Effect of levetiracetam on cortical excitability: a transcranial magnetic stimulation study

The Effect of Epilepsy and Antiepileptic Drugs on Cortical Motor Excitability in Patients With Temporal Lobe Epilepsy

OBJECTIVES

Transcranial magnetic stimulation (TMS) has been used to assess cortical disinhibition/excitation with epilepsy and determine the degree of patients' response to antiepileptic drugs (AEDs). However, the results of studies are variable and conflicting. We assessed cortical motor excitability in adults with temporal lobe epilepsy (TLE).

METHODS

The TMS parameters used for assessment were: resting (RMT) and active (AMT) motor thresholds, cortical silent period (CSP), and central motor conduction time (CMCT).

RESULTS AND CONCLUSIONS

This study included 40 adults (males, 22; females, 18) with TLE with impaired awareness or to bilateral tonic clonic seizures (mean age, 32.50 ± 3.38 years; duration of illness, 6.15 ± 2.02 years) and on treatment with AEDs (valproate, 15; carbamazepine, 15; levetiracetam, 10]. The majority (62.5%) were seizure-free for ≥1 year on AEDs before TMS testing. All had normal brain magnetic resonance imaging except two, who had mesial temporal sclerosis. Comparing the entire patients with controls, patients had significantly bihemispheric higher RMT and AMT particularly over the epileptic hemisphere and shorter CSP and CMCT in the epileptic hemisphere. Shorter CSP and CMCT were observed in patients on valproate or carbamazepine and those who were uncontrolled on medications but not with levetiracetam. Significant correlations were identified between RMT and AMT (P = 0.01) and between CSP and CMCT (P = 0.001). We conclude that chronic TLE had increased cortical disinhibition in the epileptic hemisphere which can spread outside the epileptogenic zone despite the apparent control on AEDs. The TMS studies using CSP and CMCT may help future prediction of pharmacoresistance and, therefore, the need of combined AEDs with multiple mechanisms of action.

Cortical excitability in epilepsy and the impact of antiepileptic drugs: transcranial magnetic stimulation applications

INTRODUCTION

Epileptic conditions are characterized by impaired cortical excitation/inhibition balance and interneuronal disinhibition. Transcranial magnetic stimulation (TMS) is a neurophysiological method that assesses brain excitation/inhibition.

AREA COVERED

This review was written after a detailed search in PubMed, EMBASE, ISI web of science, SciELO, Scopus, and Cochrane Controlled Trials databases from 1990 to 2020. It summarizes TMS applications for diagnostic and therapeutic purposes in epilepsy. TMS studies help to distinguish different epilepsy conditions and explore the antiepileptic drugs' (AEDs') effects on neuronal microcircuits and plasticity mechanisms. Repetitive TMS studies showed that low-frequency rTMS (0.33-1 Hz) can reduce seizures' frequency in refractory epilepsy or pause ongoing seizures; however, there is no current approval for its use in such patients as adjunctive treatment to AEDs.

EXPERT OPINION

There are variable and conflicting TMS results which reflect the distinct pathogenic mechanisms of each epilepsy condition, the dynamic epileptogenic process over the long disease course resulting in the development of recurrent spontaneous seizures and/or progression of epilepsy after it is established, and the differential effect of AEDs on cortical excitability. Future epilepsy research should focus on combined TMS/functional connectivity studies that explore the complex cortical excitability circuits and networks using different TMS parameters and techniques.

Effects of antiepileptic drugs on cortical excitability in humans: A TMS-EMG and TMS-EEG study

Brain responses to transcranial magnetic stimulation (TMS) recorded by electroencephalography (EEG) are emergent noninvasive markers of neuronal excitability and effective connectivity in humans. However, the underlying physiology of these TMS-evoked EEG potentials (TEPs) is still heavily underexplored, impeding a broad application of TEPs to study pathology in neuropsychiatric disorders. Here we tested the effects of a single oral dose of three antiepileptic drugs with specific modes of action (carbamazepine, a voltage-gated sodium channel (VGSC) blocker; brivaracetam, a ligand to the presynaptic vesicle protein VSA2; tiagabine, a gamma-aminobutyric acid (GABA) reuptake inhibitor) on TEP amplitudes in 15 healthy adults in a double-blinded randomized placebo-controlled crossover design. We found that carbamazepine decreased the P25 and P180 TEP components, and brivaracetam the N100 amplitude in the nonstimulated hemisphere, while tiagabine had no effect. Findings corroborate the view that the P25 represents axonal excitability of the corticospinal system, the N100 in the nonstimulated hemisphere propagated activity suppressed by inhibition of presynaptic neurotransmitter release, and the P180 late activity particularly sensitive to VGSC blockade. Pharmaco-physiological characterization of TEPs will facilitate utilization of TMS-EEG in neuropsychiatric disorders with altered excitability and/or network connectivity.

Motor Cortex Reorganization in Patients with Glioma Assessed by Repeated Navigated Transcranial Magnetic Stimulation-A Longitudinal Study

OBJECTIVE

Evidence for cerebral reorganization after resection of low-grade glioma has mainly been obtained by serial intraoperative cerebral mapping. Noninvasively collected data on cortical plasticity in tumor patients over a surgery-free period are still scarce. The present study therefore aimed at evaluating motor cortex reorganization by navigated transcranial magnetic stimulation (nTMS) in patients after perirolandic glioma surgery.

METHODS

nTMS was performed preoperatively and postoperatively in 20 patients, separated by 26.1 ± 24.8 months. Further nTMS mapping was conducted in 14 patients, resulting in a total follow-up period of 46.3 ± 25.4 months. Centers of gravity (CoGs) were calculated for every muscle representation area, and Euclidian distances between CoGs over time were defined. Results were compared with data from 12 healthy individuals, who underwent motor cortex mapping by nTMS in 2 sessions.

RESULTS

Preoperatively and postoperatively pooled CoGs from the area of the dominant abductor pollicis brevis muscle and of the nondominant leg area differed significantly compared with healthy individuals (P < 0.05). Most remarkably, during the ensuing follow-up period, a reorganization of all representation areas was observed in 3 patients, and a significant shift of hand representation areas was identified in further 3 patients. Complete functional recovery of postoperative motor deficits was exclusively associated with cortical reorganization.

CONCLUSIONS

Despite the low potential of remodeling within the somatosensory region, long-term reorganization of cortical motor function can be observed. nTMS is best suited for a noninvasive evaluation of this reorganization.

The Effect of Lamotrigine and Levetiracetam on TMS-Evoked EEG Responses Depends on Stimulation Intensity

The combination of transcranial magnetic stimulation and electroencephalography (TMS-EEG) has uncovered underlying mechanisms of two anti-epileptic medications: levetiracetam and lamotrigine. Despite their different mechanism of action, both drugs modulated TMS-evoked EEG potentials (TEPs) in a similar way. Since both medications increase resting motor threshold (RMT), the current aim was to examine the similarities and differences in post-drug TEPs, depending on whether stimulation intensity was adjusted to take account of post-drug RMT increase. The experiment followed a placebo controlled, double blind, crossover design, involving a single dose of either lamotrigine or levetiracetam. When a drug-induced increase of RMT occurred, post-drug measurements involved two blocks of stimulations, using unadjusted and adjusted stimulation intensity. A cluster based permutation analysis of differences in TEP amplitude between adjusted and unadjusted stimulation intensity showed that lamotrigine induced a stronger modulation of the N45 TEP component compared to levetiracetam. Results highlight the impact of adjusting stimulation intensity.

The variability of motor evoked potential latencies in neurosurgical motor mapping by preoperative navigated transcranial magnetic stimulation

Background

Recording of motor evoked potentials (MEPs) is used during navigated transcranial magnetic stimulation (nTMS) motor mapping to locate motor function in the human brain. However, factors potentially underlying MEP latency variability in neurosurgical motor mapping are vastly unknown. In the context of this study, one hundred brain tumor patients underwent preoperative nTMS-based motor mapping of the tumor hemisphere between 2010 and 2013. Fourteen predefined predictor variables were recorded, and MEP latencies of abductor pollicis brevis muscle (APB), abductor digiti minimi muscle (ADM), and flexor carpi radialis muscle (FCR) were analyzed using linear mixed-effect multiple regression analysis with the forward step-wise model comparison approach.

Results

Common factors (relevant to APB, ADM, and FCR) for MEP latency variability were gender, most likely due to body height, and antiepileptic drug (AED) intake. Muscle-specific factors (relevant to APB, ADM, or FCR) for MEP latency variability were resting motor threshold (rMT), tumor side, and tumor location.

Conclusions

Based on a large cohort of neurosurgical patients, this study provides data on a wide range of clinical factors that may underlie MEP latency variability. The factors that significantly contributed to MEP latency variability should be standardly recorded and taken into consideration during neurosurgical motor mapping.

Clinical Factors Underlying the Inter-individual Variability of the Resting Motor Threshold in Navigated Transcranial Magnetic Stimulation Motor Mapping

Correctly determining individual's resting motor threshold (rMT) is crucial for accurate and reliable mapping by navigated transcranial magnetic stimulation (nTMS), which is especially true for preoperative motor mapping in brain tumor patients. However, systematic data analysis on clinical factors underlying inter-individual rMT variability in neurosurgical motor mapping is sparse. The present study examined 14 preselected clinical factors that may underlie inter-individual rMT variability by performing multiple regression analysis (backward, followed by forward model comparisons) on the nTMS motor mapping data of 100 brain tumor patients. Data were collected from preoperative motor mapping of abductor pollicis brevis (APB), abductor digiti minimi (ADM), and flexor carpi radialis (FCR) muscle representations among these patients. While edema and age at exam in the ADM model only jointly reduced the unexplained variance significantly, the other factors kept in the ADM model (gender, antiepileptic drug intake, and motor deficit) and each of the factors kept in the APB and FCR models independently significantly reduced the unexplained variance. Hence, several clinical parameters contribute to inter-individual rMT variability and should be taken into account during initial and follow-up motor mappings. Thus, the present study adds basic evidence on inter-individual rMT variability, whereby some of the parameters are specific to brain tumor patients.

Lamotrigine and levetiracetam exert a similar modulation of TMS-evoked EEG potentials

Objective

Antiepileptic drug (AED) treatment failures may occur because there is insufficient drug in the brain or because of a lack of relevant therapeutic response. Until now it has not been possible to measure these factors. It has been recently shown that the combination of transcranial magnetic stimulation and electroencephalography (TMS‐EEG) can measure the effects of drugs in healthy volunteers. TMS‐evoked EEG potentials (TEPs) comprise a series of positive and negative deflections that can be specifically modulated by drugs with a well‐known mode of action targeting inhibitory neurotransmission. Therefore, we hypothesized that TMS‐EEG can detect effects of two widely used AEDs, lamotrigine and levetiracetam, in healthy volunteers.

Methods

Fifteen healthy subjects participated in a pseudo‐randomized, placebo‐controlled, double‐blind, crossover design, using a single oral dose of lamotrigine (300 mg) and levetiracetam (3,000 mg). TEPs were recorded before and 120 min after drug intake, and the effects of drugs on the amplitudes of TEP components were statistically evaluated.

Results

A nonparametric cluster‐based permutation analysis of TEP amplitudes showed that AEDs both increased the amplitude of the negative potential at 45 msec after stimulation (N45) and suppressed the positive peak at 180 msec (P180). This is the first demonstration of AED‐induced modulation of TMS‐EEG measures.

Significance

Despite the different mechanism of action that lamotrigine and levetiracetam exert at the molecular level, both AEDs impact the TMS‐EEG response in a similar way. These TMS‐EEG fingerprints observed in healthy subjects are candidate predictive markers of treatment response in patients on monotherapy with lamotrigine and levetiracetam.

Effect of a single dose of retigabine in cortical excitability parameters: A cross-over, double-blind placebo-controlled TMS study

BACKGROUND

Antiepileptic drugs (AEDs) decrease the occurrence of epileptic seizures and modulate cortical excitability through several mechanisms that likely interact. The modulation of brain excitability by AEDs is believed to reflect their antiepileptic action(s) and could be used as a surrogate marker of their efficacy. Transcranial magnetic stimulation (TMS) is one of the best noninvasive methods to study cortical excitability in human subjects. Specific TMS parameters can be used to quantify the various mechanisms of action of AEDs. A new AED called retigabine increases potassium efflux by changing the conformation of KCNQ 2-5 potassium channels, which leads to neuronal hyperpolarisation and a decrease in excitability.

HYPOTHESIS

The purpose of this study is to investigate the effect of retigabine on cortical excitability. Based on the known mechanisms of action of retigabine, we hypothesized that the oral intake of retigabine would increase the resting motor threshold (RMT).

METHODS

Fifteen healthy individuals participated in a placebo-controlled, double-blind, randomised, clinical trial (RCT). The primary outcome measure was the RMT quantified before and after oral intake of retigabine. Several secondary TMS outcome measures were acquired.

RESULTS

The mean RMT, active motor threshold (AMT) and intensity to obtain a 1mV peak-to-peak amplitude potential (SI1mV) were significantly increased after retigabine intake compared to placebo (RMT: P=0.039; AMT: P=0.014; SI1mV: P=0.019). No significant differences were found for short-interval intracortical inhibition/intracortical facilitation (SICI/ICF), long-interval intracortical inhibition (LICI) or short-interval intracortical facilitation (SICF).

CONCLUSION

A single dose of retigabine increased the RMT, AMT and S1mV in healthy individuals. No modulating intracortical facilitation or inhibition was observed. This study provides the first in vivo demonstration of the modulating effects of retigabine on the excitability of the human brain, and the results are consistent with the data showing that retigabine hyperpolarizes neurons mainly by increasing potassium conductance.

Altered paired associative stimulation-induced plasticity in NMDAR encephalitis

OBJECTIVE

To determine whether neurophysiological mechanisms indicating cortical excitability, long-term potentiation (LTP)-like plasticity, GABAergic and glutamatergic function are altered in patients with anti-N-methyl-d-aspartate receptor (NMDAR) encephalitis and whether they can be helpful as markers of diagnostic assessment, disease progression, and potentially therapy response.

METHODS

Neurophysiological characterizations of patients with NMDAR encephalitis (n = 34, mean age: 28 ± 11 years; 30 females) and age/gender-matched healthy controls (n = 27, 28.5 ± 10 years; 25 females) were performed using transcranial magnetic stimulation-derived protocols including resting motor threshold, recruitment curve, intracortical facilitation, short intracortical inhibition, and cortical silent period. Paired associative stimulation (PAS) was applied to assess LTP-like mechanisms which are mediated through NMDAR. Moreover, resting state functional connectivity was determined using functional magnetic resonance imaging.

RESULTS

PAS-induced plasticity differed significantly between groups (P = 0.0056). Cortical excitability, as assessed via motor-evoked potentials after PAS, decreased in patients, whereas it increased in controls indicating malfunctioning of NMDAR in encephalitis patients. Lower PAS-induced plasticity significantly correlated with the modified Rankin Scale (mRS) (r = -0.41; P = 0.0031) and was correlated with lower functional connectivity within the motor network in NMDAR encephalitis patients (P < 0.001, uncorrected). Other neurophysiological parameters were not significantly different between groups. Follow-up assessments were available in six patients and demonstrated parallel improvement of PAS-induced plasticity and mRS.

INTERPRETATION

Assessment of PAS-induced plasticity may help to determine NMDAR dysfunction and disease severity in NMDAR encephalitis, and might even aid as a sensitive, noninvasive, and well-tolerated "electrophysiological biomarker" to monitor therapy response in the future.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov: Identifier: NCT01865578.

Transient and reproducible loss of motor-evoked potential signals after intravenous levetiracetam in a child undergoing craniotomy for resection of astrocytoma

Transcranial electrical motor-evoked potential (tceMEP) monitoring is used in complex intracranial and spinal surgeries to detect and prevent neurological injury. We present a case of transient, reproducible loss of tceMEPs after an infusion of levetiracetam during craniotomy and tumor resection in a child. Cessation of the infusion resulted in restoration of baseline tceMEPs. When the infusion was resumed at the end of the procedure, a similar decrease in tceMEPs was seen as before, after the infusion was stopped. The surgery and postoperative course proceeded without incident, and the patient experienced a full recovery.

Suppression of myoclonus in corticobasal degeneration by levetiracetam

Myoclonus in corticobasal degeneration (CBD) has often been associated with severe and difficult to treat disabilities. Levetiracetam is a new antiepileptic agent with antimyoclonic effects. Herein, we present a 72-year-old woman with clinically probable CBD and with spontaneous rhythmic myoclonus in the right foot, which was markedly ameliorated through treatment with levetiracetam. The effect of levetiracetam was associated with the decreased amplitude of enlarged cortical somatosensory evoked potentials. This result suggests that the antimyoclonic effect of levetiracetam might be mediated through the suppression of increased cortical excitability.

CORTICAL EXCITABILITY AS A POTENTIAL CLINICAL MARKER OF EPILEPSY: A REVIEW OF THE CLINICAL APPLICATION OF TRANSCRANIAL MAGNETIC STIMULATION

Transcranial magnetic stimulation (TMS) can be used for safe, noninvasive probing of cortical excitability (CE). We review 50 studies that measured CE in people with epilepsy. Most showed cortical hyperexcitability, which can be corrected with anti-epileptic drug treatment. Several studies showed that decrease of CE after epilepsy surgery is predictive of good seizure outcome. CE is a potential biomarker for epilepsy. Clinical application may include outcome prediction of drug treatment and epilepsy surgery.

Applicability of nTMS in locating the motor cortical representation areas in patients with epilepsy

BACKGROUND

Transcranial magnetic stimulation (TMS) is increasingly used for non-invasive functional mapping in preoperative evaluation for brain surgery, and the reliability of navigated TMS (nTMS) motor representation maps has been studied in the healthy population and in brain tumor patients. The lesions behind intractable epilepsy differ from typical brain tumors, ranging from developmental cortical malformations to injuries early in development, and may influence the functional organization of the cortical areas. Moreover, the interictal cortical epileptic activity and antiepileptic medication may affect the nTMS motor threshold. The reliability of the nTMS motor representation localization in epilepsy patients has not been addressed.

METHODS

We compared the nTMS motor cortical representation maps of hand and arm muscles with the results of invasive electrical cortical stimulation (ECS) in 13 patients with focal epilepsy. The nTMS maps were projected to the cortical surface segmented from preoperative magnetic resonance images (MRI), and the positions of the subdural electrodes were extracted from the postoperative low-dose computed tomography (CT) images registered with preoperative MRI.

RESULTS

The 3D distance between the average nTMS site and average ECS electrode location was 11 ± 4 mm for the hand and 16 ± 7 mm for arm muscle representation areas. In all patients the representation areas defined with nTMS and ECS were located on the same gyrus, also in patients with abundant interictal epileptic activity on the motor gyrus.

CONCLUSIONS

nTMS can reliably locate the hand motor cortical representation area with the accuracy needed for pre-surgical evaluation in patients with epilepsy.

Motor cortex evaluation by nTMS after surgery of central region tumors: a feasibility study

BACKGROUND

Largely discussed during the past decade, motor cortex reorganization in brain tumor surgery has been investigated only by few studies. We therefore aimed to investigate cortical motor representation after resection of perirolandic WHO grade II and III gliomas using navigated transcranial magnetic stimulation (nTMS).

METHODS

Five patients were examined before neurosurgery and after a follow-up period of 17.7 ± 6.8 months. As a control, five healthy age-matched subjects were equally studied by nTMS in two sessions spaced 12.6 (range 2-35) days apart. Resting motor thresholds (RMT), hotspots and centers of gravity (CoG) were identified for the first dorsal interosseous (FDI), abductor pollicis brevis (APB), extensor digitorum (EXT), tibialis anterior (TA) and abductor hallucis (AH) muscles. Euclidian distances, coefficients of variance and intraclass correlation coefficients (ICC) were calculated.

RESULTS

Healthy subjects showed moderate to excellent reliability measurement of RMT (ICC = 0.69-0.94). Average displacement of CoGs across sessions was 0.68 ± 0.34 cm in the dominant and 0.76 ± 0.38 cm in the non-dominant hemisphere; hotspots moved 0.87 ± 0.51 cm and 0.83 ± 0.45 cm, respectively. In one patient these parameters differed significantly from the control group (p < 0.05 for both CoGs and hotspots). Overall, all patients' CoGs moved 1.12 ± 0.93 cm, and hotspots were 1.06 ± 0.7 cm apart. In both patients and healthy subjects, movement of assessed parameters was more important along the X- than the Y-axis.

CONCLUSIONS

nTMS allows evaluating cortical reorganization after brain tumor surgery. It may contribute to the understanding of neurofunctional dynamics, thus influencing therapeutic strategy.

Effects of intravenous antidepressant drugs on the excitability of human motor cortex: a study with paired magnetic stimulation on depressed patients

BACKGROUND

The effect of various drugs was investigated by using transcranial magnetic stimulation (TMS) both in healthy subjects and patients, and the results indicated an influence of antidepressant drugs (ADs) on motor excitability.

OBJECTIVE

The aim of our study was to analyze the effects of two ADs, the tricyclic (TCA) clomipramine and the serotoninergic antidepressant (SSRI) citalopram on the motor cortex excitability in major depressed patients with TMS.

METHODS

Thirty affected subjects were placed into three groups: two received an intravenous dose of 25 mg clomipramine or 40 mg citalopram, and one received an injection of a placebo. Motor cortex excitability was studied by single and paired TMS before and after 3.5, 8, and 24 hours from administration of the drugs and placebo. Motor cortical excitability was measured using different TMS parameters: resting motor threshold (RMT), motor-evoked potential (MEP) amplitude, intracortical inhibition (ICI), and intracortical facilitation (ICF).

RESULTS

The results indicated a temporary but significant increase of RMT and ICI and a decrease of ICF after the administration of both drugs, with a longer inhibition for the clomipramine rather than the citalopram. MEP amplitude was not significantly affected by the antidepressant injections.

CONCLUSIONS

Our findings highlight that a single intravenous dose of clomipramine or citalopram exerts a significant but transitory suppression of motor cortex excitability in depressed patients. TMS represents a useful research tool in assessing the effects of motor cortical excitability of drugs used in the treatment of mental disorders.

Transcranial magnetic stimulation

PURPOSE OF REVIEW

To present state-of-the-art transcranial magnetic stimulation (TMS) therapy, especially when it is used in psychiatric disorders, on the basis of an exhaustive literature search from 2006 to date (June 2008) on TMS papers published in Medline and Embase. Other references and comments from our own experience started 8 years ago have also been taken into account.

RECENT FINDINGS

The mechanism of action of TMS is now better understood. There is strong evidence of the safety and tolerability of TMS when standard protocols are used. The efficacy of the stimulation of the dorsolateral prefrontal cortex in depression is well documented, and there is evidence of the utility of TMS in posttraumatic stress disorder, in persistent auditory hallucinations in schizophrenia and in attention-deficit disorder with hyperactivity.

SUMMARY

There is enough evidence of the efficacy and safety of TMS in depression to include this technique in the therapeutic protocols of major depression. However, more research is needed on the use of this technique in other psychiatric and nonpsychiatric disorders such as posttraumatic stress disorder, persistent auditory hallucinations, attention-deficit disorder with hyperactivity and tinnitus.