Ictal motor signs and interictal regional cerebral hypometabolism

FDG-PET/MRI in the presurgical evaluation of pediatric epilepsy

In patients with drug-resistant epilepsy, difficulties in identifying the epileptogenic zone are well known to correlate with poorer clinical outcomes post-surgery. The integration of PET and MRI in the presurgical assessment of pediatric patients likely improves diagnostic precision by confirming or widening treatment targets. PET and MRI together offer superior insights compared to either modality alone. For instance, PET highlights abnormal glucose metabolism, while MRI precisely localizes structural anomalies, providing a comprehensive understanding of the epileptogenic zone. Furthermore, both methodologies, whether utilized through simultaneous PET/MRI scanning or the co-registration of separately acquired PET and MRI data, present unique advantages, having complementary roles in lesional and non-lesional cases. Simultaneous FDG-PET/MRI provides precise co-registration of functional (PET) and structural (MR) imaging in a convenient one-stop-shop approach, which minimizes sedation time and reduces radiation exposure in children. Commercially available fusion software that allows retrospective co-registration of separately acquired PET and MRI images is a commonly used alternative. This review provides an overview and illustrative cases that highlight the role of combining 18F-FDG-PET and MRI imaging and shares the authors' decade-long experience utilizing simultaneous PET/MRI in the presurgical evaluation of pediatric epilepsy.

Interictal Electroencephalography and Functional Magnetic Resonance Imaging Reveals Involvement of Mesial Anterior Frontal Structures in Patients With Hyperkinetic Semiology Type I

PURPOSE

This work investigates the presence of common anatomic regions associated with interictal activity in patients with hyperkinetic seizures type I by means of concurrent electroencephalography and functional magnetic resonance imaging.

METHODS

Six patients with hyperkinetic seizures type I were evaluated with video-EEG and electroencephalography and functional magnetic resonance imaging in the context of their presurgical evaluation. Statistical Parametric Mapping was used to perform a correlation study between the occurrence of interictal spikes on EEG and suprathreshold blood oxygen level-dependent changes in the whole-brain volume.

RESULTS

In all patients, Statistical Parametric Mapping revealed suprathreshold blood oxygen level-dependent clusters in the mesial anterior frontal areas, including the rostral mesial superior frontal gyrus and the anterior cingulate, associated with the patients' typical interictal activity.

CONCLUSIONS

The electroencephalography and functional magnetic resonance imaging findings contribute to our understanding of hyperkinetic seizures type I semiology generation and can inform stereo-EEG targeting for surgical planning in refractory cases.

The Role of SPECT and PET in Epilepsy

OBJECTIVE. The purpose of this article is to summarize the role of molecular imaging of the brain by use of SPECT, FDG PET, and non-FDG PET radiotracers in epilepsy. CONCLUSION. Quantitative image analysis with PET and SPECT has increased the diagnostic utility of these modalities in localizing epileptogenic onset zones. A multi-modal platform approach integrating the functional imaging of PET and SPECT with the morphologic information from MRI in presurgical evaluation of epilepsy can greatly improve outcomes.

Investigation of networks underlying hyperkinetic seizures utilizing ictal SPECT

Objective

To study neural networks involved in hyperkinetic seizures (HKS) using ictal SPECT.

Methods

We retrospectively identified 18 patients with HKS evaluated at the Cleveland Clinic between 2005 and 2015 with video-EEG monitoring and ictal SPECT. Semiology was confirmed by the consensus of 2 epileptologists' independent reviews and classified as type 1, 2, or 3 HKS. SPECT data were analyzed by 2 independent physicians using a z score of 1.5. Ictal hyperperfusion patterns for each group were analyzed visually and with SPM. Spatial normalization to Montreal Neurological Institute space for each patient’s data was performed, followed by flipping of data from patients with left-sided ictal onset to the right side. Finally, an average z score map for each group was calculated.

Results

Visual analysis and SPM identified different patterns of ictal hyperperfusion in the 3 subtypes of HKS. Type 1 seizures showed hyperperfusion in a more anteriorly located network involving the anterior insula, orbitofrontal cortex, cingulate, and anterior perisylvian region and rostral midbrain. Type 2 seizures were associated with hyperperfusion in a more caudally located network involving the orbitofrontal cortex, cingulate (middle and posterior), basal ganglia, thalami, and cerebellum. Type 3 seizures showed a mixed pattern of SPECT hyperperfusion involving the temporal pole and anterior perisylvian region.

Conclusions

Each of the 3 different semiologic subtypes of HKS is associated with distinct patterns of hyperperfusion, providing further insight into the neural networks involved. This knowledge may inform placement of invasive EEG electrodes in patients with HKS semiology undergoing presurgical evaluation.

Utility of MRI, PET, and ictal SPECT in presurgical evaluation of non-lesional pediatric epilepsy

Children with epilepsy and normal structural MRI pose a particular challenge in localization of epileptic foci for surgical resection. Many of these patients have subtle structural lesions such as mild cortical dysplasia that can be missed by conventional MRI but may become detectable by optimized and advanced MRI acquisitions and post-processing. Specificity of objective analytic techniques such as voxel-based morphometry remains an issue. Combination of MRI with functional imaging approaches can improve the accuracy of detecting epileptogenic brain regions. Analysis of glucose positron emission tomography (PET) combined with high-resolution MRI can optimize detection of hypometabolic cortex associated with subtle cortical malformations and can also enhance presurgical evaluation in children with epileptic spasms. Additional PET tracers may detect subtle epileptogenic lesions and cortex with enhanced specificity in carefully selected subgroups with various etiologies; e.g., increased tryptophan uptake can identify epileptogenic cortical dysplasia in the interictal state. Subtraction ictal SPECT can be also useful to delineate ictal foci in those with non-localizing PET or after failed surgical resection. Presurgical delineation of language and motor cortex and the corresponding white matter tracts is increasingly reliable by functional MRI and DTI techniques; with careful preparation, these can be useful even in young and sedated children. While evidence-based pediatric guidelines are still lacking, the data accumulated in the last decade strongly indicate that multimodal imaging with combined analysis of MRI, PET, and/or ictal SPECT data can optimize the detection of subtle epileptogenic lesions and facilitate seizure-free outcome while minimizing the postsurgical functional deficit in children with normal conventional MRI.

Semiology of hypermotor (hyperkinetic) seizures

BACKGROUND

Hypermotor seizures (HMSs) consist of complex movements involving proximal segments of the limbs and trunk that appear violent and inappropriate for the situation.

METHODS

We analyzed hypermotor seizure videos in seizure-free patients (Engel class I) following resective epilepsy surgery. After completion of video analysis, we reviewed EEG and neuroimaging data.

RESULTS

Search of our epilepsy surgery database yielded 116 patients classified as having hypermotor seizures between 1996 and 2013. From this subset, 17/31 (55%) patients had been seizure-free for >6months (mean follow-up: 3.3years). Mean seizure duration was 35s (range: 6-91s), of which the HM phase lasted a mean of 22s (range: 3-53s). In 16 patients (95%), hypermotor activity was seen at or within 10s of clinical seizure onset. Type I semiology occurred in 6 patients, type II semiology in 10 patients, and 1 patient exhibited features of both. Type I and type II semiologies were noted in patients who had frontal lobe as well as extrafrontal resections. Nonversive head and body turning occurred in 10 patients (ranging from 90° to 270°) which was ipsilateral to the side of resection in all patients and seen both in frontal and extrafrontal resections. Six out of eleven patients with abnormal MRI and 4/6 patients with nonlesional MRI underwent invasive EEG evaluation. Eight patients (47%) had frontal lobe resection, 4/17 (23%) patients had temporal lobe resection, and one patient each had parietal lobe, insular, temporoparietooccipital, or motor sparing resection; 1 patient had functional hemispherectomy.

CONCLUSION

Hypermotor semiology typically occurs at or within 10s after seizure onset. Ipsilateral head/body turning appears to be of lateralizing value whereas asymmetry of limb movement was not lateralizing. Hypermotor semiology is most often seen in frontal lobe epilepsy but may occur in seizures arising from other locations.

Sustained Reduction of Cerebellar Activity in Experimental Epilepsy

Clinical and experimental evidence suggests a role for the cerebellum in seizure control, while no data are available on cerebellar activity between seizures. We hypothesized that interictal regional activity of the deep cerebellar nuclei is reduced in epilepsy and tested this in an animal model by using ΔFosB and cytochrome oxidase (COX) (immuno)histochemistry. The expression of these two markers of neuronal activity was analysed in the dentate nucleus (DN), interpositus nucleus (IN), and fastigial nucleus (FN) of the cerebellum of fully amygdala kindled rats that were sacrificed 48 hours after their last seizure. The DN and FN of kindled rats exhibited 25 to 29% less ΔFosB immunopositive cells than their respective counterpart in sham controls (P < 0.05). COX expression in the DN and FN of kindled animals was reduced by 32 to 33% compared to respective control values (P < 0.05). These results indicate that an epileptogenic state is characterized by decreased activity of deep cerebellar nuclei, especially the DN and FN. Possible consequences may include a decreased activation of the thalamus, contributing to further seizure spread. Restoration of FN activity by low frequency electrical stimulation is suggested as a possible treatment option in chronic epilepsy.

Metabolic changes in occipital lobe epilepsy with automatisms

PURPOSE

Some studies suggest that the pattern of glucose hypometabolism relates not only to the ictal-onset zone but also reflects seizure propagation. We investigated metabolic changes in patients with occipital lobe epilepsy (OLE) that may reflect propagation of ictal discharge during seizures with automatisms.

METHODS

Fifteen patients who had undergone epilepsy surgery for intractable OLE and had undergone interictal Fluorine-18-fluorodeoxyglucose positron-emission tomography ((18)F-FDG-PET) between 1994 and 2004 were divided into two groups (with and without automatisms during seizure). Significant regions of hypometabolism were identified by comparing (18)F-FDG-PET results from each group with 16 healthy controls by using statistical parametric mapping.

KEY FINDINGS

Significant hypometabolism was confined largely to the epileptogenic occipital lobe in the patient group without automatisms. In patients with automatisms, glucose hypometabolism extended from the epileptogenic occipital lobe into the ipsilateral temporal lobe.

SIGNIFICANCE

We identified a distinctive hypometabolic pattern that was specific for OLE patients with automatisms during a seizure. This finding supports the postulate that seizure propagation is a cause of glucose hypometabolism beyond the region of seizure onset.

The impact of positron emission tomography imaging on the clinical management of patients with epilepsy

Clinical positron emission tomography (PET) imaging of human epilepsy has a 30-year history, but it is still searching for its exact role among rapidly advancing neuroimaging techniques. The vast majority of epilepsy PET studies used this technique to improve detection of epileptic foci for surgical resection. Here, we review the main trends emerging from three decades of PET research in epilepsy, with a particular emphasis on how PET imaging has impacted on the clinical management of patients with intractable epilepsy. While reviewing the latest studies, we also present an argument for a changing role of PET and molecular imaging in the future, with an increasing focus on epileptogenesis and newly discovered molecular mechanisms of epilepsy. These new applications will be facilitated by technological advances, such as the use of integrated PET/MRI systems and utilization of novel radiotracers, which may also enhance phenotype-genotype correlations and assist rational, individualized treatment strategies.

Psychogenic nonepileptic seizures

Psychogenic nonepileptic seizures (PNES) are clinical events resembling epileptic seizures but lacking abnormal cortical electrical discharges. They are involuntary manifestations of a psychological distress. PNES are less frequent in the pediatric population than in adults, they represent from 3.5 to 9% of patients admitted for prolonged video-EEG (PV-EEG). Diagnosis is rarely made on history only and PV-EEG is mandatory to obtain a definitive diagnosis. Children as young as 5 years can present with PNES. They are more frequent in girls except in school age children where boys are identically or more represented than girls. PNES can either present with subtle signs, even unresponsiveness, or prominent motor activity. Major differential diagnosis is absences, day dreaming, and complex partial seizures including hyperkinetic frontal seizures. PNES are usually rapidly registered during PV-EEG and provocative methods have not been thoroughly studied in children. Major risk factors are psychological stressors, such as school or family problems. Psychiatric conditions are less frequent than in adults though they should be looked for. Prognosis is better than in adults, and most children become PNES-free. There are no guidelines for treatment, however stressors should be addressed. In general, it should be clearly explained that PNES are not epileptic seizures.

Physiopathogenetic Interrelationship between Nocturnal Frontal Lobe Epilepsy and NREM Arousal Parasomnias

Aims. To build up a coherent shared pathophysiology of NFLE and AP and discuss the underlying functional network. Methods. Reviewing relevant published data we point out common features in semiology of events, relations to macro- and microstructural dynamism of NREM sleep, to cholinergic arousal mechanism and genetic aspects. Results. We propose that pathological arousals accompanied by confused behavior with autonomic signs and/or hypermotor automatisms are expressions of the frontal cholinergic arousal function of different degree, during the condition of depressed cognition by frontodorsal functional loss in NREM sleep. This may happen either if the frontal cortical Ach receptors are mutated in ADNFLE (and probably also in genetically not proved nonlesional cases as well), or without epileptic disorder, in AP, assuming gain in receptor functions in both conditions. This hypothesis incorporates the previous “liberation theory” of Tassinari and the “state dissociation hypothesis” of Bassetti and Terzaghi). We propose that NFLE and IGE represent epileptic disorders of the two antagonistic twin systems in the frontal lobe. NFLE is the epileptic facilitation of the ergotropic frontal arousal system whereas absence epilepsy is the epileptic facilitation of burst-firing working mode of the spindle and delta producing frontal thalamocortical throphotropic sleep system. Significance. The proposed physiopathogenesis conceptualize epilepsies in physiologically meaningful networks.

[The medial temporal area and parietal lobe are involved in epileptic polyopia and palinopsia: A case report]

This report presents the case of an 83-year-old female with a tumor in the right temporal lobe. She experienced various epileptic visual auras including visual perseveration. Visual perseveration is classified into polyopia and palinopsia. Epileptic visual perseveration is a rare phenomenon, and the mechanism has not been fully explained. MRI revealed a tumor in the right temporal lobe with edema in the occipital white matter. To reveal mechanisms of epileptic polyopia and palinopsia, we recorded EEG and (123)I-IMP-SPECT when she experienced epileptic attacks. EEG showed epileptic discharges beginning at the occipital area, which spread to the temporal and parietal areas. During the EEG recording, the main symptom was an unformed hallucination. SPECT showed that blood flow increased in the right medial temporal and parietal lobes and, to a slightly lesser extent, in the right occipito-temporal area when the polyopia and palinopsia frequently appeared. Involvement of the multiple foci may have caused the different kinds of visual symptoms. The medial temporal and parietal areas were likely responsible for polyopia and palinopsia at least for this patient.

Nocturnal Frontal Lobe Epilepsy

Nocturnal frontal lobe epilepsy (NFLE) is a condition primarily characterized by seizures occurring exclusively or predominantly during sleep, the semiology of which suggest a frontal lobe origin and, more specifically, the involvement of the orbitofrontal or mesial frontal regions. It is usually considered as a relatively benign and homogeneous epileptic syndrome, the neuropsychological impact of which should be minimal. However, several issues complicate this view. 1. NFLE is rather a heterogeneous disorder which includes both sporadic and familial forms, various seizure types, and drug resistance in about 30% of patients. 2. The frontal origin of seizures has rarely been demonstrated, and mainly relies on the presence of ictal signs suggestive of frontal lobe epilepsy, but which might only reflect the propagation of ictal discharges of extrafrontal origin. 3. NFLE-like seizures were recently found to be associated with temporobasal cortical dysplasia, or an insular epileptogenic zone, including one patient with autosomal dominant frontal lobe epilepsy (ADNFLE). 4. No study has yet specifically evaluated the neuropsychological profile of patients with NFLE. Available data suggest that behavioral problems and mental retardation might be associated with ADNFLE, especially when it is related to a mutation of the nicotinic receptor subunits. Conversely, the majority of NFLE patients does not seem to present with gross cognitive disturbance, even though many of these patients complain of chronically disrupted sleep and daytime sleepiness. Further research is warranted in this field, keeping in mind that the neural networks underlying NFLE remain poorly known and might primarily involve extrafrontal brain regions in some patients.

Epileptic polyopia with right temporal lobe epilepsy as studied by FDG-PET and MRI: a case report

Polyopia is one of rare, visual hallucinations. A 61-year-old man suffered from daily episodes of polyopia and generalized convulsions, and he was diagnosed as right temporal lobe epilepsy. MRI revealed right amygdalar swelling. FDG-PET showed hypometabolism in the right anterior temporal and the mesial occipital areas. Polyopia is thought to be caused by dysfunction of updating process of visual information in the visual association cortices. It was most likely that, in this patient, both mesial temporal and ipsilateral occipital areas were responsible for manifesting epileptic polyopia, as ictal onset zone and symptomatogenic zone, respectively.

Nocturnal Hypermotor Seizures, Suggesting Frontal Lobe Epilepsy, Can Originate in the Insula

PURPOSE

To report three patients with drug-resistant nocturnal hypermotor seizures (NHSs), no detectable brain lesion, and clinically defined nocturnal frontal lobe epilepsy (NFLE) or autosomal dominant NLFE (ADNFLE), whose intracerebral EEG ictal onset primarily involved the insula, rather than the mesial or orbital frontal cortex.

METHODS

Fourteen to 15 intracerebral electrodes were implanted in each patient, primarily sampling the frontal lobes with 80 to 91 recording leads covering the most likely side of seizure onset, and two to six leads placed within the ipsilateral insula. Electrical stimulation was used to test the epileptic threshold of frontal and insular brain regions at the various recording sites.

RESULTS

In all three patients, a low-voltage fast activity was recorded within the anterosuperior aspect of the insula at ictal onset, either in isolation, or extending to the nearby frontal operculum in the ADNFLE patient. The role of the insula was further supported in all three patients either by the presence of high-amplitude spikes that clearly predominated over that region (n = 2) or by triggering the patient's typical aura or seizure when applying an electrical stimulation at that site, selectively (n = 2).

CONCLUSIONS

The anterosuperior portion of the insula might play a pivotal role in generating nocturnal hypermotor seizures in some patients with nonlesional drug-resistant epilepsy suggesting NFLE or ADNFLE. Whether these patients are amenable to successful surgery remain an open issue.

Atypical language representation in epilepsy: implications for injury-induced reorganization of brain function

This review addresses language function and reorganization associated with various forms of epilepsy. Longstanding epilepsy, particularly types with onset early in life, may be associated with changes in the representation of language function in the brain. As a result of this reorganization, language function may be relatively spared despite injury to areas of the brain that normally subserve these functions. We examine the changes seen in language function in two types of epilepsy: hemispheric epilepsy of childhood and focal epilepsies. Findings from behavioral studies, intracarotid amytal testing, intraoperative cortical testing, and more recent functional imaging studies are reviewed. Studying changes in the representation of language function seen in some forms of epilepsy provides information about brain plasticity with implications for other neurologic diseases, as well as for the neuroscientific understanding of how and when functional reorganization may occur.

Hyperkinetic seizures in children

The objective of this study was to delineate the clinical and video-electroencephalographic (EEG) manifestations of children with complex partial seizures with a predominant "hyperkinetic" presentation. Certain types of partial seizures can be difficult to differentiate from nonepileptic seizures because of their intense motor presentation and, at times, lack of alteration of consciousness. Based on a published semiologic seizure classification, this type of seizures can be described as "hyperkinetic," characterized by intense motor activity involving the extremities and trunk. We report five children diagnosed with hyperkinetic seizures by video-EEG monitoring. All patients were referred for video-EEG evaluation because of an initial suspicion of pseudoseizures. Presented in this study is a review of the patients' clinical data, including video-EEG evaluation. There were three boys and two girls; the mean age at presentation was 10 +/- 3 years. In four patients, there was a history of behavioral disorder, with two patients carrying a diagnosis of attention-deficit hyperactivity disorder (ADHD). One girl had significant developmental delay and an abnormal neurologic examination. Brain magnetic resonance imaging was normal in three patients and abnormal in two. The semiology of the seizures consisted of stereotypic intense motor activity, mainly upper extremity flailing and kicking. Screaming and shouting were noted in three cases, and intense fear was present in two patients. The hyperkinetic ictal activity progressed to tonic-clonic seizures in two patients. Seizures occurred out of sleep or on awakening in four patients. The interictal EEG activity was normal in one patient and revealed a continuous generalized slowing and slowing of the posterior dominant rhythm in two patients. One of the latter patients had interictal epileptiform activity in the frontal and midline regions. An intermittent rhythmic slow activity of the left hemisphere with superimposed bifrontal sharp waves was noted in the fifth patient. The ictal EEG revealed profuse superimposed electromyographic (EMG) activity in all patients, making some of the EEG interpretation difficult to analyze, particularly a longitudinal bipolar montage. However, with digital manipulation of the ictal EEG data, such as changes in EEG sensitivity, application of fast frequency filters, and use of different EEG montages, it was possible to discern an ictal EEG pattern or postictal slowing following the diffuse EMG artifact in all patients. On clinical follow-up, adequate seizure control was achieved in three patients. Based on the clinical history, one patient was diagnosed with autosomal dominant nocturnal frontal lobe epilepsy. Diagnosis of hyperkinetic seizures can be difficult because of the similarity of the clinical manifestations with nonepileptic events such as certain parasomnias and pseudoseizures. Video-EEG is the most effective way of diagnosing this type of seizure.

Temporal lobe epilepsy with sensory aura: interictal glucose hypometabolism

Patients with mesial temporal lobe epilepsy (mTLE) exhibit marked depressions of the regional cerebral glucose metabolism (rCMRGlu) in the mesiotemporal region. We hypothesised that patients with temporal lobe epilepsy (TLE) who have a bilateral somatosensory or acoustic ( = temporolateral/SII-) aura can be differentiated from mTLE by rCMRGlu depressions primarily involving temporo-perisylvian locations. We therefore used this ictal semiology as a clinical criterion to define a subgroup of such patients and measured the rCMRGlu in 16 patients with TLE as evident from interictal and ictal EEG-video monitoring. Clinically, they presented with medically refractory complex partial seizures and were subjected to presurgical evaluation. The pattern of the interictal rCMRGlu in the TLE patients was different from that observed in patients with mTLE and showed significant depressions ipsilateral to the epileptic focus in mesial temporal and lateral temporal regions but spared the thalamus. The neocortical metabolic depressions were spatially more extended in right than in left TLE patients. Magnetic resonance images (MRI) were either normal (n = 5) or revealed unilateral or bilateral hippocampal atrophy/sclerosis (n = 7), or temporal or extratemporal focal cortical dysplasia (n = 4). The selected TLE patients presented here comprise a heterogeneous group showing most pronounced metabolic depressions in the lateral temporal cortex. Thus, our data suggest that non-invasive metabolic imaging can assist in identifying the neocortical symptomatogenic zone in putative temporo-perisylvian lobe epilepsy.

Uncoupling of blood flow and metabolism in focal epilepsy

PURPOSE

Interictal measurements of cerebral blood flow are less helpful in localizing epileptic foci than are measurements of brain metabolism. This may be related to an uncoupling of blood flow and metabolism. In this study, brain metabolism and blood flow were compared in an acute experimental model of focal interictal epilepsy.

METHODS

Interictal epileptic foci were induced by an epicortical application of penicillin in rats. After 1 h, stereotyped interictal activity was initiated, lasting until the end of the experiment. Brain metabolism was determined with [14C]deoxyglucose, and cerebral blood flow with [14C]iodoan-tipyrine autoradiography.

RESULTS

In control experiments, metabolism and blood flow were coupled. In animals with focal interictal epileptic activity, the metabolism was strongly increased in the focus and reduced in areas lateral to the focus. In contralateral brain areas, blood flow and metabolism varied in a parallel fashion. Ipsilateral to the focus, however, blood flow and metabolism were altered disproportionately. In the focus, the increase of blood flow was less marked than the increase of metabolism, and the area with increased blood flow was larger than the area with increased metabolism. Lateral to the focus, in the area with a hypometabolism, blood flow was not concomitantly reduced.

CONCLUSIONS

The experiments show that blood flow and metabolism in focal epilepsy may be uncoupled in widespread regions. This is due neither to structural abnormalities nor to the duration or discharge pattern of epileptic activity. The results explain why interictal metabolic investigations have a higher predictive value in presurgical epilepsy evaluation than do interictal measurements of blood flow.

Thalamocortical circuits causing remote hypometabolism during focal interictal epilepsy

The functional circuit causing depression of cerebral glucose metabolism in brain areas remote from an epileptic focus was investigated in experiments on the cortex of the rat. Epileptic activity was induced by direct epicortical application of Na-penicillin onto the motor cortical area Fr1/Fr2. The increased neuronal activity was associated with an increase of metabolism in the focal area and a decrease in somatosensory cortical areas. Metabolism was also massively increased in the thalamus, predominantly in the posterior nucleus. Stereotactic radiofrequency lesioning of this nucleus, 30 days prior to the induction of the epileptic focus, restricted the area with increase of metabolism to the upper cortical laminae, and abolished the cortical hypometabolism in the sensory cortex. It is suggested that the primary functional circuit affected by the acute epileptic focus in the present model consists of the motor cortex, the thalamic nucleus posterior and the somatosensory cortex.

Interictal regional slow activity in temporal lobe epilepsy correlates with lateral temporal hypometabolism as imaged with 18FDG PET: neurophysiological and metabolic implications

OBJECTIVES

The phenomenon of interictal regional slow activity (IRSA) in temporal lobe epilepsy and its relation with cerebral glucose metabolism, clinical data, MRI, and histopathological findings was studied.

METHODS

Interictal 18F-fluorodeoxyglucose positron emission tomography (FDG PET) was performed under continuous scalp EEG monitoring in 28 patients with temporal lobe epilepsy not associated with intracranial foreign tissue lesions, all of whom subsequently underwent resective surgery. Regions of interest (ROIs) were drawn according to a standard template. IRSA was considered lateralised when showing a 4:1 or greater ratio of predominance on one side.

RESULTS

Sixteen patients (57%) had lateralised IRSA which was always ipsilateral to the resection and of maximal amplitude over the temporal areas. Its presence was significantly related to the presence of hypometabolism in the lateral temporal neocortex (p=0.0009). Logistic regression of the asymmetry indices for all measured cerebral regions confirmed a strong association between IRSA and decreased metabolism of the posterior lateral temporal neocortex only (p=0.009). No significant relation could be shown between slow activity and age at onset, duration of the epilepsy, seizure frequency, and MRI evidence for hippocampal atrophy. Furthermore, IRSA was not specifically related to mesial temporal sclerosis or any other pathology.

CONCLUSIONS

Interictal regional slowing in patients with temporal lobe epilepsy not associated with a mass lesion is topographically related to the epileptogenic area and therefore has a reliable lateralising, and possibly localising, value. Its presence is irrelevant to the severity or chronicity of the epilepsy as well as to lateral deactivation secondary to neuronal loss in the mesial temporal structures. Although slow EEG activity is generally considered as a non-specific sign of functional disturbance, interictal regional slowing in temporal lobe epilepsy should be conceptualised as a distinct electrographic phenomenon which is directly related to the epileptogenic abnormality. The strong correlation between interictal regional slowing and lateral temporal hypometabolism suggests in turn that the second may delineate a field of reduced neuronal inhibition which can receive interictal and ictal propagation.

Mesial frontal epilepsy

The mesiofrontal cortex comprises a number of distinct anatomic and functional areas. Structural lesions and cortical dysgenesis are recognized causes of mesial frontal epilepsy, but a specific gene defect may also be important, as seen in some forms of familial frontal lobe epilepsy. The predominant seizure manifestations, which are not necessarily strictly correlated with a specific ictal onset zone, are absence, hypermotor, and postural tonic seizures. Other seizure types also occur. The task of localization of the epileptogenic zone can be challenging, whether EEG or imaging methods are used. Successful localization can lead to a rewarding outcome after epilepsy surgery, particularly in those with an imaged lesion.

Brain hypometabolism in a model of chronic focal epilepsy in rat neocortex

PURPOSE

Metabolic mapping of the human brain has become a widely used method for identifying and localizing epileptic foci. A reduction of glucose consumption usually is found interictally in the area of the focus. By contrast, animal models of acute epilepsy show a hypermetabolism in the epileptic focus. Here we investigated how metabolism is altered in an animal model of chronic epilepsy caused by focal injection of tetanus toxin into rat neocortex.

METHODS

A total of 27 male Wistar rats were anesthetized and injected into the motor or sensory cortex either with dissolved tetanus toxin or with the solvent only. Animals recovered for 7, 14, or 30 days and then were anesthetized again for quantitative 14C-deoxyglucose autoradiography. Data were analyzed with an imaging program, and regional cerebral glucose metabolism (rCMRGlc) was determined.

RESULTS

Injection of tetanus toxin into the motor cortex caused a focal hypometabolism which was confined to the cytoarchitectonic boundaries of the injected area, whereas sensory cortex injection caused a more widespread hypometabolism in all sensory cortical and connected, areas. None of the animals displayed focal hypermetabolism and we observed no significant time-dependent alteration of brain metabolism.

CONCLUSIONS

Tetanus toxin injection into the cortex of the rat induces chronic epileptic activity accompanied by a focal hypometabolism. The data suggest that the spread of the metabolic alterations depends on the connectivity of the injected cortical area.