Interictal EEG Discharges Research Articles

Effect of medication withdrawal on the interictal epileptiform EEG discharges in presurgical evaluation

Medication withdrawal (MW) is an important method of provoking seizures and activating epileptiform EEG activity during the diagnostic work-up of patients evaluated for epilepsy surgery. Previously it was suggested that MW might influence the seizure-type and activate cortical areas otherwise not producing epileptiform discharges, leading to a false localization of the irritative zone. In order to investigate this we reviewed 42 consecutive cases of MW, of 36 patients, during a 3-year period. We compared seizure frequency, seizure-types and the localization of interictal epileptiform discharges before and after MW. Seizure frequency was significantly higher after MW. In the whole group we found an increase in seizure propagation: the proportion of the complex partial seizures and secondarily generalised seizures increased, while the proportion of the simple partial seizures decreased following MW. In one-third of the patients the interictal EEGs after the MW were different from those recorded before the MW. However, in these discordant cases the EEG findings after the MW (and not before the MW) were concordant with the seizure onset zone and the lesional zone. We conclude that MW is an effective and reliable seizure provoking method, and it does not lead to false localization of the irritative zone.

Possíveis interfaces entre TDAH e epilepsia

OBJETIVO: Identificar na literatura elementos para explicar uma possível associação entre o transtorno de déficit de atenção e hiperatividade (TDAH) e a epilepsia e orientar quanto ao manejo clínico dos pacientes que compartilham esses transtornos. MÉTODOS: Realizou-se revisão da literatura dos últimos 10 anos nas bases de dados MedLine e Lilacs com a combinação dos descritores "attention deficit hyperactivity disorder", "ADHD" e "epilepsy". RESULTADOS: Sintomas de TDAH são frequentes em síndromes epilépticas idiopáticas. Vários fatores podem contribuir para a coexistência desses transtornos: 1) possibilidade de uma mesma propensão genética; 2) participação dos neurotransmissores noradrenalina e dopamina no TDAH e na modulação da excitabilidade neuronal; 3) anormalidades estruturais do cérebro evidenciadas em epilépticos portadores de TDAH; 4) influência dos efeitos crônicos das crises e das descargas epileptiformes interictais sob a atenção; 5) efeitos adversos das drogas antiepilépticas sob a cognição. CONCLUSÕES: As evidências atuais apontam que crises epilépticas e TDAH podem apresentar bases neurobiológicas comuns. Estudos que avaliam disfunções nas vias de sinalização das catecolaminas cerebrais e o papel das descargas epileptiformes interictais na geração dos sintomas são fundamentais na investigação desses mecanismos. Drogas psicoestimulantes são seguras e eficazes para o tratamento do TDAH na maioria dos portadores de epilepsia.

THO16 Selective visual impairment during posterior/diffuse interictal EEG discharges. A psychophysiological and neurophysiological demonstration

THO16 Selective visual impairment during posterior/diffuse interictal EEG discharges. A psychophysiological and neurophysiological demonstration

Verbal dichotic listening performance and its relationship with EEG features in benign childhood epilepsy with centrotemporal spikes

Benign epilepsy of childhood with centrotemporal spikes (BECTS) is the most common form of idiopathic partial epilepsy in children from 3 to 12 years old. Little and far from conclusive information is available on its chronic impact on the organization of higher cognitive functions during development. The aim of this study was to assess the effect of interictal EEG discharges in the peri-sylvian regions on language lateralization in BECTS. Twenty-four 7-12-year-old children with BECTS were compared with a control group of 16 healthy children matched for age, gender and schooling. Hemispheric speech lateralization was determined with the vowel-consonant dichotic listening (DL) test. DL data showed that BECTS children lacked the typical right ear/left hemisphere functional advantage. The side of the interictal spikes had no specific influence on DL performance, while a multifocal location of the discharges had a particularly significant effect on the laterality index, as shown by the complete loss of the right-ear advantage in favor of a symmetrical performance with the overall level of accuracy remaining constant. No correlation was found between spike frequency and DL data. BECTS coincides with an atypical performance in DL test with the loss of the usual right ear/left hemisphere advantage, suggesting that interictal activity may induce a reorganization of speech perception lateralization, with a bilateral representation of the phonological processing of auditory and verbal stimuli. This was particularly evident in the group with multifocal spikes, which may mean that a widespread hyperexcitability can affect the network underlying DL performance more severely.

433: The topographical relationship between the source localization of interictal and ictal EEG discharges recorded with subdural grid electrodes using low-resolution electromagnetic tomography (sLORETA)

Purpose: In patients with medically refractory partial epilepsy, the topographic relationship between the location and the extent of the irritative zone, ictal onset zone, and the epileptogenic zone is controversial. Previous studies investigating the relationship between these zones have been based on a two-dimensional analysis of scalp or intracranial EEG recording, which can give misleading information regarding location of the underlying source generators. In this study patients who underwent chronic intracranial EEG monitoring with subdural electrodes, source localization was utilised using low resolution electromagnetic tomography (sLORETA) and co-registration of MRI and CT images, to examine the three-dimensional topographic relationship of the source of the interictal spikes with the ictal onset zone and regions of immediate spread.

Intellectual and language findings and their relationship to EEG characteristics in benign childhood epilepsy with centrotemporal spikes

Recent research has revealed that benign childhood epilepsy with centrotemporal spikes (BECTS) causes deficient performance in various neuropsychological areas, without arriving at a definition of a uniform profile. The purpose of this study was to examine intelligence and certain language functions in 24 children with an active centrotemporal focus, comparing them with a group of 16 controls matched for age and schooling. Test results were correlated with several EEG characteristics, including focal versus multifocal presentation of interictal epileptiform activity, lateralization, spike maximum on midtemporal or extratemporal electrodes, and rate of interictal activity when awake and during non-REM sleep. Our study demonstrated that children with BECTS have mild language defects, revealed by tests measuring phonemic fluency, verbal re-elaboration of semantic knowledge, and lexical comprehension. Interictal EEG discharges demonstrated that a high rate of occurrence while awake, multifocal location, and temporal prominence seem to impair the efficiency of some of the neuropsychological functions investigated. However, because the last EEG was obtained within the last 2 months (on average) before the assessment, and because BECTS is a form of epilepsy with signs of cortical hyperexcitability that vary over time in terms of rate, side, and location, the pattern of neuropsychological deficiencies could have changed (at least to some degree) by the time of the test, with respect to the EEG variables considered.

Monday July 3, 2006 7:30-9:00 Hall 5B Teaching Session To treat or not to treat the EEG in paediatric epilepsy syndromes

Abstract 1 R. Pressler ( 1 Department of Clinical Neurophysiology, National Hospital for Neurology, UK ) Treatment of interictal discharges can improve behaviour in children with epilepsy Increased behavioural problems in children with epilepsy are a consequence of various factors including underlying brain lesion, age of onset, antiepileptic drugs, psychosocial issues, seizure type and frequency, and interictal EEG abnormalities. Suppression of discharges will improve behaviour in children with nonconvulsive status epilepticus presenting as pseudo-dementia or more subtle behavioural changes, and in children with prolonged nocturnal discharges such as ESES. The effect of intermittent interictal EEG discharges on behaviour and cognition is still controversial. Whether cognitive and behavioural problems can be directly caused by discharges or are a coexisting phenomenon can be determining through improvement of cognition and behaviour, if EEG discharges are suppressed. In children with drug resistant epilepsy and learning difficulties suppression of discharges was associated with improvement in global rating of psychosocial function. In children showing interictal discharges but without epilepsy, suppression of discharges showed no definite effect. In children with well-controlled or mild epilepsy, improved behaviour was only observed in children who showed a reduction of discharges during active treatment, but not in patients without a change in discharge rate. The issue of ‘treating the EEG’ remains controversial. The question is not whether to treat the EEG, but whether seizures, so subtle as to be recognisable only by EEG and behavioural monitoring, produce disability sufficient to justify treatment.

Localizing value of scalp EEG spikes: A simultaneous scalp and intracranial study

Objective To determine the relationship between cortical origins of interictal and ictal EEG discharges in patients with temporal lobe epilepsy. Methods Simultaneous cortical and scalp EEG recordings were obtained from six patients with temporal lobe epilepsy. Subdural electrode contacts active at seizure onset and when scalp ictal rhythms became evident were identified. Similarly, cortical substrates of scalp EEG spikes were identified at spike peak and at the initial rising phase of the potential. Results Intracranial seizure onsets were commonly focal and involved only a few electrode contacts, as opposed to scalp ictal rhythms, which required synchronous activation of multiple electrode contacts. At the peak of scalp spikes, multiple electrode contacts were similarly active. However, at spike onset, cortical substrates were more discrete and commonly involved electrodes similar to that of seizure onsets. Conclusions Scalp EEG ictal rhythms and the peak of a scalp spike may poorly localize the epileptogenic focus because of propagation. Cortical source area at scalp spike onset is more discrete, however, and the seizure onset zone often lies within this area. Significance Analysis of scalp spikes, such as source modeling, at their initial rising phase might provide useful localizing information about seizure origins in the same patient.

FMRI temporal clustering analysis in patients with frequent interictal epileptiform discharges: Comparison with EEG-driven analysis

Temporal clustering analysis (TCA) is an exploratory data-driven technique that has been proposed for the analysis of resting fMRI to localise epileptiform activity without need for simultaneous EEG. Conventionally, fMRI of epileptic activity has been limited to those patients with subtle clinical events or frequent interictal epileptiform EEG discharges, requiring simultaneous EEG recording, from which a linear model is derived to make valid statistical inferences from the fMRI data. We sought to evaluate TCA by comparing the results with those of EEG correlated fMRI in eight selected cases. Cases were selected with clear epileptogenic localisation or lateralisation on the basis of concordant EEG and structural MRI findings, in addition to concordant activations seen on EEG-derived fMRI analyses. In three, areas of activation were seen with TCA but none corresponding to the electro-clinical localisation or activations obtained with EEG driven analysis. Temporal clusters were closely coincident with times of maximal head motion. We feel this is a serious confound to this approach and recommend that interpretation of TCA that does not address motion and physiological noise be treated with caution. New techniques to localise epileptogenic activity with fMRI alone require validation with an appropriate independent measure. In the investigation of interictal epileptiform activity, this is best done with simultaneous EEG recording.

Orbitofrontal Epilepsy: Electroclinical Analysis of Surgical Cases and Literature Review

Clinical and electrographic data were reviewed on 2 of our patients with orbitofrontal epilepsy who were seizure free at 5-year follow-up, and on 2 similar patients from the literature. One of our patients was lesional, and the other was nonlesional. Interictal EEG discharges were lateralized to the side of invasively recorded orbitofrontal seizures in the nonlesional case. In this case, no clinical manifestations occurred until the orbitofrontal discharge had spread to the opposite orbitofrontal and both mesial temporal areas. Unresponsiveness or arrest of activity were the initial manifestations of complex partial seizures in both cases. The 2 cases from the literature with long-term seizure-free follow-up had little impairment of awareness and displayed vigorous motor automatisms. Interictal epileptiform activity was bifrontally synchronous in 1 case. Ipsilateral frontotemporal discharges were seen in both. Invasive ictal epileptiform activity appeared maximal in the ipsilateral orbitofrontal region in both patients. No consistent electrographic or clinical pattern characterized these 4 cases. Seizures of orbitofrontal origin may be characterized by either unresponsiveness associated with oroalimentary automatisms or limited alteration of awareness and associated with vigorous motor automatisms. Invasive monitoring of the orbitofrontal cortex should be considered in nonlesional cases with complex partial seizures that show nonlocalizing ictal patterns and interictal frontal or frontotemporal epileptiform discharges.

Effect of interstitial stereotactic radiosurgery on behavior and subjective handicap of epilepsy in patients with gelastic epilepsy

Patients with symptomatic epilepsy due to hypothalamic hamartomas often are compromised not only by pharmacoresistant epileptic seizures but also by behavioral disturbances and cognitive dysfunction. We report the effect of successful treatment with stereotactic interstitial radiosurgery by intrahypothalamic implantation of 125I seeds on behavior and subjective handicap. In all patients rendered seizure-free or suffering only from auras, improvement of behavior was reported by parents and colleagues or schoolteachers. Parents' ratings according to the Child Behavior Checklist showed improvements with respect to social problems and attention. Self-ratings of quality of life by adult patients showed improvements in activities, working situation, and self-perception. These improvements were not observed in patients in whom clinically manifest seizures and interictal EEG discharges persisted after radiosurgery.

Effects of epileptiform EEG discharges on cognitive function: Is the concept of “transient cognitive impairment” still valid?

In this article we review the existing evidence on the cognitive impact of interictal epileptiform EEG discharges. Such cognitive impairment occurs exclusively in direct relation to episodes of epileptiform EEG discharges and must be distinguished from (post) ictal seizure effects and from the nonperiodic long-term “stable” interictal effects caused by the clinical syndrome or the underlying etiology. Especially in patients with short nonconvulsive seizures, characterized often by difficult-to-detect symptoms, the ictal or postictal effects may be overlooked and the resulting cognitive effects may be erroneously related to the epileptiform EEG discharges. The existing epidemiological data show that the prevalence of cognitive impairment during epileptiform EEG discharges is low. In one study 2.2% of the patients referred to a specialized epilepsy center for EEG recording showed a definite relationship between epileptiform EEG discharges and cognitive impairments (“transient cognitive impairment”). Several studies have sought to analyze to what extent cognitive impairment can be attributed to epileptiform EEG discharges among the other epilepsy factors (such as the effect of the clinical syndrome). These studies show that epileptiform EEG discharges have an additional and independent effect, but this effect is mild and limited to transient mechanistic cognitive processes (alertness, mental speed). This finding concurs with clinical studies that also reported only mild effects. In only exceptional cases are epileptiform EEG discharges the dominant factor explaining cognitive impairment. In addition, some studies have indicated that such mild effects may accumulate over time (when frequent epileptiform EEG discharges persist over years) and consequently result in effects on stable aspects of cognitive function such as educational achievement and intelligence. Hence, the clinical relevance is that early detection of cognitive effects of epileptiform EEG discharges and subsequent treatment may prevent a definite impact on cognitive and educational development. The disruptive effects of epileptiform EEG discharges on long-term potentiation, as established in animal experiments, may be one of the neurophysiological mechanisms underlying this accumulation. In conclusion the concept of “transient cognitive impairment” is still valid, but refinement of methodology has shown that a large proportion of presumed transient cognitive impairment can be attributed to subtle seizures, while interictal epileptic activity accounts for a much smaller part of the cognitive effects than previously thought. In particular cryptogenic partial epilepsies are associated with the risk of cognitive impairment. We hope that increased clinical awareness of this need for early detection will stimulate longitudinal and prospective research that eventually also will provide an answer to the questions of when and how epileptiform discharges that are not part of a seizure need to be treated.

EEG quality during simultaneous functional MRI of interictal epileptiform discharges.

This article concerns the evaluation of the quality of interictal epileptiform EEG discharges recorded throughout simultaneous echo planar imaging (EPI). BOLD (blood oxygen level dependent) functional MRI (fMRI) images were acquired continuously on a patient with intractable epilepsy. EEG was sampled simultaneously, during and after imaging, with removal of pulse and imaging artifacts by subtraction of channel-specific running averages. Contiguous EEG epochs recorded with and without fMRI (fMRI+ve vs. fMRI-ve) were next randomized and presented to two blinded observers. Epileptiform discharges were identified retrospectively, and comparison was made in terms of the number of identified events, their amplitude, and spatiotemporal distribution. A spectral analysis was also performed on the EEG. In the randomized comparison of EEG segments, 80 (fMRI+ve) vs. 69 (fMRI-ve) discharges were noted with good interobserver agreement (69%). There were no significant differences in amplitude or spatio-temporal distribution. Comparison of the events detected and measured by two expert observers demonstrated that the Interictal Epileptiform Discharge (IED) characteristics were indistinguishable with and without scanning. We review briefly the existing literature on EEG recording quality for combined EEG/fMRI.

Identifying potential surgical candidates in patients with evidence of bitemporal epilepsy.

To determine which patients with evidence of medically refractory bitemporal epilepsy are potentially good candidates for surgical therapy. We reviewed 42 adults with intractable seizures who were found to have bitemporal ictal onsets, based on scalp video-EEG long-term monitoring (LTM). All underwent invasive LTM before surgery. Surgical outcomes were classified as seizure free, >75% reduction in seizures, or <75% reduction in seizures, >or=1 year after resection. We related the following factors to outcome: (a). >75% preponderance of interictal scalp EEG discharges to one temporal region; (b). magnetic resonance imaging (MRI) findings; (c). lateralizing deficits on verbal or visual reproduction memory testing; and (d). memory failure with injection contralateral to side of surgery on Wada testing. Twenty-six (62%) of 42 patients had unilateral ictal onsets based on intracranial studies. Seizure freedom (occurring in 64% of this group), or >75% seizure reduction (found in 12% of subjects) occurred only when at least one of the following three factors was concordant with the side of surgery: preponderance of interictal scalp EEG discharges, unilateral temporal lesion on MRI, or lateralizing verbal or visual reproduction memory deficits on neuropsychological tests (p = 0.004). Seven subjects with bilateral ictal onsets based on intracranial studies had resections based on preponderance of seizures to one side, or other lateralizing noninvasive abnormality. Five of these (all of whom had >or=80% of seizures originating from one side) had >75% reduction in seizures. Invasive monitoring to pursue possible surgical therapy for patients with surface EEG evidence of bitemporal epilepsy may be justified only when some lateralizing feature is found in other noninvasive assessments.

Preoperative clinical, EEG, and imaging findings do not predict seizure outcome following temporal lobectomy in childhood.

Although certain clinical, electroencephalographic (EEG), magnetic resonance imaging (MRI), and pathologic findings in adults with intractable temporal lobe epilepsy predict seizure outcome following temporal lobectomy, predictors of seizure outcome have not been studied systematically in pediatric temporal lobectomy series. We retrospectively analyzed preoperative clinical, EEG, and neuroimaging findings with reference to seizure outcome (seizure free or non-seizure free) in 33 children (mean age, 9.3 years) who underwent tailored temporal lobe resections for intractable temporal lobe epilepsy. Trends were apparent with (1) younger age at seizure onset, younger age at surgery, shorter duration of epilepsy, localized unilateral temporal lesions on MRI, and right-sided surgery more frequently associated with a seizure-free outcome, and (2) significant prior history, daily preoperative seizures, generalized motor seizures, mental retardation, and localized unilateral temporal epileptiform EEG activity more frequently associated with a non-seizure-free outcome. However, none of these findings, alone or in combination, correlated with postoperative seizure status at a statistically significant level. Submitting the four variables generally considered to be most predictive of favorable outcome (ie, normal intelligence, unilateral ictal and interictal EEG discharges, and focal temporal MRI lesion) to a multiple-cutoff procedure did not predict seizure freedom. Our data indicate that predictors of outcome of temporal lobectomy in adults may not apply in children, perhaps due to inherent neurobiologic differences in the etiology and expression of temporal lobe epilepsy, and should therefore not be used as sole determinants of surgical candidacy in children.

Electrocardiograph QT lengthening associated with epileptiform EEG discharges—a role in sudden unexplained death in epilepsy?

EEG with co-registered electrocardiography was recorded during at least two interictal epileptiform EEG discharges in each of 11 patients who later suffered from sudden unexpected death in epilepsy (SUDEP), and from another 11 age and sex matched patients, also with uncontrolled tonic-clonic seizures, drawn from the same centre who were still alive at the time of investigation (non-SUDEPs). A corrected QT interval for rate (QTc) was obtained and a mean value calculated for the period immediately prior to discharge, during discharge and immediately post discharge. Mean QTc was also obtained interictally without discharge. There was a significant (P = 0.01) increase in the mean QTc during discharge compared to that measured interictally without discharge for the whole population of SUDEPs and non-SUDEPs, and this was maintained for the SUDEPs alone (P = 0.02) but did not hold for the non-SUDEP group alone. Although reaching statistical significance, increases in mean QTc in SUDEP patients only exceeded currently accepted upper limits in one case, and then only marginally. The clinical significance of these findings merits further investigation.

Ictal EEG changes with corpus callosum section.

Corpus callosum section diminishes but does not completely abolish secondary bilaterally synchronous interictal EEG discharges, yet often causes cessation of generalized seizures. The effects of corpus callosum section on ictal EEG patterns have not been described. We contrasted ictal EEG patterns before and after anterior callosotomy in 18 patients and before and after total callosotomy in 10 patients. Bilaterally synchronous seizure onset was disrupted in 5 of 11 anterior section patients and 5 of 5 total section patients. Seven of 18 anterior section patients and 5 of 10 total section patients had more localized seizure onset after the procedure; localization to the frontal lobe was observed after anterior or total section, but only total section patients had newly demonstrated posterior locations of seizure onset. These data suggest that the mechanisms by which bilaterally synchronous interictal and ictal discharges are generated differ. Although brainstem or diencephalic structures may contribute to formation of interictal bilateral synchrony, the corpus callosum may be the only pathway used in producing apparent bilateral synchronous seizure onset in patients with secondarily generalized seizures.

Partial childhood epilepsy and reaction time: the effect of interictal EEG discharges

A study was conducted on seven children (five females and two males, aged 5.7-13.1 years) affected with partial epilepsy which was well controlled by therapy. A computer was connected on-line to a polygraph and during two EEG recordings, the subject had to react to the appearance of a colored rectangle on the display screen by pushing a key on the keyboard: these events were automatically marked on the trace of a polygraphic channel. By means of Anova analysis it was demonstrated that during the same recording, reactions simultaneous to paroxysmal discharges were not significantly slower than those measured during free intervals. However, in the same patient, reaction times were significantly prolonged during recordings characterized by a higher rate of EEG paroxysmal activity.

Differentiation of Epileptic from Nonepileptic Head Drops in Children

To study the differences between epileptic and nonepileptic head drops, 351 episodes in 24 children were analyzed by EEG-videotelemetry monitoring. Drops were classified as either epileptic or nonepileptic depending on the presence or absence of concomitant ictal EEG discharges. Ictal discharges included generalized spike-wave, polyspike-wave, bilateral sharp wave, generalized delta, and generalized beta activity. Children with epileptic drops (group I) were similar to children with nonepileptic drops (group II) with respect to age, sex, number of recorded episodes, and presence of mental retardation or other abnormalities on neurologic examination. Group I patients had a significantly higher prevalence of ictal changes in facial expression, subtle myoclonic extremity movements, generalized interictal EEG discharges, and other seizure types. Drops characterized by rapid head descent followed by slow recovery to the upright position were significantly more common in group I patients, whereas drops in which the velocity of recovery matched that of head descent (head nods) were equal in the two groups. Repetitive nods (head bobs) were observed exclusively in group II patients. These clinical and electrophysiologic features may assist in differentiating epileptic from nonepileptic head drops in children.

Effects of corpus callosum section on secondary bilaterally synchronous interictal EEG discharges.

We studied the effect of corpus callosum section on secondary bilaterally synchronous interictal EEG discharges in 13 patients with partial and secondarily generalized seizures before and after partial or complete section of the corpus callosum. Bilaterally synchronous discharges were completely eliminated in one patient. In 12 patients, there was a distinct reduction in frequency. Our clinical experience agrees with experimental data to suggest that epileptic discharges follow pathways, both across the corpus callosum and/or down to diencephalic/mesencephalic structures, before there is bilateral spread.