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.     

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.     

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.     

Simulation and analysis of the electromyographic interference pattern in normal muscle. Part II: Activity, upper centile amplitude, and number of small segments

We have defined three new features of the electromyographic (EMG) interference pattern (IP): activity, upper centile amplitude (UCA), and number of small segments (NSS). These parameters were measured in simulated IPs constructed by adding together motor unit action potentials (MUAPs) recorded with a concentric needle EMG electrode. The activity increases linearly with the number of MUAP discharges to approximately 80% of its theoretical maximum value. The UCA correlates strongly with the peak-to-peak amplitude of the largest MUAP in the IP and the mean segment amplitude and does not depend on the discharge rate of the largest MUAPs. We infer that the UCA defines the upper limit of the peak-to-peak amplitude of the MUAPs contained in the IP. The NSS increases with the number of MUAP discharges, but reaches a constant value at higher MUAP discharge rates, probably because small amplitude MUAPs are masked by the large amplitude MUAPs. The potential value of these parameters in automated IP analysis is discussed.     

Isometric features of orthostatic tremor: an electromyographic analysis

A patient is described with "orthostatic" tremor. Electromyography revealed tremor bursts of 15 Hz in the lower extremities while standing and with isometric activation of the muscles, but the bursts disappeared with isotonic activation of muscles. Similar tremor was recorded in the arms with isometric, but not isotonic activation. Review of previously reported cases confirms these findings. The clinical and electrophysiologic features of this tremor distinguish it from other recognized forms of tremor.     

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.     

Syringomyelia: a retrospective study. Part I: Clinical features

We performed a retrospective study of 62 patients with syringomyelia. Most noteworthy among the clinical features in our patient population are the following: segmental sensory disturbances are usually less restrictive than the classical thermoanalgesia, pain is a presenting symptom in almost 50% of cases, and skeletal abnormalities of the "status dysraphicus" are very common. The different hypotheses about the pathogenesis are also discussed.     

Delirium tremens. Some clinical features. Part I

Twenty patients with delirium tremens and related states were investigated from the time of admission until the acute state was over. Using strict diagnostic criteria the material was divided into two groups according to the severity of the clinical condition; nine patients had fully developed delirium tremens (grade 3), 11 patients had a less severe clinical state, known as "Predelirium" (grade 2). The material was found to be representative for the condition under discussion. Patients with grade 2 were admitted during the day and the evening, but not during the night; patients with fully developed delirium tremens (grade 3) were admitted during both the day and the night, and this difference is discussed. The two groups had the same pattern of alcohol abuse, but patients with proper delirium tremens had had a drinking bout preceding the acute state; this was not seen among patients with a less severe clinical state. Patients with grade 2 had had symptoms like sleep disturbances and gastro-intestinal disturbances for 12-24 hours before the admission, whereas grade 3 patients had had such symptoms for about 48 hours. Patients with grade 2 stopped drinking when the first symptoms of the acute state appeared, whereas patients with fully developed delirium tremens continued to drink in spite of their condition. These anamnestic were supported by the finding that significantly more patients with proper delirium tremens had alcohol in the blood--several even concentrations about 2 g/l--at the time of admission compared to patients with a less severe clinical state. This lack of "latency period", which previously has been described as a typical feature in the development of delirium tremens, is discussed. It is concluded that due to the methodology used, it has been possible to point out some of the differences between the milder, often harmless, conditions and the potentially serious, fully developed delirium tremens.     

A comparison of two commercial quantitative electromyographic algorithms with manual analysis.

Quantitative EMG (QEMG) is a useful technique in the evaluation of neuromuscular disease. Manual waveform measurements have been replaced by automated computer-based measurements, but there is no uniformity in computer algorithms used to make waveform measurements. We compared QEMG measurements made by algorithms in two commercially available EMG machines with manual measurements. Motor unit action potentials (MUAPs) were simultaneously fed into the two machines and analyzed using QEMG default settings and automatic waveform marking. The averaged MUAPs were also manually marked. The two algorithms and manual marking did not differ significantly for MUAP amplitude. There were significant differences between algorithms for duration and number of phases. Our study indicates that, although automated algorithms make QEMG more practical, visual inspection, and remarking of each MUAP if needed, is necessary before making clinical judgments from the data.     

The utility of interference pattern analysis

The interference pattern of the electrical activity of muscle can be quantified by amplitude measurements, different spike counting methods, and power spectrum analyses. Interference pattern analysis (IPA) methods are used to describe the degree of activation of different muscles, muscle fatigue, occupational work, muscles in chronic pain syndromes, disused muscle, and dystonic muscle treated with botulinum toxin. In patients with neuromuscular disorders, the turns/amplitude analysis is useful for diagnosis. High diagnostic yields can be obtained without force measurements, for example, by using the amplitude as an indicator of force (the peak ratio method) or plotting the amplitude against the turns (cloud analysis). The diagnostic possibilities of the power spectrum analysis and the motor unit firing rate obtained by decomposition techniques are still unclear.     

Cerebellar astrocytomas. Part I. Macroscopic and microscopic features

Some of the pathological features of 112 cerebellar astrocytomas seen at The Radcliffe Infirmary between 1938 and 1984 have been described. These include the following: Macroscopic appearance: Cerebellar astrocytomas, when compared to other gliomas, have an unusual tendency to become cystic. Thus, if all ages are considered only 22% are total solid tumors while the others have either a large solitary cyst or many smaller ones. Although patients with cystic tumors remain free of recurrence far longer than those with totally solid astrocytomas, the proportion of cystic and solid elements does not significantly influence the overall survival period. Moreover, the degree of tumor demarcation is not an absolute indicator of the degree of malignancy. Extent of disease: Approximately 8% of cerebellar astrocytomas infiltrate the brainstem and these cases are associated with the poorest prognosis. Supratentorial invasion is very rare and CSF dissemination is very uncommon. Only one example of the latter was recorded in the present study. It is important to note that subarachnoid spread may also occur from histologically benign tumors as well as malignant cerebellar astrocytomas. Classification by growth pattern: The classification of cerebellar astrocytomas by "growth pattern" is clearly of limited use. This is due to the presence of substantial transitional forms in both the "juvenile" and "diffuse" as well as in the "fibrillary" and "protoplasmic" classifications. Confusion also arises because of the disregard for the quantity and distribution of certain features which, in turn, limits the usefulness of the "A" and "B" type classification system. Failure to define rigorously the cell type which predominates in the "cerebral" and "diffuse" forms also creates substantial difficulties in using Ringertz' nomenclature. Further problems are caused by Zülich's "polar spongioblastomas" since cerebellar astrocytomas are not composed of primitive spongioblasts, the "polar spongioblastomas" merely representing one subtype of cerebellar astrocytoma, namely the piloid or pilocytic variety. Attempts to classify cerebellar astrocytomas in a manner which does not rely upon any specific cell type but which depends instead upon the degree of homogeneity or heterogeneity of cell growth is of limited value. Grading schemes: Although the tumors studied in the present report were not graded, previous authors have shown that "grading schemes" are of little predictive value in assessing the behavior of cerebellar astrocytomas.(ABSTRACT TRUNCATED AT 400 WORDS)     

Turns-amplitude analysis of the electromyographic recruitment pattern following upper motor neuron lesions

OBJECTIVE: To assess the pattern of motor unit recruitment of weak muscles in upper motor neuron (UMN) lesions. MATERIALS AND METHODS: Ten patients underwent turns-amplitude analysis (TAA) on the paretic and healthy brachial biceps muscles, in the acute and subacute stages of hemiparesis. The control group comprised 10 age- and sex-matched subjects. RESULTS: Although absent in the acute stage, five patients developed a myogenic cloud pattern in their paretic extremities in the subacute stage; which was statistically significant when compared with controls (P = 0.033). Mean amplitude was reduced in both acute and subacute stages of the hemiparesis compared with controls (P = 0.000). The turns/mean amplitude ratio in the subacute stage was increased compared with both the paretic limbs examined in the acute stage (P = 0.000) and to controls (P = 0.000). CONCLUSION: Abnormalities in the recruitment of motor units in UMN lesions give rise to a myogenic cloud pattern in the TAA, which is prominent in the third month after the initial insult. This may result from the increase in motor unit activity, while the recruitment of bigger motor units is still defective.     

Novel measurement for automated interference pattern analysis of the diaphragm

The automated interference pattern analysis for limb muscles was modified to take into account the unique features of the needle EMG of the diaphragm. The modification was successful in recording more accurately the number of small and large segments and the activity levels with inspiratory effort. “Clouds” were generated in ten healthy subjects. The techniques may prove useful in electrophysiological investigations. © 1997 John Wiley and Sons, Inc.     

Peak-ratio interference pattern analysis in the detection of neuromuscular disorders

Peak-ratio interference pattern analysis (peak-ratio method) is said to have a high sensitivity and to be independent of sex and age. This study was carried out to prove or disprove these findings. The peak-ratio method and qualitative motor unit action potential (MUAP) analysis were applied to the right brachial biceps and anterior tibial muscles of 44 healthy subjects, aged 23–87 years, 25 neuropathy patients, aged 21–83 years, and 29 myopathy patients, aged 19–70 years. Peak-ratio parameters were independent of sex and age. They tended to be lower in the anterior tibial muscle than in the brachial biceps muscle. Neuropathy patients typically showed decreased peak-ratio, short time intervals and increased amplitude/turn. Myopathy patients typically showed increased peak-ratio, turns/s and short time intervals. The sensitivity of the peak-ratio method was 72% for neuropathy patients and 59% for myopathy patients. The sensitivity of the peak-ratio method was similar to that of the MUAP analysis in neuropathy patients and higher than that of the MUAP analysis in myopathy patients. The specificity of the peak-ratio method was 80%. The peak-ratio method proved to be a valuable, supplementary electromyographic tool for the detection of neuromuscular disorders.     

Relationship between stress and relapse in multiple sclerosis: Part I. Important features

OBJECTIVE: The aim of this two-year prospective study was to examine the relationship between multiple aspects of life-event stress and relapse in multiple sclerosis (MS) patients. BACKGROUND: Few studies have defined the critical features of this life-event stress; for example, stressor duration, frequency, severity, disease-dependency, valency, or stressor constructs, such as the propensity to cause emotional distress/threat or the frustration of life goals. METHODS: 101 consecutive participants with MS were recruited from two MS clinics in Sydney, Australia. Stressful life events were assessed at study-entry and at three-monthly intervals for two years. Patient-reported relapses were recorded and corroborated by neurologists or evaluated against accepted relapse criteria. RESULTS: Acute events, but not chronic difficulties (CDs), predicted relapse occurrence: acute stressor frequency counts predicted greater relapse risk, along with low disability score (EDSS) and being male. We also confirmed the bi-directional stress-illness hypothesis: stressors predicted relapse, and relapse separately predicted stressors. CONCLUSIONS: Life-event stress impacts to a small degree on MS relapse. The number and not the severity of acute stressors are most important; chronic stressors do not predict later relapse. Males and those with early stage disease are also at greater risk of relapse. MS patients should be encouraged to reduce acute stressors during times of high stress, and feel reassured that disease-related chronic stressors do not increase their relapse risk.     

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.     

Reliability of quantitative EEG features.

OBJECTIVE: To investigate the reliability of several well-known quantitative EEG (qEEG) features in the elderly in the resting, eyes closed condition and study the effects of epoch length and channel derivations on reliability. METHODS: Fifteen healthy adults, over 50 years of age, underwent 10 EEG recordings over a 2-month period. Various qEEG features derived from power spectral, coherence, entropy and complexity analysis of the EEG were computed. Reliability was quantified using an intraclass correlation coefficient. RESULTS: The highest reliability was obtained with the average montage, reliability increased with epoch length up to 40s, longer epochs gave only marginal improvement. The reliability of the qEEG features was highest for power spectral parameters, followed by regularity measures based on entropy and complexity, coherence being least reliable. CONCLUSIONS: Montage and epoch length had considerable effects on reliability. Several apparently unrelated regularity measures had similar stability. Reliability of coherence measures was strongly dependent on channel location and frequency bands. SIGNIFICANCE: The reliability of regularity measures has until now received limited attention. Low reliability of coherence measures in general may limit their usefulness in the clinical setting.     

Chondrodystrophic myotonia: electromyographic and cardiac features of a case

The Schwartz-Jampel syndrome or chondrodystrophic myotonia is a rare disease characterized by dwarfism, diffuse osteoarticular alterations, ble-pharospasm, perioral muscular contractions and electromyographic alterations. The authors present a case of chondrodystrophic myotonia focusing mainly on facial electromyographic and cardiac findings. The electromyo-graphy of the orbicularis oculi muscles showed abundant myotonic discharges like other facial muscles as well as muscles of the members. It was not possible to obtain true electrical silence between myotonic discharges, suggesting that the blepharospasm is a consequence of persistent muscular contraction. No conclusive evidence of myocardiopathy was given by clinical or laboratory cardiac examinations. General characteristics of the syndrome are discussed as well as the treatment with procamide and phenytoin.