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WS-2-1 Single fiber EMG in neuromuscular disorders
Workshop 2. Single fiber EMG
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to midbrain as well as in the more caudal structures such as the medulla oblongata. G e n e r a t o r sources of far-field P30 and N33 components produced by posterior tibial nerve stimulation were compared with those of the P14 and N18 components of median nerve stimulated SSEPs. Intracranial spacio-temporal distributions of P30 and N33 were similar to those of the P14 and N18. In clinical cases, the changes in P30 and N33 were correlated with those in P14 and N18, indicative that P30 and N33 are derived from activities similar to those that produce P14 a n d N18.
In ALS, jitter values increase with stimulation rates of up to 20 Hz that indicate involvement of nerve terminal. In neuropathies, S F E M G is useful in detecting and quantitating axonal degeneration in demyelinating neuropathy. In myopathy, fiber density may increase slightly due to involvement of intramuscular nerve and fiber splitting. Jitter is sometimes increased in voluntary S F E M G due to velocity recovery function (VRF). A n o t h e r advantage of S-SFEMG is its ability to exclude the V R F effect due to stable firing rate. The combined application of voluntary S F E M G and S-SFEMG is useful to study the neurogenic nature in myopathy.
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Far-field potentials in surface EMG
Dick F. Stegeman, Karin Roeleveld, Dick M. Vingerhoets.
Institute of Neurology, Department of Clinical Neurophysiology, University Hospital Nijmegen, The Netherlands Most potentials recorded in neuromuscular electrophysiology change in amplitude, wave shape and even polarity when the recording electrode is moved over a small distance. First in the electroencephalogram, components were described which hardly change their characteristics with electrode position over the body or over the scalp. In this contribution it will be shown that these "far-fields" also form a part of surface E M G recordings during voluntary contractions. From basic electric field theory it can be concluded that these far-field p h e n o m e n a are generated by dipolar sources in any finite volume conductor. Propagating action potentials of nerve and muscle fibres are composed of two equal dipoles of opposite direction. For such a source the far-field contributions cancel. Therefore, propagating nerve and muscle fibre action potentials are not expected to generate far-fields. However, when the constant propagation of an action potential is disturbed in the widest sense of the word, far-field potentials are generated. This can be understood from an incomplete cancellation for some time. Such a disturbance can be caused by: 1) A change in the size of the extracellular medium, 2) a changing extracellular conductivity, 3) the generation or the blocking of an action potential and 4) a change in the direction of action potential propagation. It is evident that situations described in the above are numerous all over the neuromuscular system. It will be shown that far-field components in E M G records are predominantly caused by the blocking of action potentials at the fibre-tendon transition (see cause 3) above).
WS-2. SINGLE FIBER EMG
IW~2-~
Single fiber EMG in neuromuscular disorders
Stimulation SFEMG: a diagnostic method and a tool in research Jo2e V. Trontelj 1, Erik V. Sffdberg 2. 1 Institute of Clinical Neurophysiology, Ljubljana University Medical Center, Slovenia; 2 Department of Clinical Neurophysiology, University Hospital, Uppsala Stimulation S F E M G has evolved into a useful modification of the original method introduced in the 60s by Ekstedt and St/tlberg. It is based on a combination of well controllable, highly selective activation with highly selective recording. A m o n g the advantages of the method is its greater precision, since only single neuromuscular junctions rather than pairs are studied, and the often disturbing effect of muscle fiber velocity recovery function can be eliminated. The main use of stimulation S F E M G remains in the diagnosis of neuromuscular transmission disorders, in which it offers additional sensitivity (close to 100%). Moreover, the study of individual neuromuscular junctions at different stimulation rates allows a better differentiation between the pre- and post-synaptic abnormalities. The method is suitable to detect muscle fiber splitting, a common finding in certain neuromuscular disorders. Direct intrafascicular muscle fiber stimulation allows precise measurement of propagation velocity (a function of muscle fiber diameter) and its recovery function (abnormal in muscular dystrophies). The p h e n o m e n o n of action potential recovery function may provide a useful and sensitive parameter in evaluating depolarisation/repolarisation abnormalities, such as in genetically determined or drug-induced myotonic disorders. Myogenic block of conduction can be detected in ion channel abnormalities. Stimulation S F E M G allows reliable identification of the various late responses to nerve stimulation, e.g., differentiation between the recurrent (F) and H-reflex responses. The measurement of reflex jitter allows the recognition of monosynaptic, oligosynaptic and polysynaptic reflex responses. The method has been used to identify the monosynaptic and oligosynaptic contacts between the cortico-spinal tract neurons and the lower motor neurons of different limb and cranial muscles.
Kimiyoshi Arimura. The Third Department of lnternal Medicine,
Kagoshima University School of Medicine Single fiber E M G ( S F E M G ) has gained importance in the study of motor unit microphysiology in neuromuscular disorders. Among other features, determination of fiber density, indicating reinnervation and jitter, indicating abnormality of neuromuscular transmission, have been applied clinically. In anterior horn cell disease, abnormal jitter and blocking are usually prominent in ALS indicating rapid progression, whereas increased fiber density is prominent in spinal muscular atrophy. Decremental response in ALS may suggest lowering safety factor due to presynaptic involvement. Stimulation S F E M G (S-SFEMG) is a new method for jitter measurement. The main advantage of S-SFEMG over voluntary S F E M G is its ability to study in detail the pathomechanism of neuromuscular transmission at different stimulation frequencies.
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Single fiber EMG (SFEMG) in the diagnosis and management of myasthenla gravis (MG) Donald B. Sanders. Duke University Medical Center, Durham, NC, USA S F E M G demonstrates abnormal jitter in virtually all patients with MG, but in some patients it may be necessary to examine several muscles to demonstrate the characteristic findings. Jitter is abnormal in the extensor digitorum communis muscle (EDC) in about 85% of M G patients overall, in over 60% of those with ocular M G and in over 50% of patients in clinical remission. Jitter is abnormal in a face muscle in almost all patients with MG: the EDC, frontalis or both are abnormal in over 95% of patients at the initial evaluation. Jitter is usually greater in facial muscles than
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to midbrain as well as in the more caudal structures such as the medulla oblongata. G e n e r a t o r sources of far-field P30 and N33 components produced by posterior tibial nerve stimulation were compared with those of the P14 and N18 components of median nerve stimulated SSEPs. Intracranial spacio-temporal distributions of P30 and N33 were similar to those of the P14 and N18. In clinical cases, the changes in P30 and N33 were correlated with those in P14 and N18, indicative that P30 and N33 are derived from activities similar to those that produce P14 a n d N18.
In ALS, jitter values increase with stimulation rates of up to 20 Hz that indicate involvement of nerve terminal. In neuropathies, S F E M G is useful in detecting and quantitating axonal degeneration in demyelinating neuropathy. In myopathy, fiber density may increase slightly due to involvement of intramuscular nerve and fiber splitting. Jitter is sometimes increased in voluntary S F E M G due to velocity recovery function (VRF). A n o t h e r advantage of S-SFEMG is its ability to exclude the V R F effect due to stable firing rate. The combined application of voluntary S F E M G and S-SFEMG is useful to study the neurogenic nature in myopathy.
•
•
Far-field potentials in surface EMG
Dick F. Stegeman, Karin Roeleveld, Dick M. Vingerhoets.
Institute of Neurology, Department of Clinical Neurophysiology, University Hospital Nijmegen, The Netherlands Most potentials recorded in neuromuscular electrophysiology change in amplitude, wave shape and even polarity when the recording electrode is moved over a small distance. First in the electroencephalogram, components were described which hardly change their characteristics with electrode position over the body or over the scalp. In this contribution it will be shown that these "far-fields" also form a part of surface E M G recordings during voluntary contractions. From basic electric field theory it can be concluded that these far-field p h e n o m e n a are generated by dipolar sources in any finite volume conductor. Propagating action potentials of nerve and muscle fibres are composed of two equal dipoles of opposite direction. For such a source the far-field contributions cancel. Therefore, propagating nerve and muscle fibre action potentials are not expected to generate far-fields. However, when the constant propagation of an action potential is disturbed in the widest sense of the word, far-field potentials are generated. This can be understood from an incomplete cancellation for some time. Such a disturbance can be caused by: 1) A change in the size of the extracellular medium, 2) a changing extracellular conductivity, 3) the generation or the blocking of an action potential and 4) a change in the direction of action potential propagation. It is evident that situations described in the above are numerous all over the neuromuscular system. It will be shown that far-field components in E M G records are predominantly caused by the blocking of action potentials at the fibre-tendon transition (see cause 3) above).
WS-2. SINGLE FIBER EMG
IW~2-~
Single fiber EMG in neuromuscular disorders
Stimulation SFEMG: a diagnostic method and a tool in research Jo2e V. Trontelj 1, Erik V. Sffdberg 2. 1 Institute of Clinical Neurophysiology, Ljubljana University Medical Center, Slovenia; 2 Department of Clinical Neurophysiology, University Hospital, Uppsala Stimulation S F E M G has evolved into a useful modification of the original method introduced in the 60s by Ekstedt and St/tlberg. It is based on a combination of well controllable, highly selective activation with highly selective recording. A m o n g the advantages of the method is its greater precision, since only single neuromuscular junctions rather than pairs are studied, and the often disturbing effect of muscle fiber velocity recovery function can be eliminated. The main use of stimulation S F E M G remains in the diagnosis of neuromuscular transmission disorders, in which it offers additional sensitivity (close to 100%). Moreover, the study of individual neuromuscular junctions at different stimulation rates allows a better differentiation between the pre- and post-synaptic abnormalities. The method is suitable to detect muscle fiber splitting, a common finding in certain neuromuscular disorders. Direct intrafascicular muscle fiber stimulation allows precise measurement of propagation velocity (a function of muscle fiber diameter) and its recovery function (abnormal in muscular dystrophies). The p h e n o m e n o n of action potential recovery function may provide a useful and sensitive parameter in evaluating depolarisation/repolarisation abnormalities, such as in genetically determined or drug-induced myotonic disorders. Myogenic block of conduction can be detected in ion channel abnormalities. Stimulation S F E M G allows reliable identification of the various late responses to nerve stimulation, e.g., differentiation between the recurrent (F) and H-reflex responses. The measurement of reflex jitter allows the recognition of monosynaptic, oligosynaptic and polysynaptic reflex responses. The method has been used to identify the monosynaptic and oligosynaptic contacts between the cortico-spinal tract neurons and the lower motor neurons of different limb and cranial muscles.
Kimiyoshi Arimura. The Third Department of lnternal Medicine,
Kagoshima University School of Medicine Single fiber E M G ( S F E M G ) has gained importance in the study of motor unit microphysiology in neuromuscular disorders. Among other features, determination of fiber density, indicating reinnervation and jitter, indicating abnormality of neuromuscular transmission, have been applied clinically. In anterior horn cell disease, abnormal jitter and blocking are usually prominent in ALS indicating rapid progression, whereas increased fiber density is prominent in spinal muscular atrophy. Decremental response in ALS may suggest lowering safety factor due to presynaptic involvement. Stimulation S F E M G (S-SFEMG) is a new method for jitter measurement. The main advantage of S-SFEMG over voluntary S F E M G is its ability to study in detail the pathomechanism of neuromuscular transmission at different stimulation frequencies.
•
Single fiber EMG (SFEMG) in the diagnosis and management of myasthenla gravis (MG) Donald B. Sanders. Duke University Medical Center, Durham, NC, USA S F E M G demonstrates abnormal jitter in virtually all patients with MG, but in some patients it may be necessary to examine several muscles to demonstrate the characteristic findings. Jitter is abnormal in the extensor digitorum communis muscle (EDC) in about 85% of M G patients overall, in over 60% of those with ocular M G and in over 50% of patients in clinical remission. Jitter is abnormal in a face muscle in almost all patients with MG: the EDC, frontalis or both are abnormal in over 95% of patients at the initial evaluation. Jitter is usually greater in facial muscles than