Clinical Neuroscience

[The role of transcranial magnetic stimulation in clinical diagnosis: motor evoked potential (MEP)]

ARÁNYI Zsuzsanna, SIMÓ Magdolna

OCTOBER 20, 2002

Clinical Neuroscience - 2002;55(09-10)

[Transcranial magnetic stimulation allows painless, non-invasive stimulation, neurophysiological evaluation of nervous structure covered by bone or difficult to access for other reasons. In the clinical setting the technique is mainly used for the investigation of the corticospinal tract (motor evoked potential: MEP). Based upon our experience with patients examined over the course of four years, we have attempted to highlight the clinical situations, where diagnostic help is provided by this technique. MEP in general has proved to be a sensitive and reliable examination. Its significance is apparent mainly in situations where clinical signs of corticospinal tract dysfunction are not evident, or they are masked by lower motoneurone involvement, and where neuroimaging techniques are not informative. The demonstration of subclinical corticospinal lesion is often essential to establish the diagnosis in multiple sclerosis and amyotrophic lateral sclerosis. The technique however received little attention so far with respect to its role in the diagnosis of various spinal cord disorders, and in the demonstration of intact corticospinal function in case of weakness, psychogenic in origin. We have endeavoured to provide further evidence in support of this, and thereby advocating a wider clinical application of the technique.]



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[There are a great number of psychopathological symptoms which manifest themselves in 70-75% of epileptic patients but most of them remain unrecognised and untreated. These symptoms may affect the patients’ quality of life more negatively than the epileptic seizures themselves. Anxiety is one of the most frequently occurring interictal psychopathological symptom. A number of specialists agree that chronic epilepsy causes the amplification of endogenic seizure suppressing mechanisms which hinder the epileptic seizures and are responsible for the development of interictal psychopathological symptoms. However the physiological effects of the interictal psychopathological conditions (e.g. anxiety) have epileptogenic effect as well. There is a high chance that the conditions of epilepsy and anxiety will mutually create a destructive vicious circle and it will be illustrated by our two case reports. In our experience, before modifying the pharmacotherapy of a patient suffering from chronic epilepsy with increased frequency of seizures, the anxiety level should be defined; and if it is high it should be treated first. From our perspective, the so-called ”rational bitherapy” is very effective when a high potential antiepileptic drug is combined with an anxiety reducing method. The latter can be drug related or consists only of psychotherapy. We need more controlled clinical research to prove that inside epilepsy there are risk groups as well as conditions of high risk when the connection between anxiety and epilepsy is more than evident. The described cases seem to indicate that the existence of periictal anxiety can be a risk factor in developing later interictal anxiety.]

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The effects of 30 Hz, 50 Hz AND 100 Hz continuous theta burst stimulation via transcranial magnetic stimulation on the electrophysiological parameters in healthy individuals

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Transcranial magnetic stimulation is a non-invasive procedure that uses robust magnetic fields to create an electrical current in the cerebral cortex. Dual stimulation consists of administering subthre­shold conditioning stimulation (CS), then suprathreshold test stimulation (TS). When the interstimulus interval (ISI) is 1-6 msec, the motor evoked potential (MEP) decreases in amplitude; this decrease is termed “short interval intracortical inhibition” (SICI); when the ISI is 7-30 msec, an increase in MEP amplitude occurs, termed “short interval intracortical facilitation” (SICF). Continuous theta burst stimulation (cTBS), often applied at a frequency of 50 Hz, has been shown to decrease cortical excitability. The primary objective is to determine which duration of cTBS achieves better inhibition or excitation. The secondary objective is to compare 50 Hz cTBS to 30 Hz and 100 Hz cTBS. The resting motor threshold (rMT), MEP, SICI, and SICF were studied in 30 healthy volunteers. CS and TS were administered at 80%-120% and 70%-140% of rMT at 2 and 3-millisecond (msec) intervals for SICI, and 10- and 12-msec intervals for SICF. Ten individuals in each group received 30, 50, or 100 Hz, followed by administration of rMT, MT-MEP, SICI, SICF immediately and at 30 minutes. Greater inhibition was achieved with 3 msec than 2 msec in SICI, whereas better facilitation occurred at 12 msec than 10 msec in SICF. At 30 Hz, cTBS augmented inhibition and suppressed facilitation, while 50 Hz yielded less inhibition and greater inter-individual variability. At 100 Hz, cTBS provided slight facilitation in MEP amplitudes with less interindividual variability. SICI and SICF did not differ significantly between 50 Hz and 100 Hz cTBS. Our results suggest that performing SICI and SICF for 3 and 12 msec, respectively, and CS and TS at 80%-120% of rMT, demonstrate safer inhibition and facilitation. Recently, TBS has been used in the treatment of various neurological diseases, and we recommend preferentially 30 Hz over 50 Hz cTBS for better inhibition with greater safety and less inter-individual variability.

Clinical Neuroscience

[The role of transcranial magnetic stimulation in clinical diagnosis: facial nerve neurography]

ARÁNYI Zsuzsanna, SIMÓ Magdolna

[Facial nerve neurography involving magnetic stimulation techniques can be used to assess the intracranial segment of the facial nerve and the entire facial motor pathway, as opposed to the traditional neurography, involving only extracranial electric stimulation of the nerve. Both our own experience and data published in the literature underline the value of the method in localising facial nerve dysfunction and its role in clinical diagnosis. It is non-invasive and easy to perform. Canalicular hypoexcitability has proved to be the most useful and sensitive parameter, which indicates the dysfunction of the nerve between the brain stem and the facial canal. This is an electrophysiological finding which offers for the first time positive criteria for the diagnosis of Bell’s palsy. The absence of canalicular hypoexcitability practically excludes the possibility of Bell’s palsy. The technique is also able to demonstrate subclinical dysfunction of the nerve, which can be of considerable help in the etiological diagnosis of facial palsies. For example, in a situation where clinically unilateral facial weakness is observed, but facial nerve neurography demonstrates bilateral involvement, etiologies other than Bell’s palsy are more likely, such as Lyme’s disease, Guillain-Barré syndrome, meningeal affections etc. Furthermore, the technique differentiates reliably between peripheral facial nerve lesion involving the segment in the brain stem or the segment after leaving the brainstem.]

Clinical Neuroscience


ARÁNYI Zsuzsanna

[Transcranial magnetic stimulation (TMS) is a relatively new technique that allows painless activation of cortical motor neurons. In the clinical setting, TMS is primarily used for the investigation of the corticospinal tract in various neurological diseases, being especially useful in the detection of subclinical dysfunction. In addition to the motor cortex, TMS can be applied to examine other structures inaccessible to electrical stimulation, such as the canalicular portion of the facial nerve. In healthy individuals, TMS can be utilized to monitor excitability changes of the motor system in various situations and muscles, providing valuable information to the understanding of the physiology of motor control. Furthermore, TMS can be used to explore interhemispheric connections as well as intracortical inhibitory and excitatory processes both in health and disease. Finally, with the help of TMS cortical maps of the representation areas of muscles can be constructed, giving insight to both short and long-term cortical plasticity and to the reorganisation of the motor cortex following damage to the brain or acquisition of new motor skills]

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SIMÓ Magdolna, ARÁNYI Zsuzsanna

[Introduction - Motor evoked potential (MEP) is the only method that is able to assess the function of the corticospinal tract in various neurological conditions, such as myelopathies. Myelopathy associated with cervical spondylosis, especially at an early stage, has often slight and non-specific clinical signs, pointing to the importance of the electrophysiological assessment of the spinal cord. The authors' aim was to investigate the sensitivity of MEP examination in the detection of myelopathy secondary to cervical spondylosis. Patients and methods - Patients were classified into three groups according to clinical signs and symptoms: Group I includes patients who have cervical spondylosis as demonstrated by MRI (narrowing of the spinal canal, discal herniation, spinal cord compression) but no complaints or signs suggestive of myelopathy. Results - In Group II patients had minor, non-specific complaints, such as paraesthesia of the legs and gait disturbance raising the possibility of myelopathy, but neurological examination revealed no pyramidal signs. In Group III patients had pyramidal signs as well. In Group I corticospinal function was normal in all patients, as assessed by MEP examination. In Group II all patients had prolonged central motor conduction time or absent responses to cortical stimulation. Likewise, in Group III MEP revealed abnormal corticospinal function in all patients but one. Conclusions - In summary, MEP proved sensitive in the detection of corticospinal dysfunction in myelopathy associated with cervical spondylosis at a stage when clinical signs of pyramidal lesion are not yet present and patients have only minor complaints. On the other hand, if patients are completely symptom free with regard to myelopathy, MEP is also unlikely to disclose corticospinal dysfunction. If pyramidal lesion is evident already by clinical examination, MEP provides no further help. ’Falsenegative’ results are also possible.]