Intractable epilepsy in children

Conceptualization and implementation of an interdisciplinary clinic for children with drug-resistant epilepsy during the COVID-19 pandemic

OBJECTIVE

To describe the rapid conceptualization and implementation of an interdisciplinary epilepsy clinic for children with drug-resistant epilepsy (DRE) at Arkansas Children's Hospital (ACH) during the COVID 19 pandemic.

METHODS

Focusing on care design and care coordination for children with DRE, multiple stakeholder groups decided to implement a clinic after the systematic rating of constructs present in a theoretical meta-analytic framework. Based on the projected success, the new interdisciplinary clinic (composed of an epileptologist, a neurosurgeon, and a neuropsychologist and coordinated by a full-time nurse) was established. Clinic operations were further refined through discussions with patients, families, and care providers. We collected data retrospectively (August 2020 to June 2021) to determine referral patterns, clinic scheduling metrics, patient characteristics, clinical recommendations, and epilepsy quality metrics.

RESULTS

Of the 32 Consolidated Framework for Implementation Research constructs assessed, 24 were positively rated to predict a high probability of successful implementation of the clinic. For approximately 100 patient visits, appearance and usage rates were >75%, yielding a clinic utilization rate of approximately 60%. Among 76 unique patients (average age of 12 years, 60% focal epilepsy), 39 patients (51.3%) were deemed eligible for epilepsy surgery evaluation. The majority of the patients (53.9%) were advised for additional diagnostic testing, and 31.6% of patients were scheduled for vagus nerve stimulation. More patients (33%) had changes in their existing anti-seizure medication (ASM) regimen rather than an addition of a new ASM (7.9%). Standardized epilepsy quality measures showed >80% to 90% adherence in 3 (reproductive counseling, depression and anxiety screening, documentation of seizure frequency) out of 4 metrics.

SIGNIFICANCE

This is the first study to show that an interdisciplinary clinic can be a valuable attribute of care models in high-need children with DRE by enabling comprehensive one-stop service for diagnostic evaluation, surgical consideration, and brief assessment of psychiatric comorbidities without compromising consensus-based best practices.

Epilepsias na Infância

As crises epilépticas representam um dos mais freqüentes problemas neurológicos na infância. Entre 0,5% e 1% de crianças e adolescentes apresentam uma crise epiléptica associada com um distúrbio metabólico agudo ou um insulto neurológico, muitos dos quais ocorrem no período neonatal. Elevada incidência de epilepsia ocorre no primeiro ano de vida. A síndrome de West ocorre em cerca de 9% das epilepsias na infância, síndrome de Lennox-Gastaut por volta de 1% a 2%, epilepsia de ausência de 10% a 15%, epilepsias mioclônica juvenil ocorre em cerca de 5% e as epilepsia parciais benignas ocorrem em 10% de todas as epilepsias na infância, mas 20% a 25% das epilepsias são diagnosticadas entre 5 e 15 anos.

Long-term EEG in children

Long-term video-EEG corresponds to a recording ranging from 1 to 24 h or even longer. It is indicated in the following situations: diagnosis of epileptic syndromes or unclassified epilepsy, pre-surgical evaluation for drug-resistant epilepsy, follow-up of epilepsy or in cases of paroxysmal symptoms whose etiology remains uncertain. There are some specificities related to paediatric care: a dedicated pediatric unit; continuous monitoring covering at least a full 24-hour period, especially in the context of pre-surgical evaluation; the requirement of presence by the parents, technician or nurse; and stronger attachment of electrodes (cup electrodes), the number of which is adapted to the age of the child. The chosen duration of the monitoring also depends on the frequency of seizures or paroxysmal events. The polygraphy must be adapted to the type and topography of movements. It is essential to have at least an electrocardiography (ECG) channel, respiratory sensor and electromyography (EMG) on both deltoids. There is no age limit for performing long-term video-EEG even in newborns and infants; nevertheless because of scalp fragility, strict surveillance of the baby's skin condition is required. In the specific context of pre-surgical evaluation, long-term video-EEG must record all types of seizures observed in the child. This monitoring is essential in order to develop hypotheses regarding the seizure onset zone, based on electroclinical correlations, which should be adapted to the child's age and the psychomotor development.

[French guidelines on electroencephalogram]

Electroencephalography allows the functional analysis of electrical brain cortical activity and is the gold standard for analyzing electrophysiological processes involved in epilepsy but also in several other dysfunctions of the central nervous system. Morphological imaging yields complementary data, yet it cannot replace the essential functional analysis tool that is EEG. Furthermore, EEG has the great advantage of being non-invasive, easy to perform and allows control tests when follow-up is necessary, even at the patient's bedside. Faced with the advances in knowledge, techniques and indications, the Société de Neurophysiologie Clinique de Langue Française (SNCLF) and the Ligue Française Contre l'Épilepsie (LFCE) found it necessary to provide an update on EEG recommendations. This article will review the methodology applied to this work, refine the various topics detailed in the following chapters. It will go over the summary of recommendations for each of these chapters and underline proposals for writing an EEG report. Some questions could not be answered by the review of the literature; in those cases, an expert advice was given by the working and reading groups in addition to the guidelines.

Ictal MEG onset source localization compared to intracranial EEG and outcome: improved epilepsy presurgical evaluation in pediatrics

PURPOSE

Magnetoencephalography (MEG) has been shown a useful diagnostic tool for presurgical evaluation of pediatric medically intractable partial epilepsy as MEG source localization has been shown to improve the likelihood of seizure onset zone (SOZ) sampling during subsequent evaluation with intracranial EEG (ICEEG). We investigated whether ictal MEG onset source localization further improves results of interictal MEG in defining the SOZ.

METHODS

We identified 20 pediatric patients with one habitual seizure during MEG recordings between October 2007 and April 2011. MEG was recorded with sampling rates of 600Hz and 4000Hz for 10 and 2min respectively. Continuous head localization (CHL) was applied. Source localization analyses were applied using multiple algorithms, both at the beginning of ictal onset and for interictal MEG discharges. Ictal MEG onsets were identified by visual inspection and power spectrum using short-time Fourier transform (STFT). Source localizations were compared with ICEEG, surgical procedure and outcome.

KEY FINDINGS

Eight patients met all inclusion criteria. Five of the 8 patients (63%) had concordant ictal MEG onset source localization and interictal MEG discharge source localizations in the same lobe, but the source of ictal MEG onset was closer to the SOZ defined by ICEEG.

SIGNIFICANCE

Although the capture of seizures during MEG recording is challenging, the source localization for ictal MEG onset proved to be a useful tool for presurgical evaluation in our pediatric population with medically intractable epilepsy.

Ipsilateral responses of motor evoked potential correlated with the motor functional outcomes after cortical resection

The aim of this study was to evaluate if ipsilateral motor evoked potential (MEP) elicited by transcranial magnetic stimulation (TMS) could provide neurosurgeons preoperatively with useful information regarding surgical procedure for patients with severe cerebral hemiatrophy or unilateral malformation. Thirteen epilepsy patients with severe cerebral hemiatrophy or unilateral malformation were studied before operation using MEPs recorded on bilateral abductor pollicis brevis (APBs) muscles, elicited by transcranial magnetic stimulation of the motor cortex. Ten subjects served as controls.

RESULTS

(1) no ipsilateral MEP responses were recorded in all the 10 healthy subjects; (2) in the 13 patients, the results of MEPs could be divided into four types. Type A: in 3 patients bilateral MEPs were recorded when unaffected hemisphere was stimulated, while no responses were elicited when the affected hemisphere was stimulated. Type B: in another 3 patients, the MEPs were elicited from bilateral APB muscles when the unaffected hemisphere was stimulated, and the contralateral MEP was also elicited when the affected hemisphere was stimulated. Type C: in two patients contralateral MEP was elicited when the unaffected hemisphere was stimulated, while no MEP was induced in APB muscles of either side following the affected hemisphere stimulation. Type D: in the remaining 5 patients, contralateral magnetic MEPs were elicited either when the affected or the unaffected hemisphere was stimulated. Patients of type A, B and C received hemispherectomy showed no significant permanent motor functional deficit. Among the total 8 patients, 7 patients got seizure free after the operation. Patients of type D showed minor muscle strength decrease after localized cortical resection. Three out of 5 patients of type D got seizure free after the operation. Ipsilateral MEP response might be useful for neurosurgeons to plan appropriate surgical procedure which helps avoid post-operative motor deficits.

Epilepsy surgery in children: outcomes and complications

OBJECT

Ideal epilepsy surgery would eliminate seizures without causing any functional deficits. The aim of the present study was to assess seizure outcomes and complications after epilepsy surgery in children with intractable epilepsy.

METHODS

Data obtained in 134 children (75 boys and 59 girls) age 17 years or younger who underwent epilepsy surgery at Seoul National University Children's Hospital between 1993 and 2005 were retrospectively reviewed. Epilepsy surgery included temporal resection (59 cases), extratemporal resection (56 cases), functional hemispherectomy (7 cases), callosotomy (9 cases), multiple subpial transection (1 case), and disconnection of a hamartoma (2 cases). The mean follow-up duration was 62.3 months (range 12-168 months).

RESULTS

The overall seizure-free rate was 69% (93 of 134 cases). The seizure-free rate was significantly higher in children who underwent temporal resection than in those in whom extratemporal resection was performed (88 vs 55%, p < 0.05). The most frequent causes of treatment failure were related to the absence of structural abnormality demonstrated on magnetic resonance imaging, development-associated disease, widespread disease documented by postoperative electroencephalography, and limited resection due to the presence of functional cortex. There were no postoperative deaths. Visual field defects were the most common complication after temporal resection (22% [13 of 59 cases]), whereas hemiparesis (mostly transient) was the most common morbidity after extratemporal resection (18% [10 of 56 cases]).

CONCLUSIONS

Epilepsy surgery is an effective and safe therapeutic modality in childhood. In children with extratemporal epilepsy, more careful interpretation of clinical and investigative data is needed to achieve favorable seizure outcome.

Hemispherectomy for catastrophic epilepsy in infants

PURPOSE

To report our experience with hemispherectomy in the treatment of catastrophic epilepsy in children younger than 2 years.

METHODS

In a single-surgeon series, we performed a retrospective analysis of 18 patients with refractory epilepsy undergoing hemispherectomy (22 procedures). Three different surgical techniques were performed: anatomic hemispherectomy, functional hemispherectomy, and modified anatomic hemispherectomy. Pre- and postoperative evaluations included extensive video-EEG monitoring, magnetic resonance imaging, and positron emission tomography scanning. Seizure outcome was correlated with possible variables associated with persistent postoperative seizures. The Generalized Estimation Equation (GEE) and the Barnard's exact test were used as statistical methods.

RESULTS

The follow-up was 12-74 months (mean, 34.8 months). Mean weight was 9.3 kg (6-12.3 kg). The population age was 3-22 months (mean, 11.7 months). Thirteen (66%) patients were seizure free, and four patients had >90% reduction of the seizure frequency and intensity. The overall complication rate was 16.7%. No deaths occurred. Twelve (54.5%) of 22 procedures resulted in incomplete disconnection, evidenced on postoperative images. Type of surgical procedure, diagnosis categories, persistence of insular cortex, and bilateral interictal epileptiform activity were not associated with persistent seizures after surgery. Incomplete disconnection was the only variable statistically associated with persistent seizures after surgery (p<0.05).

CONCLUSIONS

Hemispherectomy for seizure control provides excellent and dramatic results with a satisfactory complication rate. Our results support the concept that early surgery should be indicated in highly selected patients with catastrophic epilepsy. Safety factors such as an expert team in the pediatric intensive care unit, neuroanesthesia, and a pediatric epilepsy surgeon familiar with the procedure are mandatory.

Diagnostic performance of 18F-FDG PET and ictal 99mTc-HMPAO SPET in pediatric temporal lobe epilepsy: quantitative analysis by statistical parametric mapping, statistical probabilistic anatomical map, and subtraction ictal SPET

We investigated the diagnostic performance of 18F-FDG PET and ictal (99m)Tc-HMPAO SPET in pediatric temporal lobe epilepsy (TLE). Twenty-one pediatric TLE patients were enrolled in this study. Their diagnoses were confirmed by histology and post-surgical outcome (Engel class I or II). The patients' ages were 18 or younger (15+/-3 years). Of the 21 patients, 21 patients underwent 18F-FDG PET scan and 15 underwent ictal (99m)Tc-HMPAO SPET. Preoperative PET and/or ictal SPET images were reviewed by simple visual assessment and by statistical parametric mapping (SPM). Asymmetric indices (AI) were calculated using statistical probabilistic anatomical map (SPAM) on 18F-FDG PET. In nine patients who underwent both ictal and interictal SPET, SISCOM (subtraction ictal SPET coregistered to MR template) was performed. PET correctly localized epileptogenic zones in 20 of 21 (95%) by visual assessment. SPM analysis of PET correctly localized epileptogenic zones in 18 of 21 (86%). Ictal SPET correctly localized epileptogenic zones in 12 of 15 (80%) by visual assessment. SPM analysis of ictal SPET correctly localized epileptogenic zones in 12 of 15 (80%). SISCOM correctly localized 8 of 9 (89%), which was equal to that of visual assessment of ictal SPET. The AIs of the temporal lobes by PET were -15+/-8.4 in the left and 9.9+/-8.9 in the right TLE (normal control: -2.9+/-2.8), and correctly localized epileptogenic zones in all cases. As is found in adult TLE, PET and ictal SPET efficiently localized epileptogenic zones in pediatric TLE. SPM analysis of PET or ictal SPET could be used as an aid to visual assessment. Moreover, SISCOM was equal visual assessment of ictal SPET images in terms of lesion localizations.

Neurosurgical management of pediatric epilepsy

Pediatric neurosurgeons are often involved early in the evaluation and management of children with epilepsy. Surgery should not be viewed merely as the end stage of multiple diagnostic decisions made by neurologists and pediatricians. Instead, when a reasonable trial of several AEDs has failed to provide adequate seizure control, a pediatrician can refer the patient directly to a pediatric neurosurgeon with a specialty interest in epilepsy. The diagnosis and treatment of focal versus diffuse epilepsy can be discussed in an honest and educated fashion with the families and the caregivers. Although full seizure control may be impossible, improved neurologic development and avoidance of self-injurious drop attacks may be worthy alternative surgical outcomes.

Is refractory epilepsy preventable?

About a third of the patients diagnosed with epilepsy will not be fully controlled with antiepileptic drugs (AEDs), and many of them will have frequent and disabling seizures. These patients will undergo multiple drug trials, most often without complete seizure remission. Moreover, refractory epilepsy is associated with increased morbidity (from seizures and medications), social isolation, unemployment, and overall reduced quality of life. There is evidence that refractory epilepsy can be a progressive disorder, which, if controlled early, might never develop into a full syndrome with all of its associated sequelae. The difficulty lies in identifying at an early stage patients who are likely to progress to intractability. No currently known markers enable clinicians to make this identification with confidence. Advances in pharmacogenomics and our understanding of pharmacologic responsiveness in epilepsy may change this situation. Even now, we are able to identify many patients with a poor prognosis earlier than before, particularly in the pediatric population, in which syndromic classification may provide an approach to predict intractability. The early initiation of aggressive therapy may improve outcome and overall quality of life.

Surgical treatment of intractable epilepsy in children: indication for resective surgery

Good surgical outcome can be expected for intractable epilepsy in children by resective surgery when a focal cortical abnormality is demonstrated by neuroimaging studies such as MRI, SPECT, and PET. Improvement in behavioral and cognitive development can be expected with seizure cessation after surgery. Early surgical intervention for intractable epilepsy in children is considered a safe and effective choice of treatment to avoid cognitive delay and learning disability.

L-type Ca(2+) channel blocker inhibits mossy fiber sprouting and cognitive deficits following pilocarpine seizures in immature mice

Behavioral and cognitive deficits are one of the most frequent sequelae of childhood epilepsy. Accumulating evidence indicates that epilepsy induces aberrant development of the mossy fibers in the hippocampus, the region that is commonly accepted to play a key role in learning and memory. We have therefore proposed that such abnormal maturation of the central nervous system may cause the adverse prognoses following epilepsy. Based on this hypothesis, using primary cultures of the dentate granule cells, we showed that the L-type Ca(2+) channel blocker nicardipine was neuroprotective against excessive mossy fiber synaptogenesis induced by prolonged depolarization that was assumed to mimic epileptiform conditions. Therefore, we evaluated the in vivo effect of nicardipine on aversive sequelae following epileptiform seizures. We found aberrant sprouting of the mossy fibers and poor performance of spatial and contextual tasks in the mice that had received treatment with pilocarpine at their early postnatal age. Repetitive administration of nicardipine prevented the mossy fiber sprouting and ameliorated the cognitive deterioration, although it did not show anticonvulsant actions against pilocarpine seizures. In the present study, we proposed two in vitro and in vivo models for evaluating epilepsy sequelae and noticed that L-type Ca(2+) channel blocker nicardipine was effective in both models. L-type Ca(2+) channel blocker may be a good candidate for a preventive for childhood epilepsy sequelae. Likewise, these useful systems will disclose additional candidates in future.

Validity of diagnosis using the French translation of the semi-structured interview for seizure classification

PURPOSE

The purpose of this study was to assess the acceptability and validity of the French cross-cultural translation of a semistructured interview for seizure classification (SISC). We used the first revised version, the original of which was validated in 1990.

METHODS

We administered the French SISC to a sample of 67 adults older than 15 years, comprising 17 controls and 50 patients with epilepsy (without provoked or isolated seizures). A cross-cultural translation was made from American English into French. Medical records were reviewed by epileptologists, who classified seizures, syndromes, and risk factors in accordance with the International League Against Epilepsy (ILAE) classifications. Agreement between interview- and physician-based diagnoses was assessed with a kappa coefficient (kappa) at each level of the recognized schemes for the classification of seizures (both broad and specific categories), syndromes, and risk factors.

RESULTS

The sensitivity of the French SISC in diagnosing an epileptic seizure was 100%, with a specificity of 94%. Interview-based diagnoses agreed with those of physicians in 90% of patients for broad seizure categories [i.e., generalized or focal in origin (kappa = 0.74)]. When diagnoses agreed on focal origin, the agreement on seizure types-simple or complex-was 91% (kappa = 0.84). Among generalized seizures, the agreement was 73% (kappa = 0.60). Agreement on epilepsy syndromes was excellent for generalized epilepsy but moderate for focal epilepsy. Agreement on identified risk factors was 93%.

CONCLUSIONS

The kappa coefficients demonstrated a good level of reliability. These results support the acceptability of this type of interview and the validity of the French version of the SISC.

Diagnostic value of short duration outpatient video electroencephalographic monitoring

There is little published on the diagnostic value of short duration outpatient video electroencephalographic (VEEG) monitoring in children. The authors performed a prospective study on 37 patients (mean age = 10.4 years), with daily paroxysmal events who underwent short duration (mean = 3.2 hours) outpatient VEEG monitoring. Events were detected in 23 patients (62.2%), and a change in management as a result of outpatient VEEG monitoring was documented in 25 patients (67.6%). Despite the short duration of the outpatient VEEG in this study, the detection rate was comparable with the previously reported studies with longer duration monitoring. The authors found it convenient for the patient and less costly. The study demonstrated that short duration outpatient VEEG monitoring was able to differentiate between seizures and nonseizures in 11 patients (78.6%) and resulted in changing seizure classification in five patients (62.5%), and in selecting epilepsy surgery candidates in nine patients (60%). Short duration outpatient VEEG is useful as a diagnostic tool in patients with daily paroxysmal events, particularly in identifying nonepileptic events.

Risk of epilepsy in patients with multiple sclerosis: a population-based study in Iceland

PURPOSE

Several clinical series reported an association between multiple sclerosis (MS) and epilepsy. We conducted a total population study in Iceland to determine the risk for developing epilepsy in patients with MS compared with that expected in the general population.

METHODS

Medical records of the 188 incidence cases of clinically definite MS first diagnosed in Iceland during the 25-year study period (1965-1989) were reviewed. The cases were followed up through 1994 or until death to identify those developing seizures or epilepsy. The expected number of cases with epilepsy in the MS-incidence cohort were calculated based on the age-specific incidence for epilepsy in Iceland and the age-specific person years of follow-up in the MS cohort.

RESULTS

During the 2,771 person years of observation after diagnosis of clinically definite MS, three MS patients developed epilepsy. One additional case developed epilepsy after onset of MS symptoms but before diagnosis of MS. The cumulative incidence of epilepsy by 10 years after diagnosis of MS was 1.9%. Given the age-specific person years of follow-up after diagnosis of MS, only one case of epilepsy would have been expected; standardized incidence ratio (SIR), 3.0 (95% confidence interval (CI), 0.6-8.8).

CONCLUSIONS

MS is a risk factor for developing epilepsy. Patients with MS have a threefold increase in risk for developing epilepsy when compared with that expected in the general population. The reason for this increased risk is unclear and needs further investigation.

Intractable epilepsy in a population-based series of mentally retarded children

PURPOSE

The characteristics of intractable epilepsy were analyzed in a population-based study of active epilepsy in mentally retarded children aged 6-13 years.

METHODS

Diagnostic registers, EEG laboratory registers, and registers for the Education of the Subnormal were searched. Medical files were scrutinized. Clinical examinations and interviews with parents and caregivers or both were performed. EEG recordings, computed tomography (CT) and magnetic resonance imaging (MRI) of the CNS were reevaluated.

RESULTS

Forty-five percent (44 of 98) of the children with mental retardation (MR) and active epilepsy had intractable seizures, defined as one or more seizures every day or week. The median age at onset was 0.8 years, as compared with 3.0 years for those with controlled epilepsy. Predictive factors for frequent seizures were the number of seizure types, severe MR, status epilepticus (SE) and tonic seizures. Epileptiform EEG activity was present in 91%, and focal activity in 65%. Brain lesions were detected on CT and MRI in 70%, with generalized lesions in 60%. Concurrent focal epileptiform activity and focal brain lesions on CT/MRI were detected in 26%. The percentages and prevalence rates for infantile spasms (IS) and Lennox-Gastaut syndrome (LGS) were 18% (0.25 in 1,000) and 7% (0.06 in 1,000), respectively. One of 8 children with IS had had previous neonatal seizures, 3 had SE and 1 later developed LGS.

CONCLUSIONS

Children with MR and intractable epilepsy have a high frequency of severe MR and additional major neuroimpairments. EEG recordings frequently showed focal changes despite generalized lesions in neuroradiology.

Neuroimaging in the evaluation of children and adolescents with intractable epilepsy: I. Magnetic resonance imaging and the substrates of epilepsy

Recent advances in neuroimaging, particularly the magnetic resonance imaging (MRI) scan, have greatly enhanced our ability to visualize intraparenchymal anatomy. With the linkage between intracranial pathology and epilepsy now clearly established, the MRI data provides detailed information for the clinician treating patients with epilepsy. This article supplies the reader with an overview of the new techniques in MRI brain imaging that allow us to identify intracranial abnormalities, and a survey of some of the MRI-identified substrates of epilepsy.

Practical aspects of the use of topiramate in patients with epilepsy

Practical recommendations for the treatment of patients with the new antiepileptic drug (AED) topiramate (TPM) were developed on the basis of review of the results of controlled and open studies of TPM reported to date and on postmarketing clinical experience with TPM at two specialized epilepsy clinics in the United Kingdom. Recommendations considered important for optimal utilization of TPM include dosage titration guidelines, options for managing side effects occurring early in treatment, advice concerning the withdrawal of concomitant AEDs, indications for discontinuation of TPM, and recognition of the need for adequate patient counseling.

Pharmacokinetic profile of topiramate in comparison with other new antiepileptic drugs

Antiepileptic drugs (AEDs) in broad use today have a number of pharmacokinetic liabilities, including a propensity for clinically meaningful drug interactions. Therefore, new AEDs with improved pharmacokinetic characteristics would be welcomed. The pharmacokinetic profiles of six newer AEDs--topiramate (TPM), gabapentin (GBP), vigabatrin (VGB), lamotrigine (LTG), oxcarbazepine (OCBZ), and felbamate--were reviewed. Some of these AEDs offer an improvement in one or more pharmacokinetic parameters compared with traditional AEDs, with TPM, GBP, VGB, and OCBZ demonstrating the most advantageous overall pharmacokinetic profiles.

Morphological and functional consequences of chronic epilepsy in rat hippocampal slice cultures

We have developed an in vitro model of chronic epilepsy in order to study the consequences of prolonged periods of epileptic activity. After applying the convulsants bicuculline and/or picrotoxin to mature rat hippocampal slice cultures for 3 days, large numbers of swollen and vacuolated cells were observed throughout all hippocampal subfields. The number of dendritic spines of pyramidal cells was massively reduced. These changes were similar to those observed previously in post-mortem studies of hippocampal tissue from human epilepsy patients. Intracellular recordings from CA3 pyramidal cells revealed that spontaneous synaptic activity was greatly reduced in treated cultures. gamma-Aminobutyric acid-mediated inhibition was apparently not affected by sustained convulsant activity, although synaptic excitation was markedly depressed. Acute re-application of bicuculline to treated cultures elicited, upon stimulation of the mossy fibre tract, a typical interictal burst lasting several hundred milliseconds, with a wave form similar to those occurring in untreated cultures, but of a shorter duration. In contrast, ictal bursts (lasting tens of seconds), which always occur spontaneously in control cultures during initial perfusion of bicuculline, were not observed in treated cultures. These pathological changes were reversible when treated cultures were returned to normal medium for 1 week. The surviving cells had a healthy morphology and a normal complement of dendritic spines. Spontaneous synaptic activity was normal, and ictal bursts occurred spontaneously upon perfusion of bicuculline. The findings suggest that the morphological and functional changes are a consequence, rather than a direct cause of epilepsy.