Coexistence of focal and idiopathic generalized epilepsy in the same patient population

Electron microscopic GABA evaluation in hippocampal mossy terminals of genetic absence epilepsy rats receiving kindling stimulations

Objective: The hypotheses related to the fact of epileptic mechanisms are mainly based on excitation-inhibition imbalance in central nervous system. GAERS (Genetic Absence Epilepsy Rats from Strasbourg) is a well-known animal model of absence epilepsy, and frequently used in experimental studies. In the present study, we aimed to examine possible morphological and gamma-aminobutyric acid (GABA) density changes in GAERS hippocampus after electrical kindling stimulations. Methods: All control and test group rats received 6 kindling stimulations. Rats were decapitated 1 h after the last stimulation. Ultrastructural GABA immunocytochemistry was used to evaluate GABA density quantitatively in mossy terminals of hippocampal CA3 region. Results: GABA levels were less in kindling groups compared to their controls, and in GAERS groups compared to Wistar groups; mitochondrial and dendritic spine area ratios were greater in GAERS groups compared to Wistar groups, although all these evaluations were statistically nonsignificant. Depletion of synaptic vesicles was evident in the mossy terminals of kindling groups. Conclusion: The reason of decreased levels of GABA found in the present study might be that GABA has been released from the synaptic pool rapidly at an early time period after the last stimulation, for compansation mechanisms. Depletion of synaptic vesicles observed in kindling groups shows that even 6 kindling stimulations have an impact of changing hippocampal morphology in trisynaptic cycle. The increased mitochondrial area in GAERS might be related to the increased mitochondrial activity. The increased dendritic spine area might be related to the increased performance of learning in GAERS. Our findings indicating that absence epilepsy and temporal lobe epilepsy have different mechanisms of epileptogenesis might be a basis for further experimental studies

Drug resistance in idiopathic generalized epilepsies: Evidence and concepts

Although approximately 10%-15% of patients with idiopathic generalized epilepsy (IGE)/genetic generalized epilepsy remain drug-resistant, there is no consensus or established concept regarding the underlying mechanisms and prevalence. This review summarizes the recent data and the current hypotheses on mechanisms that may contribute to drug-resistant IGE. A literature search was conducted in PubMed and Embase for studies on mechanisms of drug resistance published since 1980. The literature shows neither consensus on the definition nor a widely accepted model to explain drug resistance in IGE or one of its subsyndromes. Large-scale genetic studies have failed to identify distinct genetic causes or affected genes involved in pharmacokinetics. We found clinical and experimental evidence in support of four hypotheses: (1) "network hypothesis"-the degree of drug resistance in IGE reflects the severity of cortical network alterations, (2) "minor focal lesion in a predisposed brain hypothesis"-minor cortical lesions are important for drug resistance, (3) "interneuron hypothesis"-impaired functioning of γ-aminobutyric acidergic interneurons contributes to drug resistance, and (4) "changes in drug kinetics"-genetically impaired kinetics of antiseizure medication (ASM) reduce the effectiveness of available ASMs. In summary, the exact definition and cause of drug resistance in IGE is unknown. However, published evidence suggests four different mechanisms that may warrant further investigation.

Generalized Tonic-Clonic Seizures after Self-Limited Epilepsy with Centrotemporal Spikes: A Case Series

Purpose: Patients with self-limited epilepsy with centrotemporal spikes (SLECTS) rarely experience generalized tonic-clonic seizures (GTCS) after remission, and post-remission GTCS has not been thoroughly described in earlier studies. Herein, we describe the clinical and electrographic features of GTCS after a substantial period of seizure freedom in patients with SLECTS.Methods: This study included six patients (three boys and three girls) diagnosed with SLECTS who later developed GTCS after or near remission. Medical records, including clinical data and serial electroencephalography (EEG) recordings, were retrospectively reviewed for all patients.Results: Patients’ age at SLECTS onset ranged from 5.2 to 10.2 years (mean, 8.4 years), while seizure cessation was achieved between 8 and 12.2 years. During SLECTS, typical centrotemporal spikes were observed in all patients, and generalized spike-and-wave discharges were observed in three patients. The age at the first episode of subsequent GTCS ranged from 14.4 to 17.3 years (mean, 15.8 years), constituting an average interval of 5.6 years after the last episode of seizures (range, 4.1 to 8.1 years). EEG at subsequent episodes of GTCS revealed generalized discharges in two patients, focal discharges in two other patients, and normal discharges in the remaining two patients. Two patients had multiple episodes of GTCS.Conclusion: Although rare, GTCS may occur near or after remission in patients with SLECTS, and clinicians should be aware of this. Subsequent GTCS may be a manifestation of idiopathic generalized epilepsy. However, large-scale studies are needed to determine the nature of such episodes of GTCS and their associated risk factors.

Temporal Onset Focal Seizures Induced by Intermittent Photic Stimulation

The study aimed to review the clinical, radiological, and pathological findings and electroencephalogram (EEG) of pediatric epilepsy patients with temporal onset focal seizures induced by intermittent photic stimulation (IPS). Four patients with temporal onset photosensitivity focal seizures were analyzed. Three (75%) of the four patients were female. The average age of seizure-onset was 4.4 years. The interictal EEG showed both generalized and focal spike and waves in one patient and focal or multifocal spike and waves alone in three patients. Photoparoxysmal response (PPR) was evoked in all patients and showed generalized discharges (patients 2–4), both generalized and posterior discharges (patient 1). Both generalized and focal discharges could coexist in interictal discharges and PPR. The sensitive frequencies of PPR and photoconvulsive response (PCR) were 12–30 and 10–16 Hz, respectively, which were close to the occipital rhythm. In all patients, the onset of PCR was recorded, namely, the left anterior and mesial temporal lobe (TL), the left posterior TL, and the whole left TL, which showed two forms: the seizure of two patients was the onset of slow waves in the temporal area without spreading generalized discharges (patients 1 and 4), and the other one was fast rhythmic activities in the temporal area, spreading to the occipital area or gradually evolving into the generalized discharges (patients 2 and 3). During follow-up, except for patient 3 who had occasional seizures, the seizures of the remaining patients were under control. Temporal onset focal seizures could be induced by IPS. Temporal onset photosensitivity seizures were mostly easy to control with antiseizure drugs.

The baboon in epilepsy research: Revelations and challenges

The baboon offers a natural model for genetic generalized epilepsy with photosensitivity. In this review, we will summarize some of the more important clinical, neuroimaging, and elctrophysiological findings form recent work performed at the Southwest National Primate Research Center (SNPRC, Texas Biomedical Research Institute, San Antonio, Texas), which houses the world's largest captive baboon pedigree. Due to the phylogenetic proximity of the baboon to humans, many of the findings are readily translatable, but there may be some important differences, such as the mutlifocality of the ictal and interictal epileptic discharges (IEDs) on intracranial electroencephalography (EEG) and greater parieto-occipital connectivity of baboon brain networks compared to juvenile myoclonic epilepsy in humans. Furthermore, there is still limited knowledge of the natural history of the epilepsy, which could be transformative for research into epileptogenesis in genetic generalized epilepsy (GGE) and sudden unexpected death in epilepsy (SUDEP).

Are Absence and Limbic Seizures Mutually Exclusive?: An Experimental Approach to Enigmatic Clinical Concept

The impressive advances in the several disciplines including neurophysiology, molecular biology, neuroimmunology, neurogenetics, neuroimaging, and neuropharmacology of epilepsies have been stimulating a mutual interaction among basic scientists, clinicians, and professionals from other disciplines, leading to the identification of clinical questions and then the design of basic science paradigms to test enigmatic clinical issues. Based on a clinical observation that the coexistence of genetic (idiopathic) generalized typical absence and mesial temporal lobe epilepsy in the same patient is extremely rare and debatable, we addressed the rare coexistence in the same individual, designed an experimental approach to test the validity of this clinical concept and to study the underlying mechanisms involved. Here we presented evidence of a mutual cross-interaction in the circuits involved in typical absence and temporal lobe epilepsy. This article delineates a phenomenological picture and comprehends a theoretical understanding of a mutual cross-interaction in typical absence as a representative of genetic generalized epilepsies and limbic epilepsy in which seizures often start from the mesial temporal lobe.

Genetic generalized epilepsies with frontal lesions mimicking migratory disorders on the epilepsy monitoring unit

Objective

Some patients with genetic generalized epilepsy (GGE) may present with ambiguous and atypical findings and even focal brain abnormalities. Correct diagnosis may therefore be difficult.

Methods

We retrospectively collected six patients investigated on the epilepsy monitoring unit with MRI abnormalities mimicking focal cortical dysplasia (FCD-like) or heterotopias, but with semiology and EEG features of GGE. We compared them to four additional patients with GGE and nonmigratory abnormalities.

Results

All six patients presented with frontal MRI lesions: radial ("transmantle," n = 4), cortical-subcortical (n = 1), and periventricular heterotopia (n = 1). Five had positive family histories. Semiologic lateralizing signs compatible with the lesion were seen in four. Five patients had 3/s spike-wave complexes, with an asymmetric appearance in three. Regional EEG changes matched with the side of the abnormality in three patients. Invasive EEG (n = 2) or postoperative outcomes (n = 3) argued against an ictogenic role of the MRI abnormalities. Histology showed mild malformation of cortical development, but no focal cortical dysplasia. The six patients were finally diagnosed with juvenile myoclonic epilepsy (n = 2), juvenile absence epilepsy (n = 2), or GGE not further specified (nfs, n = 2). Compared to these patients, the other four (final diagnoses: childhood absence epilepsy, n = 1; perioral myoclonia with absences, n = 1; and GGE nfs, n = 2) had no lateralizing EEG findings.

Significance

Patients with GGE may have coincidental MRI abnormalities. These cases are challenging as frontal epilepsy and GGE can present with similar semiologies. GGE with coincidental FCD-like lesions/heterotopias is in particular difficult to diagnose as patients have more lateralizing features (in semiology and EEG) than those with tumors. A detailed noninvasive presurgical evaluation may be justified. We point out red flags that may help to distinguish GGE from frontal epilepsy, even in the presence of brain abnormalities: 3/s spike waves (even if asymmetric), changing lateralizing signs at different times, and a positive family history hinting at GGE.

Investigation of Generalized EEG Paroxysms Accompanying Focal Epilepsies

Interictal focal EEG features were frequently observed in generalized, epilepsies, but there is limited information about interictal, epileptiform/nonepileptiform generalized paroxysms in focal epilepsies. We aimed to report the frequency and associated factors of generalized EEG discharges in focal epilepsy with unknown cause (FEUC) and mesial, temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS). A total of 200 patients (FEUC in 90 patients; MTLE-HS in 110 patients) were included. Generalized epileptiform (spike/sharp waves simultaneously in all regions) and nonspecific generalized discharges (paroxysmal slow waves) were investigated. All clinical and laboratory findings of 2 groups were compared with each other and with remaining control group, without generalized paroxysms, statistically. Generalized EEG features were present in 22 (11%; 4 males) patients; 9 in the FEUC group (10%; 2) and 13 in the MTLE-HS group (11.8%). Female gender (P < .021), febrile seizure (P < .034), precipitant factors (P < .025), and parental consanguinity (P < .033) were significantly higher in the group with generalized EEG findings. Monotherapy rates were lower in the MTLE-HS group (P < .05). The relationship of generalized EEG features with female gender and parental consanguinity may point out to a genetic property among focal epilepsies, while the relationship with febrile seizures and precipitant factors may be a clue about mechanisms with more extensive involvement of the neuronal networks.

Focal interictal epileptiform discharges in idiopathic generalized epilepsy

Are idiopathic generalized epilepsies (IGEs) truly generalized? Do IGEs represent a continuum or rather distinct syndromes? Focal changes in the electroencephalography (EEG) have been reported in IGEs. The aim of this work is to investigate focal interictal epileptiform discharges (IEDs) in IGEs, and their relation to clinical variables. Forty-one IGE patients (classified according to ILAE, 2001) were recruited from a tertiary center (age 23 ± 10.938 years). Their files were reviewed and they were subjected to clinical examination and interictal EEG. Patients with focal IEDs were compared to those without focal IEDs. Nine patients had juvenile myoclonic epilepsy (JME) and 32 had idiopathic epilepsy with generalized tonic-clonic seizures only (EGTCSA). Focal IEDs were found in 20 patients, mostly in the frontal (45.5 %) and temporal (31.8 %) distribution. Patients with focal IEDs were treated with a larger number of combined antiepileptic drugs (AEDs) (p value = 0.022). No significant difference was found between the two groups regarding age, sex, age at onset, epilepsy syndrome, seizure frequency, family history, AEDs used (sodium valproate and carbamazepine) and their doses. Seventeen EGTCSA patients had focal IEDs. They were treated with larger number of combined AEDs (p value = 0.0142). No significant difference was found between the EGTCSA patients with and those without focal IEDs regarding age, sex, age at onset, seizure frequency, family history and AEDs doses. Caution must be applied in the interpretation of interictal focal IEDs. These focal changes may be related to prognosis, however this needs further investigation.

A unique ictal EEG pattern in a patient with the coexistence of generalized and focal epilepsy

The coexistence of focal and generalized epilepsy is rare. We report on a 17-year-old male with drug-resistant focal epilepsy and idiopathic generalized epilepsy (IGE). He began to experience generalized tonic-clonic seizures (GTCS) at the age of 3 years, with a good response to phenobarbital. At the age of 14 years, he began to experience complex partial seizures (CPS). Video-electroencephalography (video-EEG) telemetry showed the coexistence of right temporal spikes and bursts of generalized spike-wave (GSW). The ictal EEG showed a unique EEG pattern characterized by a 4- to 5-second burst of GSW followed by rhythmic delta activity over the right temporal region. A magnetic resonance image (MRI) showed right hippocampal sclerosis. The patient underwent a right temporal lobectomy that significantly improved his seizure control. He was rendered seizure free of the complex partial seizures and improvement of the GTCS. This case illustrates a very uncommon ictal EEG pattern, and shows that the decision for surgery in patients with focal drug-resistant epilepsy should not be affected by coexistent generalized epilepsy.

Subdural electrode recording of generalized photoepileptic responses

We evaluated the spatiotemporal distribution of photic driving (PDR), photoparoxysmal (PPR), and photoconvulsive (PCR) responses recorded by intracranial electrodes (ic-EEG) in a patient with generalized photosensitivity and right frontal lobe cortical dysplasia. Intermittent light stimulation (ILS) was performed thirteen times in nine days. Cortical responses to ILS recorded by ic-EEG were reviewed and classified as PDRs, PPRs, and PCRs. Photic driving responses were restricted to the occipital lobe at ILS frequencies below 9 Hz, spreading to the parietal and central regions at > 9 Hz. Photoparoxysmal responses commonly presented as focal, medial occipital, and parietal interictal epileptic discharges (IEDs), the latter propagating to the sensorimotor cortices. Generalized IEDs were also generated in the setting of PPRs. Photoconvulsive responses, characterized by repetitive bilateral upper extremity myoclonus sustained until the end of the stimulus, were associated with propagation of the medial parieto-occipital discharge to the primary sensorimotor and supplementary area cortices, while generalized myoclonic seizures were associated with a generalized spike-and-wave discharge with an interhemispheric posterior cingulate onset sparing the sensorimotor cortices. Both types of PCR could occur during the same stimulus. Regardless of the pathway, PCRs only occurred when PDRs involved the parietal cortices. While there may be more than one pathway underlying PCRs, parietal lobe association cortices appear to be critical to their generation.

A case of temporal onset partial seizure induced by photic stimuli

There are only a few case reports of photic stimulation induced partial seizures arising from the temporal lobe. A 12-year-old female with a history of three convulsions was admitted for a diagnostic evaluation. During continuous video-electroencephalogram monitoring, a complex partial seizure with secondary generalization was induced immediately after a photoparoxysmal response with a 15-Hz photic stimulation. This is a rare case of photosensitive temporal lobe seizure.

The pathology of magnetic-resonance-imaging-negative epilepsy

Patients with magnetic-resonance-imaging (MRI)-negative (or 'nonlesional') pharmacoresistant focal epilepsy are the most challenging group undergoing presurgical evaluation. Few large-scale studies have systematically reviewed the pathological substrates underlying MRI-negative epilepsies. In the current study, histopathological specimens were retrospectively reviewed from MRI-negative epilepsy patients (n=95, mean age=30 years, 50% female subjects). Focal cortical dysplasia cases were classified according to the International League Against Epilepsy (ILAE) and Palmini et al classifications. The most common pathologies found in this MRI-negative cohort included: focal cortical dysplasia (n=43, 45%), gliosis (n=21, 22%), hamartia+gliosis (n=12, 13%), and hippocampal sclerosis (n=9, 9%). The majority of focal cortical dysplasia were ILAE type I (n=37) or Palmini type I (n=39). Seven patients had no identifiable pathological abnormalities. The existence of positive pathology was not significantly associated with age or temporal/extratemporal resection. Follow-up data post surgery was available in 90 patients; 63 (70%) and 57 (63%) attained seizure freedom at 6 and 12 months, respectively. The finding of positive pathology was significantly associated with seizure-free outcome at 6 months (P=0.035), but not at 12 months. In subgroup analysis, the focal cortical dysplasia group was not significantly correlated with seizure-free outcome, as compared with the negative-pathology groups at either 6 or 12 months. Of note, the finding of hippocampal sclerosis had a significant positive correlation with seizure-free outcome when compared with the negative-pathology group (P=0.009 and 0.004 for 6- and 12-month outcome, respectively). Absence of a significant histopathology in the resected surgical specimen did not preclude seizure freedom. In conclusion, our study highlights the heterogeneity of epileptic pathologies in MRI-negative epilepsies, with focal cortical dysplasia being the most common finding. The existence of positive pathology in surgical specimen may be a good indication for short-term good seizure outcome. There is a small subset of cases in which no pathological abnormalities are identified.

Surgically proven coexistence of focal and generalized epilepsy: a case report

The coexistence of focal and idiopathic generalized epilepsy (IGE) is rarely observed, and the mechanism underlying this situation remains unknown. We report a 13-year-old girl with well-controlled generalized epilepsy and medically-refractory left temporal lobe epilepsy. She underwent intracranial EEG recording, which demonstrated two characteristic seizure patterns of generalized ictal onset and left mesial temporal onset. In addition, two types of interictal spike distribution, including the left mesial temporal region and generalized spikes, were also supportive of the coexistence of left mesial temporal lobe epilepsy and IGE. Thereafter, a left anterior temporal lobectomy and post-surgical medication significantly improved her seizure outcome. This case illustrates the importance of considering surgical management for patients with medically-intractable focal epilepsy coexisting with generalized epilepsy.

Evidence that temporal lobe is a default area in absence epilepsy

Correctly classifying seizures is essential for appropriate epilepsy management. Focal and generalized epilepsy rarely occur independently in the same patient. Cases of focal ictal evolution during seizures that are generalized in onset have been reported though these have included a small heterogeneous series of patients with generalized epilepsy and features on the EEG. We wish to report two patients with absence epilepsy that were noted on video-EEG monitoring to manifest a focal temporal electroclinical transformation from a typical absence seizure. Defining the electroclinical spectrum of absence seizures could add to our understanding of the selective cortical and subcortical networks that are involved in patients with "prototypic" generalized and focal seizures.

Long term outcomes in patients with preoperative generalized interictal epileptiform abnormalities following amygdalohippocampectomy

We evaluated long term surgical outcomes in 21 patients with temporal lobe epilepsy and presurgical generalized interictal epileptiform discharges (IEDs). Following amygdalohippocampectomy, 12 patients (57.1%) were noted to have favorable outcomes (Engel classification of I-II). Favorable outcomes were significantly associated with a history of auras prior to seizure onset (p=0.021), the absence of generalized IEDs on postoperative EEG (p=0.024), and the presence of focal slowing on postoperative EEG (p=0.045).

Coexistence of idiopathic generalized epilepsy among surgically treated patients with drug-resistant temporal lobe epilepsy

INTRODUCTION

Failure to identify the association antiepileptic drug (AED)-resistant temporal lobe epilepsy (TLE) with idiopathic generalized epilepsy (IGE) can interfere with decision for anterior temporal lobectomy (ATL) and prediction of post-ATL seizure outcome.

METHODS

Out of the 664 consecutive patients who underwent ATL between March 1995 and December 2007, 12 (1.8%) had coexisting IGE. The decision for ATL was made after a thorough discussion in the multidisciplinary patient management conference based upon the concordance between the clinical, electroencephalographic and magnetic resonance imaging data. All of them underwent epilepsy surgery for AED-resistant TLE.

RESULTS

In seven of the 12 patients, IGE was not identified until post-ATL. During a median follow-up period of 8.5 years, 8 of our 12 patients were seizure-free; the remaining 4 patients only had infrequent myoclonus. In two them, AEDs were discontinued; others were on montherapy for IGE.

CONCLUSIONS

Our study highlights the rare association of IGE with TLE, the most common AED-resistant focal epilepsy syndrome. As the seizure outcome following ATL is similar in AED-resistant TLE patients with and without IGE, their co-existence is not a contraindication for ATL. Future studies should explore the molecular genetic basis of the rare association between these two epilepsy syndromes.

Ultrastructural GABA immunocytochemistry in the mossy fiber terminals of Wistar and genetic absence epileptic rats receiving amygdaloid kindling stimulations

The existence of absence epilepsy and temporal lobe epilepsy in the same patient is not common in clinical practice. The reason why both types of seizures are rarely seen in the same patient is not well understood. Therefore, we aimed to investigate kindling in a well known model of human absence epilepsy, genetic absence epilepsy rats from Strasbourg (GAERS). In the present study, we analyzed whether the GABA content of GAERS that received kindling stimulations was altered in the hippocampal mossy fiber terminals compared to non-epileptic control (NEC) Wistar rats. For this purpose, we used an immunocytochemical technique at the ultrastructural level. Ultrathin sections were immunolabeled with anti-GABA antibody and transmission electron microscopy was used for the ultrastructural examination. The number of gold particles per nerve terminal was counted and the area of the nerve terminal was determined using NIH image analysis program. The GABA density was found to be higher in sham-operated GAERS than sham-operated Wistar rats. The density was increased in kindling Wistar group compared to sham-operated Wistar and kindling GAERS groups. No statistical difference was observed between sham-operated GAERS and kindling GAERS groups. The increase in GABA levels in stimulated Wistar rats may be a result of a protective mechanism. Furthermore, there may be strain differences between Wistar rats and GAERS and our findings addressing different epileptogenesis mechanisms in these strains might be a basis for future experimental studies.

Fyodor Dostoevsky and his falling sickness: a critical analysis of seizure semiology

Fyodor Dostoevsky is a great Russian writer who had epilepsy. As a consequence, there are many references to seizure-related phenomena in his work. His epilepsy syndrome has been a focus of debate. The goal of this article is to delineate his epilepsy syndrome based on a semiological description of seizures, which could be considered one of the most reliable pieces of circumstantial evidence available. It was hypothesized that seizure-related descriptions in his books were based on his own personal experience. The semiology of seizures and related phenomena was compiled from Dostoevsky's own work, his letters to family and friends, and reminiscences of his wife and friend. Those descriptions were analyzed in detail to elicit localizing and lateralizing features of seizures. On the basis of this evidence, it was postulated that Dostoevsky had a partial epilepsy syndrome most probably arising from the dominant temporal lobe.

Coexistence of symptomatic focal and absence seizures: video-EEG and EEG-fMRI evidence of overlapping but independent epileptogenic networks

The distinction between typical absences and hypomotor seizures in patients having frontal lesions is difficult. In focal epilepsy, generalized-like interictal discharges can reflect either a coexistent generalized epileptic trait or a secondary bilateral synchrony. Using combined measures of the EEG and blood oxygenation level dependent (BOLD) activity, we studied a 50-year-old patient with both absence-like and symptomatic focal motor seizures. Focal activity induced activation in the lesional area and deactivation in the contralateral central cortex. Generalized spike-and-wave discharges (GSWDs) resulted also in perilesional activation, and multifocal symmetrical cortical and thalamic activations, and deactivation in associative cortical areas. Although the central cortex was involved during both types of epileptic activity, electroencephalography (EEG)-functional magnetic resonance imaging (fMRI) revealed distinct neuronal networks at the time of the focal or generalized discharges, allowing a clear-cut differentiation of the generators. Whether the patient had distinct epileptic syndromes or distinct electrographic patterns from the lesional trigger remains debatable.

Characteristics of generalised epileptiform activity

OBJECTIVE

To study the age-related occurrence of specific features of generalised epileptiform activity (GEA), their correlation with EEG background activity (BA), and their internal correlation.

METHODS

17,723 consecutive routine EEGs from 12,511 patients were annotated and categorised into a database. The first EEG containing GEA from all 325 patients with such activity were selected and categorised for GEA features. The BA was studied in multivariable fractional polynomial regression models including intervening variables. The GEA features were studied in similar models for age-dependency and internal correlation.

RESULTS

High GEA-amplitude and low GEA-frequency correlated with BA slowing. The occurrence of 'irregular spike/sharp slow wave' pattern increased with age (p=0.003). Hyperventilation sensitivity was not age-related. There was no correlation between hyperventilation sensitivity and photoparoxysmal response. The age-related probability for specific GEA-types was established.

CONCLUSIONS

High GEA-amplitude and low GEA-frequency correlate with BA slowing, indicating cerebral cortical dysfunction. Hyperventilation sensitivity and photoparoxysmal response independently increase the yield of EEG. There is no age-dependency for hyperventilation sensitivity showing that an upper age threshold for hyperventilation provocation is inappropriate.

SIGNIFICANCE

The results extend our understanding of GEA and help the electroencephalographer in weighing the various GEA components.

Epilepsy surgery: eligibility criteria and presurgical evaluation

Epilepsy surgery has benefited from major advances during the last 20 years, thanks to the development of neuroimaging and long-term video-electroencephalographic (EEG) monitoring. However, it remains the case that only a small minority of potential epilepsy surgery candidates will have access to a comprehensive presurgical evaluation. Furthermore, this subset of patients are operated on after an average of 20 to 25 years of epilepsy duration. Among the various reasons that prevent many patients from benefiting from a timely presurgical evaluation, we need to emphasize the role of inaccurate information regarding eligibility criteria and lack of standardized practice. This review aims at providing an indepth discussion of the current views regarding the definition of surgical candidates, and the role of the numerous investigations used in the presurgical evaluation of patients with drug-resistant epilepsy.

The eligibility criteria required to enter a presurgical evaluation in 2008 should be relatively liberal, provided that the patient suffers from disabling seizures unrelated to an idiopathic generalized epileptic syndrome, despite appropriate antiepileptic drug treatment However, the decision as to whether or not to perform a presurgical evaluation must be individualized, and take into account the likelihood of meeting the patient's expectations in terms of outcome. These expectations need to be balanced with the apparent severity of the epileptic condition, the chance of achieving a successful surgical treatment, and the risk of a postoperative neurological, cognitive, or psychiatric deterioration. The roles and specific features of the main types of presurgical investigations are reviewed.