EPILEPSIA

El Umbral Motor medido por estimulación magnética transcraneana está reducido en pacientes portadores de epilepsia libre de medicación. La EMT-r se está utilizando en condiciones prequirúrgicas a los efectos de localizar el hemisferio dominante portador de la actividad del lenguaje.

Existe un reporte sobre efectos terapéuticos beneficiosos del EMT-r de baja frecuencia en el mioclonus

Es posible la realización de estudios farmacodinámicos de la excitabilidad cerebral luego de la administración de drogas antiepilépticas , entre otras.

J Clin Neurophysiol 1993 Jan;10(1):111-5

Hyperventilation and transcranial magnetic stimulation: two methods of activation of epileptiform EEG activity in comparison.

Schuler P, Claus D, Stefan H

Department of Neurology, University Erlangen-Nurnberg, Germany.

In a prospective study, we compared the established method for an activation of epileptiform activity in EEG, hyperventilation (HV), with the recently presented new activational technique of transcranial magnetic stimulation (TMS) in 10 patients with drug-resistant partial epilepsies. Long-term EEG recordings included subdural electrodes in the course of presurgical evaluation. Epileptiform activity was evaluated visually 500 s before, during, and 500 s after stimulation, and the results were compared statistically. TMS was not better than HV: HV caused an activation of the epileptogenic foci in 6 of 10 cases, TMS only in 3 of 10. Seizures could be induced by HV in 2 of 10, by TMS in no cases. In 2 of 10 cases, TMS even caused a significant reduction of epileptiform activity.

Epilepsy Res 1998 Mar;30(1):11-30

Transcranial magnetic stimulation: its current role in epilepsy research.

Ziemann U, Steinhoff BJ, Tergau F, Paulus W

Department of Clinical Neurophysiology, University of Gottingen, Germany.

This paper reviews the current role of transcranial magnetic stimulation (TMS) in epilepsy research. After a brief introduction to the technical principles, the physiology and the safety aspects of TMS, emphasis is put on how human cortex excitability can be assessed by TMS and how this may improve our understanding of pathophysiological mechanisms in epilepsy and the mode of action of antiepileptic drugs (AEDs). Also, potential therapeutical applications of TMS are reviewed. For all aspects of this paper, a clear distinction was made between single-/paired-pulse TMS and repetitive TMS, since these two techniques have fundamentally different scopes and applications.

Effects of antiepileptic drugs on motor cortex excitability in humans: a transcranial magnetic stimulation study.

Ziemann U, Lonnecker S, Steinhoff BJ, Paulus W

Department of Clinical Neurophysiology, University of Gottingen, Germany.

The effect of a single oral dose of various antiepileptic drugs on the excitability of the motor system was studied in healthy volunteers by means of transcranial magnetic stimulation. Motor threshold, duration of the cortical silent period, and intracortical excitability after double-shock transcranial stimulation were tested before and at defined intervals after drug intake. Antiepileptic drugs that support the action of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) in the neocortex (vigabatrin, baclofen) reduced intracortical excitability but had no effect on motor threshold. Gabapentin, whose mechanism of action has not yet been unequivocally identified, showed a similar profile. By contrast, sodium and calcium channel blockers without considerable neurotransmitter properties (carbamazepine, lamotrigine, losigamone) elevated motor threshold but did not change intracortical excitability. The cortical silent period was lengthened by gabapentin and carbamazepine. Changes in peripheral motor excitability (maximum M wave, peripheral silent period) were not observed. We conclude that the changes in intracortical excitability are caused by GABA-controlled interneuronal circuits in the motor cortex while changes in motor threshold are dependent on ion channel conductivity and may reflect membrane excitability. Transcranial magnetic stimulation may be a promising noninvasive approach to study the selective effects of antiepileptic drugs on brain function.

EEG changes following repetitive transcranial magnetic stimulation in patients with temporal lobe epilepsy.

Jennum P, Winkel H, Fuglsang-Frederiksen A, Dam M

Department of Clinical Neurophysiology, Hvidovre Hospital, University of Copenhagen, Denmark.

Transcranial magnetic stimulation (TMS) has been proposed as an epileptogenic activating procedure in the evaluation of patients with partial epilepsy. With the introduction of repetitive (rapid rate) transcranial magnetic stimulation (RTMS), it has been possible to apply cortical stimuli with a stimulus rate up to 50 Hz. This study was conducted in order to evaluate the epileptogenic effect of RTMS. Ten patients suffering from medically intractable temporal lobe epilepsy were included. As a part of the presurgical evaluation all patients were studied with ictal video-EEG scalp recordings during a period of discontinuation of the antiepileptic treatment. Eight RTMS trains were applied to left and right temporal and frontal areas, using a stimulus intensity of 1.2 x Tm (the motor threshold to a twitch in the right hand), a stimulus duration of 1 s and a stimulus frequency of 30 Hz. 50 Hz stimulations, with a stimulus duration of 1 s and a stimulus intensity of 1.2 x Tm, were applied on both anterior temporal regions, in total 10 TMS and 340 RTMS pulses to each patient. The numbers of sharp waves/spikes and low-frequency potentials were lower (P < 0.01) compared to prestimulus values and returned to prestimulation values within 10 min. In no cases paroxysmal activity was provoked and no seizures developed. The study indicates that RTMS as used in this study is not effective as an activation procedure for paroxysmal activity. As the risk of seizures may depend on the stimulus parameters, further studies are needed in order to evaluate the safety of the RTMS.

Ann Neurol 1990 Jan;27(1):49-60

Activation of the epileptic focus by transcranial magnetic stimulation of the human brain.

Hufnagel A, Elger CE, Durwen HF, Boker DK, Entzian W

Department of Epileptology, University of Bonn, Federal Republic of Germany.

To establish whether transcranial magnetic stimulation is able to activate the primary epileptic focus preferentially, 13 patients who had medically intractable complex partial seizures were examined prior to surgical therapy. Single or a series of magnetic stimuli were applied to various regions of the skull. The effects of transcranial magnetic stimulation were monitored via subdurally implanted electrodes. In the process of presurgical evaluation, the dosage of anticonvulsant medication had been reduced in all patients but one. Transcranial magnetic stimulation was able to activate the epileptic focus (or foci) in 12 of the 13 patients. Distinct patterns of focal activation were observed in 3 patients who had several foci. No epileptiform potentials were induced outside epileptic foci, which had been identified by corticographic recordings. In one patient a complex partial seizure that was induced was identical to her habitual seizures. In another patient, a complete transition from a nonactive theta focus to a self-sustained epileptic focus occurred. A facilitation of epileptiform afterdischarge was seen with sequential stimulation. No adverse effects were either reported by the patients or observed by the investigators. In summary transcranial magnetic stimulation is able to activate the epileptic focus (or foci) and consequently may be an additional tool for the localization of epileptic foci in presurgical evaluation.

PMID: 2301928, UI: 90146193

Neurology 1990 Jul;40(7):1132-3

Transcranial magnetic stimulation in epileptic patients: usefulness and safety.

Tassinari CA, Michelucci R, Forti A, Plasmati R, Troni W, Salvi F, Blanco M, Rubboli G

Neurological Clinic, University of Bologna School of Medicine, Italy.

We studied 58 patients with partial or generalized epilepsy who had transcranial magnetic stimulation (TMS) of the brain motor regions. Short-term monitoring disclosed that the stimulation did not provoke seizures or EEG changes in any patient. Long-term follow-up disclosed that the epileptic condition was not made worse by TMS. TMS, as currently used for monitoring conduction in central motor pathways, does not induce seizures in drug-treated epileptic patients.

PMID: 2113205, UI: 90287385

Transcranial Magnetic Stimulation in Childhood Epilepsies and some Correlations with Electroencephalographic Abnormalities

L Belopitova, V Bojinova, V Tomov, P Dimova(Medical Univ., Sofia, Bulgaria)

Transcranial magnetic stimulation (TMS) was applied on 80 children with different clinical forms of epilepsy: simple focal seizures with or without secondary generalisation (38 children or 47.5%); complex partial seizures (15 children or 18.75%) and primary generalised seizures (27 children or 33.75%). The neurological status is normal in all patients, with intellectual deficiency of different degree are 12 cases (15%). The aim of the study is to reveal changes in the central motor conduction time (CMCT) despite the lack of data of injury in the corticospinal tract and to analyse the possible influence of the anticonvulsive therapy on the conduction through the central motorneuron. Bilaterally delayed CMCT was found in 13 children (16.25%); unilaterally delayed - in 20 patients (25.0%); lack of motor evoked potential during the maximal intensive stimulation (100%) - in 12 children (15%). With normal CMCT are 35 patients (43.75%), out of which 15 are with complex partial seizures. In 10 children (12.5%) EEG was done immediately after the TMS and only in one an insignificant worsening of the bioelectrical activity was found, but without seizure provocation. A follow-up study in 15 children with unilateral or bilateral delayed CMCT was done, in which the dynamic of the TMS findings correspondence to the EEG was revealed. The possibility to increase of the excitato threshold of the cerebral cortex under influence of the anticonvulsive therapy, in case with olygophrenia and the interactions between the EEG focal abnormality in the motor region and the delayed CMCT are discussed. Our results suggest that TMS do not activate the epileptic seizures and can be applied in children with epilepsy. }

Transcranial Magnetic Stimulation Shows Promise In Epilepsy

LONDON, UK -- June 25, 1999 -- Epilepsy can prove difficult to treat, with some patients continuing to have many fits a week despite taking several drugs. In a study in this week’s The Lancet, researchers from Germany have tried a new treatment - repetitive transcranial magnetic stimulation (rTMS) - with encouraging results.
In nine patients who continued to have frequent seizures despite drug treatment, Dr. Frithjof Tergau and colleagues from the Department of Clinical Neurophysiology, University of Gottingen, in Germany, applied a low frequency from a repetitive magnetic stimulator placed against the head. They found that most patients described an improvement in the number or severity of seizures, although after six-eight weeks the effects of the treatment had worn off.

"Low-frequency rTMS may temporarily improve intractable epilepsy", the authors write, although they point out that their work needs confirmation in placebo-controlled studies.

BILATERAL INTERICTAL CHANGES OF MOTOR CORTEX EXCITABILITY IN CRYPTOGENIC PARTIAL EPILEPSY: A SINGLE- AND DOUBLE-PULSE TRANSCRANIAL MAGNETIC STIMULATION STUDY.

Cantello-R, Civardi-C, Cavalli-A, Varrasi-C, Gianelli-M, Tarletti-R, Monaco-F
Dept. of Clinical Neurology, University of Turin, School of Medicine, Novara, Italy

Introduction: Our objective was to determine if single- and double-pulse transcranial magnetic stimulation (s- and d-TMS) can study the interictal brain excitability of patients with cryptogenic partial epilepsy (CPE). Also, to assess which TMS variable is the most sensitive to this aim. Consequently, to characterize the possible derangement of the balance between excitation and inhibition in the CPE patient and its clinical correlations. Changes in the neural balance between excitation and inhibition are the core pathophysiology of focal epileptogenesis. S- and d-TMS are the actual means to measure suchbalance in the primary motor cortex (MI) of the intact man Methods: After extensive investigation, we selected 18 CPE patients, whose EEG spike focus had a clear laterality, and who showed homogeneous Epileptic Seizures Triggered Directly by Focal Transcranial Magnetic Stimulation.

Last modified on: Wednesday, January 13, 1999 12:03:10 document

Ann Neurol 1990 Jan;27(1):49-60

Activation of the epileptic focus by transcranial magnetic stimulation of the human brain.

Hufnagel A, Elger CE, Durwen HF, Boker DK, Entzian W

Department of Epileptology, University of Bonn, Federal Republic of Germany.

clinical features. All were taking antiepileptic drugs. We had 11 age- and sex-matched healthy controls. For both the right and the left primary motor cortices we determined the threshold to TMS, the duration of cortical silent period and the corticocortical inhibition and facilitation curve. We used a Magstim/Bistim apparatus, and a Nicolet Viking IV machine. Results: TMS was safe. The following changes were statistically significant in the patient group. The threshold to TMS was generally increased without any correlation to the side of the EEG spike focus or other clinical features. The silent period was prolonged, mainly contralateral to the spike focus. The behaviour on the corticocortical inhibition and facilitation curve distinguished two patient subgroups: the "spreaders", who had signs of bilateral hyperexcitability, and the "inhibitors", who had some hyperexcitability ipsilateral to the spike focus, but tended to a contralateral hypoexcitability. The "spreaders" had a higher amount of generalized epileptiform EEG abnormalities. Conclusions: In CPE, alterations of brain excitability spread from the epileptogenic region to the primary motor cortex, where TMS can detect them in a noninvasive and nonexpensive way. The pattern of these changes, which depicts two major patient subgroups, has an actual pathophysiological interest and potential clinical applications.

Acta Neurol Scand Suppl 1994;152:93-6

Transcranial magnetic stimulation. Its role in the evaluation of patients with partial epilepsy.

Jennum P, Winkel H

Department of Clinical Neurophysiology, Hvidovre Hospital, Copenhagen, Denmark.

Transcranial magnetic stimulation (TMS) is a relative new method in the evaluation of patients with various neurological diseases. With the introduction of repetitive (rapid rate) transcranial magnetic stimulators (RTMS), it has been possible to apply cortical stimuli with a stimulus rate up to 100 Hz. The preliminary results with TRMS suggest that it may be used in the study of speech lateralization. Seizures have been reported in patients with partial epilepsy during TMS. In these cases it remains uncertain whether the seizures were induced by the TMS or coincidentally with it. Minor changes in paroxysmal activity have been reported in some patients. These data suggest, that TMS is neither sensitive nor specific as an activation procedure of the epileptic focus in patients with partial epilepsy. Seizures have been provoked using RTMS, but its use as a seizure-inducing method is not yet evaluated.

Transcranial magnetic stimulation: its current role in epilepsy research.

Author

Ziemann U; Steinhoff BJ; Tergau F; Paulus W

Address

Department of Clinical Neurophysiology, University of Gottingen, Germany.

Source

Epilepsy Res, 30(1):11-30 1998 Mar

Abstract

La EMT-r (rTMS) sobre la corteza temporal, bloquea la producción del habla ; sobre la corteza DLPF , impide la memoria de tarea , y , sobre la corteza occipital induce defectos visuales (fosfenos ) . Estos fenómenos disruptivos temporarios se utilizan en neurología con fines diagnósticos y de investigación.

Speech Apraxia During Low Rate Transcranial Magnetic Stimulation (TMS) to Dorsolateral Frontal Cortex

Shalini Narayana , Nitin Tandon , Roger Ingham , Jan Ingham , Michael Martinez , Jack L. Lancaster , Steven Dodd , Jinhu Xiong , Peter T. Fox

Research Imaging Center, University of Texas Health Science Center at San Antonio
Division of Neurosurgery, University of Texas Health Science Center at San Antonio
Department of Speech and Hearing Sciences, Univeristy of California at Santa Barbara

Abstract
Introduction
A major drawback of high stimulus rates used in surgical procedures (50-60Hz) and high rate TMS (15-30Hz) to localize language areas is the absence of differentiation of function. Further, there is no consensus on the location of speech arrest, rate, and the mechanism of action of high rate TMS (Table 1)(1-5). We report the identification and localization of a frontal area in the language dominant hemisphere which causes speech apraxia in normals using low rate TMS.

Methods
Six normals were fitted with a cap marked with the 10-20 electrode system (6). Under video monitoring, rTMS was delivered over left and right frontal regions at 4 Hz in 5 second trains. While subjects read aloud, the TMS coil was moved anteriorly and laterally from C3/C4, until speech was disrupted. The position of TMS coil on the scalp producing speech disruption was marked with lipid capsules which were identifiable on MRI. A 3D aMRI, and fMRI while subjects performed a silent verb generation task were acquired.

Results
4 Hz rTMS over left D3 and D5 areas (6) produced reproducible speech apraxia in all volunteers, the hallmark of which was cessation of fluent reading and utterance of repetitive and meaningless syllables. All subjects could not get past the word they were reading at the start of rTMS. Silent reading and comprehension were preserved. Review of video recording confirmed that contractions of facial muscles and tongue were not causing this apraxia. rTMS of the homologous location in the right hemisphere produced a milder apraxia in one subject. fMRI of verb generation task confirmed the left hemisphere language dominance in all subjects. An additional activation (-32, 40, 24) corresponding to BA 9/8 was identified. In 3 subjects, this cortical area was directly beneath the fiducial where TMS was applied (Figure 1). In others, the cortical area beneath the fiducial (-47, 4, 44) was identified to be lateral premotor cortex (BA6).

Conclusion
The location of speech apraxia area reported here is in agreement with published speech arrest reports (2,4,5). Activation of lateral premotor cortex in articulatory planning has been demonstrated in a PET study (7). Our data supports this, and indicates that the mechanism of action of rTMS is by interference with articulatory processing in the dominant hemisphere, and not by interrupting short term memory or by direct motor interference. However, unlike other reports, we have demonstrated that low rate TMS can produce speech disruption. With its ability to locate language areas and identify their function, low rate TMS of language areas may bridge the gap between high rate TMS and surgical procedures, which identify only location of language areas, and lesion data which are more indicative of the function of individual regions.

References
1. Epstein C.M, et al., Clinical Neurophysiology 1999; 110:1073-1079
2. Pascual-Leone A, et al., Neurology 1991; 41:697-702
3. Jennum P, et al., Neurology 1994; 44:269-273
4. Flitman S.S, et al., Neurology 1998; 50:175-181

TRANSCRANIAL MAGNETIC STIMULATION (TCMS) IN REHABILITATION

J.C. ROTHWELL, MRC, Human Movement & Balance Unit, Institute of Neurology Queen Square, London WC1N 3BG, UK.

TCMS in patients shortly after stroke has shown a useful correlation between the presence of EMG responses in the likelihood of good recovery. Although functional imaging studies show activation of the ipsilateral cortex during movement of the affected hand in recovered stroke, there is little evidence from TCMS of the development of large diameter projections from the damaged hemisphere which could account for this activation. The situation is different in more proximal muscles. TMS can activate upper oesophagus and pharynx. They are innervated bilaterally, although in most subjects, one or other hemisphere seems to be dominant, unrelated to handedness. Dysphagia after hemispheric stroke seems to occur only if damage affects the hemisphere with the dominant oesophagus/pharyngeal projection. Recovery from dysphagia is often evident at around 3 months post stroke. In such cases TCMS gives clear evidence of increased excitability of the remaining projection from the undamaged hemisphere. Finally, we have shown in normal subjects that the excitability of the cortical pathway to the pharynx can be increased for up to 30 minutes following continuous electrical stimulation of the pharynx for 10 minutes. Treatment with continuous afferent stimulation may therefore be a possible mechanism of accelerating the changes in the ipsilateral hemisphere after stroke.

THE PHYSIOANATOMICAL CHARACTERISTICS OF SHORT LATENCY SOMATOSENSORY EVOKED POTENTIALS FOLLOWING STIMULATION OF THE MEDIAN NERVE

Tohru Yamada, MD (University of Iowa, Iowa City, Iowa U.S.A.)

The short latency median nerve somatosensory evoked potentials (SSEP) consists of multiple components having characteristics of far-field, stationary field and near-field potentials. They are P9, N9, N1O, P11, N11, N13, P13, P14, N14, N18, N20 and P20/ P22. Two components having the same latency with opposite or same polarity may or may not be of the same origins. For example, P9 far-field potential recorded from the scalp and N9 stationary field potentials recorded from the stimulated are of the same origin, whereas P13 far-field potential from the scald and N13 negative potential from the neck arise from separate generators, i.e. P13 arising from brainstem and N13 from cervical cord. Further, N13 from the high and low cervical regions are now considered to have separate origins. Because of intricate mixture of these potentials within short time domain, a given component may be abolished or enhanced depending on the electrode derivations. Also inappropriate use of electrode derivation may lead to erroneous identification of peak of interest. Understanding of physiological characteristics and field distribution of each component is important to accurately delineate these potentials.

ELECTRODIAGNOSIS IN REHABILITATION MEDICINE

Murray E. Brandstater (Loma Linda University, Loma Linda, CA, USA)

Many of the patients treated by physicians in physical medicine and rehabilitation have neuromuscular disorders. The information provided by electrodiagnosis in these patients is essential for the physician to provide optimal patient care. This paper will describe how the electrodiagnostic evaluation can assist the physician in making the diagnosis and in guiding subsequent treatment.

(1) The initial study. Information from the initial study helps to establish the diagnosis. In addition, careful examination of the electrodiagnostic data may reveal the severity of the disease process, and may indicate its acuteness or chronicity. The information can assist the physician in making a prognosis.

(2) Follow-up study. When patients are seen for follow-up examination, the data give information about progression of the disease, or recovery, and may be quite helpful in monitoring the response to treatment. Statements about prognosis can be refined. All of these points will be illustrated with examples.

5. Bartres-Faz D, et al., Neuroimage 1999; 9(6):S1051
6. Morris H.H, et al., Electroencephalogr Clin Neurophysiol 1986; 63:107-111
7. Wise R.J.S, et al., The Lancet 1999; 353:1057-1061