphological (microscopical, histochemical and submicroscopical) investigations.

Although oculopharyngeal dystrophy is generally considered to be a purely myogenic condition, in one of our patients some neurogenic indications were found (EMG and biopsy). The general picture, however, was that of a myopathy with the characteristic morphological signs of oculopharyngeal dystrophy in the skeletal musclebiopsy.     

Diagnostic value of electromyography and muscle biopsy in arthrogryposis multiplex congenita

Arthrogryposis multiplex congenita (AMC), a clinical syndrome characterized by multiple congenital joint contractures, frequently is caused by lesions in the peripheral nervous system. Two standard tests for the evaluation of the motor unit are nerve conduction studies/electromyography (NCS/EMG) and muscle biopsy. We reviewed the diagnostic value of these two studies in the evaluation of AMC over a 23-year period, analyzing 38 patients with AMC who had NCS/EMG, muscle biopsy, or both. Final diagnoses were classified as neurogenic (8 patients), myopathic (10 patients), "other" (12 patients), or unknown (8 patients). Neither test alone had consistently high sensitivities, positive predictive values, or specificities. However, when NCS/EMG and muscle biopsy were concordant for neurogenic or myopathic findings, they were more accurate than either test alone, especially for neurogenic diseases. Test results were most commonly discordant in patients with "other" or unknown diagnoses. These findings suggest that when the clinical evaluation indicates a specific syndromic, developmental, or exogenous cause, NCS/EMG and muscle biopsy are not helpful and may not need to be performed. When the history, examination, and genetic evaluation are unrevealing, NCS/EMG and muscle biopsy together provide valuable diagnostic information.     

副肿瘤综合征电生理及病理学研究(附一例报告)

目的探讨以运动神经元病为表现的副肿瘤综合征的临床、电生理学、病理学特点。方法对1例肠癌肺转移患者的临床表现、肌电图神经重复刺激检查、肌肉组织化学进行研究。结果该例患者表现为进行性肌肉力弱,肌电图显示神经源性损害,神经重复刺激检查示波幅下降,肌肉病理显示小簇状肌肉萎缩,电镜下除极少数肌纤维膜溶解外其他未见特殊。结论肠癌合并副肿瘤综合征可表现为运动神经元病。     

脂质沉积性肌病二例

目的探讨脂质沉积性肌病(LSM)的临床和肌肉病理特点。方法分析2例LSM的临床特点、辅助检查及肌肉病理资料。结果 LSM的临床表现为进行性肌无力,以近端肌无力为主,伴肌萎缩;发作期血清肌酶轻、中度升高,血脂升高或正常,肌电图多为肌源性损害,合并神经源性损害;肌肉病理为I型纤维受累重,肌纤维内散在大小不等的圆形空泡或缺损(脂质颗粒),线粒体受压变形;对激素治疗反应好。结论临床表现和肌酶检查对LSM的诊断具有重要意义,确诊依靠肌肉病理活检,早期治疗效果好。     

Oculopharyngodistal myopathy with early onset and neurogenic features.

Some clinical variants of oculopharyngeal dystrophy are known; a rare form is described in this article: the early-adult form of oculopharyngodistal myopathy. The diagnosis was made in 2 patients ((brother and sister) on the grounds of extensive clinical, biochemical and morphological (microscopical, histochemical and submicroscopical) investigations. Although oculopharyngeal dystrophy is generally considered to be a purely myogenic condition, in one of our patients some neurogenic indications were found (EMG and biopsy). The general picture, however, was that of a myopathy with the characteristic morphological signs of oculopharyngeal dystrophy in the skeletal musclebiopsy.     

98例神经肌肉病的临床、肌电图与病理研究

目的 探讨肌电图（EMG），肌活检对神经肌肉病的诊断价值。比较EMG，肌活检及初始临床诊断3者之间的关系。方法 将98例神经肌肉病分成肌病。重症肌无力和运动神经元病3组进行研究。结果 肌病组（80例），68.8%(55/80)肌活检，75%（60/80）EMG呈肌源性损害；重症肌无力组（10例）；针极EMG（不包括重视频率电刺激）及肌活检均未显示特异性改变；运动神经元病组（8例），75?/8）肌活检，100%（8/8）EMG呈神经源性损害。结论 肌活检对肌病明确诊断可提供直接信息。对运动神经元病只能做出神经源性损害结果。缺乏特异性。EMG对神经肌肉病只能做出分类诊断；单纯凭借初始临床资料易导致该类疾病误诊。     

Diagnostic accuracy of clinical data, quantitative electromyography and histochemistry in neuromuscular disease. A study of 105 cases

One hundred and five (105) cases of muscle weakness were reviewed in order to evaluate the reliability of clinical diagnosis, quantitative EMG, and muscle histochemistry in neuromuscular disorders. Patients were grouped into 3 categories: group I, disorders which could be diagnosed by clinical observation alone (38 patients); group II, disorders in which the EMG and biopsy were necessary for delineation (63 patients); disorders in which it was not possible to make a diagnosis because the clinical and laboratory studies were contradictory (4 patients). In group I, only one patient showed an inconsistency between clinical and laboratory data. In group II, the EMG and biopsy were concordant in all but 4 cases of Kugelberg-Welander syndrome with neuropathic EMG and myopathic biopsy. In group III, 4 patients had a myopathic EMG and neuropathic biopsy.The overall concordance of EMG and histochemistry was greater than 90%. The laboratory studies also discerned 2 different categories of disease, “neuropathic” and “myopathic”. The consistency in EMG and histochemistry correlation suggests that a true division between neuropathic and myopathic disorders exists.     

Muscle “islands”: An MRI signature distinguishing neurogenic from myopathic causes of early onset distal weakness

Muscle MRI has an increasing role in diagnosis of inherited neuromuscular diseases, but no features are known which reliably differentiate myopathic and neurogenic conditions. Using patients presenting with early onset distal weakness, we aimed to identify an MRI signature to distinguish myopathic and neurogenic conditions. We identified lower limb MRI scans from patients with either genetically (n = 24) or clinically (n = 13) confirmed diagnoses of childhood onset distal myopathy or distal spinal muscular atrophy. An initial exploratory phase reviewed 11 scans from genetically confirmed patients identifying a single potential discriminatory marker concerning the pattern of fat replacement within muscle, coined “islands”. This pattern comprised small areas of muscle tissue with normal signal intensity completely surrounded by areas with similar intensity to subcutaneous fat. In the subsequent validation phase, islands correctly classified scans from all 12 remaining genetically confirmed patients, and 12/13 clinically classified patients. In the genetically confirmed patients MRI classification of neurogenic/myopathic aetiology had 100% accuracy (24/24) compared with 65% accuracy (15/23) for EMG, and 79% accuracy (15/19) for muscle biopsy. Future studies are needed in other clinical contexts, however the presence of islands appears to highly suggestive of a neurogenic aetiology in patients presenting with early onset distal motor weakness.     

Classification of EMG signals using wavelet neural network

An accurate and computationally efficient means of classifying electromyographic (EMG) signal patterns has been the subject of considerable research effort in recent years. Quantitative analysis of EMG signals provides an important source of information for the diagnosis of neuromuscular disorders. Following the recent development of computer-aided EMG equipment, different methodologies in the time domain and frequency domain have been followed for quantitative analysis. In this study, feedforward error backpropagation artificial neural networks (FEBANN) and wavelet neural networks (WNN) based classifiers were developed and compared in relation to their accuracy in classification of EMG signals. In these methods, we used an autoregressive (AR) model of EMG signals as an input to classification system. A total of 1200 MUPs obtained from 7 normal subjects, 7 subjects suffering from myopathy and 13 subjects suffering from neurogenic disease were analyzed. The success rate for the WNN technique was 90.7% and for the FEBANN technique 88%. The comparisons between the developed classifiers were primarily based on a number of scalar performance measures pertaining to the classification. The WNN-based classifier outperformed the FEBANN counterpart. The proposed WNN classification may support expert decisions and add weight to EMG differential diagnosis.     

Electromyography (EMG) accuracy compared to muscle biopsy in childhood

Reports show wide variability of electromyography (EMG) in detecting pediatric neuromuscular disorders. The study's aim was to determine EMG/nerve conduction study accuracy compared to muscle biopsy and final clinical diagnosis, and sensitivity for myopathic motor unit potential detection in childhood. Of 550 EMG/nerve conduction studies performed by the same examiner from a pediatric neuromuscular service, 27 children (ages 6 days to 16 years [10 boys; M:F, 1:1.7]) with muscle biopsies and final clinical diagnoses were compared retrospectively. Final clinical diagnoses were congenital myopathies (5 of 27,18%), nonspecific myopathies (biopsy myopathic, final diagnosis uncertain; 6 of 27, 22%), congenital myasthenic syndrome (3 of 27, 11%), juvenile myasthenia gravis (1 of 27, 4%), arthrogryposis multiplex congenita (2 of 27, 7%), hereditary motor and sensory neuropathy (1 of 27, 4%), bilateral peroneal neuropathies (1 of 27, 4%), and normal (8 of 27, 30%). There were no muscular dystrophy or spinal muscular atrophy patients. EMG/nerve conduction studies had a 74% agreement with final clinical diagnoses and 100% agreement in neurogenic, neuromuscular junction, and normal categories. Muscle biopsies concurred with final diagnoses in 87%, and 100% in myopathic and normal categories. In congenital myasthenic syndrome, muscle biopsies showed mild variation in fiber size in 2 of 3 children and were normal in 1 of 3. EMG sensitivity for detecting myopathic motor unit potentials in myopathies was 4 of 11 (36%), greater over 2 years of age (3 of 4, 75%), compared to infants less than 2 years (1 of 7, 14%), not statistically significant (P = .0879). EMGs false-negative for myopathy in infants < 2 years of age were frequently neurogenic (3 of 6, 50%). In congenital myopathies EMG detected myopathic motor unit potentials in 40%, with false-negative results neurogenic (20%) or normal (40%). Because our study has no additional tests for active myopathies, for example Duchenne muscular dystrophy genetic testing, our sensitivity for myopathies is lower than if we used a more global view. In conclusion, EMG detection rate of myopathic motor unit potentials at a young age was low, improving in children over 2 years of age. In neurogenic and neuromuscular junction disorders, the EMG has a very high detection rate. In children with mild to moderate neurogenic EMG findings and normal nerve conduction, a myopathy should always be considered.     

Concentric-needle versus macro EMG. II. Detection of neuromuscular disorders.

OBJECTIVE: Little is known about the relation and sensitivity of macro-EMG (MA-EMG) compared with concentric-needle EMG (CN-EMG) in the detection of neuromuscular disorders. METHODS: CN-EMGs and MA-EMGs were recorded from the right brachial biceps muscle of 40 healthy subjects, aged 17-83 years, 20 patients with neurogenic disorders, aged 25-75 years, and 20 patients with myopathy, aged 18-76 years. Motor unit action potentials (MUAPs) were examined. RESULTS: In patients with neurogenic disorders CN-MUAP duration, CN-MUAP amplitude, percent polyphasia, MA-MUAP amplitude, MA-MUAP area and fibre density were significantly increased. In patients with myopathy, only fibre density was significantly increased. In patients with neurogenic disorders, the sensitivity of CN-EMG was 80%, and that of MA-EMG 85%. In myopathies, the sensitivity was 50% for each technique. Pooling the results of both EMG techniques, the sensitivity increased to 90% in patients with neurogenic disorders, and to 65% in myogenic disease. CONCLUSIONS: MA-EMG has a similar sensitivity in the detection of neuromuscular disorders as CN-EMG. Particularly when myopathy is suspected, both techniques should be applied if one is unrevealing.     

Welander''s distal myopathy: clinical, neurophysiological and muscle biopsy observations in young and middle aged adults with early symptoms.

Nine young or middle aged patients with early symptoms of Welander's distal myopathy were subjected to a detailed neurological examination including quantitative sensory testing, determination of motor and sensory nerve conduction velocity (NCV), sensory nerve action potentials, electromyography (EMG) and muscle biopsy from the tibialis anterior muscle (TA). Slight weakness of the extensors of the fingers and hands was found in all nine patients, and of the dorsiflexors of the feet in seven. All patients had a distal sensory disturbance most prominent for temperature which agrees with earlier observations. EMG changes in TA and extensor digitorum communis (EDC) muscles were of myopathic type. Slight abnormalities compatible with either myopathy or early neuropathy were found in one muscle biopsy. These findings indicate that a neurogenic lesion affecting at least the peripheral sensory system is present at an early stage of Welander's distal myopathy and that the neurogenic lesion might precede the myopathic changes.     

Muscular dystrophies and related skeletal muscle disorders in an Indian population--a prospective correlative study.

Since most centers in developing countries have limited facilities for investigation of patients with muscular dystrophies and similar disorders, this study was conducted with the aim of assessing the correlation between clinical, electromyographic (EMG) and histopathological findings in this group. We included 100 patients with muscular dystrophy and clinically similar disorders and subjected them to detailed clinical, electrophysiological and histopathological as well as immunohistochemical evaluation. Sensitivity, specificity, positive and negative predictive values and concordance rates for clinical and EMG diagnosis compared to diagnosis after histopathological examination were analyzed. With histopathology as standard, clinical diagnosis and a concordant EMG have very high sensitivity and negative predictive value (100%), but low specificity (33.3%). We conclude that detailed histopathological evaluation with immunohistochemical analysis is essential for the work-up of patients with suspected muscular dystrophies, since occasionally treatable muscle disorders like inflammatory myopathies can be detected when not suspected clinically. Muscle biopsies should only be conducted at major centers where full histochemical facilities are available.     

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.     

Correlation between specific histological and electromyographic findings in neuromuscular disorders

An attempt was made to find a correlation between specific electromyography (EMG) abnormalities with histological findings in muscle biopsies (MB) in 100 patients with neuromuscular disorders. Quantified EMG and MB with histochemistry was made in the same muscle, but on the opposite side, within a period of 3 weeks. The isolated findings of EMG and MB were analysed with a computer through a chi-square test. A statistical relation (p less than 0.01) was found between the isolated findings of MB and EMG in only 6.99% (39 in 558 attempts) of the abnormalities expected to occur in myopathy and denervation. Also was found 2.51% (14 in 558 attempts) of inconsistences with the current literature.     

EMG power spectrum, turns-amplitude analysis and motor unit potential duration in neuromuscular disorders

The diagnostic value of power spectrum analysis of the needle EMG pattern at a force of 30% of maximum was compared to that of turns-amplitude analysis and to that of manual measurements of motor unit potential (MUP) duration in the brachial biceps muscle of 20 patients with myopathy and 11 patients with neurogenic disorders. In myopathy the power spectrum analysis had the same diagnostic value as the turns-amplitude analysis and MUP duration measurements and the 3 methods supplemented each other. In patients with neurogenic disorders the diagnostic value of the power spectrum analysis as well as that of the turns-amplitude analysis were lesser than that of MUP duration measurement. In diseased muscles the amount of high frequencies increased with increasing ratio of turns to mean amplitude while there was no relation between the power spectrum and the MUP changes. The results suggest that the power spectrum analysis of EMG can be used as a diagnostic tool in patients with neuromuscular disorders.     

Different clinical aspects of debrancher deficiency myopathy

OBJECTIVE: To characterise the main clinical phenotypes of debrancher deficiency myopathy and to increase awareness for this probably underdiagnosed disorder. METHODS: The diagnosis of debrancher deficiency was established by laboratory tests, EMG, and muscle and liver biopsy. RESULTS: Four patients with debrancher deficiency myopathy were identified in the Tyrol, a federal state of Austria with half a million inhabitants. Clinical appearance was highly variable. The following phenotypes were differentiated: (1) adult onset distal myopathy; (2) subacute myopathy of the respiratory muscles; (3) severe generalised myopathy; and (4) minimal variant myopathy. Exercise intolerance was uncommon. The clinical course was complicated by advanced liver dysfunction in two patients and by severe cardiomyopathy in one. All had raised creatine kinase concentrations (263 to 810 U/l), myogenic and neurogenic features on EMG, and markedly decreased debrancher enzyme activities in muscle or liver biopsy specimens. The findings were substantiated by a review of 79 previously published cases with neuromuscular debrancher deficiency. CONCLUSIONS: This study illustrates the heterogeneity of neuromuscular manifestations in debrancher deficiency. Based on the clinical appearance, age at onset, and course of disease four phenotypes may be defined which differ in prognosis, frequency of complications, and response to therapy.     

Some remarks on computer-aided clinical electromyography based on experience with the Polish ANOPS minicomputer

Summary The author evaluates the application of the Polish minicomputer Analyser of Noise of Periodic Signals (ANOPS) in practical electromyography (EMG) and compares the diagnostic yield of ANOPS with that of manual quantitative EMG. The advantages of ANOPS—at least in the past—include speed, large samples, new data, reduced examiner bias, quantified evaluation of maximal effort record and online recording. The most important limitations of ANOPS are absence of complex potentials due to distortion of signals, loss of phase evaluation, and lack of comparability of amplitude with other methods. ANOPS is compared with other automated methods applied to evaluation of interference pattern and parameters of single motor unit potentials (MUPs). Most of the latter are based on pattern recognition. ANOPS does not meet all of the criteria which an automatic method should meet to be accepted in EMG practice. The most important problem is the distortion of properties of the EMG signal. Further search for computer-aided EMG methods and their careful testing in practice are necessary.Paper presented at the II. International Conference on Computerized Electromyography, Monte Carlo, 15–19 June 1985