Cortical excitability correlates with seizure control and epilepsy duration in chronic epilepsy

Localizing seizure onset zone by a cortico-cortical evoked potentials-based machine learning approach in focal epilepsy

OBJECTIVE

We aimed to develop a new approach for identifying the localization of the seizure onset zone (SOZ) based on corticocortical evoked potentials (CCEPs) and to compare the connectivity patterns in patients with different clinical phenotypes.

METHODS

Fifty patients who underwent stereoelectroencephalography and CCEP procedures were included. Logistic regression was used in the model, and six CCEP metrics were input as features: root mean square of the first peak (N1RMS) and second peak (N2RMS), peak latency, onset latency, width duration, and area.

RESULTS

The area under the curve (AUC) for localizing the SOZ ranged from 0.88 to 0.93. The N1RMS values in the hippocampus sclerosis (HS) group were greater than that of the focal cortical dysplasia (FCD) IIa group (p < 0.001), independent of the distance between the recorded and stimulated sites. The sensitivity of localization was higher in the seizure-free group than in the non-seizure-free group (p = 0.036).

CONCLUSIONS

This new method can be used to predict the SOZ localization in various focal epilepsy phenotypes.

SIGNIFICANCE

This study proposed a machine-learning approach for localizing the SOZ. Moreover, we examined how clinical phenotypes impact large-scale abnormality of the epileptogenic networks.

The ventral precuneal-posterior cingulate region as a site of epileptogenicity

The ventral precuneal and posterior cingulate area (VP-PC) represents a distinct but topographically variable mesial parietal site of epileptogenicity that may manifest as a common temporal lobe-mediated ictal expression. In a review of records of 62 presumptive epilepsy surgery cases, two cases of primary epileptogenicity expressed within the VP-PC were identified and are detailed to bring attention to this electroencephalographically-hidden area of ictal expression. Details of their investigation and surgical treatment illustrate distinctly different approaches addressing the problem and bringing about a seizure-free outcome.

Betahistine Attenuates Seizures, Neurodegeneration, Apoptosis, and Gliosis in the Cerebral Cortex and Hippocampus in a Mouse Model of Epilepsy: A Histological, Immunohistochemical, and Biochemical Study

Epilepsy is a prevalent and chronic neurological disorder marked by recurring, uncontrollable seizures of the brain. Chronic or repeated seizures produce memory problems and induce damage to different brain regions. Histamine has been reported to have neuroprotective effects. Betahistine is a histamine analogue. The current research investigated the effects of convulsions on the cerebral cortex and hippocampus of adult male albino mice and assessed the possible protective effect of betahistine. Four groups of 40 adult male mice were organized: control, betahistine (10 mg/kg/day), pentylenetetrazole (PTZ) (40 mg/kg/ on alternate days), and Betahistine-PTZ group received betahistine 1 h before PTZ. PTZ induced a substantial rise in glutamate level and a considerable decrease in histamine level. Structural changes in the cerebral cortex and cornu ammonis (CA1) of the hippocampus were detected in the pattern of neuron degeneration. Some neurons were shrunken with dark nuclei, and others had faintly stained ones. Focal accumulation of neuroglial cells and ballooned nerve cells of the cerebral cortex were also detected. Cleaved caspase-3, glial fibrillary acidic protein, and ionized calcium-binding adaptor molecule 1 showed substantial increases, while synaptophysin expression was significantly reduced. Interestingly, these changes were less prominent in mice pretreated with betahistine. In conclusion, betahistine had shown neuroprotective properties against brain damage induced by convulsions.

Distinct Functional Cortico-Striato-Thalamo-Cerebellar Networks in Genetic Generalized and Focal Epilepsies with Generalized Tonic-Clonic Seizures

This study aimed to delineate cortico-striato-thalamo-cerebellar network profiles based on static and dynamic connectivity analysis in genetic generalized and focal epilepsies with generalized tonic-clonic seizures, and to evaluate its potential for distinguishing these two epilepsy syndromes. A total of 342 individuals participated in the study (114 patients with genetic generalized epilepsy with generalized tonic-clonic seizures (GE-GTCS), and 114 age- and sex-matched patients with focal epilepsy with focal to bilateral tonic-clonic seizure (FE-FBTS), 114 healthy controls). Resting-state fMRI data were examined through static and dynamic functional connectivity (dFC) analyses, constructing cortico-striato-thalamo-cerebellar networks. Network patterns were compared between groups, and were correlated to epilepsy duration. A pattern-learning algorithm was applied to network features for classifying both epilepsy syndromes. FE-FBTS and GE-GTCS both presented with altered functional connectivity in subregions of the motor/premotor and somatosensory networks. Among these two groups, the connectivity within the cerebellum increased in the static, while the dFC variability decreased; conversely, the connectivity of the thalamus decreased in FE-FBTS and increased in GE-GTCS in the static state. Connectivity differences between patient groups were mainly located in the thalamus and cerebellum, and correlated with epilepsy duration. Support vector machine (SVM) classification had accuracies of 66.67%, 68.42%, and 77.19% when using static, dynamic, and combined approaches to categorize GE-GTCS and FE-GTCS. Network features with high discriminative ability predominated in the thalamic and cerebellar connectivities. The network embedding of the thalamus and cerebellum likely plays an important differential role in GE-GTCS and FE-FBTS, and could serve as an imaging biomarker for differential diagnosis.

Plasticity in the developing brain: neurophysiological basis for lesion-induced motor reorganization

The plasticity of the developing brain can be observed following injury to the motor cortex and/or corticospinal tracts, the most commonly injured brain area in the pre- or peri-natal period. Factors such as the timing of injury, lesion size and lesion location may affect a single hemisphere’s ability to acquire bilateral motor representation. Bilateral motor representation of single hemisphere origin is most likely to occur if brain injury occurs before the age of 2 years; however, the link between injury aetiology, reorganization type and functional outcome is largely understudied. We performed a retrospective review to examine reorganized cortical motor maps identified through transcranial magnetic stimulation in a cohort of 52 patients. Subsequent clinical, anthropometric and demographic information was recorded for each patient. Each patient’s primary hand motor cortex centre of gravity, along with the Euclidian distance between reorganized and normally located motor cortices, was also calculated. The patients were classified into broad groups including reorganization type (inter- and intrahemispheric motor reorganization), age at the time of injury (before 2 years and after 2 years) and injury aetiology (developmental disorders and acquired injuries). All measures were analysed to find commonalities between motor reorganization type and injury aetiology, function and centre of gravity distance. There was a significant effect of injury aetiology on type of motor reorganization (P < 0.01), with 60.7% of patients with acquired injuries and 15.8% of patients with developmental disorders demonstrating interhemispheric motor reorganization. Within the interhemispheric motor reorganization group, ipsilaterally and contralaterally projecting hand motor cortex centres of gravity overlapped, indicating shared cortical motor representation. Furthermore, the data suggest significantly higher prevalence of bilateral motor representation from a single hemisphere in cases of acquired injuries compared to those of developmental origin. Functional outcome was found to be negatively affected by acquired injuries and interhemispheric motor reorganization relative to their respective counterparts with developmental lesions and intrahemispheric motor reorganization. These results provide novel information regarding motor reorganization in the developing brain via an unprecedented cohort sample size and transcranial magnetic stimulation. Transcranial magnetic stimulation is uniquely suited for use in understanding the principles of motor reorganization, thereby aiding in the development of more efficacious therapeutic techniques to improve functional recovery following motor cortex injury.

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.

Are there differences in cortical excitability between akinetic-rigid and tremor-dominant subtypes of Parkinson's disease?

OBJECTIVE

To assess by transcranial magnetic stimulation (TMS) the excitability of various cortical circuits in akinetic-rigid and tremor-dominant subtypes of Parkinson's disease (PD).

METHODS

The study included 92 patients with PD according to UK Brain Bank criteria, with akinetic-rigid (n = 64) or tremor-dominant (n = 28) subtype. Cortical excitability study, including resting and active motor thresholds (rMT and aMT), input-output curve of motor evoked potentials, contralateral and ipsilateral silent periods (cSP and iSP), short and long-interval intracortical inhibition (SICI and LICI), and intracortical facilitation (ICF) were measured. The results obtained were compared to a control group of 30 age- and sex-matched healthy subjects.

RESULTS

The patients in the tremor group had significantly lower rMT and aMT compared to controls and akinetic-rigid patients and significantly shorter iSP duration compared to akinetic-rigid patients, while iSP latency tended to be longer in akinetic-rigid patients compared to controls. There were no significant differences between the two PD subgroups regarding other cortical excitability parameters, including paired-pulse TMS parameters.

CONCLUSIONS

Only subtle differences of cortical excitability were found between patients with akinetic-rigid vs. tremor-dominant subtype of PD.

SIGNIFICANCE

The clinical heterogeneity of PD patients probably has an impact on cortical excitability measures, far beyond the akinetic-rigid versus tremor-dominant profile.

Functional Neurophysiological Biomarkers of Early-Stage Alzheimer's Disease: A Perspective of Network Hyperexcitability in Disease Progression

Network hyperexcitability (NH) has recently been suggested as a potential neurophysiological indicator of Alzheimer’s disease (AD), as new, more accurate biomarkers of AD are sought. NH has generated interest as a potential indicator of certain stages in the disease trajectory and even as a disease mechanism by which network dysfunction could be modulated. NH has been demonstrated in several animal models of AD pathology and multiple lines of evidence point to the existence of NH in patients with AD, strongly supporting the physiological and clinical relevance of this readout. Several hypotheses have been put forward to explain the prevalence of NH in animal models through neurophysiological, biochemical, and imaging techniques. However, some of these hypotheses have been built on animal models with limitations and caveats that may have derived NH through other mechanisms or mechanisms without translational validity to sporadic AD patients, potentially leading to an erroneous conclusion of the underlying cause of NH occurring in patients with AD. In this review, we discuss the substantiation for NH in animal models of AD pathology and in human patients, as well as some of the hypotheses considering recently developed animal models that challenge existing hypotheses and mechanisms of NH. In addition, we provide a preclinical perspective on how the development of animal models incorporating AD-specific NH could provide physiologically relevant translational experimental data that may potentially aid the discovery and development of novel therapies for AD.

Connective profiles and antagonism between dynamic and static connectivity underlying generalized epilepsy

This study aims to characterize the connective profiles and the coupling relationship between dynamic and static functional connectivity (dFC and sFC) in large-scale brain networks in patients with generalized epilepsy (GE). Functional, structural and diffuse MRI data were collected from 83 patients with GE and 106 matched healthy controls (HC). Resting-state BOLD time course was deconvolved to neural time course using a blind hemodynamic deconvolution method. Then, five connective profiles, including the structural connectivity (SC) and BOLD/neural time course-derived sFC/dFC networks, were constructed based on the proposed whole brain atlas. Network-level weighted correlation probability (NWCP) were proposed to evaluate the association between dFC and sFC. Both the BOLD signal and neural time course showed highly concordant findings and the present study emphasized the consistent findings between two functional approaches. The patients with GE showed hypervariability and enhancement of FC, and notably decreased SC in the subcortical network. Besides, increased dFC, weaker anatomic links, and complex alterations of sFC were observed in the default mode network of GE. Moreover, significantly increased SC and predominantly increased sFC were found in the frontoparietal network. Remarkably, antagonism between dFC and sFC was observed in large-scale networks in HC, while patients with GE showed significantly decreased antagonism in core epileptic networks. In sum, our study revealed distinct connective profiles in different epileptic networks and provided new clues to the brain network mechanism of epilepsy from the perspective of antagonism between dynamic and static functional connectivity.

A Systematic Review of Long-Interval Intracortical Inhibition as a Biomarker in Neuropsychiatric Disorders

Long-interval intracortical inhibition (LICI) is a paired-pulse transcranial magnetic stimulation (TMS) paradigm mediated in part by gamma-aminobutyric acid receptor B (GABA_B) inhibition. Prior work has examined LICI as a putative biomarker in an array of neuropsychiatric disorders. This review conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) sought to examine existing literature focused on LICI as a biomarker in neuropsychiatric disorders. There were 113 articles that met the inclusion criteria. Existing literature suggests that LICI may have utility as a biomarker of GABA_B functioning but more research with increased methodologic rigor is needed. The extant LICI literature has heterogenous methodology and inconsistencies in findings. Existing findings to date are also non-specific to disease. Future research should carefully consider existing methodological weaknesses and implement high-quality test-retest reliability studies.

Cortical Excitability in Temporal Lobe Epilepsy with Bilateral Tonic-Clonic Seizures

OBJECTIVE

We investigated motor cortical excitability (CE) in unilateral temporal lobe epilepsy (TLE) and its relationship to bilateral tonic-clonic seizure (BTCS) using paired-pulse transcranial magnetic stimulation (TMS).

METHODS

In this cross-sectional study, we enrolled 46 unilateral TLE patients and 16 age-and sex-matched healthy controls. Resting motor thresholds (RMT); short-interval intracortical inhibition (SICI, GABAA receptor-mediated); facilitation (ICF, glutamatergic-mediated) with interstimulus intervals (ISIs) of 2, 5, 10, and 15 ms; and long-interval intracortical inhibition (LICI, GABAB receptor-mediated) with ISIs of 200-400 ms were measured via paired-pulse TMS. Comparisons were made between controls and patients with TLE, and then among the TLE subgroups (no BTCS, infrequent BTCS and frequent BTCS subgroup).

RESULTS

Compared with controls, TLE patients had higher RMT, lower SICI and higher LICI in both hemispheres, and higher ICF in the ipsilateral hemisphere. In patients with frequent BTCS, cortical hyperexcitability in the ipsilateral hemisphere was found in a parameter-dependent manner (SICI decreased at a stimulation interval of 5 ms, and ICF increased at a stimulation interval of 15 ms) compared with patients with infrequent or no BTCS.

CONCLUSIONS

Our results demonstrate that motor cortical hyper-excitability in the ipsilateral hemisphere underlies the epileptogenic network of patients with active BTCS, which is more extensive than those with infrequent or no BTCS.

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.

Cortical Excitability by Transcranial Magnetic Stimulation as Biomarkers for Seizure Controllability in Temporal Lobe Epilepsy

OBJECTIVE

To investigate whether indicators of cortical excitability are good biomarkers of seizure controllability in temporal lobe epilepsy (TLE).

MATERIALS AND METHODS

Three groups of subjects were recruited: those with poorly controlled (PC) TLE (N = 41), well-controlled (WC) TLE (N = 71), and healthy controls (N = 44). Short- and long-latency recovery curves were obtained by paired-pulse transcranial magnetic stimulation. Linear mixed effect models were used to study the effects of group, interstimulus interval (ISI), and antiepileptic drugs on long-interval intracortical inhibition (LICI) and short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF).

RESULTS

The mixed effect model that did not incorporate antiepileptic drugs showed that group and ISI were significant factors for LICI and SICI/ICF. LICI in the healthy control group was greater than in the two epilepsy groups, and the difference was significant at ISIs of 50, 150, and 200 msec. In contrast, SICI/ICF in the PC group was greater than in the healthy control and WC groups, and the difference was significant at an ISI of 15 msec. However, due to large variance, it was difficult to identify a cutoff value with both good sensitivity and good specificity. Incorporating the information of antiepileptic drugs to the mixed effect model did not change the overall results.

CONCLUSIONS

Although LICI and SICI/ICF parameters were significantly different at the group level, they may not be suitable biomarkers for the controllability of TLE at the subject level.

Betahistine, prevents kindling, ameliorates the behavioral comorbidities and neurodegeneration induced by pentylenetetrazole

A seizure may occur because of the imbalance between glutamate and gamma-aminobutyric acid (GABA). Recurrent seizures induce some cognitive problems, such as, depression, learning and memory deficits, and neurodegeneration. Histamine is an appropriate therapeutic target for epilepsy via its effect on regulating neurotransmitter release. Also, evidence indicates the effect of histamine on neuroprotection and alleviating cognitive disorders. An ideal antiepileptic drug is a substance, which has both anticonvulsant effects and decreases the comorbidities that are induced by repeated seizures. Betahistine dihydrochloride (betahistine) is a structural analog of histamine. It acts as histamine H1 receptor agonist and H3 receptor antagonist, which enhances histaminergic neuronal activities. In the present study, we examined the effect of betahistine administration on seizure scores, memory deficits, depression, and neuronal loss induced by pentylenetetrazole (PTZ). Eight- to ten-week-old BALB/c male mice (20-25 g) received betahistine, 1, and 10 mg/kg daily from 7 days before the onset of PTZ-induced kindling until the end of the establishment of the kindling. We found that betahistine prevented generalized tonic-clonic seizures induction and diminished forelimb clonic seizures intensity. Also, it decreased cell death in the hippocampus and cortex, ameliorated the memory deficit and depression induced by PTZ in the kindled animals. Altogether, these results indicate that pretreatment and repetitive administration with betahistine exerts antiepileptogenic and anticonvulsant activity. These findings might be due to the neuroprotective impact of betahistine in the hippocampus and cortex.

TMS as a pharmacodynamic indicator of cortical activity of a novel anti-epileptic drug, XEN1101

Objective

Transcranial magnetic stimulation (TMS) produces characteristic deflections in the EEG signal named TMS‐evoked EEG potentials (TEPs), which can be used to assess drug effects on cortical excitability. TMS can also be used to determine the resting motor threshold (RMT) for eliciting a minimal muscle response, as a biomarker of corticospinal excitability. XEN1101 is a novel potassium channel opener undergoing clinical development for treatment of epilepsy. We used TEPs and RMT to measure the effects of XEN1101 in the human brain, to provide evidence that XEN1101 alters cortical excitability at doses that might be used in future clinical trials.

Methods

TMS measurements were incorporated in this Phase I clinical trial to evaluate the extent to which XEN1101 modulates TMS parameters of cortical and corticospinal excitability. TEPs and RMT were collected before and at 2‐, 4‐, and 6‐hours post drug intake in a double‐blind, placebo‐controlled, randomized, two‐period crossover study of 20 healthy male volunteers.

Results

Consistent with previous TMS investigations of antiepileptic drugs (AEDs) targeting ion channels, the amplitude of TEPs occurring at early (15–55 msec after TMS) and at late (150–250 msec after TMS) latencies were significantly suppressed from baseline by 20 mg of XEN1101. Furthermore, the RMT showed a significant time‐dependent increase that correlated with the XEN1101 plasma concentration.

Interpretation

Changes from baseline in TMS measures provided evidence that 20 mg of XEN1101 suppressed cortical and corticospinal excitability, consistent with the effects of other AEDs. These results support the implementation of TMS as a tool to inform early‐stage clinical trials.

Slower alpha rhythm associates with poorer seizure control in epilepsy

Objective

Slowing and frontal spread of the alpha rhythm have been reported in multiple epilepsy syndromes. We investigated whether these phenomena are associated with seizure control.

Methods

We prospectively acquired resting-state electroencephalogram (EEG) in 63 patients with focal and idiopathic generalized epilepsy (FE and IGE) and 39 age- and gender-matched healthy subjects (HS). Patients were divided into good and poor (≥4 seizures/12 months) seizure control groups based on self-reports and clinical records. We computed spectral power from 20-sec EEG segments during eyes-closed wakefulness, free of interictal abnormalities, and quantified power in high- and low-alpha bands. Analysis of covariance and post hoc t-tests were used to assess group differences in alpha-power shift across all EEG channels. Permutation-based statistics were used to assess the topography of this shift across the whole scalp.

Results

Compared to HS, patients showed a statistically significant shift of spectral power from high- to low-alpha frequencies (effect size g = 0.78 [95% confidence interval 0.43, 1.20]). This alpha-power shift was driven by patients with poor seizure control in both FE and IGE (g = 1.14, [0.65, 1.74]), and occurred over midline frontal and bilateral occipital regions. IGE exhibited less alpha power shift compared to FE over bilateral frontal regions (g = -1.16 [-0.68, -1.74]). There was no interaction between syndrome and seizure control. Effects were independent of antiepileptic drug load, time of day, or subgroup definitions.

Interpretation

Alpha slowing and anteriorization are a robust finding in patients with epilepsy and might represent a generic indicator of seizure liability.

Static magnetic fields reduce epileptiform activity in anesthetized rat and monkey

Increasing evidence indicates that static magnetic fields (SMF) reduce cortical activity in both human and animal models. The aim of this work was to investigate the effect of SMF on epileptiform cortical activity, a condition related to an abnormal increase in neuronal excitability. The first experimental block included a Pilocarpine rat model of epilepsy, in which a magnetic neodymium nickel-plated cylinder, a magnetic field of 0.5 T, or “sham” were placed over the skull. In the second experimental block, we recorded epileptic-like activity in the visual cortex of a monkey (Macaca mulatta) under control conditions and in the presence of the magnet. Between 15 and 30 minutes after the second dose of Pilocarpine, EEG changes compatible with seizure like events induced by Pilocarpine were clearly observed in the control animals (sham stimulation). Similar effects were visible in the animals exposed to the real magnet after 1–2 hours. In the monkey, SMF over the cortical focus clearly reduced abnormal activity: the intensity threshold for visual induction increased and the severity and duration decreased. These results reinforce the view that static magnets modulate cortical activity and open the door to the future therapeutic use of SMF in epilepsy as a complement to current pharmacological treatments.

Language mapping with navigated transcranial magnetic stimulation in pediatric and adult patients undergoing epilepsy surgery: Comparison with extraoperative direct cortical stimulation

Objective

Navigated transcranial magnetic stimulation (nTMS) is becoming increasingly popular in noninvasive preoperative language mapping, as its results correlate well enough with those obtained by direct cortical stimulation (DCS) during awake surgery in adult patients with tumor. Reports in the context of epilepsy surgery or extraoperative DCS in adults are, however, sparse, and validation of nTMS with DCS in children is lacking. Furthermore, little is known about the risk of inducing epileptic seizures with nTMS in pediatric epilepsy patients. We provide the largest validation study to date in an epilepsy surgery population.

Methods

We compared language mapping with nTMS and extraoperative DCS in 20 epilepsy surgery patients (age range 9‐32 years; 14 children and adolescents).

Results

In comparison with DCS, sensitivity of nTMS was 68%, specificity 76%, positive predictive value 27%, and negative predictive value 95%. Age, location of ictal‐onset zone near or within DCS‐mapped language areas or severity of cognitive deficits had no significant effect on these values. None of our patients had seizures during nTMS.

Significance

Our study suggests that nTMS language mapping is clinically useful and safe in epilepsy surgery patients, including school‐aged children and patients with extensive cognitive dysfunction. Similar to in tumor surgery, mapping results in the frontal region are most reliable. False negative findings may be slightly more likely in epilepsy than in tumor surgery patients. Mapping results should always be verified by other methods in individual patients.

Long-interval intracortical inhibition as biomarker for epilepsy: a transcranial magnetic stimulation study

Cortical excitability, as measured by transcranial magnetic stimulation combined with electromyography, is a potential biomarker for the diagnosis and follow-up of epilepsy. We report on long-interval intracortical inhibition data measured in four different centres in healthy controls (n = 95), subjects with refractory genetic generalized epilepsy (n = 40) and with refractory focal epilepsy (n = 69). Long-interval intracortical inhibition was measured by applying two supra-threshold stimuli with an interstimulus interval of 50, 100, 150, 200 and 250 ms and calculating the ratio between the response to the second (test stimulus) and to the first (conditioning stimulus). In all subjects, the median response ratio showed inhibition at all interstimulus intervals. Using a mixed linear-effects model, we compared the long-interval intracortical inhibition response ratios between the different subject types. We conducted two analyses; one including data from the four centres and one excluding data from Centre 2, as the methods in this centre differed from the others. In the first analysis, we found no differences in long-interval intracortical inhibition between the different subject types. In all subjects, the response ratios at interstimulus intervals 100 and 150 ms showed significantly more inhibition than the response ratios at 50, 200 and 250 ms. Our second analysis showed a significant interaction between interstimulus interval and subject type (P = 0.0003). Post hoc testing showed significant differences between controls and refractory focal epilepsy at interstimulus intervals of 100 ms (P = 0.02) and 200 ms (P = 0.04). There were no significant differences between controls and refractory generalized epilepsy groups or between the refractory generalized and focal epilepsy groups. Our results do not support the body of previous work that suggests that long-interval intracortical inhibition is significantly reduced in refractory focal and genetic generalized epilepsy. Results from the second analysis are even in sharper contrast with previous work, showing inhibition in refractory focal epilepsy at 200 ms instead of facilitation previously reported. Methodological differences, especially shorter intervals between the pulse pairs, may have contributed to our inability to reproduce previous findings. Based on our results, we suggest that long-interval intracortical inhibition as measured by transcranial magnetic stimulation and electromyography is unlikely to have clinical use as a biomarker of epilepsy.