Automatic analysis of the EMG interference pattern

Electromyographic turns analysis of sustained contraction in human masseter muscles at various isometric force levels

The jaw-closing muscles differ from peripheral limb muscles in that the maximum attainable force does not decline following a sustained isometric contraction. Also, the averaged electromyographic (EMG)/force ratio in these muscles does not change with sustained contraction, whereas it increases in fatiguing limb muscles. The present study analysed EMG records from masseters in healthy male subjects. No statistically significant difference was seen between average rectified EMG signals at the beginning or the end of a sustained isometric contraction at 25-100% of maximum voluntary contraction (MVC). However, when the number of turns, or reversals of direction, was taken at various percentage MVC levels, a significant decrease was seen after 60s or at the end of the contraction. The turns/force ratio decreased monotonically with percentage MVC, but the ratio was not significantly different at the end of a contraction from that at the beginning. This result confirms an earlier suggestion that neuromuscular fatigue does not accompany sustained contractions of these muscles.

Konzo: a distinct disease entity with selective upper motor neuron damage

Two Tanzanian patients with konzo were severely disabled by a non-progressive spastic paraparesis, since the sudden onset during an epidemic six years earlier. At the time of onset they had a high dietary intake of cyanide from exclusive consumption of insufficiently processed bitter cassava roots. MRI of brain and spinal cord were normal but motor evoked potentials on magnetic brain stimulation were absent, even in the only slightly affected upper limbs. Other neurophysiological investigations were largely normal but the more affected patient had central visual field defects. Konzo is a distinct disease entity with selective type upper motor neuron damage.

X-linked bulbospinal muscular atrophy (Kennedy's syndrome): a report of three cases

Two cases of X-linked bulbo-spinal muscular atrophy and one sporadic case with the same clinical features are presented. All three cases were extensively studied by electrophysiological methods. One of the patients showed some transient weakness, which was partly improved by pyridostigmin. In this patient the Decrement test and jitter revealed a mild degree of motor-end plate dysfunction. Clinical and electrophysiological findings obtained from all three patients suggest that in Kennedy syndrome cell bodies of group IA muscle afferents are also affected selectively, with other peripheral afferents.

Turns-amplitude analysis of the electromyographic recruitment pattern disregarding force measurement. I. Method and reference values in healthy subjects

We used turns-amplitude analysis to characterize the EMG recruitment pattern disregarding force measurement. The electrical muscle pattern of the brachial biceps (BB), abductor pollicis brevis (APB), medial vastus (MV), and anterior tibial (AT) muscles was analyzed during progressive increase in force from rest to maximum using the mean amplitude as an indicator of the force of the muscle. The following parameters were obtained on-line: the maximal ratio of turns to mean amplitude (peak-ratio, PR), the mean amplitude, and the number of time intervals (TI) between turns at PR and at near maximum force (NMF). The highest PR values were obtained in BB, the lowest in MV. Analysis of the distribution of the TI between turns at different degrees of voluntary contraction showed fewer spikes with short duration and small amplitude at high force compared with low force.

Turns-amplitude analysis of the electromyographic recruitment pattern disregarding force measurement. II. Findings in patients with neuromuscular disorders

Turns-amplitude analysis of the electromyographic recruitment pattern was performed on-line in the brachial biceps muscle of 46 patients with neuromuscular disorders using the mean amplitude as an indicator of force. The parameters, peak-ratio (PR) and number of time intervals (TI) from 0 to 1.5 ms, were increased in patients with myopathy. In patients with neurogenic involvement, the characteristic pattern was a decreased PR and a decreased incidence of TI between 0 and 1.5 ms. The results indicate that the two parameters supplement each other as some of the patients were identified only by one or the other. In patients with myopathy, the method had a higher diagnostic yield than the individual motor unit action potential analysis. The method is objective, fast, and reliable.

Turn and phase counts of individual motor unit potentials: correlation and reliability

Different turn algorithms are used for quantitative motor unit potential (MUP) analysis. To compare their retest reliability, 420 myopathic and neuropathic MUPs were recorded twice and the turn count of the first registration was correlated with that of the second. Reliability was best for the algorithm according to Willison as compared to the conventionally used algorithms based on amplitude criteria for 2 or 3 successive relative extrema. As demonstrated by discriminant analysis, an amplitude limit of 25 microV yielded more useful turn counts than a limit of 50 microV if myopathic MUPs had to be discriminated from normal MUPs. For this discrimination the turn count was superior to the phase count which did not further improve the discriminant model. This was different for the discrimination between normal and neuropathic MUPs. In this case, both parameters measured partly independent features of the MUP and had to be considered together.

Myopathy in Marinesco-Sjögren syndrome: an electrophysiological study

Electrophysiological studies were performed in 7 patients with Marinesco-Sjögren syndrome in order to search for neuromuscular involvement in this multiorgan disorder. In 6 patients muscle biopsies were also obtained. Light microscopic examinations of the biopsies showed extensive myopathic changes, and in two patients ragged red fibers were found. Electron microscopy showed subsarcolemmal accumulation of abnormal mitochondria in all. Concentric needle EMG revealed unequivocal myopathic changes, more extensive in the anterior tibial than in the biceps brachii muscle. Motor and sensory conduction velocities in the peripheral nerves were normal. There were remarkably high amplitudes of sensory responses. Macro EMG studies in the biceps brachii muscle in four patients showed increased amplitude and area of the macro MUPs. This may be due to abnormal membrane function. Both electrophysiological and morphological findings confirm myopathic features of Marinesco-Sjögren syndrome.

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.

Turns-amplitude analysis at different sampling frequencies

In the EMG interference pattern the number of potential reversals of more than 100 microV (i.e., turns) measured may be low if a low sampling frequency is used. This might be more pronounced in a myopathic muscle with small short potentials than in a control muscle, resulting in a decreased diagnostic yield. The influence of sampling frequencies from 6 to 200 kHz on the turns, mean amplitude and ratio of turns to mean amplitude analysed on the interference pattern at a force of 30% of maximum was examined at 10 sites in each of 5 control muscles, 5 myopathic muscles and 5 neurogenic muscles (i.e., 150 sites in all). In this small group of muscles low sampling frequency did not tend to reduce the diagnostic yield of the measurements. Proper reproducibility was obtained with sampling frequencies down to 17 kHz. However, due to systematic errors, measurements obtained with sampling frequencies below 25 kHz require comparable control values or compensations for errors. As time intervals between turns (not studied here) have a skew distribution with many small time intervals a sampling frequency of 50 kHz or higher is probably required.

Recording characteristics of monopolar EMG electrodes

Motor unit action potentials (MUAPs) and the electromyographic (EMG) interference pattern (IP) were recorded from the biceps muscle of 5 normal subjects using both a concentric needle (CN) and a disposable monopolar needle (MN) electrode. The MUAPs recorded by the MN electrode had higher amplitude and area and were more frequently complex than those recorded with the CN electrode. The MUAP duration and area: amplitude ratio were similar for both electrodes. Although the MN electrode had a larger recording surface, its dimensions (maximum diameter and length of the cone shaped tip) were similar to those of the CN electrode (minor and major axes of the elliptical recording tip). Based on these observations, we infer that the MN electrode may be more selective than the CN electrode, ie, the AP amplitude recorded by the MN electrode decreases faster than the AP amplitude recorded by a CN electrode when the distance of the muscle fiber from the recording electrode increases. Photomicrographs of the MN electrode after use demonstrated no evidence that the insulating material had peeled off. There was also no evidence that MUAP measurement values changed during the recordings as would be expected if the recording surface changed due to peeling of the insulating material.

A comparison of turns analysis and motor unit analysis in electromyography

We compared the results of turns analysis and motor unit analysis on 4056 electromyographic interference patterns (IPs) from normal subjects and patients with neuromuscular disorders. The motor unit analysis involved decomposing the IPs into their component motor unit action potentials (MUAPs) using automatic decomposition electromyography (ADEMG). We checked the accuracy of the decompositions by attempting to reconstruct some of the IPs from their identified MUAPs using computer simulations. The simulations revealed that ADEMG typically identified more than 60% (but not all) of the MUAPs in a given IP. Both turns and MUAP properties showed regular and related changes with force, age, muscle, and recording electrode type. The number of turns in each IP was highly correlated with the number of active MUAPs (r = 0.65), the mean MUAP firing rate (r = 0.72), the mean number of turns per MUAP (r = 0.34), and the product of these 3 properties (r = 0.83). The mean amplitude change per turn was highly correlated with the mean MUAP amplitude (r = 0.82), but also depended on the number of turns per MUAP. Due to the lack of a one-to-one relationship between the turns analysis properties and the MUAP properties, the turns analysis properties by themselves did not provide sufficient information to infer unambiguous physiological information about motor unit morphology or firing behavior.

Quantitative analysis of laryngeal EMG in normal subjects

A method for quantitative analysis of the electromyographic interference pattern called "turns/amplitude analysis" was carried out with recordings from the cricothyroid and thyroarytenoid muscles of 12 normal subjects, 6 males and 6 females. The purpose was to investigate how the two muscles vary contraction force in relation to variations in pitch and voice intensity. Sustained phonations with systematic variation of pitch and intensity were analysed. The contraction force, in terms of turns and amplitude, increased with increasing pitch in both the cricothyroid and thyroarytenoid. More variability in contraction activity as a function of intensity was noted in the cricothyroid than in the thyroarytenoid. The increase in turns and amplitude in the thyroarytenoid with increasing pitch was highly significant, while little effect was seen of intensity variation. No great differences between males and females were noted.

On the shape of the normal turns--amplitude cloud

Factors that affect the shape of the so-called "normal cloud" of the turns and amplitude measurements of the electromyographic interference pattern are investigated. As the force of voluntary contraction increases from low to moderate levels, the number of turns in the signal increase faster than does the mean amplitude change between turns. This results in a cloud that is concave downward. At higher force levels, the pattern is reversed. The overall shape of the cloud thus depends on the maximum effort at which recordings are made, which is determined by the procedure of muscle activation.

Nerve-muscle involvement in a large family with mitochondrial cytopathy: electrophysiological studies

Thirteen patients with mitochondrial cytopathy were investigated. They represent different generations, ages, stages, and severities of the disease. All were assumed to have the same metabolic defect. The disease is a multisystem disorder with a metabolic defect located at complex 1 in the respiratory chain. Clinically, the disorder gives symptoms such as hearing loss, retinal pigmental degeneration, ataxia, cardiomyopathy, muscular fatiguability and neuropathy. The patients were investigated with nerve conduction studies, concentric needle EMG, SFEMG, and macro EMG examinations. Neurophysiologic studies revealed signs of myopathy in both the younger members and in those with slight muscular symptoms. In the more advanced stages, neuropathic changes of the axonal type were seen as well. Macro EMG was interpreted as indicating muscle fiber membrane abnormalities in the early stages. Single fiber EMG studies indicate that this metabolic defect does not disturb neuromuscular transmission.

Measurement of the amplitude of the EMG envelope

When the force of muscle contraction is increased, the amplitude of the EMG envelope (ENAMP) increases. The ENAMP is usually assessed subjectively and its value in EMG analysis has been established. In this article we describe a method to make automatic measurements of the ENAMP. This method was tested on recordings of the EMG interference pattern (IP) from the biceps muscle of normal subjects. Normal values of this feature in the biceps muscle are described. There was a good concordance between the ENAMP measurements made by subjective assessment and by automatic analysis and the ENAMP values correlated strongly with a previously described feature of the IP called the upper centile amplitude. We infer that ENAMP is a robust feature of the IP that reflects the amplitude of the largest MUAP in the IP.

Evaluation of laryngeal muscle function by quantitative analysis of the EMG interference pattern

A computerized method for quantitative analysis of the EMG interference pattern was tested in the cricothyroid and thyroarytenoid muscles with the purpose of evaluating its usefulness for clinical purposes. In a normal male subject the mean amplitude and the number of turns/s were extracted from the EMG signal of sustained chest register phonations, with systematic variation of vocal pitch and intensity. In the cricothyroid, as well as the thyroarytenoid muscle, there was a considerable increase in mean amplitude and turns/s with both increased pitch and increased intensity. Pitch variation was the most effective way to induce changes in turns and amplitude levels in both muscles. In contrast to results from studies of larger muscles, the increase in both amplitude and turns was proportional to muscle force also at the highest loads.

Skin biopsy findings in glycogenosis III: clinical, biochemical, and electrophysiological correlations

Electron microscopy of skin specimens was performed in 4 patients (age range, 7 months-40 years) with glycogenosis III and revealed consistent abnormalities. Massive glycogen storage was observed in epithelial secretory cells of eccrine sweat glands and, less markedly, in smooth muscle fibers from the erector pili. Other cells, including Schwann cells of myelinated and unmyelinated fibers, were not affected. The extent of glycogen storage was similar in all patients and unrelated to age or duration of disease. The extralysosomal nature and selectivity of glycogen deposits, sparing fibroblasts and other cells, differ clearly from the findings in skin from patients with glycogenosis II. The purpose of this study was to show that glycogen deposits in glycogenosis III are not restricted to skeletal muscle and liver, and to assess the usefulness of skin biopsy in this disorder.

Electromyography of the muscles of oropharyngeal swallowing: basic concepts

Electromyography (EMG) has a valuable role in the evaluation of swallowing and its disorders, because it can assess the activity of individual muscles. Electromyographic kinesiology is a method for examining the physiology of swallowing. Analysis of individual myoelectric potentials is a technique for studying the integrity of the motor unit. This paper introduces the concepts of the motor unit, explains basic principles of EMG, and explores their relevance to the study of oropharyngeal swallowing. Several cases are presented to illustrate how EMG contributes to clinical diagnosis.

Type 1 fiber abnormalities in skeletal muscle of patients with hypertrophic and dilated cardiomyopathy: evidence of subclinical myogenic myopathy

Abnormalities of skeletal muscle have been described in patients with dilated and hypertrophic cardiomyopathy. Eleven patients with dilated and eight with hypertrophic cardiomyopathy without overt symptomatic skeletal myopathy underwent extensive neuromuscular studies. Quantitative electromyography showed abnormal reduction of motor unit potential duration, indicative of myogenic myopathy, in four patients (36%) with dilated and in three (37%) with hypertrophic cardiomyopathy. Values were 21% to 40% (mean 28%) lower than those in age-matched normal control subjects. The presence of normal nerve conduction velocities and of normal motor unit fiber density in all patients indicated lack of neurogenic abnormalities. Skeletal muscle biopsy was performed in five patients with dilated and in four with hypertrophic cardiomyopathy. In all nine patients light and electron microscopy showed central hyporeactive cores, selective atrophy and mitochondrial abnormalities of type 1 fibers but not of type 2 fibers. The degree of impairment of left ventricular function in patients with electromyographic abnormalities was similar to that of those without (percent fractional shortening at two-dimensional echocardiography 21 +/- 9 versus 25 +/- 10, ejection fraction at angiography 39 +/- 13% versus 42 +/- 13% and left ventricular end-diastolic pressure 21 +/- 6 versus 21 +/- 8 mm Hg) as well as symptom duration (9 +/- 4 versus 12 +/- 8 months). Thus, subclinical electromyographic alterations indicative of myogenic myopathy are frequent in patients with dilated and hypertrophic cardiomyopathy and are unrelated to the degree of impairment of left ventricular function. The concomitant histologic alterations, characterized by selective type 1 atrophy, are similar to those observed in congenital and idiopathic myopathies, but different from those described in secondary heart failure.

Complete bilateral internal ophthalmoplegia as sole clinical sign of botulism: confirmation of diagnosis by single fibre electromyography

A case of complete bilateral internal ophthalmoplegia as the sole clinical sign of botulism is reported. Diagnosis was immediately confirmed by single-fibre electromyography (SFEMG), which revealed abnormally high blocking (14.3%), contrasting with moderately increased jitter (mean consecutive difference in the extensor digitorum communis muscle, 43.9 microseconds). After giving equine botulinum antitoxin and simultaneous forced emptying of the bowels, ocular symptoms completely disappeared within 2 days. Six days, 5 weeks and 6 months after the first SFEMG study, the jitter was still abnormal, even becoming more so with time. Blocking, however, was only rarely observed in the follow-up studies. It is concluded that SFEMG may serve as a useful and sensitive method for the rapid diagnosis of botulinum intoxication, even in cases where no clinical signs of general muscular weakness are apparent.

Automatic analysis of the electromyographic interference pattern using the turns: amplitude ratio

This study was performed to compare different techniques of analyzing the electromyographic interference pattern (IP). Recordings were made from the biceps muscle with a concentric needle electrode at different sites and at different constant levels of voluntary contraction. The number of turns per second (NT), the mean amplitude change between successive turns (MA) and NT:MA ratio were determined for epochs of 1 sec duration. Normal limits of individual epoch NT:MA ratios and the mean value of NT:MA ratio obtained from all epochs in each muscle were determined. The mean NT:MA ratio was less in normal males than in females. IP recordings were made in the biceps muscle of 69 patients with neuropathy and 54 patients with myopathy, though this muscle was not necessarily affected by the disease in all patients. The IP was abnormal by visual inspection in 82% of patients compared to 61% based on NT:MA ratio and 74% using a technique that automatically quantitates some features of the IP that are assessed subjectively by an electromyographer. All techniques demonstrated IP abnormalities in more than 80% of the muscles that were moderately to severely weak. Though measuring the NT:MA ratio without monitoring the force of contraction is not as sensitive as other IP analysis techniques, it may be useful in quantitating abnormalities when other techniques are not available.

Properties of motor unit action potentials recorded with concentric and monopolar needle electrodes: ADEMG analysis

We compared the configurational and firing properties of 7270 motor unit action potentials (MUAPs) recorded with either concentric (CNE) or monopolar (MNE) needle electrodes from the brachial biceps and anterior tibial muscles of 10 healthy young adults (mean age 27 +/- 4.5 years) using automatic decomposition electromyography (ADEMG). In both muscles, mean MUAP amplitude, rise rate, and number of turns were significantly greater when recorded with MNE (paired t-test, P less than 0.001 in each case). Similar findings were observed at all three tested levels of isometric contractile force: threshold, 10% of maximum voluntary contraction (MVC), and 30% MVC. In contrast, there was no significant difference between electrode types on measurements of mean MUAP duration or firing rate (P greater than 0.05 in each case). These findings indicate that it is acceptable to generalize normative data on MUAP duration and firing rate from one electrode type to another, but that measures of MUAP amplitude and complexity require independent normative databases.

Influence of contractile force on properties of motor unit action potentials: ADEMG analysis

We have used automatic decomposition electromyography (ADEMG) to measure the configurational and firing properties of 13,206 motor unit action potentials (MUAPs) in the brachial biceps, brachial triceps and anterior tibial muscles of 30 healthy adults (22 men, 8 women; mean age 48.6 +/- 16.9 years, range 20-76) at three levels of isometric contractile force: threshold, 10% of maximum voluntary contraction (MVC), and 30% MVC. In all muscles, the increment in contractile force from threshold to 10% MVC was associated with a significant (P less than 0.05, paired t-test) increase in mean MUAP firing rate and number of turns per MUAP. The increment from 10% to 30% MVC led to highly significant (P less than 0.005) increase in mean firing rate, number of turns, amplitude and rise rate. Each force increment was associated with an increase in the number of simultaneously-active MUAPs per recording site; and with a significant decrease in mean MUAP duration in all muscles, due to noise-dependency of the duration measurement. Quantitatively, the changes in MUAP properties with force were comparable to or exceeded the effects of age, gender differences, or intermuscular variability. Test-retest measurements 2 years apart in a subgroup of young adults showed good correspondence of mean MUAP properties with force standardization. These results demonstrate that contractile force is a major determinant of MUAP shape and behavior properties, and so must be precisely measured or controlled in clinical EMG studies.

AAEE minimonograph #29: automatic quantitative electromyography

The present status of different computerized methods of automatic quantitative electromyography are reviewed. Interference pattern methods-turns analysis, spectral analysis-are efficient, but the results usually cannot be directly related to the physiological properties of the motor units. Integration analysis does not currently have a major role in diagnostic electromyography. Traditional measurement of single motor unit action potentials during weak contraction can be facilitated and made more objective with computer assistance, but only the lowest-threshold motor units in the muscle are amenable to study. A new class of methodologies under development permit the decomposition of interference patterns into their constituent motor unit action potentials for measurement of configurational and behavioral properties. Patient data from these various methods can be statistically compared with normative data bases available on-line in computerized electromyographs. Both quantitative and quantitative electromyography have applications in the neuromuscular electrodiagnostic examination.

Autosomal dominant Emery-Dreifuss syndrome: evidence of a neurogenic variant of the disease

The first German family with autosomal dominant Emery-Dreifuss syndrome (EDS) is described, with electrophysiologic and myopathologic results providing evidence of a primary neurogenic disease. According to classification of the scapulo peroneal syndrome without cardiomyopathy, we conclude that there are two variants of EDS: one myopathic, the other neurogenic in origin. Therefore, the term Emery-Dreifuss muscular dystrophy should be avoided. Instead, each case of EDS should be classified as myopathic or neurogenic with X chromosome recessive or autosomal dominant inheritance.

Automatic analysis of the electromyographic interference pattern. Part II: Findings in control subjects and in some neuromuscular diseases

The electromyographic (EMG) interference pattern (IP) was measured in the biceps muscle of 16 normal male and 17 normal female subjects. The activity, upper centile amplitude (UCA), and the number of small segments (NSS) (defined in a companion paper) were measured from 500-msec epochs of the IP. The normal values of these features were defined separately for men and women by plotting the UCA and NSS values against activity for each epoch and defining an area on these plots, called a "cloud," that contained more than 90% of the datum points from each study. The mean deviation of the individual datum points from the overall mean values was also calculated for each study. A study in one muscle is considered to be normal if more than 90% of the datum points from that muscle are within the normal clouds and the deviation values are within their normal range. In patients with neuropathy, the characteristic pattern was increased UCA with normal or decreased NSS. In patients with myopathy, NSS was increased and the UCA was normal or decreased. In all studies, the interpretations of the IP from the plots agreed with qualitative assessments of the IP made independently by an electromyographer. The use of these features to understand and quantitate the changes in the motor units produced by disease is demonstrated by serial studies performed in a patient with motor neuron disease.

Automatic analysis of the electromyographic interference pattern. Part I: Development of quantitative features

We have developed three new features of the electromyographic interference pattern (IP), based on the turns and amplitude of the signal, to quantitate some of the features of the IP that are usually assessed subjectively by an electromyographer. The activity measures the fullness of the IP. The upper centile amplitude (UCA) defines the upper limit of the maximum peak-to-peak amplitude of the motor unit action potentials (MUAPs) contained in the IP. The number of small segments (NSS) measures the complexity of the IP, which is a reflection of the polyphasicity of the component MUAPs. The activity and the logarithm of the UCA correlate strongly with the force of muscle contraction at which the IP is measured. The NSS initially increases with the force of contraction and becomes relatively constant at higher force levels. The normal values of these features and the interpretation of their relationships are described in companion papers.

Simulation and analysis of the electromyographic interference pattern in normal muscle. Part I: Turns and amplitude measurements

The electromyographic (EMG) interference pattern (IP) was simulated by adding together motor unit action potentials (MUAPs) of different sizes that had been recorded by a concentric needle EMG electrode. The number of turns (NT) of the simulated IP increased with the number of MUAP discharges. The mean amplitude (MA) difference between successive turns in the IP increased when large amplitude MUAPs were added. Our analysis demonstrates that the MA of the IP is determined mainly by the amplitude of large MUAPs in the signal and that large amplitude spikes are more likely to be generated by single large amplitude MUAPs than by summation of several small amplitude MUAPs.

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

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.

Cisplatin neuropathy with Lhermitte's sign

Following chemotherapy with cis-diamminedichloroplatinum II (cisplatin) three patients developed Lhermitte's sign and peripheral neuropathy. The toxic side effects did not become apparent until after treatment had ceased. Because of increasing use of cisplatin to achieve lasting remission in patients with malignant disease proprioceptive and myelopathic side effects may become increasingly common.

Automatic decomposition electromyography (ADEMG): validation and normative data in brachial biceps

We describe a new, automatic method (ADEMG) for decomposing EMG interference patterns into their constituent motor unit action potentials (MUAPs), and quantitating the configurational and firing properties of the MUAPs. ADEMG is fast (90 sec analysis time for a 10 sec EMG epoch) and efficient (33-98% of MUAP occurrences correctly identified) because of 4 signal-processing innovations designated digital prefiltering, high-resolution wave form alignment, firing-time analysis and interference-cancellation averaging. Validation experiments are described involving recruitment/derecruitment of low-threshold MUAPs, and single-fiber-triggered averaging. Normative data are presented for 2000 MUAPs from brachial biceps (mean 9.7 MUAPs per site) at 3 levels of isometric contraction (7%, 15% and 30% MVC) and contrasted with normal findings obtained using traditional, low-threshold MUAP analysis. The main advantages of ADEMG are speed of data acquisition and processing in the clinical setting; ability to analyze both low- and high-threshold MUAPs during moderately strong muscular contractions; and MUAP firing-rate information.

Chronic neurogenic quadriceps amyotrophies

Two cases of quadriceps amyotrophy, probably of chronic neurogenic origin are reported. Only the knee jerks were diminished, the calves hypertrophic, and the serum creatine kinase level very high in one case, and there were neurogenic electromyographic abnormalities in the quadriceps. In the first case, biopsy of the quadriceps muscle revealed a neurogenic origin with hyalinized hypertrophic fibres. CT scan showed abnormalities not only in the quadriceps but also in the sartorius, gracilis and gastrocnemius muscles. A second biopsy specimen from the gastrocnemius muscle showed histological findings similar to those of the quadriceps. In the second case, the EMG and biopsy findings suggested a myogenic origin, but 6 years later they were compatible with neurogenic atrophy. Differentiation from Becker dystrophy is very difficult in the first case and the second case is more a focal spinal amyotrophy. Further, in spite of their localization, the extension of the affected muscles changes the diagnosis. The same applies to chronic quadriceps amyotrophy in general, which cannot be regarded as an entity, but which suggests muscular dystrophy, spinal atrophy, polymyositis or a metabolic disorder. These cases can be compared with the four cases reported in the literature, which were regarded as a "forme fruste" of chronic spinal amyotrophy.

Turns analysis (peak ratio) in EMG using the mean amplitude as a substitute of force measurement

Several modifications of turns and mean amplitude analysis of the electrical activity of muscles have been suggested to avoid measurement of force. Previously we have shown that these modifications may overlook abnormalities if the analysis is performed at high force. A new modification is suggested: analysing the maximal value of the ratio of turns to mean amplitude (peak ratio), using the mean amplitude as an indication of force. It has been applied to a material in which the force was measured. The peak ratio was increased in 82% of 17 patients with myopathy and decreased in 36% of 14 patients with neurogenic disorders.

Pattern of electrical activity and force in normal and pathological muscle: S-index of turns and amplitude

Cenkovich et al. (1982) found that a rotated hyperbolic curve fitted the relationship between the logarithm of cumulative amplitude (log A) and the logarithm of turns (log T). They found the intercept of the hyperbola (S-index) to be independent of force and suggested to use the S-index without measurement of the force as a diagnostic criterion. We have applied this modification of the method to our material previously published. In controls we found a slight increase in S-index with increasing force. The S-index was often increased in patients with myopathy and decreased in patients with neurogenic disorders, mostly at low to moderate force. The S-index was not better in discriminating patients from controls than the ratio of turns to mean amplitude.