Focal abnormalities detected by 18FDG PET in epileptic encephalopathies

Frontoparietal 18F-FDG-PET hypo-metabolism in Lennox-Gastaut syndrome: further evidence highlighting the key network

INTRODUCTION

Lennox Gastaut syndrome (LGS) can be conceptualised as a "secondary network epilepsy", in which the shared electroclinical manifestations reflect epileptic recruitment of a common brain network, despite a range of underlying aetiologies. We aimed to identify the key networks recruited by the epileptic process of LGS using interictal 2-deoxy-2-(¹⁸F)fluoro-D-glucose positron emission tomography (¹⁸F-FDG-PET).

METHODS

Group analysis of cerebral ¹⁸F-FDG-PET, comparing 21 patients with LGS (mean age = 15 years) and 18 pseudo-controls (mean age = 19 years), studied at Austin Health Melbourne, between 2004 and 2015. To minimise the influence of individual patient lesions in the LGS group, we only studied brain hemispheres without structural MRI abnormalities. The pseudo-control group consisted of age- and sex-matched patients with unilateral temporal lobe epilepsy, using only the hemispheres contralateral to the side of epilepsy. Voxel-wise permutation testing compared ¹⁸F-FDG-PET uptake between groups. Associations were explored between areas of altered metabolism and clinical variables (age of seizure onset, proportion of life with epilepsy, and verbal/nonverbal ability). Penetrance maps were calculated to explore spatial consistency of altered metabolic patterns across individual patients with LGS.

RESULTS

Although not always readily apparent on visual inspection of individual patient scans, group analysis revealed hypometabolism in a network of regions including prefrontal and premotor cortex, anterior and posterior cingulate, inferior parietal lobule, and precuneus (p < 0.05, corrected for family-wise error). These brain regions tended to show a greater reduction in metabolism in non-verbal compared to verbal LGS patients, although this difference was not statistically significant. No areas of hypermetabolism were detected on group analysis, although ∼25 % of individual patients showed increased metabolism (relative to pseudo-controls) in the brainstem, putamen, thalamus, cerebellum, and pericentral cortex.

DISCUSSION

Interictal hypometabolism in frontoparietal cortex in LGS is compatible with our previous EEG-fMRI and SPECT studies showing that interictal bursts of generalised paroxysmal fast activity and tonic seizures recruit similar cortical regions. This study provides further evidence that these regions are central to the electroclinical expression of LGS.

Underutilization of advanced presurgical studies and high rates of vagus nerve stimulation for drug-resistant epilepsy: a single-center experience and recommendations

INTRODUCTION

Epilepsy surgery continues to be profoundly underutilized despite its safety and effectiveness. We sought to investigate factors that may contribute to this phenomenon, with a particular focus on the antecedent underutilization of appropriate preoperative studies.

METHODS

We reviewed patient data from a pediatric epilepsy clinic over an 18-month period. Patients with drug-resistant epilepsy (DRE) were categorized according to brain magnetic resonance imaging (MRI) findings (lesional, MRI-negative, or multifocal abnormalities) and type of epilepsy diagnosis based on semiology and electroencephalography (EEG) (focal or generalized). We then analyzed the rates of diagnostic test utilization, surgical referral, and subsequent epilepsy surgery as well as vagus nerve stimulation (VNS).

RESULTS

Of the 249 patients with a diagnosis of epilepsy, 138 (55.4%) were found to have DRE. Excluding the 10 patients with DRE who did not undergo MRI, 76 patients (59.4%) were found to be MRI-negative (non-lesional epilepsy), 37 patients (28.9%) were found to have multifocal abnormalities, and 15 patients (11.7%) were found to have a single epileptogenic lesion on MRI (lesional epilepsy). Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) were each completed in nine patients (7.0%) and magnetoencephalography (MEG) in four patients (3.1%). Despite the low utilization rate of adjunctive studies, over half (56.3%) ultimately underwent VNS alone, and 8.6% ultimately underwent definitive intracranial resection or disconnection surgery.

CONCLUSIONS

The underutilization of appropriate non-invasive, presurgical testing in patients with focal DRE may in part explain the continued underutilization of definitive, resective/disconnective surgery. For patients without access to a high-volume, multidisciplinary surgical epilepsy center, adjunctive presurgical studies [e.g., PET, SPECT, MEG, electrical source imaging (ESI), EEG-functional magnetic resonance imaging (fMRI)], even when available, are rarely ordered, and this may contribute to excessive rates of VNS in lieu of definitive intracranial surgery.

Application of combined multimodal neuroimaging and video-electroencephalography in intractable epilepsy patients for improved post-surgical outcome prediction

AIM

To investigate the ability of a multidisciplinary approach that combines multimodal neuroimaging with video-electroencephalography (v-EEG) to predict post-surgical outcomes in patients with intractable epilepsy, and explore prognostic predictors for these patients.

MATERIALS AND METHODS

Fifty-eight patients with intractable epilepsy who underwent surgery between March 2016 and October 2019 were reviewed retrospectively. Demographic, clinical, v-EEG, neuroimaging, surgical, and regular follow-up seizure outcome data were collected. Forty-six patients with a follow-up of at least 12 months were graded by Engel scores. Univariate and multivariate analyses were applied to explore prognostic factors that could predict post-surgical seizure outcomes.

RESULTS

Of the 58 patients, 28 were males. The median age was 27 years, the median age at first seizure was 11 years, and the median duration of seizures was 10 years. The Kaplan-Meier log-rank test showed that regardless of whether the follow-up duration was considered, epilepsy type, v-EEG, PET/CT, image post-processing methods, and a multidisciplinary approach that combined multimodal imaging with v-EEG were all correlated with seizure outcomes. Multivariate analysis found that the multidisciplinary approach was an independent predictor of post-surgical outcomes in patients with intractable epilepsy (hazard ratio = 11.400, 95% confidence interval = 2.249-57.787, p=0.003).

CONCLUSIONS

The present study showed that the multidisciplinary approach could provide independent prognostic information for patients with intractable epilepsy undergoing surgery. This approach has strong potential for the easier selection of patients to undergo surgical treatment and accurate prognostication.

Voxel-based morphometric MRI post-processing and PET/MRI co-registration reveal subtle abnormalities in cingulate epilepsy

OBJECTIVE

Diagnostic challenges exist in the presurgical evaluation of patients with magnetic resonance imaging (MRI) negative cingulate epilepsy (CE) because of the heterogeneity in clinical semiology and lack of localizing findings on scalp electroencephalographic (EEG) recordings. We aimed to examine the neuroimaging characteristics in a consecutive cohort of patients with MRI-negative CE with a focus on two image post-processing methods, including the MRI post-processing morphometric analysis program (MAP) and ¹⁸F-fluorodeoxyglucose-positron emission tomography-MRI (PET/MRI) co-registration.

METHODS

Included in this retrospective study were patients with MRI-negative CE who met the following criteria: negative on preoperative MRI, invasive EEG (iEEG) confirmed cingulate gyrus-onset seizures, surgical resection of the cingulate gyrus with/without adjacent cortex, and seizure-free for more than 12 months. MAP and PET/MRI co-registration were performed and investigated by comparison to ictal intracranial EEG findings. Other characteristics obtained from scalp EEG, magnetoencephalography (MEG), iEEG, and pathological study were also reported.

RESULTS

Ten patients were included, of which eight were diagnosed with anterior CE, one with middle CE, and one with posterior CE. The semiology included fear, embarrassment, vocalization, ictal pouting, asymmetric tonic posture, hypermotor, and automatism. Scalp EEG revealed unilateral or bilateral frontal-temporal onset. MEG localized the dipoles correctly in one patient (1/10). MAP detected subtle abnormalities in regions concordant with iEEG onset in seven patients (7/10) while PET/MRI co-registration revealed focal concordant hypometabolism in five patients (5/10). Combining MAP with PET/MRI co-registration improved the detection rate to 90 % in this cohort. The pathology was focal cortical dysplasia (FCD), including FCD type IIA in three, type IIB in three, and type I in four.

CONCLUSION

MAP and PET/MRI co-registration show promising results in identifying subtle FCD abnormalities in CE with negative results on conventional MRI, which can be otherwise challenging. More importantly, a combination of MRI post-processing and PET/MRI co-registration can greatly improve the identification of epileptic abnormalities, which can be used as surgical target. MAP and PET/MRI co-registration should be incorporated into the routine presurgical evaluation.

Enhancing glucose metabolism via gluconeogenesis is therapeutic in a zebrafish model of Dravet syndrome

Energy-producing pathways are novel therapeutic targets for the treatment of neurodevelopmental disorders. Here, we focussed on correcting metabolic defects in a catastrophic paediatric epilepsy, Dravet syndrome which is caused by mutations in sodium channel NaV1.1 gene, SCN1A. We utilized a translatable zebrafish model of Dravet syndrome (scn1lab) which exhibits key characteristics of patients with Dravet syndrome and shows metabolic deficits accompanied by down-regulation of gluconeogenesis genes, pck1 and pck2. Using a metabolism-based small library screen, we identified compounds that increased gluconeogenesis via up-regulation of pck1 gene expression in scn1lab larvae. Treatment with PK11195, a pck1 activator and a translocator protein ligand, normalized dys-regulated glucose levels, metabolic deficits, translocator protein expression and significantly decreased electrographic seizures in mutant larvae. Inhibition of pck1 in wild-type larvae mimicked metabolic and behaviour defects observed in scn1lab mutants. Together, this suggests that correcting dys-regulated metabolic pathways can be therapeutic in neurodevelopmental disorders such as Dravet syndrome arising from ion channel dysfunction.

Positron Emission Tomography in Pediatric Neurodegenerative Disorders

Application of molecular neuroimaging using positron emission tomographic techniques to assess pediatric neurodegenerative disorders has been limited, unlike in adults where positron emission tomography has contributed to clinical diagnosis, monitoring of neurodegenerative disease progression, and assessment of novel therapeutic approaches. Yet, there is a huge unexplored potential of molecular imaging to improve our understanding of the pathophysiology of neurodegenerative disorders in children and provide radiological biomarkers that can be applied clinically. The obstacles in performing PET scans on children include sedation, radiation exposure, and access but, as will be illustrated, these barriers can be easily overcome. This review summarizes findings from PET studies that have been performed over the past three decades on children with various neurodegenerative disorders, including the neuronal ceroid lipofuscinoses, juvenile Huntington disease, Wilson disease, Niemann-Pick disease type C, Dravet syndrome, dystonia, mitochondrial disorders, inborn errors of metabolism, lysosomal storage diseases, dysmyelinating disorders, Rett syndrome, neurotransmitter disorders, glucose transporter Glut 1 deficiency, and Lesch-Nyhan disease. Because positron emission tomographic scans have often been clinically useful and have contributed to the management of these disorders, we suggest that the time has come for glucose metabolism positron emission tomographic scans to be reimbursed by insurance carriers for children with neurodegenerative disorders, and not restricted only to epilepsy surgery evaluation.

Electroclinical features of insulo-opercular epilepsy: an SEEG and PET study

Objective

To report clinical experience with presurgical evaluation in patients with insulo‐opercular epilepsy. Quantitative analysis on PET imaging and stereoelectroencephalography (SEEG) signals was used to summarize their electroclinical features.

Methods

Twenty‐two patients with focal epilepsy arising from the insular and/or opercular cortex according to SEEG were retrospectively analyzed. Presurgical noninvasive data were analyzed in detail. Interictal PET data of patients were then statistically compared with those of healthy controls to identify the interictal hypometabolic network. The epileptogenicity index (EI) of ictal SEEG signal was computed to identify areas of spread at the beginning of seizure onset.

Results

Focal tonic seizures of the face and/or neck (16/22, 73%) were the most prevalent early objective signs. Epileptic discharges in the interictal and ictal scalp‐EEG mostly showed an ipsilateral perisylvian distribution. Statistical analysis of interictal PET showed significant hypometabolism in the insular lobe, central operculum, supplementary motor area, middle cingulate cortex, bilateral caudate nuclei, and putamen. According to the EI analysis, insulo‐opercular epilepsy could be classified as insulo‐opercular epilepsy (50%), opercular epilepsy (41%), and insular cortex epilepsy (9%).

Significance

Clinical diagnosis of insulo‐opercular epilepsy is challenging because of its complex seizure semiology and nonlocalizing discharges on scalp‐EEG. A common hypometabolic network involving the insulo‐opercular cortex, mesial frontal cortex and subcortical nuclei may be involved in the organization of the insulo‐opercular epilepsy network. Furthermore, quantified SEEG analysis suggested that pure insular epilepsy is rare, and the close connection between insular and opercular cortex necessitates SEEG implantation to define the epileptogenic zone.

Multimodality Image Post-processing in Detection of Extratemporal MRI-Negative Cortical Dysplasia

Purpose: To determine the diagnostic value of individual image post-processing techniques in a series of patients who underwent extratemporal operations for histologically proven, MRI-negative focal cortical dysplasia (FCD). Methods: The morphometric analysis program (MAP), PET/MRI co-registration and statistical parametric mapping (SPM) analysis of PET (SPM-PET) techniques were analyzed in 33 consecutive patients. The epileptogenic zone (EZ) assumed by MAP, PET/MRI, and SPM-PET was compared with the location of the FCD lesions determined by stereoelectroencephalography (SEEG) and histopathological study. The detection rate of each modality was statistically compared. Results: Three lesions were simultaneously detected by the three post-processing methods, while two lesions were only MAP positive, and 8 were only PET/MRI positive. The detection rate of MAP, PET/MRI, SPM-PET and the combination of the three modalities was 24.2, 90.9, 57.6, and 97.0%, respectively. Taking the pathological subtype into account, no type I lesions were detected by MAP, and PET/MRI was the most sensitive method for detecting FCD types II and IIA. During a mean follow-up period of 22.94 months, seizure freedom was attained in 26/33 patients (78.8%) after focal corticectomy. Conclusions: MAP, PET/MRI, and SPM-PET provide complementary information for FCD detection, intracranial electrode design, and lesion resection. PET/MRI was particularly useful, with the highest detection rate of extratemporal MRI-negative FCD.

Conceptualizing lennox-gastaut syndrome as a secondary network epilepsy

Lennox–Gastaut Syndrome (LGS) is a category of severe, disabling epilepsy, characterized by frequent, treatment-resistant seizures, and cognitive impairment. Electroencephalography (EEG) shows characteristic generalized epileptic activity that is similar in those with lesional, genetic, or unknown causes, suggesting a common underlying mechanism. The condition typically begins in young children, leaving many severely disabled with recurring seizures throughout their adult life. Scalp EEG of the tonic seizures of LGS is characterized by a diffuse high-voltage slow transient evolving into generalized low-voltage fast activity, likely reflecting sustained fast neuronal firing over a wide cortical area. The typical interictal discharges (runs of slow spike-and-wave and bursts of generalized paroxysmal fast activity) also have a “generalized” electrical field, suggesting widespread cortical involvement. Recent brain mapping studies have begun to reveal which cortical and subcortical regions are active during these “generalized” discharges. In this critical review, we examine findings from neuroimaging studies of LGS and place these in the context of the electrical and clinical features of the syndrome. We suggest that LGS can be conceptualized as “secondary network epilepsy,” where the epileptic activity is expressed through large-scale brain networks, particularly the attention and default-mode networks. Cortical lesions, when present, appear to chronically interact with these networks to produce network instability rather than triggering each individual epileptic discharge. LGS can be considered as “secondary” network epilepsy because the epileptic manifestations of the disorder reflect the networks being driven, rather than the specific initiating process. In this review, we begin with a summation of the clinical manifestations of LGS and what this has revealed about the underlying etiology of the condition. We then undertake a systematic review of the functional neuroimaging literature in LGS, which leads us to conclude that LGS can best be conceptualized as “secondary network epilepsy.”

Brain morphometry of Dravet syndrome

The aim of this study was to identify differential global and local brain structural patterns in Dravet Syndrome (DS) patients as compared with a control subject group, using brain morphometry techniques which provide a quantitative whole-brain structural analysis that allows for specific patterns to be generalized across series of individuals. Nine patients with the diagnosis of DS that tested positive for mutation in the SCN1A gene and nine well-matched healthy controls were investigated using voxel brain morphometry (VBM), cortical thickness and cortical gyrification measurements. Global volume reductions of gray matter (GM) and white matter (WM) were related to DS. Local volume reductions corresponding to several white matter regions in brainstem, cerebellum, corpus callosum, corticospinal tracts and association fibers (left inferior fronto-occipital fasciculus and left uncinate fasciculus) were also found. Furthermore, DS showed a reduced cortical folding in the right precentral gyrus. The present findings describe DS-related brain structure abnormalities probably linked to the expression of the SCN1A mutation.

Positron emission tomography in seizure disorders

Positron emission tomography (PET) has been widely used in the study of seizure disorders. As a research tool, PET has been used to determine the pathophysiology of different seizures disorders, prognostic and diagnostic information, and the response to various interventions. PET imaging has also been used clinically to help with the detection of seizure foci. With the continued development of a large array of radiopharmaceuticals that can evaluate all of the components of different neurotransmitter systems as well as cerebral blood flow and metabolism, PET imaging will continue to play a key role in research and clinical applications for seizure disorders.

EEG-fMRI reveals activation of brainstem and thalamus in patients with Lennox-Gastaut syndrome

PURPOSE

Even if etiologies of Lennox-Gastaut syndrome (LGS) are diverse, the multiple causes converge into a final common pathway that results in this specific epilepsy phenotype. There is little knowledge, however, about neuronal networks that may be a part of this pathway.

METHODS

To investigate these networks, 11 children with LGS and 9 control children with multifocal epileptic activity were investigated using simultaneous recordings of EEG and functional MRI (EEG-fMRI) in a 3 Tesla scanner.

KEY FINDINGS

Individual and group analyses revealed significant activation of brainstem and thalamus (especially centromedian and anterior thalamus) associated with epileptiform discharges in patients with LGS. None of the patients with multifocal epileptic activity presented with the same hemodynamic activation pattern.

SIGNIFICANCE

Because brainstem activation has been associated with infantile spasms, which often evolve into LGS, and thalamus activation has been observed in patients with primary (idiopathic generalized syndromes) and secondary (focal epilepsies) bilateral synchrony, the described network in LGS may represent the common pathogenetic pathway of these different conditions.

Children treated for epileptic encephalopathies show improved glucose metabolism

Epileptic neurological disorders in infants are often difficult to distinguish, and call for disparate treatments. Positron emission tomography (PET) using an [18F] fluoro-2-deoxyglucose (18FDG) tracer, is a powerful non-invasive technique successful in improving the diagnosis of a number of conditions. Interestingly, this technique has shown that cerebral glucose hypometabolism is present in children with epileptic encephalopathies (EE). Ten children with age-dependent EE were recruited and routine 18FDG PET images were evaluated for their ability to indicate cerebral glucose metabolism both before and after anti-epileptic treatment. We found that there is diffuse glucose hypometabolism in both hemispheres before treatment, indicating EE. Following treatment, the number of epileptic episodes significantly decreased (P < 0.05), while cerebral glucose metabolism improved. Our findings suggest that 18FDG PET can be utilized to monitor cerebral glucose metabolism as a measure of treatment progress in EE.

PET in Epilepsy and Other Seizure Disorders

Positron emission tomography (PET) imaging has been widely used in the evaluation and management of patients with seizure disorders. The ability of PET to measure cerebral function makes it ideal for studying the neurophysiologic correlates of seizure activity during ictal and interictal states. PET imaging is also useful for evaluating patients before surgical interventions to determine the best surgical method and maximize outcomes. Thus, PET will continue to play a major role not only in the clinical arena but in further investigations of the pathogenesis and management of various seizure disorders. This article reviews the literature regarding the current uses and indications for PET in the study and management of patients with seizure disorders.

PET in the Assessment of Pediatric Brain Development and Developmental Disorders

This article discusses and reviews the role and contribution of PET in understanding the structural and functional changes that occur during brain development, and how these changes relate to behavioral and cognitive development in the infant and child. Data regarding various aspects of brain development, such as glucose metabolism, protein synthesis, and maturation and development of neurotransmitter systems will help in understanding the pathogenesis and neurologic basis of various developmental and neurologic disorders. This may help in following disease evolution and progression, planning and development of various therapeutic interventions, timing these interventions and monitoring their responses, and rendering long-term prognostication.

Functional neuroimaging of spike-wave seizures

Generalized spike-wave seizures are typically brief events associated with dynamic changes in brain physiology, metabolism, and behavior. Functional magnetic resonance imaging (fMRI) provides a relatively high spatiotemporal resolution method for imaging cortical-subcortical network activity during spike-wave seizures. Patients with spike-wave seizures often have episodes of staring and unresponsiveness which interfere with normal behavior. Results from human fMRI studies suggest that spike-wave seizures disrupt specific networks in the thalamus and frontoparietal association cortex which are critical for normal attentive consciousness. However, the neuronal activity underlying imaging changes seen during fMRI is not well understood, particularly in abnormal conditions such as seizures. Animal models have begun to provide important fundamental insights into the neuronal basis for fMRI changes during spike-wave activity. Work from these models including both fMRI and direct neuronal recordings suggest that, in humans, specific cortical-subcortical networks are involved in spike-wave, while other regions are spared. Regions showing fMRI increases demonstrate correlated increases in neuronal activity in animal models. The mechanisms of fMRI decreases in spike-wave will require further investigation. A better understanding of the specific brain regions involved in generating spike-wave seizures may help guide efforts to develop targeted therapies aimed at preventing or reversing abnormal excitability in these brain regions, ultimately leading to a cure for this disorder.

Treatment of Lennox-Gastaut syndrome: overview and recent findings

Lennox-Gastaut syndrome (LGS) is a rare, age-related syndrome, characterized by multiple seizure types, a specific electro-encephalographic pattern, and mental regression. However, published data on the etiology, evolution, and therapeutic approach of LGS are contradictory, partly because the precise definition of LGS used in the literature varies. In the most recent classification, LGS belongs to the epileptic encephalopathies and is highly refractory to all antiepileptic drugs. Numerous treatments, medical and non-medical, have been proposed and results mostly from open studies or case series have been published. Sometimes, patients with LGS are included in a more global group of patients with refractory epilepsy. Only 6 randomized double-blind controlled trials of medical treatments, which included patients with LGS, have been published. Overall, treatment is rarely effective and the final prognosis remains poor in spite of new therapeutic strategies. Co-morbidities need specific treatment. This paper summarizes the definition, diagnosis and therapeutic approach to LGS, including not only recognized antiepileptic drugs, but also "off label" medications, immune therapy, diet, surgery and some perspectives for the future.

Transgenic mice over-expressing GABA(B)R1a receptors acquire an atypical absence epilepsy-like phenotype

In this study, we tested whether over-expressing the GABA(B) receptor R1a subtype in transgenic mouse forebrain neurons would be sufficient to induce spontaneous absence seizures. As hypothesized, these transgenic mice develop spontaneous, recurrent, bilaterally synchronous, 3-6 Hz slow spike and wave discharges between 2 and 4 months of age. These discharges are blocked by ethosuximide and exacerbated by baclofen confirming their absence nature. The discharges occur coincident with absence-like behaviors such as staring, facial myoclonus, and whisker twitching. However, in contrast to typical absence epilepsy models, these mice move during the ictal event, display spike and wave discharges in both thalamocortical and limbic circuitry, exhibit impaired hippocampal synaptic plasticity, and display significantly impaired learning ability. Collectively, these features are more characteristic of the less common but more debilitating atypical form of absence epilepsy. Thus, these data support a role for the GABA(B)R1a receptor subtype in the etiology of atypical absence epilepsy.

Typical versus atypical absence seizures: network mechanisms of the spread of paroxysms

PURPOSE

Typical absence seizures differ from atypical absence seizures in terms of semiology, EEG morphology, network circuitry, and cognitive outcome, yet have the same pharmacological profile. We have compared typical to atypical absence seizures, in terms of the recruitment of different brain areas. Our initial question was whether brain areas that do not display apparent paroxysmal discharges during typical absence seizures, are affected during the ictal event in terms of synchronized activity, by other, distant areas where seizure activity is evident. Because the spike-and-wave paroxysms in atypical absence seizures invade limbic areas, we then asked whether an alteration in inhibitory processes in hippocampi may be related to the spread seizure activity beyond thalamocortical networks, in atypical seizures.

METHODS

We used two models of absence seizures in rats: one of typical and the other of atypical absence seizures. We estimated phase synchronization, and evaluated inhibitory transmission using a paired-pulse paradigm.

RESULTS

In typical absence seizures, we observed an increase in synchronization between hippocampal recordings when spike-and-wave discharges occurred in the cortex and thalamus. This indicates that seizure activity in the thalamocortical circuitry enhances the propensity of limbic areas to synchronize, but is not sufficient to drive hippocampal circuitry into a full paroxysmal discharge. Lower paired-pulse depression was then found in hippocampus of rats that displayed atypical absence seizures.

CONCLUSIONS

These observations suggest that circuitries in brain areas that do not display apparent seizure activity become synchronized as seizures occur within thalamocortical circuitry, and that a weakened hippocampal inhibition may predispose to develop synchronization into full paroxysms during atypical absence seizures.

Focal cortical malformations can show asymmetrically higher uptake on interictal fluorine-18 fluorodeoxyglucose positron emission tomography (PET)

Interictal fluorine-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) is a component of the presurgical evaluation of patients with medically intractable epilepsy, including patients with malformations of cortical development. The authors describe 3 cases of focal cortical malformations that displayed asymmetrically higher uptake on FDG-PET performed in the interictal state in patients undergoing evaluation for possible focal resection for refractory localization-related epilepsy. The evaluation included routine and prolonged video electroencephalography (EEG), magnetic resonance imaging (MRI), interictal FDG-PET with concurrent EEG, and single-photon emission computed tomography (SPECT). All 3 patients had focal cortical malformations on MRI corresponding to regions of asymmetrically higher uptake on FDG-PET. EEG confirmed that the FDG-PET studies were performed in the interictal state. The lesions included a large region of subcortical heterotopia in the right frontal lobe, a left temporal lobe dysplasia, and a region of subcortical heterotopia in the right occipital lobe. In both patients with subcortical heterotopia, there were other focal regions of cortical malformation that were not associated with abnormal or asymmetric uptake on FDG-PET. Previous reports describe decreased uptake on interictal PET in most cases of focal cortical malformations. Normal to increased uptake has been reported with band heterotopia. The authors demonstrate that other types of focal malformations of cortical development, including focal subcortical heterotopia and lobar dysplasia, can be associated with asymmetrically higher uptake on interictal FDG-PET.

Hypoxic adaptation during development: relation to pattern of neurological presentation and cognitive disability

Children with acute hypoxic-ischaemic events (e.g. stroke) and chronic neurological conditions associated with hypoxia frequently present to paediatric neurologists. Failure to adapt to hypoxia may be a common pathophysiological pathway linking a number of other conditions of childhood with cognitive deficit. There is evidence that congenital cardiac disease, asthma and sleep disordered breathing, for example, are associated with cognitive deficit, but little is known about the mechanism and whether there is any structural change. This review describes what is known about how the brain reacts and adapts to hypoxia, focusing on epilepsy and sickle cell disease (SCD). We prospectively recorded overnight oxyhaemoglobin saturation (SpO2) in 18 children with intractable epilepsy, six of whom were currently or recently in minor status (MS). Children with MS were more likely to have an abnormal sleep study defined as either mean baseline SpO2 <94% or >4 dips of >4% in SpO2/hour (p = .04). In our series of prospectively followed patients with SCD who subsequently developed acute neurological symptoms and signs, mean overnight SpO2 was lower in those with cerebrovascular disease on magnetic resonance angiography (Mann-Whitney, p = .01). Acute, intermittent and chronic hypoxia may have detrimental effects on the brain, the clinical manifestations perhaps depending on rapidity of presentation and prior exposure.

Cellular and network mechanisms of spike-wave seizures

Spike-wave seizures are often considered a relatively "pure" form of epilepsy, with a uniform defect present in all patients and involvement of the whole brain homogeneously. Here, we present evidence against these common misconceptions. Rather than a uniform disorder, spike-wave rhythms arise from the normal inherent network properties of brain excitatory and inhibitory circuits, where they can be provoked by many different insults in several different brain networks. Here we discuss several different cellular and molecular mechanisms that may contribute to the generation of spike-wave seizures, particularly in idiopathic generalized epilepsy. In addition, we discuss growing evidence that electrical, neuroimaging, and molecular changes in spike-wave seizures do not involve the entire brain homogeneously. Rather, spike-wave discharges occur selectively in some thalamocortical networks, while sparing others. It is hoped that improved understanding of the heterogeneous defects and selective brain regions involved will ultimately lead to more effective treatments for spike-wave seizures.

PET in seizure disorders

PET imaging has been widely used in the evaluation and management of patients with seizure disorders. The ability of PET to measure cerebral function is ideal for studying the neurophysiologic correlates of seizure activity during both ictal and interictal states. PET imaging is also valuable for evaluating patients before surgical interventions to determine the best surgical method and maximize outcomes. PET will continue to play a major role, not only in the clinical arena, but also in investigating the pathogenesis and treatment of various seizure disorders.

Consciousness and epilepsy: why are patients with absence seizures absent?

Epileptic seizures cause dynamic, reversible changes in brain function and are often associated with loss of consciousness. Of all seizure types, absence seizures lead to the most selective deficits in consciousness, with relatively little motor or other manifestations. Impaired consciousness in absence seizures is not monolithic, but varies in severity between patients and even between episodes in the same patient. In addition, some aspects of consciousness may be more severely involved than other aspects. The mechanisms for this variability are not known. Here we review the literature on human absence seizures and discuss a hypothesis for why effects on consciousness may be variable. Based on behavioral studies, electrophysiology, and recent neuroimaging and molecular investigations, we propose absence seizures impair focal, not generalized brain functions. Impaired consciousness in absence seizures may be caused by focal disruption of information processing in specific corticothalamic networks, while other networks are spared. Deficits in selective and varying cognitive functions may lead to impairment in different aspects of consciousness. Further investigations of the relationship between behavior and altered network function in absence seizures may improve our understanding of both normal and impaired consciousness.

Learning and memory impairment in rats with chronic atypical absence seizures

Atypical absence seizures (AASs) represent a pediatric malignant seizure type that commonly exists as a component of Lennox-Gastaut syndrome. AAS involves both the hippocampal and thalamocortical circuitry in slow spike-and-wave discharges (SSWD) and is associated with cognitive dysfunction. The electrographic, behavioral, and pharmacological features of clinical AAS have been reproduced in rats chronically in the AY-9944 (AY) model. AY rats show spontaneous SSWD involving the hippocampus, a structure that is highly implicated in learning and memory. The purpose of the present study was to determine whether AY rats exhibit cognitive deficits that mirror those observed in AAS clinically. Hippocampal function was examined in AY animals both in vitro with electrophysiology (i.e., synaptic plasticity) and in vivo with a hippocampus-dependent radial arm maze (RAM) task that is designed to assess spatial cognition. In vitro tests of synaptic plasticity revealed impairments in long-term potentiation (LTP), paired-pulse facilitation (PPF), and presynaptic depression (PD). Consistently, performance of AY animals in RAM revealed fewer perfect entries, a greater number of errors, and required more training days to learn the task than saline-treated controls. The abolishment of spontaneous seizures by ethosuximide failed to recover the perturbed spatial learning and working memory in AY animals. AY rats demonstrate altered hippocampal functioning as manifested by altered synaptic plasticity and cognition. The relationship between AAS and cognitive deficit remains uncertain and the pathophysiology of both in AY treated requires further investigation.

18FDG-PET in epilepsies of infantile onset with pharmacoresistant generalised tonic-clonic seizures

AIMS

To investigate the pathophysiology of pharmacoresistant epilepsies with cryptogenic generalised tonic-clonic seizures (GTCS) from infancy.

METHODS

18F-Deoxy-Glucose-Positron Emission Tomography 18FDG-PET) with statistical parametric mapping (SPM). Inclusion criteria were: pharmacoresistant chronic epilepsy with GTCS commencing in infancy, no focal seizures except alternating hemiconvulsions and no focal epileptic discharges in the EEG during the first year of the disease, no focal changes upon routine neuroradiological investigations, no indication of brain damage according to history and clinical examination.

RESULTS

15 boys and 15 girls with a mean age of 6.4 years (range l-14 years) were included. All still suffered from seizures despite past treatment with a mean of five drugs. Nearly all were mentally retarded, 19 to a severe and 10 to a minor degree. Fifteen were ataxic and 11 hypotonic. The EEG in 23 showed irregular generalised spike-wave discharges. PET SPM analysis revealed bioccipital hypometabolism related to sedation. Pathological monofocal hypometabolic areas were found in three, multifocal hypometabolic areas in 22 and diffuse bilateral hypometabolism in three patients. Frontal hypometabolism correlated to the degree of mental retardation, hypotonia, and ataxia. Temporomesial hypometabolism correlated to the occurrence of obtunded states and prominent delta rhythms in the EEG. Central and parietal changes were associated with the occurrence of myoclonic seizures and spike-wave discharges.

CONCLUSIONS

18FDG-PET in many of these children with cryptogenic generalised epilepsies showed multifocal hypometabolic areas of unknown aetiology. Primary cortical microdysgenesis and secondary changes due to the severe and long-standing epilepsy must be considered. Only a minority of patients showed restricted focal hypometabolism as a possible indication for surgical treatment.

Why do seizures cause loss of consciousness?

Model systems are needed for the scientific investigation of consciousness. A good model system should include variable states of consciousness, allowing the relationship between brain activity and consciousness to be investigated. Examples include sleep, anesthesia, focal brain lesions, development, evolution, and epilepsy. One advantage of epilepsy is that changes are dynamic and rapidly reversible. The authors review previous investigations of impaired consciousness in epilepsy and describe new findings that may shed light on both normal and abnormal mechanisms of consciousness. Abnormal increased activity in fronto-parietal association cortex and related subcortical structures is associated with loss of consciousness in generalized seizures. Abnormal decreased activity in these same networks may cause loss of consciousness in complex partial seizures. Thus, abnormally increased or decreased activity in the same networks can cause loss of consciousness. Information flow during normal conscious processing may require a dynamic balance between these two extremes of excitation and inhibition.

Atypical Lennox-Gastaut syndrome successfully treated with removal of a parietal dysembryoplastic tumour

Focal brain lesions may be associated with the atypical form of Lennox-Gastaut syndrome (LGS). We describe a drug resistant LGS patient with daily seizures and a left parietal dysembryoplastic neuroepithelial tumour. Pre-surgical evaluation showed, in addition to diffuse paroxysmal EEG discharges associated with atonic and tonic axial seizures, lateralizing EEG and clinical signs pointing to left hemisphere origin of the seizures. The patient was treated with lesionectomy and after 12 months of follow-up is still seizure free. This case suggests that in patients with LGS and focal lesions the possibility of correct identification of the epileptogenic zone using anatomo-electro-clinical correlations may be the key element for 'curative' surgery.

Vagal nerve stimulation in epileptic encephalopathies

OBJECTIVE

To study the effect of vagal nerve stimulation (VNS) in children with epileptic encephalopathies.

METHODS AND MATERIALS

All children receiving VNS during a 2-year period at our center were studied prospectively for changes in seizure frequency, electroencephalogram (EEG), adaptive behavior, quality of life, and where appropriate, verbal/nonverbal performance. Assessments were made before and for at least 1 year after implant.

RESULTS

Sixteen children were studied. One device was removed because of infection. Of the remaining 15 children, 4 had a >50% reduction and 2 had a >50% increase in seizure frequency at 1 year after implant. Median reduction in seizure frequency was 17%. There was no trend toward improvement of the EEG or adaptive behavior. Quality of life was unchanged in most areas, except in perceived treatment side effects and general behavior that were improved. In 6 children undergoing further assessment, there was a significant improvement in verbal performance; this did not correlate with reduction in seizure frequency.

CONCLUSION

VNS did not significantly improve seizure frequency, severity, adaptive behavior, or the EEG during the first year of treatment for the group as a whole, although 4 children (27%) had a worthwhile reduction in seizure frequency. There were significant improvements in perceived treatment side effects and general behavior.

Plasma amino acids in childhood epileptic encephalopathies

Abnormalities in plasma amino acid levels have been noted in patients with various epilepsies, and sometimes also in their first degree relatives. We sought to study plasma amino acid levels in children with epileptic encephalopathies and their parents, relating findings to the pattern of cortical glucose metabolism as determined by 18fluorodeoxyglucose (FDG) positron emission tomography (PET). Twenty-eight children with cryptogenic epileptic encephalopathies were studied prospectively. Cortical glucose metabolism was evaluated by FDG PET with combined visual and semiquantitative analysis used to detect focal cortical defects. The plasma concentration of 21 amino acids in the children and their parents was measured by ion exchange chromatography and compared with control values using non-parametric statistical methods. Multivariate analysis was used to assess antiepileptic drug effects. Children were classified as: Lennox-Gastaut syndrome following infantile spasms (six patients); de-novo Lennox-Gastaut syndrome (eight); severe myoclonic epilepsy in infancy (eight) and myoclonic-astatic epilepsy (two). Four patients remained unclassified. Fourteen patients had focal/multifocal abnormalities on PET scans. The plasma level of aspartate was significantly lower in both the children with epileptic encephalopathies and in their parents (P < 0.005). The lowered aspartate levels could not be accounted for by the antiepileptic drug medication taken by the children. Further analysis showed the lowered aspartate levels to be confined to children and their parents who lacked focal PET abnormalities. These findings suggest a possible genetic abnormality in the aspartate neurotransmitter systems in the pathogenesis of seizures in the childhood epileptic encephalopathies.

Neuroimaging and spectroscopy in children with epileptic encephalopathies

AIMS

To investigate the nature of the unifocal cortical abnormalities on FDG positron emission tomography (PET) in children with an epileptic encephalopathy but no focal abnormality on electroencephalogram or standard magnetic resonance imaging (MRI).

METHODS

Repeat FDG PET, surface rendered high resolution MRI, and single voxel magnetic resonance proton spectroscopy of the areas of abnormal metabolism compared to the contralateral side in 11 children aged 2 to 12 years. Imaging was repeated after a median of 13 months.

RESULTS

Visual analysis of repeat FDG PET revealed similar abnormalities in 10 of 11 children. Semiquantitative analysis revealed similar sited abnormalities in eight children. One child with ictal hypermetabolism initially had an inconsistent second scan. Magnetic resonance spectra in three children showed the N-acetyl-aspartate/choline ratio was lower in the hypometabolic focus than in the reciprocal area on the opposite side, in two children it was higher, and in one child it was equal. Surface rendered MRI was normal in seven of eight children, and showed temporal lobe asymmetry in one.

CONCLUSION

In children with established epileptic encephalopathies most hypometabolic areas on FDG PET are stable over time. While focal neuronal loss is likely in these areas in some children, microdysplasias or other focal cortical dysplasias are probable in others.

Cortical and subcortical glucose metabolism in childhood epileptic encephalopathies

OBJECTIVES

Nearly one third of children with cryptogenic epileptic encephalopathies have been reported to have focal cortical defects on 18fluorodeoxyglucose (FDG) PET. As diffuse cortical dysfunction and involvement of subcortical structures, particularly the thalami, is postulated to underlie the propensity to seizures in these conditions, the aim was to determine the frequency of bilateral and diffuse cortical metabolic defects and of subcortical metabolic abnormalities in the same patients.

METHODS

The interictal uptake of FDG was studied in 32 children with epileptic encephalopathies. Using a semiquantitative technique, the ratio of uptake in cortical regions and subcortical structures to that in the cerebellum was compared with that of age matched historical controls. Uptake more than 2 SD above ("hypermetabolic") or below ("hypometabolic") that of age matched controls was considered abnormal.

RESULTS

Diffusely abnormal cortical up-take (nearly always hypometabolic) occurred in almost two thirds of patients; in all but two of the remaining patients at least one cortical region showed significantly decreased uptake bilaterally. When analysed as age cohorts, the mean cortical:cerebellar FDG uptake was significantly lower than that of controls in all cortical regions (P<0.005). Ninety per cent of patients had evidence of relative thalamic hypometabolism and in each age group there was a significant reduction in relative thalamic FDG uptake compared with that of controls (P<0.005). In nine out of 11 patients with unilateral cortical hypometabolic defects thalamic FDG up-take was lower ipsilateral to the cortical abnormality.

CONCLUSIONS

Diffuse cortical dysfunction is common in the epileptic encephalopathies and may reflect the underlying cause of the condition or arise as a consequence of uncontrolled seizures. Altered thalamic glucose metabolism is further evidence of subcortical involvement in these conditions.