Epilepsy Duration, Febrile Seizures, and Cerebral Glucose Metabolism

Zinc-α2-glycoprotein relieved seizure-Induced neuronal glucose uptake impairment via insulin-like growth factor 1 receptor-regulated glucose transporter 3 expression

Glucose hypometabolism is observed in epilepsy and promotes epileptogenesis. Glucose hypometabolism in epilepsy may be attributed to decreased neuronal glucose uptake, but its molecular mechanism remains unclear. Zinc-α2-glycoprotein (ZAG) is related to glucose metabolism and is reported to suppress seizures. The anti-epileptic effect of ZAG may be attributed to its regulation of neuronal glucose metabolism. This study explored the effect of ZAG on neuronal glucose uptake and its molecular mechanism via insulin-like growth factor 1 receptor (IGF1R)-regulated glucose transporter 3 (GLUT-3) expression. The ZAG level was modulated by lentivirus in primary culture neurons. Neuronal seizure models were induced by Mg²⁺ -free artificial cerebrospinal fluid. We assessed neuronal glucose uptake by the 2-NBDG method and Glucose Uptake Colorimetric Assay Kit. IGF1R was activated by IGF1 and blocked by AXL1717. The expression and distribution of IGF1R and GLUT-3, together with IGF1R phosphorylation, were measured by western blot. The binding between ZAG and IGF1R was determined by coimmunoprecipitation. Neuronal glucose uptake and GLUT-3 expression were significantly decreased by seizure or ZAG knockdown, whereas ZAG over-expression or IGF1 treatment reversed this decrease. The effect of ZAG on neuronal glucose uptake and GLUT-3 expression was blocked by AXL1717. ZAG increased IGF1R distribution and phosphorylation possibly by binding. Additionally, IGF1R increased GLUT-3 activity by increasing GLUT-3 expression. In epilepsy/seizure, neuronal glucose uptake suppression may be attributed to a decrease in ZAG, which suppresses neuronal GLUT-3 expression by regulating the activity of IGF1R. ZAG, IGF1R, and GLUT-3 may be novel potential therapeutic targets of glucose hypometabolism in epilepsy and seizures.

Deep brain stimulation of the anterior nucleus of the thalamus for drug-resistant epilepsy

Despite the use of first-choice anti-epileptic drugs and satisfactory seizure outcome rates after resective epilepsy surgery, a considerable percentage of patients do not become seizure free. ANT-DBS may provide for an alternative treatment option in these patients. This literature review discusses the rationale, mechanism of action, clinical efficacy, safety, and tolerability of ANT-DBS in drug-resistant epilepsy patients. A review using systematic methods of the available literature was performed using relevant databases including Medline, Embase, and the Cochrane Library pertaining to the different aspects ANT-DBS. ANT-DBS for drug-resistant epilepsy is a safe, effective and well-tolerated therapy, where a special emphasis must be given to monitoring and neuropsychological assessment of both depression and memory function. Three patterns of seizure control by ANT-DBS are recognized, of which a delayed stimulation effect may account for an improved long-term response rate. ANT-DBS remotely modulates neuronal network excitability through overriding pathological electrical activity, decrease neuronal cell loss, through immune response inhibition or modulation of neuronal energy metabolism. ANT-DBS is an efficacious treatment modality, even when curative procedures or lesser invasive neuromodulative techniques failed. When compared to VNS, ANT-DBS shows slightly superior treatment response, which urges for direct comparative trials. Based on the available evidence ANT-DBS and VNS therapies are currently both superior compared to non-invasive neuromodulation techniques such as t-VNS and rTMS. Additional in-vivo research is necessary in order to gain more insight into the mechanism of action of ANT-DBS in localization-related epilepsy which will allow for treatment optimization. Randomized clinical studies in search of the optimal target in well-defined epilepsy patient populations, will ultimately allow for optimal patient stratification when applying DBS for drug-resistant patients with epilepsy.

Temporal lobe epilepsy: Hippocampal pathology modulates connectome topology and controllability

OBJECTIVE

To assess whether hippocampal sclerosis (HS) severity is mirrored at the level of large-scale networks.

METHODS

We studied preoperative high-resolution anatomical and diffusion-weighted MRI of 44 temporal lobe epilepsy (TLE) patients with histopathologic diagnosis of HS (n = 25; TLE-HS) and isolated gliosis (n = 19; TLE-G) and 25 healthy controls. Hippocampal measurements included surface-based subfield mapping of atrophy and T2 hyperintensity indexing cell loss and gliosis, respectively. Whole-brain connectomes were generated via diffusion tractography and examined using graph theory along with a novel network control theory paradigm that simulates functional dynamics from structural network data.

RESULTS

Compared to controls, we observed markedly increased path length and decreased clustering in TLE-HS compared to controls, indicating lower global and local network efficiency, while TLE-G showed only subtle alterations. Similarly, network controllability was lower in TLE-HS only, suggesting limited range of functional dynamics. Hippocampal imaging markers were positively associated with macroscale network alterations, particularly in ipsilateral CA1-3. Systematic assessment across several networks revealed maximal changes in the hippocampal circuity. Findings were consistent when correcting for cortical thickness, suggesting independence from gray matter atrophy.

CONCLUSIONS

Severe HS is associated with marked remodeling of connectome topology and structurally governed functional dynamics in TLE, as opposed to isolated gliosis, which has negligible effects. Cell loss, particularly in CA1-3, may exert a cascading effect on brain-wide connectomes, underlining coupled disease processes across multiple scales.

Depression comorbidity in epileptic rats is related to brain glucose hypometabolism and hypersynchronicity in the metabolic network architecture

OBJECTIVE

Temporal lobe epilepsy (TLE) is one of the most common types of epilepsy syndromes in the world. Depression is an important comorbidity of epilepsy, which has been reported in patients with TLE and in different experimental models of epilepsy. However, there is no established consensus on which brain regions are associated with the manifestation of depression in epilepsy. Here, we investigated the alterations in cerebral glucose metabolism and the metabolic network in the pilocarpine-induced rat model of epilepsy and correlated it with depressive behavior during the chronic phase of epilepsy.

METHODS

Fluorodeoxyglucose (¹⁸ F-FDG) was used to investigate the cerebral metabolism, and a cross-correlation matrix was used to examine the metabolic network in chronically epileptic rats using micro-positron emission tomography (microPET) imaging. An experimental model of epilepsy was induced by pilocarpine injection (320 mg/kg, ip). Forced swim test (FST), sucrose preference test (SPT), and eating-related depression test (ERDT) were used to evaluate depression-like behavior.

RESULTS

Our results show an association between epilepsy and depression comorbidity based on changes in both cerebral glucose metabolism and the functional metabolic network. In addition, we have identified a significant correlation between brain glucose hypometabolism and depressive-like behavior in chronically epileptic rats. Furthermore, we found that the epileptic depressed group presents a hypersynchronous brain metabolic network in relation to the epileptic nondepressed group.

SIGNIFICANCE

This study revealed relevant alterations in glucose metabolism and the metabolic network among the brain regions of interest for both epilepsy and depression pathologies. Thus it seems that depression in epileptic animals is associated with a more diffuse hypometabolism and altered metabolic network architecture and plays an important role in chronic epilepsy.

Structural and Functional Alterations at Pre-Epileptic Stage Are Closely Associated with Epileptogenesis in Pilocarpine-induced Epilepsy Model

Pilocarpine-induced rat epilepsy model is an established animal model that mimics medial temporal lobe epilepsy in humans. The purpose of this study was to investigate neuroimaging abnormalities in various stages of epileptogenesis and to correlate them with seizure severity in pilocarpine-induced rat epilepsy model. Fifty male Sprague-Dawley rats were subject to continuous video and electroencephalographic monitoring after inducing status epilepticus (SE) and seizure severity was estimated by frequency and total durations of class 3 to 5 spontaneous recurrent seizures (SRS) by modified Racine's classification. The 7.0 Tesla magnetic resonance imaging (MRI) with high resolution flurodeoxyglucose positron emission tomography (FDG-PET) was performed at 3 hours, 1, 3, 7 days and 4 weeks after the initial insult. The initial SRS was observed 9.7±1.3 days after the pilocarpine injection. MRI revealed an abnormal T2 signal change with swelling in both hippocampi and amygdala in acute (day 1 after injection) and latent phases (days 3 and 7), in association with PET hypometabolism in these areas. Interestingly, the mean frequency of class 3 to 5 SRS was positively correlated with abnormal T2 signals in hippocampal area at 3 days. SRS duration became longer with more decreased glucose metabolism in both hippocampi and amygdala at 7 days after pilocarpine injection. This study indicates that development and severity of SRS at chronic phase could be closely related with structural and functional changes in hippocampus during the latent period, a pre-epileptic stage.

Occurrence predictors of the temporal interictal epileptic discharges in epilepsy patients with extratemporal lesions: A prospective cohort study

OBJECTIVE

Electrical kindling models of epilepsy suggest that medial temporal structures are more prone to be irritated. The aim of this study is to investigate the occurrence rate of temporal interictal epileptic discharges (TIEDs) in the epilepsy patients with extratemporal lesions (ETLs), and to determine the predictive factors for TIEDs in this cohort.

METHODS

Totally 221 patients were admitted for presurgical evaluation, and focal ETL were found in all of them by MRI examination. The occurrence rates of TIEDs in several groups with different brain lobe locations, durations; of epilepsy, seizure frequencies, and onset ages stages were assessed. We also evaluated the surgical outcome of; resection in this cohort.

RESULTS

The total occurrence rate of TIEDs in this cohort was 29.9%. The occurrence rate of TIEDs in the patients with longer durations (>5 or 10 years) was significantly higher than those with shorter duration (<1 year). These; patients with lower seizure frequency (<1 seizure/month) had a significantly decreased incidence of TIEDs; compared with those with higher frequency (>1 seizure/month or week). In the terms of the brain lobe locations; and age at onset, there were no differences between the groups. Furthermore, there were no differences in terms of the surgical outcomes between the patients with TIEDs and other patients in this series.

CONCLUSIONS

TIEDs were frequently recorded in these patients with ETLs, and the predictive factors for TIEDs included the epilepsy duration and seizure frequency.

SIGNIFICANCE

This study is instrumental for the presurgical EEG interpretationand the counseling of these ETLs patients considered for epilepsy surgery.

Long-term metabolic alterations in a febrile seizure model

OBJECTIVE

Febrile seizures (FS) are the most common neurological disease in infancy and early childhood, it can lead to metabolic changes and have long-term health implications. Aim of this study was to investigate the long-term effects of FS on metabolism.

METHODS

We measured certain metabolic parameters in hyperthermia-prone (HP) rats, which were developed using a selective breeding process and showed a lower seizure threshold than wild-type (WT) rats. Body weight, body length, abdominal circumference and the levels of fasting blood glucose, serum triglyceride, and total cholesterol concentrations were analyzed. The mRNA expression of genes involved in glucose and lipid metabolism was determined by qPCR and the histone methylation level in the liver was determined by western blot.

RESULTS

We found that the body weight of the HP rats was significantly lower than that of the WT rats. Similarly, the fasting blood glucose and serum triglyceride levels were lower in the HP group compared with the WT group. These changes were accompanied by increased mRNA expression of genes such as phosphoenolpyruvate carboxykinase (PEPCK) and carnitine palmitoyl transferase-1 (CPT-1), but not peroxisome proliferator-activated receptor α (PPARα). We also found tri-methylation of histone 3 at Lys9 and Lys27 was decreased in the HP group.

CONCLUSIONS

These data may suggest an underlying mechanism by which FS have a long-term effect on energy metabolism via histone methylation.

Revisiting hippocampal sclerosis in mesial temporal lobe epilepsy according to the "two-hit" hypothesis

Hippocampal sclerosis (HS) is the most common neuropathological pattern observed in pharmacoresistant epilepsy and represents a critical feature in mesial temporal lobe epilepsy syndrome. However, its pathophysiological mechanisms and neuropathological consequences on seizures remain mostly unresolved. The new international classification of hippocampal sclerosis aims at standardizing its description to allow comparisons between different clinical studies. However, several aspects are not considered in this classification (granule cell dispersion, sprouting, glial modifications…). In this chapter, we discuss these different features associated with hippocampal sclerosis in perspective with the "two-hit" hypothesis and propose mechanisms that could be involved in the modulation of some specific neuropathological aspects like early life stress, hyperthermic seizures, brain lesions or hormonal modifications.

Epilepsy as progressive disorders: what is the evidence that can guide our clinical decisions and how can neuroimaging help?

There is evidence that some types of epilepsy progress over time, and an important part of this knowledge has derived from neuroimaging studies. Different authors have demonstrated structural damage more pronounced in individuals with a longer duration of epilepsy, and others have been able to quantify this progression over time. However, others have failed to demonstrate progression possibly due to the heterogeneity of individuals evaluated. Currently, temporal lobe epilepsy associated with hippocampal sclerosis is regarded as a progressive disorder. Conversely, for other types of epilepsy, the evidence is not so clear. The causes of this damage progression are also unknown although there is consistent evidence that seizure is one of the mechanisms. The conflicting data about epilepsy progression can be a challenge for clinical decisions for an individual patient. Studies with homogenous groups and longer follow-up are necessary for appropriate conclusions about the real burden of damage progression in epilepsies, and neuroimaging will be essential in this context.

Pediatric functional hemispherectomy: outcome in 92 patients

BACKGROUND

The revival of epilepsy surgery after the introduction of modern presurgical evaluation procedures has led to an increase in hemispherectomy or hemispherotomy procedures. Since a large part of our pediatric series was done using a newer hemispherotomy technique, we focus mainly on the outcomes after a recently developed hemispherotomy technique (transsylvian keyhole).

METHODS

Ninety-six pediatric patients (aged 4 months to 18 years, mean 7.3) were operated on between 1990 and 2009; 92 were available with follow-up.

RESULTS

The most frequent diagnosis was porencephaly in 46 % of all patients. Progressive etiologies were present in 20 % and developmental etiologies in 22 %. At last available outcome (LAO), 85 % of the patients were seizure free (ILAE class 1). Year-to-year outcome was rather stable; usually over 80 % were class 1 for up to 13 years (n = 24). Of 92 assessable patients, 71 were treated with the transsylvian keyhole technique, with 89 % being seizure free. The overall shunt rate was 5.3 % for the whole series and 3 % for the keyhole technique subgroup. Mortality was 1 of 96 patients. Excluding patients with hemimegalencephaly (HME), patients with the shortest duration of epilepsy and the lowest age at seizure onset had the highest rates of seizure freedom. The etiology does influence outcome, with HME patients having the poorest seizure outcome and patients with Sturge-Weber syndrome and porencephaly having excellent seizure control.

CONCLUSION

Hemispherotomies/functional hemispherectomies are very effective and safe procedures for treating drug-resistant epilepsy with extensive unihemispheric pathology. Etiology and surgery type clearly influence seizure outcome.

Hippocampal sclerosis in children younger than 2 years

BACKGROUND

Hippocampal sclerosis (HS) is rarely considered as a diagnosis in children younger than 2 years.

OBJECTIVE

To describe imaging features in conjunction with clinical information in patients with hippocampal sclerosis who are younger than 2 years.

MATERIALS AND METHODS

We retrospectively reviewed MR brain imaging and clinical information in five children in whom the diagnosis of HS was made both clinically and by MRI prior to 2 years of age.

RESULTS

Imaging features establishing the diagnosis of hippocampal sclerosis were bright T2 signal and volume loss, while the internal architecture of the hippocampal formation was preserved in almost all children. Clinically, all children had an infectious trigger.

CONCLUSION

It is necessary for radiologists to consider HS in children with certain clinical features to plan an MRI protocol that is appropriate for detection of hippocampal pathology.

Surgical decision making in temporal lobe epilepsy: a comparison of [(18)F]FDG-PET, MRI, and EEG

OBJECTIVES

The goals of this work were (1) to determine the effect of [(18)F]fluorodeoxyglucose positron emission tomography (FDG-PET), MRI, and EEG on the decision to perform temporal lobe epilepsy (TLE) surgery, and (2) to determine if FDG-PET, MRI, or EEG predicts surgical outcome.

METHODS

All PET scans ordered (2000-2010) for epilepsy or seizures were tabulated. Medical records were investigated to determine eligibility and collect data. Statistical analysis included odds ratios, κ statistics, univariate analysis, and logistic regression.

RESULTS

Of the 186 patients who underwent FDG-PET, 124 had TLE, 50 were surgical candidates, and 34 had surgery with post-operative follow-up. Median length of follow-up was 24 months. MRI, FDG-PET, and EEG were significant predictors of surgical candidacy (P<0.001) with odds ratios of 42.8, 20.4, and 6.3, respectively. FDG-PET was the only significant predictor of postoperative outcome (P<0.01).

CONCLUSION

MRI showed a trend toward having the most influence on surgical candidacy, but only FDG-PET predicted surgical outcome.

Presurgical epilepsy localization with interictal cerebral dysfunction

Localization of interictal cerebral dysfunction with 2-[(18)F]fluoro-2-D-deoxyglucose (FDG) positron emission tomography (PET) and neuropsychological examination usefully supplements electroencephalography (EEG) and brain magnetic resonance imaging (MRI) in planning epilepsy surgery. In MRI-negative mesial temporal lobe epilepsy, correlation of temporal lobe hypometabolism with extracranial ictal EEG can support resection without prior intracranial EEG monitoring. In refractory localization-related epilepsies, hypometabolic sites may supplement other data in hypothesizing likely ictal onset zones in order to intracranial electrodes for ictal recording. Prognostication of postoperative seizure freedom with FDG PET appears to have greater positive than negative predictive value. Neuropsychological evaluation is critical to evaluating the potential benefit of epilepsy surgery. Cortical deficits measured with neuropsychometry are limited in lateralizing and localizing value for determination of ictal onset sites, however. Left temporal resection risks iatrogenic verbal memory deficits and dysnomia, and neuropsychological findings are useful in predicting those at greatest risk. Prognostication of cognitive risks with resection at other sites is less satisfactory.

Epilepsy duration impacts on brain glucose metabolism in temporal lobe epilepsy: results of voxel-based mapping

OBJECTIVE

[(18)F]Fluorodeoxyglucose positron emission tomography ([(18)F]FDG-PET) is a valuable method for detecting focal brain dysfunction associated with epilepsy. Evidence suggests that a progressive decrease in [(18)F]FDG uptake occurs in the epileptogenic cortex with an increase in the duration of epilepsy. In this study, our aim was to use statistical parametric mapping (SPM) to test the validity of this relationship in a retrospective study of patients with temporal lobe epilepsy (TLE).

METHODS

[(18)F]FDG-PET scans of 46 adult patients with pharmacoresistant unilateral TLE (25 RTLE and 21 LTLE) were subjected to SPM analysis.

RESULTS

Forty-six patients were diagnosed with nonlesional TLE, 16 of whom had hippocampal sclerosis (HS). The average duration of epilepsy was 17.4 +/- 12.3 years (3-46 years), <5 years in 10 patients and >or=10 years in 30 patients. Visual analysis of [(18)F]FDG-PET scans revealed hypometabolism in the epileptogenic temporal cortex in 31 (67%) patients. After SPM analysis of all [(18)F]FDG-PET images, hypometabolism was unilateral and reported in lateral and mesial structures of the epileptogenic temporal cortex in addition to the ipsilateral fusiform and middle occipital gyrus. Subsequent analysis revealed that temporal lobe hypometabolism was present only in patients with longer epilepsy duration (>or=10 years) in parahippocampal gyrus, uncus, and middle and superior temporal gyrus (P < 0.05 corrected). Epilepsy duration was inversely correlated with decreased glucose uptake in the inferior temporal gyrus, hippocampus, and parahippocampal gyrus of the epileptogenic temporal cortex (P < 0.05). Age at seizure onset did not affect the correlation between epilepsy duration and glucose uptake except in the inferior temporal gyrus (P < 0.05).

CONCLUSION

Voxel-based mapping supports the assertion that glucose hypometabolism of the epileptogenic temporal lobe cortex and other neighboring cortical regions increases with longer epilepsy duration in TLE.

Cognition across the lifespan: antiepileptic drugs, epilepsy, or both?

Cognitive problems in persons with epilepsy manifest over a lifetime; however, whether abnormal cognition in an individual with epilepsy is a result of comorbid brain substrate, the epilepsy itself or its underlying etiology, the antiepileptic agents used to control it, or a combination of these and other factors remains controversial. There is a continuing need for improved therapies to control seizures and reduce the incidence of adverse events, especially those involving the central nervous system that compromise attention, intelligence, language skills, verbal and nonverbal memory, executive function, and psychomotor speeds. Although cognitive decline typically occurs among patients with more severe epilepsy, physicians must judiciously select therapy with an eye toward not only controlling seizures but also ensuring that all patients retain as much function as possible throughout their lives.

Cognitive disorders associated with epilepsy: diagnosis and treatment

INTRODUCTION

Cognitive disorders are common in patients with epilepsy. Their aetiology is multifactorial, being affected by the type and location of the epileptogenic lesion, epileptic syndrome, type of seizures, age of onset, frequency and severity. Timely diagnosis and treatment can help to reduce their impact on the patient's quality of life.

RESULTS

The most significant cognitive deficits are associated with focal epilepsy, although some, usually mild, neuropsychological disorders can be found in idiopathic generalized epilepsy. The use of antiepileptic drugs (AEDs) can cause additional neuropsychological disorders that are of particular concern in learning-age children and elderly patients with cognitive disorders before the start of treatment. Recent studies have raised the concern that the use of some AEDs during pregnancy may cause cognitive disorders in the child exposed to them in utero. Cognitive disorders can also present as a complication of surgery for refractory epilepsy. Some risk factors for significant memory loss after surgery for temporal lobe epilepsy have been described. They include intervention in the dominant hemisphere, good preoperative function and poor functional reserve in the contralateral hippocampus.

CONCLUSIONS

The heterogeneity of different types of epilepsy makes case-control studies difficult; however, thanks to the growing interest in the neuropsychological deficits associated with epilepsy, we now know some factors that could lead to the appearance of these disorders and their prognosis. Special care must be taken to detect cognitive side effects associated with AEDs, which seem to be more common with classic than with new AEDs, and in those patients receiving polytherapy. Neuropsychological assessment should be routinely performed before epilepsy surgery to predict possible postsurgical cognitive deficits.

The mortality and morbidity of febrile seizures

Approaches to the treatment and investigation of febrile seizures have changed since the main reference studies on outcomes were conducted in the 1960s and 1970s. We have, therefore, conducted a systematic review of literature from the past 15 years to see whether outcomes have also changed. We found that simple febrile seizures do not carry a risk of death, but there is a very small risk of death after complex febrile seizures (CFSs), particularly febrile status epilepticus. There is no evidence that SUDEP (sudden unexpected death in epilepsy) occurs in association with febrile seizures. The risk of later epilepsy after a febrile seizure lies between 2.0% and 7.5%, and the risk of developing epilepsy after CFSs is estimated at around 10-20%. There is no evidence of any risk of hippocampal or mesial temporal sclerosis (HS/MTS) in association with simple febrile seizures. Serial imaging has shown that HS/MTS develops in 0-25% of patients over time after prolonged febrile seizures; the range in prevalence reflects selection bias in different studies. The overall risk of HS/MTS associated with CFSs is around 3%. Approximately 40% of patients with medically refractory temporal lobe epilepsy and HS/MTS on neuroimaging have a history of febrile seizures.

Ang II and Ang IV: unraveling the mechanism of action on synaptic plasticity, memory, and epilepsy

The central angiotensin system plays a crucial role in cardiovascular regulation. More recently, angiotensin peptides have been implicated in stress, anxiety, depression, cognition, and epilepsy. Angiotensin II (Ang II) exerts its actions through AT(1) and AT(2) receptors, while most actions of its metabolite Ang IV were believed to be independent of AT(1) or AT(2) receptor activation. A specific binding site with high affinity for Ang IV was discovered and denominated "AT(4) receptor". The beneficiary effects of AT(4) ligands in animal models for cognitive impairment and epileptic seizures initiated the search for their mechanism of action. This proved to be a challenging task, and after 20 years of research, the nature of the "AT(4) receptor" remains controversial. Insulin-regulated aminopeptidase (IRAP) was first identified as the high-affinity binding site for AT(4) ligands. Recently, the hepatocyte growth factor receptor c-MET was also proposed as a receptor for AT(4) ligands. The present review focuses on the effects of Ang II and Ang IV on synaptic transmission and plasticity, learning, memory, and epileptic seizure activity. Possible interactions of Ang IV with the classical AT(1) and AT(2) receptor subtypes are evaluated, and other potential mechanisms by which AT(4) ligands may exert their effects are discussed. Identification of these mechanisms may provide a valuable target in the development in novel drugs for the treatment of cognitive disorders and epilepsy.

'MRI-negative PET-positive' temporal lobe epilepsy (TLE) and mesial TLE differ with quantitative MRI and PET: a case control study

Background

'MRI negative PET positive temporal lobe epilepsy' represents a substantial minority of temporal lobe epilepsy (TLE). Clinicopathological and qualitative imaging differences from mesial temporal lobe epilepsy are reported. We aimed to compare TLE with hippocampal sclerosis (HS+ve) and non lesional TLE without HS (HS-ve) on MRI, with respect to quantitative FDG-PET and MRI measures.

Methods

30 consecutive HS-ve patients with well-lateralised EEG were compared with 30 age- and sex-matched HS+ve patients with well-lateralised EEG. Cerebral, cortical lobar and hippocampal volumetric and co-registered FDG-PET metabolic analyses were performed.

Results

There was no difference in whole brain, cerebral or cerebral cortical volumes. Both groups showed marginally smaller cerebral volumes ipsilateral to epileptogenic side (HS-ve 0.99, p = 0.02, HS+ve 0.98, p < 0.001). In HS+ve, the ratio of epileptogenic cerebrum to whole brain volume was less (p = 0.02); the ratio of epileptogenic cerebral cortex to whole brain in the HS+ve group approached significance (p = 0.06). Relative volume deficits were seen in HS+ve in insular and temporal lobes. Both groups showed marked ipsilateral hypometabolism (p < 0.001), most marked in temporal cortex. Mean hypointensity was more marked in epileptogenic-to-contralateral hippocampus in HS+ve (ratio: 0.86 vs 0.95, p < 0.001). The mean FDG-PET ratio of ipsilateral to contralateral cerebral cortex however was low in both groups (ratio: HS-ve 0.97, p < 0.0001; HS+ve 0.98, p = 0.003), and more marked in HS-ve across all lobes except insula.

Conclusion

Overall, HS+ve patients showed more hippocampal, but also marginally more ipsilateral cerebral and cerebrocortical atrophy, greater ipsilateral hippocampal hypometabolism but similar ipsilateral cerebral cortical hypometabolism, confirming structural and functional differences between these groups.

"Magnetic resonance imaging negative positron emission tomography positive" temporal lobe epilepsy: FDG-PET pattern differs from mesial temporal lobe epilepsy

PURPOSE

Some patients with temporal lobe epilepsy (TLE) lack evidence of hippocampal sclerosis (HS) on MRI (HS-ve). We hypothesized that this group would have a different pattern of 2-deoxy-2-[F-18]fluoro-D-glucose (FDG)-positron emission tomography (PET) hypometabolism than typical mesial TLE/HS patients with evidence of hippocampal atrophy on magnetic resonance imaging (MRI) (HS+ve), with a lateral temporal neocortical rather than mesial focus.

PROCEDURES

Thirty consecutive HS-ve patients and 30 age- and sex-matched HS+ve patients with well-lateralized EEG were identified. FDG-PET was performed on 28 HS-ve patients and 24 HS+ve patients. Both groups were compared using statistical parametric mapping (SPM), directly and with FDG-PET from 20 healthy controls.

RESULTS

Both groups showed lateralized temporal hypometabolism compared to controls. In HS+ve, this was antero-infero-mesial (T = 17.13); in HS-ve the main clustering was inferolateral (T = 17.63). When directly compared, HS+ve had greater hypometabolism inmesial temporal/hippocampal regions (T = 4.86); HS-ve had greater inferolateral temporal hypometabolism (T = 4.18).

CONCLUSIONS

These data support the hypothesis that focal hypometabolism involves primarily lateal neocortical rather than mesial temporal structures in 'MRI-negative PET-positive TLE.'

Positron emission tomography in Rasmussen's encephalitis

This report presents unusual positron emission tomography findings in an 11-year-old male with Rasmussen's encephalitis. This patient underwent fluorine-18 fluorodeoxyglucose positron emission tomography to localize his ictal focus before surgical consideration. Positron emission tomography disclosed marked hypermetabolism in the left cerebral hemisphere and basal ganglia with subnormal right cerebral activity and crossed cerebellar diaschisis. The heterogeneous distribution of metabolism suggests a combination of areas in different stages of ictal and postictal involvement. The hypermetabolic region in the left hemisphere was larger in size and extent (now including the left frontoparietal lobe) than the sole hypermetabolic left temporal lobe on his positron emission tomography from 2 years ago. While this positron emission tomography pattern of progression appears most commonly in Rasmussen's encephalitis case studies, few serial reports exist. The complex positron emission tomography findings of this case emphasize the importance of knowing the history of recent seizures, seizure type, clinical status at time of injection, and electroencephalographic correlation before interpreting functional neuroimaging studies. Finally, positron emission tomography studies can help clarify whether patients with Rasmussen's encephalitis with dominant hemisphere involvement are appropriate candidates for surgery or not.

Effects of Illness Duration on Memory Processing of Patients with Temporal Lobe Epilepsy

PURPOSE

To examine the effects of illness duration on the neural processing of memory in patients with temporal lobe epilepsy (TLE) by using functional MRI.

METHODS

Twenty-three TLE patients (16 left, seven right) performed a complex visual scene-encoding task during functional MRI. Region-of-interest (ROI) analyses were used to quantity functional activation in the mesial temporal and frontal lobes. The patients' verbal and visual memory performances were evaluated by standardized neuropsychological tests. Analyses included group comparison and correlations of duration of epilepsy with functional activation and memory performance.

RESULTS

Compared with normal controls, TLE patients demonstrated reduced activation bilaterally in the mesial temporal lobe (p=0.003), and the reduction was more pronounced on the ipsilateral side of the seizure focus. Moreover, a longer duration of illness was associated with fewer voxels activated in both the left (p=0.038) and right (p=0.017) mesial temporal lobe. Furthermore, the duration of illness was found to be significantly and negatively correlated with both verbal (p=0.020) and visual (p=0.000) memory functioning.

CONCLUSIONS

TLE seems to affect the memory processes in the mesial temporal lobes progressively (i.e., the longer the duration of illness, the lower the brain activation). In turn, the reduction of brain activation negatively affects memory functioning. Finally, the reduction is not limited to the side of seizure but also is observed in the contralateral hemisphere.

PET imaging of glucose metabolism in a mouse model of temporal lobe epilepsy

Here we present the first demonstration that 2-deoxy-2[18F]fluoro-D-glucose (18FDG) and micro Positron Emission Tomography (microPET) can be used successfully to monitor regional changes in brain metabolism during acute seizure induction in C57Bl/6 mice. These longitudinal studies show a significant increase in 18FDG uptake in the hippocampus (33.2%) which correlates directly with seizure severity (R2=0.86). 18FDG microPET can potentially be used to monitor the development of TLE in mouse models from the acute phase of status epilepticus to the chronic phase of spontaneous recurrent seizures. These studies provide a foundation upon which we can begin to identify genetic contributions to the metabolic signature of TLE in mice, since many transgenics are in the C57Bl/6 background strain.

Older adults with epilepsy demonstrate cognitive impairments compared with patients with amnestic mild cognitive impairment

Little is known about the cognitive effects of chronic epilepsy in older adults. To better characterize cognitive impairment in seniors with epilepsy, we compared cognitive performance of 26 seniors with epilepsy with that of 26 well-matched patients with mild cognitive impairment (MCI) and 26 well-matched healthy older adults. Participants completed neuropsychological testing with the Dementia Rating Scale (DRS), Logical Memory, and CFL Word Fluency. There were no significant demographic group differences, although seniors with epilepsy had higher self-reported depression. Seniors with epilepsy performed below controls on virtually all neuropsychological tests, and performed below patients with MCI on DRS Total score, Initiation/Perseveration, and CFL Fluency. Seniors with epilepsy on antiepileptic drug (AED) polytherapy had the most severe cognitive deficits, whereas seniors with epilepsy on AED monotherapy were comparable to cholinesterase inhibitor-naïve patients with MCI. This study emphasizes the clinical importance of cognitive impairment in seniors with epilepsy and highlights the need for future studies addressing causes and treatment of cognitive impairment.

The myth of silent cortex and the morbidity of epileptogenic tissue: implications for temporal lobectomy

This article reviews two commonly held myths regarding temporal lobe epilepsy-it is a static disorder with minimal morbidity and mortality, and epileptogenic tissue impairs only the functions of the seizure focus-and one myth concerning temporal lobe functions-they contain areas of nonfunctional, "silent" cortex. Chronic temporal lobe epilepsy can cause progressive structural, cognitive, and behavioral changes. Aside from the seizure focus, primary epileptogenic cortex may have a deleterious influence on distant brain areas. Removing this "nociferous" cortex and reducing the antiepileptic drug burden can improve cognitive or behavioral and metabolic function in areas remote from the resection. Anterior temporal lobectomy often removes functional tissue that may or may not be epileptogenic. Because normal brain does not contain functionless, "silent" areas, the procedure can have negative as well as positive cognitive or behavioral consequences. To improve the outcomes of focal cortical resections for seizure control, we need to better define functional and nociferous cortex and more clearly understand their boundaries and interactions.

Sickle cell disease: ischemia and seizures

Although the prevalence of seizures in children with sickle cell disease (SCD) is 10 times that of the general population, there are few prospectively collected data on mechanism. With transcranial Doppler and magnetic resonance imaging (MRI) and angiography, we evaluated 76 patients with sickle cell disease, 29 asymptomatic and 47 with neurological complications (seizures, stroke, transient ischemic attack, learning difficulty, headaches, or abnormal transcranial Doppler), who also underwent bolus-tracking perfusion MRI. The six patients with recent seizures also had electroencephalography. Group comparisons (seizure, nonseizure, and asymptomatic) indicated that abnormal transcranial Doppler was more common in the seizure (4/6; 67%) and nonseizure (26/41; 63%) groups than in the asymptomatic (10/29; 34%) group (chi2; p = 0.045), but abnormal structural MRI (chi2; p = 0.7) or magnetic resonance angiography (chi2; p = 0.2) were not. Relative decreased cerebral perfusion was found in all seizure patients and in 16 of 32 of the remaining patients with successful perfusion MRI (p = 0.03). In the seizure patients, the perfusion abnormalities in five were ipsilateral to electroencephalographic abnormalities; one had normal electroencephalogram results. These findings suggest that vasculopathy and focal hypoperfusion may be factors in the development of sickle cell disease-associated seizures.

The Prognostic Value of [18F]FDG-PET in Nonrefractory Partial Epilepsy

PURPOSE

Regional abnormalities of cerebral glucose metabolism, as identified by 18-fluorodeoxyglucose positron emission tomography (FDG-PET) have prognostic value regarding the outcome of epilepsy surgery in patients with refractory partial epilepsy. The value of FDG-PET abnormalities in nonrefractory patients has not been investigated systematically. This study examines whether FDG-PET could be used for early identification of nonrefractory epilepsy in patients who will become pharmacoresistant later during the course of their disease.

METHODS

We investigated interictal abnormalities of cerebral glucose metabolism by using FDG-PET in 125 consecutive patients with nonrefractory cryptogenic partial epilepsy and normal cranial magnetic resonance imaging (MRI), and we compared relative changes in seizure frequency in 90 patients after > or =2 years of follow-up.

RESULTS

Regional asymmetry of tracer distribution was seen in 43 of the 90 patients. Forty-one patients had regional glucose hypometabolism in the temporal and two patients in an extratemporal region. No difference between patients with and without a hypometabolic focus was found regarding seizure freedom after follow-up. This held true also for the subgroup of patients with epilepsy onset within 1 year before admission. Only patients with regional glucose metabolism showed an increase in seizure frequency. Multivariate analysis showed that only anticonvulsive treatment before index admission and the possibility of localizing the epileptogenic focus by using all available clinical and EEG data were independently associated with continuing seizures after a median follow-up period of 43 months.

CONCLUSIONS

Regional hypometabolism in FDG-PET is not significantly associated with a lower likelihood of successful anticonvulsant drug therapy in patients with nonrefractory partial epilepsy. Careful analysis of all routinely available clinical and neurophysiologic data has a much better predictive power to identify patients with medically refractory epilepsy early in the course of the disease. However, if PET data are available, they could help in identifying patients with a less benign course.

Metabolic Changes of Subcortical Structures in Intractable Focal Epilepsy

PURPOSE

Intractable focal epilepsy is commonly associated with cortical glucose hypometabolism on interictal 2-deoxy-2[18F]-fluoro-D-glucose (FDG) positron emission tomography (PET). However, subcortical brain structures also may show hypometabolism on PET and volume changes on magnetic resonance imaging (MRI) studies, and these are less well understood in terms of their pathophysiology and clinical significance. In the present study, we analyzed alterations of glucose metabolism in subcortical nuclei and hippocampus by using FDG-PET in young patients with intractable epilepsy.

METHODS

Thirty-seven patients (mean age, 7.5 years; age range, 1-27 years) with intractable frontal (n = 23) and temporal (n = 14) lobe epilepsy underwent FDG-PET scanning as part of their presurgical evaluation. Normalized glucose metabolism was measured in the thalamus and caudate and lentiform nuclei, as well as in hippocampus, both ipsi- and contralateral to the epileptic focus, and correlated with duration and age at onset of epilepsy, presence or absence of secondary generalization, location of the epileptic focus, and extent of cortical glucose hypometabolism.

RESULTS

Long duration of epilepsy was associated with lower glucose metabolism in the ipsilateral thalamus and hippocampus. Duration of epilepsy was a significant predictor of ipsilateral thalamic glucose metabolism in both temporal and frontal lobe epilepsy. Presence of secondarily generalized seizures also was associated with lower normalized metabolism in the ipsilateral thalamus and hippocampus. Extent of cortical hypometabolism did not correlate with subcortical metabolism, and glucose metabolism in the caudate and lentiform nuclei did not show any correlation with the clinical variables.

CONCLUSIONS

The findings suggest that metabolic dysfunction of the thalamus ipsilateral to the seizure focus may become more severe with long-standing temporal and frontal lobe epilepsy, and also with secondary generalization of seizures.

The role of positron emission tomography with [18F]fluorodeoxyglucose in the evaluation of the epilepsies

Cerebral glucose metabolic mapping using positron emission tomography (PET) and 2-[18F]fluoro-2-deoxyglucose (FDG) has been extensively studied in the epilepsies. Regions of interictal glucose hypometabolism are highly associated with cerebral sites of seizure generation-propagation in focal epilepsies. The volume of reduced glucose metabolism is often widespread and even bilateral in focal epilepsies, although ictal onset zones typically are located at the sites of most severe hypometabolism within a larger volume of hypometabolism.