Clinical Neuroscience

[ELECTROMYOGRAPHY AT THE BEGINNING OF THE 21st CENTURY]

DIÓSZEGHY Péter

DECEMBER 10, 2005

Clinical Neuroscience - 2005;58(11-12)

[This review article is concerned with the role of electromyography (EMG) in the clinical diagnostic work. After a summary on the developmental history of electromyography, the most important EMG methods are presented. The modern quantitative EMG methods are sensitive and accurate thus providing important information in the evaluation of various neurological diseases, particularly in the diagnosis of neuromuscular disorders. The EMG examinations are useful tool for the clinician only if the applied methods are carefully chosen and properly performed and the rules of interpretation are strictly followed.]

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[THE ROLE OF EVOKED POTENTIAL METHODS IN THE NEUROLOGICAL CLINICAL PRACTICE]

KUNDRA Olga

[The author provides an overview on the value of evoked potential (EP) methods (VEP, SEP, BAEP, MEP) in the diagnosis and follow-up of various neurological diseases (multiple sclerosis, cerebrovascular disorders, degenerative diseases, coma, epilepsy, migraine) by reviewing the literature supported by his own clinical experience. While in the past EP was mainly used for establishing the diagnosis, recently, with the expansion of neuroradiology, it has gained a wider use in the assessment of the severity and extent of the pathologic process and especially in longitudinal follow-up. Its role in the diagnostic phase has diminished. In patients with multiple sclerosis the abnormality of the evoked potentials correlate better with the clinical state than with the MRI results. The method is also suitable to monitor the response to therapy. The importance of the EP tests is illustrated by several case demonstrations.]

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[PSYCHOPHYSIOLOGICAL AND CLINICAL ASPECTS OF THE EEG SYNCHRONIZATION RELATED TO COGNITIVE PROCESSES]

MOLNÁR Márk, CSUHAJ Roland, CSIKÓS Dóra, HAMVAI Csaba, CZIGLER Balázs, BÁLINT Andrea, GAÁL Zsófia Anna

[The authors review the various forms of EEG-synchronization with special emphasis on the characteristics of the induced and enhanced rhythms. The suggested role of the various EEG frequency bands in the cognitive processes is demonstrated by examples from the literature. The relationship between linear and nonlinear electrophysiological complexity and EEG synchronization is analyzed, with a touch on the use of Omega-complexity and synchronization likelihood methods. In the present study the EEG recorded during adding and subtracting tasks was analyzed with the above methods. It was found that during the adding task the theta band increased in the frontal area, which may be related to activation of working memory processes. Mapping the scalp-distribution of synchronization likelihood also confirmed increased synchronization in the frontal area in addition to which increased values were found in the left temporo-parietal area. The analysis of linear and nonlinear EEG synchronization associated with cognitive processing is suitable to explore the task-related and region specific features of these events.]

Clinical Neuroscience

[BASIC NEUROGRAPHY AND ITS DIAGNOSTIC IMPORTANCE]

KISS Gábor

[Nerve conduction studies are fundamental elements of the neurophysiological investigation of neuromuscular diseases. They provide information on peripheral nerve function. Knowledge of the biological and technical basis of the method is essential for the clinician to understand the place of nerve conduction testing in the diagnostic process. A characteristic feature of the nerve fibers is their ability to conduct electrical potentials. This conductivity changes in pathologic circumstances; therefore, the patient's nerve conduction data may be important if a neuromuscular disorder is suspected. The electrical activity spreading along the nerve fibres can be detected with special techniques and instruments. To perform an examination, a stimulator, a high quality amplifier and a computer with various accessories are necessary. The examination is usually carried out by surface stimulation and recording electrodes and requires some cooperation. By supramaximal stimuli all nerve fibers in the peripheral nerve are activated, and their summated activity is recorded bipolarly. For technical reasons the procedures for the motor and the sensory nerve conduction measurements are somewhat different, but their principles are similar. A number of parameters, such as the latency, the amplitude, the area and the shape of the evoked potentials are analyzed. These parameters are influenced by many biological (age, gender, body height, etc.), physical (such as limb temperature) and technical factors. The results are compared with the reference data. Nerve conduction studies may help distinguish between normal and diseased nerve function. The latter has two main categories; axonal lesion and demyelinisation. Axonal lesion is characterized by relatively normal conduction velocity and lower than normal amplitude of the potentials. Demyelinisation is almost the opposite with long latencies, slow conduction velocity and relatively spared potential amplitudes. Nerve conduction studies help differentiate between these two forms. Abnormalities found by nerve conducion measurement may reflect the severity of the disease. Repeated studies are suitable for quantitative follow-up. The anatomical, physiological, pathophysiological and technical details are discussed below. The characteristic neurographic findings of various diseases are also summarized.]

Clinical Neuroscience

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[Introduction - While it is several decades ago that electrophysiological studies in the early stages after an ischaemic stroke revealed spontaneous activity in the affected muscles, today few data are available on the peripheral changes in later stages after a cerebrovascular event. The aim of this study was to detect electrophysiological signs that could indicate changes at the motor unit level occurring within a longer post-stroke period. Patients and methods - Forty-four patients who had developed hemiparesis after an ischaemic stroke in the area of the middle cerebral artery were involved in the study. Motor and sensory nerve conduction studies and electromyography were carried out on each side on six nerves and in five muscles respectively. Values between the affected and unaffected side were compared by statistical methods. Results - In patients with hemiparesis present for less then nine months, low M wave amplitudes, fibrillation potentials and an increased number of complex motor unit potentials were found on the affected side; in patients with symptoms present for more then nine months the mean duration and size index of the motor unit potentials in the paretic abductor digiti minimi muscle were increased. These data suggest a process of neurogenic type. The signs of distal axonal damage observed in the early period after stroke have been replaced later by chronic neurogenic changes. These changes could be the consequence of spinal motor neuron damage and axonal transport disturbance due to the loss of supraspinal trophic inputs. Conclusion - The correlation between the extent of electrophysiological changes and of the central motor deficit of the patient indicates the importance of delaying this process by appropriate rehabilitation procedures.]