Identification of abnormal neuronal metabolism outside the seizure focus in temporal lobe epilepsy

Simultaneous high-resolution whole-brain MR spectroscopy and [18F]FDG PET for temporal lobe epilepsy

PURPOSE

Precise lateralizing the epileptogenic zone in patients with drug-resistant mesial temporal lobe epilepsy (mTLE) remains challenging, particularly when routine MRI scans are inconclusive (MRI-negative). This study aimed to investigate the synergy of fast, high-resolution, whole-brain MRSI in conjunction with simultaneous [18F]FDG PET for the lateralization of mTLE.

METHODS

Forty-eight drug-resistant mTLE patients (M/F 31/17, age 12-58) underwent MRSI and [18F]FDG PET on a hybrid PET/MR scanner. Lateralization of mTLE was evaluated by visual inspection and statistical classifiers of metabolic mappings against routine MRI. Additionally, this study explored how disease status influences the associations between altered N-acetyl aspartate (NAA) and FDG uptake using hierarchical moderated multiple regression.

RESULTS

The high-resolution whole-brain MRSI data offers metabolite maps at comparable resolution to [18F]FDG PET. Visual examinations of combined MRSI and [18F]FDG PET showed an mTLE lateralization accuracy rate of 91.7% in a 48-patient cohort, surpassing routine MRI (52.1%). Notably, out of 23 MRI-negative mTLE, combined MRSI and [18F]FDG PET helped detect 19 cases. Logistical regression models combining hippocampal NAA level and FDG uptake improved lateralization performance (AUC=0.856), while further incorporating extrahippocampal regions such as amygdala, thalamus, and superior temporal gyrus increased the AUC to 0.939. Concurrent MRSI/PET revealed a moderating influence of disease duration and hippocampal atrophy on the association between hippocampal NAA and glucose uptake, providing significant new insights into the disease's trajectory.

CONCLUSION

This paper reports the first metabolic imaging study using simultaneous high-resolution MRSI and [18F]FDG PET, which help visualize MRI-unidentifiable lesions and may thus advance diagnostic tools and management strategies for drug-resistant mTLE.

White matter network disorder in mesial temporal epilepsy: An fMRI study

Mesial temporal lobe epilepsy (mTLE) has been considered a network disorder disease in which brain regions extending beyond the epileptogenic zones are always affected. However, abnormalities in white matter (WM) functional networks and their associations with widespread network dysfunction are still being identified in mTLE. Accordingly, we investigated the altered functional activities in WM networks in mTLE using fMRI, which has recently been used to probe WM function. We collected resting-state fMRI data from 39 unilateral mTLE patients with hippocampal sclerosis and 29 healthy controls. Eleven WM networks were clustered according to temporal correlation profile. The functional connectivity (FC) of the WM networks were evaluated and compared between the two groups. Furthermore, we assessed the capacity of WM FC for seizure lateralization. According to our analysis, mTLE led to decreased FC within deep WM networks. In addition, the cortical regions involved in seizure propagation and several brain regions displaying interhemispheric disruption showed enhanced functional coupling with deep WM networks. FCs between the ipsilateral deep WM networks and the insula, temporal lobe, and supramarginal gyrus demonstrated positive correlation with seizure frequency. Moreover, the seizure onset zones of 33 patients out of 39 patients could be correctly lateralized. Our findings reveal functional disruptions in WM networks extending to extratemporal regions, supporting the network disorder hypothesis and suggesting that deep WM networks are key network nodes associated with massive dysfunction in mTLE. Moreover, the FC of the WM represents a potentially useful functional imaging measure for the diagnosis of mTLE.

Cognitive task-related functional connectivity alterations in temporal lobe epilepsy

OBJECTIVE

We investigated cognitive task-related functional connectivity (FC) in patients with temporal lobe epilepsy (TLE). Using a visual three-stimulus paradigm (VTSP), we studied cognitive large-scale networks and the impact of TLE on connectivity outside the temporal lobe.

METHODS

High-density electroencephalography (EEG) was recorded during the paradigm from nineteen patients with epilepsy with hippocampal sclerosis (HS) and ten healthy controls (HCs). Scalp data were reconstructed into the source space, and FC was computed. Correlating with the neuropsychological data, possible compensatory mechanisms were investigated.

RESULTS

Significant changes were found in the FC of regions outside the epileptogenic network, particularly in the attentional network. These changes were more widespread in left TLE (LTLE). There were no significant differences in task performance (accuracy, time response) in comparison with HCs, implying that there must be some mechanism reducing the impact of connectivity changes on brain functions. When correlated with neuropsychological data, we found stronger compensatory mechanisms in right TLE (RTLE).

SIGNIFICANCE

Our findings confirm the hypothesis that LTLE is the more pervasive form of the disease. Even though the network alterations in TLE are severe, some mechanisms reduce the impact of epilepsy on cognitive functions; these mechanisms are more potent in RTLE. We also suggest that there are maladaptive mechanisms in LTLE.

Seizures and brain regulatory systems: consciousness, sleep, and autonomic systems

Research into the physiologic underpinnings of epilepsy has revealed reciprocal relationships between seizures and the activity of several regulatory systems in the brain. This review highlights recent progress in understanding and using the relationships between seizures and the arousal or consciousness system, the sleep-wake and associated circadian system, and the central autonomic network.

The anticonvulsant actions of carisbamate associate with alterations in astrocyte glutamine metabolism in the lithium-pilocarpine epilepsy model

As reported previously, in the lithium-pilocarpine model of temporal lobe epilepsy (TLE), carisbamate (CRS) produces strong neuroprotection, leads to milder absence-like seizures, and prevents behavioral impairments in a subpopulation of rats. To understand the metabolic basis of these effects, here we injected 90 mg/kg CRS or vehicle twice daily for 7 days starting 1 h after status epilepticus (SE) induction in rats. Two months later, we injected [1-¹³ C]glucose and [1,2-¹³ C]acetate followed by head microwave fixation after 15 min. ¹³ C incorporation into metabolites was analyzed using ¹³ C magnetic resonance spectroscopy. We found that SE reduced neuronal mitochondrial metabolism in the absence but not in the presence of CRS. Reduction in glutamate level was prevented by CRS and aspartate levels were similar to controls only in rats displaying absence-like seizures after treatment [CRS-absence-like epilepsy (ALE)]. Glutamine levels in CRS-ALE rats were higher compared to controls in hippocampal formation and limbic structures while unchanged in rats displaying motor spontaneous recurrent seizures after treatment (CRS-TLE). Astrocytic mitochondrial metabolism was reduced in CRS-TLE, and either enhanced or unaffected in CRS-ALE rats, which did not affect the transfer of glutamine from astrocytes to neurons. In conclusion, CRS prevents reduction in neuronal mitochondrial metabolism but its effect on astrocytes is likely key in determining outcome of treatment in this model. To understand the metabolic basis of the strong neuroprotection and reduction in seizure severity caused by carisbamate (CRS) in the lithium-pilocarpine (Li-Pilo) model of temporal lobe epilepsy (TLE), we injected CRS for 7 days starting 1 h after status epilepticus and 2 months later [1-¹³ C]glucose and [1,2-¹³ C]acetate. ¹³ C Magnetic resonance spectroscopy analysis was performed on brain extracts and we found that CRS prevented reduction in neuronal mitochondrial metabolism but its effect on astrocytes was likely key in determining outcome of treatment in this model. ALE = absence like epilepsy; acetyl CoA = acetyl coenzyme A; GS = glutamine synthetase; PAG = phosphate activated glutaminase; PC = pyruvate carboxylase; OAA = oxaloacetate; TCA cycle = tricarboxylic acid cycle.

Altered Brain White Matter Integrity in Temporal Lobe Epilepsy: A TBSS Study

BACKGROUND AND PURPOSE

The aim of this study is to explore the possible changed cerebral white matter regions in patients with temporal lobe epilepsy (TLE) using diffusion tensor imaging (DTI) and tract-based spatial statistics (TBSS).

METHODS

Twenty TLE patients and 22 age- and gender-matched normal controls were included in this study. Voxel-wise analyses of multiple diffusion metrics, including fractional anisotropy (FA) and mean diffusivity (MD) were performed with TBSS.

RESULTS

TLE patients exhibited significantly reduced FA in widespread white matter regions including bilateral limbic circuit, corpus callosum, thalamus, internal/external capsule, temporooccipital connections, frontotemporal connections; increase of MD was exhibited significantly almost in the left hemisphere. A significant decrease in global FA integrity was shown in epilepsy subjects compared to healthy controls. Furthermore, it exhibited a significant positive correlation between the disease duration and MD of whole brain.

CONCLUSIONS

TLE is associated with widespread abnormalities in cerebral white matter tracts and these changes may have important clinical consequences.

Identifying the affected hemisphere with a multimodal approach in MRI-positive or negative, unilateral or bilateral temporal lobe epilepsy

Patients with non-lesional or bilateral temporal-lobe epilepsy (TLE) are often excluded from surgical treatment. This study investigated focus lateralization in TLE to understand identification of the affected hemisphere with regard to non-lesional or bilateral affection and postsurgical outcome. A total of 24 TLE patients underwent presurgical evaluation with magnetic resonance imaging (MRI), proton magnetic resonance spectroscopy ((1)H-MRS), video-electroencephalogram (video-EEG), and/or intracranial EEG (icEEG), and they were classified as MRI-positive or negative, unilateral or bilateral TLE cases. In patients with positive-MRI, MRI and (1)H-MRS indicated high (100%) concordant lateralization to EEG findings in unilateral TLE, and moderate (75%) concordance to icEEG findings in bilateral TLE; whereas in patients with negative-MRI, (1)H-MRS indicated moderate (60%-75%) concordance to EEG and/or icEEG in unilateral TLE, and relatively low (50%) concordance to icEEG in bilateral TLE. Ninety point nine percent of patients with unilateral TLE and 41.7% of patients with bilateral TLE (including 50% of MRI-negative bilateral TLE) became seizure-free. The MRS findings were not correlated with seizure outcome, while non-seizure-free patients had an insignificantly higher percentage of contralateral N-acetyl aspartate (NAA) reduction compared with seizure-free patients, indicating the relatively low predictive value of (1)H-MRS for surgical outcome. Further, EEG and icEEG findings were significantly correlated with seizure outcome, and for patients with positive MRI, MRI findings were also correlated with seizure outcome, indicating the predictive value of these modalities. The results suggested that a multimodal approach including neuroimaging, EEG, and/or icEEG could identify seizure focus in most cases, and provide surgical options for non-lesional or bilateral TLE patients with a possible good outcome.

Mesial temporal sclerosis is linked with more widespread white matter changes in temporal lobe epilepsy

Temporal lobe epilepsy patients with unilateral mesial temporal sclerosis (TLE + uMTS) have been demonstrated to have extensive white matter abnormalities both ipsilateral and contralateral to the seizure onset zone. However, comparatively less is known about the white matter integrity of TLE patients without MTS (non-lesional TLE, nl-TLE). The purpose of the study was to investigate the diffusion properties of thirteen major white matter tracts in patients with TLE + uMTS and nl-TLE. Diffusion tensor imaging (DTI) was performed on 23 TLE + uMTS (15 left MTS and 8 right MTS), 15 nl-TLE and 21 controls. Thirteen tracts were delineated by tractography and their diffusion parameters compared for the two TLE groups relative to controls, with left and right hemispheres combined per tract. A subgroup analysis investigated left and right MTS separately. Compared to controls, reduced anisotropy was detected in ten tracts for TLE + uMTS, but only the parahippocampal cingulum and tapetum for nl-TLE. Right MTS subgroup showed reduced anisotropy in 7 tracts bilaterally (3 limbic, 3 association, 1 projection) and 2 tracts ipsilaterally (1 association, 1 projection) and the body of the corpus callosum whereas the left MTS subgroup showed reduced anisotropy in 4 tracts bilaterally (2 limbic, 1 association, 1 projection) and 2 tracts ipsilaterally (1 limbic, 1 association). Diffusion abnormalities in tracts were observed within and beyond the temporal lobe in TLE + uMTS and were more widespread than in nl-TLE. Patients with right MTS had more extensive, bilateral abnormalities in comparison to left MTS. These findings suggest different dysfunctional networks in TLE patients with and without MTS.

Temporal pole proton preoperative magnetic resonance spectroscopy in patients undergoing surgery for mesial temporal sclerosis

OBJECT

The purpose of this prospective study was to compare the results of proton MR spectroscopy (MRS) in temporal poles in patients with unilateral mesial temporal sclerosis (MTS) with the histopathological findings of the resected temporal poles.

METHODS

A total of 23 patients (14 male and 9 female) with a mean age of 25.2 years (range 17-45 years) were included in this study, which was conducted over a 4-year period. All patients suffered medically refractory epilepsy due to unilateral, MRI-proven MTS, with no other imaging abnormalities. All participants underwent preoperative single-voxel proton MRS using a 3-T MRI unit. The hippocampi and temporal poles were examined bilaterally. The concentrations of N-acetyl-aspartate (NAA), choline (Cho), and creatine (Cr) were measured, and the NAA/Cho, NAA/Cr, and NAA/Cho+Cr ratios were calculated. All patients underwent anterior temporal lobectomy and ipsilateral amygdalohippocampectomy, and surgical specimens from the temporal poles were sent for histopathological examination. Comparisons of the spectroscopic and histopathological results of the resected temporal poles were performed. The modified Engel classification system was used for evaluating seizure outcome in the cohort.

RESULTS

The preoperative spectroscopic profiles of the sclerotic hippocampi were abnormal in all patients, and the contralateral hippocampus showed altered spectroscopic findings in 12 patients (52.2%). Spectroscopy of the temporal poles demonstrated severely decreased concentrations of NAA, markedly increased concentrations of Cho, and increased concentrations of Cr in the temporal pole ipsilateral to the MTS in 15 patients (65.2%). Similarly, the NAA/Cho, NAA/Cr, and NAA/Cho+Cr ratios were severely decreased in the temporal pole ipsilateral to the MTS in 16 patients (69.6%). Histopathological examination of the resected temporal poles demonstrated ischemic changes in 5 patients (21.7%), gliotic changes in 4 (17.4%), demyelinating changes in 3 (13.0%), and microdysplastic changes in 1 patient (4.3%). Comparisons of the spectroscopic and histopathological findings showed that the sensitivity of proton MRS was 100%, its specificity was 80%, its positive predictive value was 87%, and its negative predictive value was 100%. The mean follow-up time in this study was 3.4 years. At the end of the 2nd postoperative year, 17 patients (73.9%) were in Engel Class I, 5 (21.7%) were in Class II, and 1 (4.3%) was in Class III.

CONCLUSIONS

Proton MRS detected altered ipsilateral temporal pole metabolism in patients with unilateral MTS. These metabolic changes were associated with permanent histological abnormalities of the temporal pole. This finding demonstrates that MTS may be a more diffuse histological process, and exact preoperative knowledge of its temporal extent becomes of paramount importance in the selection of the best surgical approach in these patients. Further validation of the observations is necessary for defining the role of temporal pole proton MRS in cases of temporal lobe epilepsy.

Visuo-spatial memory tests in right temporal lobe epilepsy foci: clinical validity

OBJECTIVE

To examine the appropriateness of visual memory tests as an identification method for right mesial temporal lobe dysfunctions in an epilepsy patient group and to study the relationship and possible overlap with non-memory cognitive domains and demographic variables.

METHODS

Eighty preoperative candidates with mesial temporal lobe epilepsy (TLE) were examined using the "Corsi Block-Tapping Test", "Diagnosticum für Cerebralschädigung" (DCS), the path subtest of the "Verbaler und Visueller Merkfähigkeitstest" (VVM), and the Rey-Osterrieth Complex Figure Test (ROCF). Factorial analyses were performed on raw scores to determine the effect of epilepsy-related variables, interictal epileptiform discharges (IEDs) and presence of cortical dysgenesis, on visual and verbal memory parameters. Sensitivity, specificity and Receiver Operating Characteristic (ROC) curves were calculated based on normative data. Furthermore, Spearman correlations between memory and non-memory cognitive tasks were performed.

RESULTS

The scores for test sensitivity and specificity and the ROC curves illustrate the tests' poor capacity to lateralize the functional deficit zone even when epilepsy-related factors, such as cortical dysgenesis or presence of contralateral IEDs were controlled. Significant correlations were found between the visual memory measures and nonverbal reasoning, processing speed, attentional flexibility, and visual planning.

CONCLUSION

These neuropsychological tests are not sensitive enough to lateralize the epileptogenic focus in temporal lobe epilepsy patients since in addition to learning and consolidation processes, they measure additional cognitive domains. These results have implications for clinical neuropsychologists, in terms of test choice and the interpretation in the context of presurgical diagnostics.

Visuoperceptual and visuospatial abilities prior to and after anterior temporal lobectomy: a case study

We describe a patient who presented with temporal lobe epilepsy and a seizure onset pattern in the right temporo-occipital area. Structural MRI revealed sclerosis in the right hippocampus. A comprehensive presurgical neuropsychological assessment allowed us to disentangle deficits in visual object recognition and visual imagery from well-preserved spatial capacities. Following a right temporal lobectomy, the patient remained seizure free, and 1 year postsurgery, the patient's scores on object recognition and imagery were in the normal range. Our findings suggest that visual object recognition and visual imagery are sustained by cortical areas located in proximity to the temporo-occipital ventral pathway and that perceptual and imagery spatial processing is subserved as well by anatomically close mechanisms. Furthermore, the results seem to indicate that nonlesional paroxysmal activity in the posterior temporal lobe can cause chronic dysfunctions of the visual system and that it may be reversible with effective seizure control.

Neurodevelopmental disruption in early-onset temporal lobe epilepsy: evidence from a voxel-based morphometry study

Childhood onset of epilepsy has long been associated with an adverse impact on brain development and cognition. In this study it is proposed that earlier (vs later) onset of temporal lobe epilepsy (TLE) has a negative developmental impact on distant brain structures. One hundred ten patients with TLE were assigned to early (≤14 years, N=58) and late (>15 years, N=52) age at onset of epilepsy groups. Voxel-based morphometry revealed onset-dependent abnormalities (in terms of a gray matter excess in the early-onset group), which were found mainly in frontal regions. An excess of gray matter is not a usual finding in TLE. However, within a neurodevelopmental framework, retained gray matter is discussed as reflecting neurodevelopmental disruption. The findings indicate the importance of quantitative MRI for the detection of subtle secondary abnormalities in focal TLE and once more underline the importance of early seizure management in children with intractable TLE.

Widespread extrahippocampal NAA/(Cr+Cho) abnormalities in TLE with and without mesial temporal sclerosis

MR spectroscopy has demonstrated extrahippocampal NAA/(Cr+Cho) reductions in medial temporal lobe epilepsy with (TLE-MTS) and without (TLE-no) mesial temporal sclerosis. Because of the limited brain coverage of those previous studies, it was, however, not possible to assess differences in the distribution and extent of these abnormalities between TLE-MTS and TLE-no. This study used a 3D whole brain echoplanar spectroscopic imaging (EPSI) sequence to address the following questions: (1) Do TLE-MTS and TLE-no differ regarding severity and distribution of extrahippocampal NAA/(Cr+Cho) reductions? (2) Do extrahippocampal NAA/(Cr+Cho) reductions provide additional information for focus lateralization? Forty-three subjects (12 TLE-MTS, 13 TLE-no, 18 controls) were studied with 3D EPSI. Statistical parametric mapping (SPM2) was used to identify regions of significantly decreased NAA/(Cr+Cho) in TLE groups and in individual patients. TLE-MTS and TLE-no had widespread extrahippocampal NAA/(Cr+Cho) reductions. NAA/(Cr+Cho) reductions had a bilateral fronto-temporal distribution in TLE-MTS and a more diffuse, less well defined distribution in TLE-no. Extrahippocampal NAA/(Cr+Cho) decreases in the single subject analysis showed a large inter-individual variability and did not provide additional focus lateralizing information. Extrahippocampal NAA/(Cr+Cho) reductions in TLE-MTS and TLE-no are neither focal nor homogeneous. This reduces their value for focus lateralization and suggests a heterogeneous etiology of extrahippocampal spectroscopic metabolic abnormalities in TLE.

Extent of neocortical resection and surgical outcome of epilepsy: intracranial EEG analysis

PURPOSE

Intracranial electroencephalography (EEG) monitoring is an important process in the presurgical evaluation for epilepsy surgery. The objective of this study was to identify the ideal resection margin in neocortical epilepsy guided by subdural electrodes. For this purpose, we investigated the relationship between the extent of resection guided by subdural electrodes and the outcome of epilepsy surgery.

METHODS

Intracranial EEG studies were analyzed in 177 consecutive patients who had undergone resective epilepsy surgery. We reviewed various intracranial EEG findings and resection extent. We analyzed the relationships between the surgical outcomes and intracranial EEG factors: the frequency, morphology, and distribution of ictal-onset discharges, the propagation speed, and the time lag between clinical and intracranial ictal onset. We also investigated whether the extent of resection, including the area showing ictal rhythm and various interictal abnormalities--such as frequent interictal spikes, pathologic delta waves, and paroxysmal fast activity--influenced the surgical outcome.

RESULTS

Seventy-five patients (42%) were seizure free. A seizure-free outcome was significantly associated with a resection that included the area showing ictal spreading rhythm during the first 3 s or included all the electrodes showing pathologic delta waves or frequent interictal spikes. However, subgroup analysis revealed that the extent of resection did not affect the surgical outcome in lateral temporal lobe epilepsy.

CONCLUSIONS

The extent of resection is closely associated with surgical outcome, especially in extratemporal lobe epilepsy. Resection that includes the area with total pathologic delta waves and frequent interictal spikes predicts a good surgical outcome.

Altered white matter integrity in temporal lobe epilepsy: association with cognitive and clinical profiles

PURPOSE

Diffusion tensor imaging (DTI) studies have reported substantial white matter abnormalities in patients with temporal lobe epilepsy (TLE). However, limited data exist regarding the extent of white matter tract abnormalities, cognitive effects of these abnormalities, and relationship to clinical factors. The current study examined these issues in subjects with chronic TLE.

METHODS

DTI data were obtained in 12 TLE subjects and 10 age-matched healthy controls. Voxel-wise statistical analysis of fractional anisotropy (FA) was carried out using tract-based spatial statistics (TBSS). White matter integrity was correlated with cognitive performance and epilepsy-related clinical parameters.

RESULTS

Subjects with TLE, as compared to healthy controls, demonstrated four clusters of reduced FA, in anterior temporal lobe, mesial temporal lobe, and cerebellum ipsilateral, as well as frontoparietal lobe contralateral to the side of seizure onset. Mean FA was positively correlated with delayed memory, in anterior temporal lobe; and immediate memory, in mesial temporal lobe. Lower FA values in the posterior region of corpus callosum were related to earlier age of seizure onset.

CONCLUSION

TLE is associated with widespread disturbances in white matter tracts and these changes have important cognitive and clinical consequences.

Application of volumetric MR spectroscopic imaging for localization of neocortical epilepsy

PURPOSE

The aim of this study was to evaluate volumetric proton magnetic resonance spectroscopic imaging (MRSI) for localization of epileptogenic foci in neocortical epilepsy.

METHODS

Twenty-five subjects reporting seizures considered to be of neocortical origin were recruited to take part in a 3-T MR study that included high-resolution structural MRI and a whole-brain MRSI acquisition. Using a fully automated MRSI processing protocol, maps for signal intensity normalized N-acetylaspartate (NAA), creatine, and choline were created, together with the relative volume fraction of grey-matter, white-matter, and CSF within each MRSI voxel. Analyses were performed using visual observation of the metabolite and metabolite ratio maps; voxel-based calculation of differences in these metabolite maps relative to normal controls; comparison of average grey-matter and white-matter metabolite values over each lobar volume; and examination of relative left-right asymmetry factors by brain region.

RESULTS

Data from 14 subjects were suitable for inclusion in the analysis. Eight subjects had MRI-visible pathologies that were associated with decreases in NAA/creatine, which extended beyond the volume indicated by the MRI. Five subjects demonstrated no significant metabolic alterations using any of the analysis methods, and one subject had no findings on MRI or MRSI.

CONCLUSIONS

This proof of principle study supports previous evidence that alterations of MR-detected brain metabolites can be detected in tissue areas affected by neocortical seizure activity, while additionally demonstrating advantages of the volumetric MRSI approach.

Single-subject voxel-based relaxometry for clinical assessment of temporal lobe epilepsy

PURPOSE

T2 relaxometry, quantitative assessment of T2 relaxation time in magnetic resonance (MR) data, typically uses manually drawn regions of interest (ROIs). This approach is limited by its subjectivity and its restricted scope of investigation. A recently developed approach called voxel-based relaxometry (VBR) provides an unbiased statistical analysis of the whole brain. Our objective was to assess the clinical utility of single-subject VBR for patients with temporal lobe epilepsy (TLE).

METHODS

Forty-five patients with TLE confirmed by history, EEG, and structural MRI and 25 control subjects were scanned at 3T using a modified Carr-Purcell-Meiboom-Gill MR sequence. ROIs were drawn for each patient and control subject, and measurements were made on unregistered T2 maps. VBR was performed on a single-subject basis at a significance level of alpha=0.05. Patients were grouped according to seizure focus (left mesial, right mesial, other), and whether structural MR imaging was normal or abnormal.

RESULTS

Up to 85% of patients in the temporal lobe groups demonstrated T2 abnormalities. VBR detected abnormalities either in equal numbers or in more patients (up to 23% more) than ROI analysis for each group. The number of detected abnormalities per patient was higher using VBR (3.38 versus 2.04, p<0.05). VBR also identified abnormalities that were missed by ROI analysis. The rate of VBR detection of abnormalities was higher for patients than controls (76% versus 36%).

CONCLUSIONS

VBR can be performed on single subjects with TLE and it detects considerably more abnormalities than ROI analysis. VBR may be a clinically useful tool for the detection of T2 abnormalities at the seizure focus and sites remote from it.

Exploring interregional brain interactivity in temporal lobe epilepsy using partial correlation analysis of fMRI data

Simultaneous recording of functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) has been recently used to measure metabolic changes related to interictal spikes in temporal lobe epilepsy (TLE). Since blood oxygen level dependent (BOLD) responses have been often observed in extratemporal regions, we propose to explore interregional brain connectivity using a data-driven method based on partial correlation analysis of fMRI data. This approach allows to extract informations about functional interactivity and to differentiate direct from mediated interactions. We demonstrated that this technique provides a deeper insight into the functional relationships between the areas involved in the generation of spikes in TLE.

EEG spectral changes underlying BOLD responses contralateral to spikes in patients with focal epilepsy

PURPOSE

Simultaneous electroencephalogram and functional magnetic resonance imaging (EEG-fMRI) in patients with focal epilepsy and unilateral spikes often shows positive blood oxygenation level-dependent (BOLD) responses (activations), not only ipsilateral but also contralateral to the spikes. We aimed to investigate whether minimal EEG changes could underlie these contralateral BOLD responses by using EEG spectral analysis.

METHODS

We studied 19 patients with focal epilepsy and unilateral spikes. According to the pattern of BOLD activation, patients were divided into Group 1 (ipsi- and contralateral to the spikes) or Group 2 (only ipsilateral). EEG from outside the scanner was used to mark spikes similar to those recorded in the scanner. Epochs of 640 ms before and after the peak of the spikes were chosen as baseline and spike epochs. Spectral analysis was performed in referential montage (FCz reference), and differences between baselines and spikes were analyzed by paired t-test.

RESULTS

Significant EEG changes in electrodes contralateral to the spikes were seen in 9 of 10 patients in Group 1 and in only 2 of 10 patients in Group 2 (one patient had two types of spikes that were analyzed separately). Spectral changes were seen in delta and/or theta bands in all patients except one (in Group 1) who had changes in all bands.

DISCUSSION

Significant contralateral EEG changes occurred in 90% of contralateral BOLD activations and in only 20% of patients without contralateral BOLD responses. The reason why these changes predominate in lower frequencies rather than in higher frequencies is unclear. These spectral changes in areas corresponding to contralateral activations might reflect poorly synchronized but possibly intense neuronal activity.

Hippocampal extracellular GABA correlates with metabolism in human epilepsy

As the major inhibitory neurotransmitter in human brain, GABA is an important modulator of hyperexcitability in epilepsy patients. Given the high energetic cost of neurotransmission and synaptic activity, GABA concentrations may be hypothesized to correlate with metabolic function. We studied human epilepsy patients undergoing intracranial EEG monitoring for seizure localization to examine microdialysis measures of extracellular GABA (ecGABA), pre-operative MR spectroscopic measures of neuronal mitochondrial function (NAA/Cr), and wherever possible, neuropathology and hippocampal volumetry. Two groups undergoing intracranial monitoring for seizure localization were studied: surgically treated hippocampal epilepsy (MTLE) and neocortical (non-hippocampal seizure onset) epilepsy. All data are hippocampal and thus these groups allow comparisons between the epileptogenic and non-epileptogenic regions. ecGABA was measured using in vivo microdialysis performed during intracranial monitoring. Pre-operative in vivo MR spectroscopic imaging was performed to measure the ratio of N-acetyl aspartate (NAA) to creatine. Standard methods for neuropathology and hippocampal volumetry were used. In the neocortical group, increased ecGABA correlated with greater NAA/Cr (R = +0.70, p < 0.015, n = 12) while in the MTLE group, increased ecGABA linked with decreased NAA/Cr (R = -0.94, p < 0.001, n = 8). In MTLE, ecGABA (increased) and NAA/Cr (decreased) correlated with increased glial cell numbers (R = +0.71, p < 0.01, n = 12, R = -0.76 p < 0.03 respectively). No relationship was seen between ecGABA and hippocampal volumes in either group. In epilepsy, ecGABA increases occur across a range of metabolic function. Outside the seizure focus, ecGABA and NAA/Cr increase together; in contrast, within the seizure focus, ecGABA increases with declining mitochondrial function.

Vulnerability of the frontal-temporal connections in temporal lobe epilepsy

OBJECTIVE

In temporal lobe epilepsy (TLE), frontal-temporal connections are integral parts of the epileptogenic network. Although frontal-temporal gray matter abnormalities have been consistently demonstrated in TLE, white matter connections between these two lobes require further study in this disease setting. We therefore investigated the integrity of two major frontal-temporal white matter association tracts, uncinate fasciculus (UF) and arcuate fasciculus (AF), and their clinical correlates.

METHODS

Using diffusion tensor imaging (DTI) tractography, integrity of the UF and AF was examined in 22 individuals (12 subjects with TLE and 10 age-matched healthy controls). DTI indices of these tracts were compared between the two subject groups and correlates examined with clinical variables that included age of seizure onset, duration of epilepsy, history of febrile seizure and antiepileptic medication exposure.

RESULTS

In subjects with TLE, the fractional anisotropy (FA) and apparent diffusion coefficient (ADC) of UF and AF ipsilateral to the side of seizure onset were abnormal when compared to healthy controls. Furthermore, lower UF FA correlated with earlier age of seizure onset.

CONCLUSION

TLE is associated with abnormal integrity of frontal-temporal white matter tracts, but only on the side of seizure onset. This suggests that frontal-temporal white matter tracts are vulnerable to recurrent seizures and/or the factors precipitating the epilepsy.

Temporal lobe epilepsy does not impair visual perception

Temporal lobe epilepsy (TLE) can impair interictal cognitive function. In the perceptual domain, previous psychophysical studies demonstrated specific deficits in auditory and tactile perception in patients with TLE. This study compared performance of 25 TLE subjects and 27 controls on two low-level, visual tasks: luminance discrimination and frequency discrimination. Both tasks were performed under a relatively easy and a relatively difficult condition, by adjusting the stimulus duration. TLE subjects performed as well as controls on both tasks at both stimulus durations. These results imply that interictal occipital lobe function, as reflected in performance on low-level visual tasks, is not impaired in TLE, consistent with functional imaging data. Furthermore, since TLE subjects performed normally while taking therapeutic doses of multiple AEDs, the data suggest that these AEDs do not impair visual perception.

Decrease of NAA with aging outside the seizure focus in mesial temporal lobe epilepsy--a proton-MRS study at 3 Tesla

There is evidence that chronic pharmacoresistant temporal lobe epilepsy (TLE) is a progressive disorder accompanied by mental deterioration. We investigated effects of aging on cerebral N-acetyl-aspartate (NAA) concentrations in the temporal lobe of 12 patients with pharmacoresistant mesial TLE (mTLE) and 22 healthy controls by means of proton-magnetic resonance spectroscopy ((1)H-MRS) at 3 T. Furthermore, we calculated correlations between NAA concentrations and measures of verbal and figural memory in patients. In mTLE patients but not in healthy controls the concentration of NAA in the lateral temporal lobe was negatively correlated with age. In patients with mTLE NAA in left lateral temporal voxels correlated with verbal memory. NAA in medial temporal voxels did not correlate with age or neuropsychological measures. Significant decrease of NAA with age in the lateral temporal lobe of patients with mTLE provides evidence for progressive neuronal dysfunction with aging. NAA is a marker of neuronal integrity since it correlates with verbal memory.

Voxel-based T2 relaxation rate measurements in temporal lobe epilepsy (TLE) with and without mesial temporal sclerosis

INTRODUCTION

Quantitative measurements of T(2) relaxation in the hippocampus for focus lateralization in mesial temporal lobe epilepsy (mTLE) are well established. Less is known to what degree such relaxation abnormalities also affect regions beyond the ipsilateral hippocampus. Therefore, the aim of this study was to characterize extent and distribution pattern of extrahippocampal relaxation abnormalities in TLE with (TLE-MTS) and without MRI evidence of mesial-temporal sclerosis (TLE-no).

METHODS

Double spin echo images (TE1/2: 20/80 ms) acquired in 24 TLE-MTS and 18 TLE-no were used to calculate relaxation rate maps. These maps were analyzed by SPM2 and by selecting regions of interest (ROI) in the hippocampus and several extrahippocampal brain regions.

RESULTS

In TLE-MTS, the results of the SPM and ROI analysis were in good agreement and showed the most severe relaxation rate decreases in the ipsilateral hippocampus but also in other ipsilateral temporal regions, orbitofrontal, and parietal regions and to a lesser degree in contralateral frontal regions. The relaxation rate decreases in TLE-no were confined to small regions in the ipsilateral anterior inferior and medial temporal lobe in the SPM analysis while ROI analysis showed additional regions in the ipsilateral hippocampus, amygdala, and anterior cingulate.

CONCLUSION

TLE-MTS showed extensive, widespread but predominantly ipsilateral temporal and also extratemporal T(2) relaxation rate decreases. In contrast, the findings of the SPM and ROI analyses in TLE-no suggested that if relaxation rate decreases are present, they are less uniform and generally milder than in TLE-MTS. This further supports the hypothesis that TLE-no is a distinct clinicopathological entity from TLE-MTS and probably heterogeneous in itself.

EEG-fMRI using z-shimming in patients with temporal lobe epilepsy

PURPOSE

To use z-shimming, a technique that reduces signal loss due to susceptibility artifacts that can result in reduced or absent activation in electroencephalography (EEG) functional MRI (fMRI) sessions in patients with temporal lobe epilepsy (TLE), to determine whether it would result in an increased ability to detect significant regions of blood oxygenation level-dependent (BOLD) signal change.

MATERIALS AND METHODS

Eight patients with TL EEG spikes underwent an EEG-fMRI scanning session using z-shimming. The signal intensities in the z-shimmed images were compared with those in the standard images. BOLD activation maps were created from the two sets of images using the timings of the spikes observed on the EEG.

RESULTS

The mean signal increase in the TLs as a result of z-shimming was 45.9%+/-4.5%. The percentage of TL voxels above a brain intensity threshold rose from 66.1%+/-7.6% to 77.6%+/-5.7%. This appreciable increase in signal did not lead to any significant differences in the statistical maps created with the two sets of functional images.

CONCLUSION

The results suggest that loss of signal is not the limiting factor for the detection of spike-related BOLD signal changes in patients with TLE activity.

1H magnetic resonance spectroscopy at 3 T in cryptogenic and mesial temporal lobe epilepsy

The objectives of this work were to compare concentrations of N-acetylaspartate (NAA), glutamate (Glu), glutamine (Gln), Glx (=Glu + Gln), myo-inositol (mI), total creatine (Cre) and other metabolites in the temporal lobes of patients with mesial temporal lobe epilepsy (mTLE), cryptogenic TLE (cTLE), who show no abnormalities in high-resolution MRI, and healthy controls using single voxel (1)H MRS at 3 T. Twelve patients with mTLE, nine with cTLE and 22 controls were investigated using a short echo time STEAM protocol. Voxels were positioned bilaterally in the medial and lateral temporal lobes. Spectra were processed with LCModel. Significantly lower mean NAA were detected in mTLE patients (P < 0.001) and a trend towards lower NAA in cTLE patients compared to controls (P = 0.053). Glx was not different between groups. Estimates of Glu showed a different metabolic pattern in mTLE with elevated Glu in lateral compared with medial voxels on the ipsilateral side to seizure onset (P = 0.019). MI concentrations were significantly lower in cTLE (P < 0.001) and in mTLE patients (P = 0.005) compared with healthy controls. MI/Cre was significantly reduced in cTLE patients only (P = 0.004). The results confirm low NAA in mTLE and to a lesser extent in cTLE patients. MI and mI/Cre were identified as potential metabolic indicators of the epileptogenic area in cTLE.

Voxel-based optimized morphometry (VBM) of gray and white matter in temporal lobe epilepsy (TLE) with and without mesial temporal sclerosis

PURPOSE

In temporal lobe epilepsy (TLE) with evidence of hippocampal sclerosis (TLE-MTS) volumetric gray (GM) and white (WM) matter abnormalities are not restricted to the hippocampus but also are found in extrahippocampal structures. Less is known about extrahippocampal volumetric abnormalities in TLE without hippocampal sclerosis (TLE-no). In this study, we used optimized voxel-based morphometry (VBM) with and without modulation with the following aims: (a) to identify WM and GM abnormalities beyond the hippocampus in TLE-MTS and TLE-no; and (b) to determine whether extratemporal WM and GM abnormalities differ between TLE-MTS and TLE-no.

METHODS

Optimized VBM of GM and WM with and without modulation was performed in 26 TLE-MTS (mean age, 35.6 +/- 9.7 years), 17 TLE-no (mean age, 35.6 +/- 11.1 years), and 30 healthy controls (mean age, 30.3 +/- 11.1 years).

RESULTS

In TLE-MTS, GM/WM volume and concentration reductions were found in the ipsilateral limbic system, ipsi- and contralateral neocortical regions, thalamus, cerebellum, internal capsule, and brainstem when compared with controls. In contrast, no differences of GM/WM volumes/concentrations were found between TLE-no and controls or between TLE-no and TLE-MTS.

CONCLUSIONS

In TLE-MTS, optimized VBM showed extensive GM and WM volume reductions in the ipsilateral hippocampus and in ipsi- and contralateral extrahippocampal regions. In contrast, no GM/WM volume or concentration reductions were found in TLE-no. This further supports the hypothesis that TLE-no is a distinct clinicopathologic entity from TLE-MTS and probably heterogeneous in itself.

Temporal and extratemporal BOLD responses to temporal lobe interictal spikes

PURPOSE

Simultaneous EEG and functional MRI (fMRI) allows measuring metabolic changes related to interictal spikes. Our objective was to investigate blood oxygenation level-dependent (BOLD) responses to temporal lobe (TL) spikes by using EEG-fMRI recording.

METHODS

We studied 35 patients who had a diagnosis of temporal lobe epilepsy (TLE) and active TL spiking on routine scalp EEG recording. Two-hour sessions of continuous EEG-fMRI were recorded, and spikes were identified after offline artifact removal and used as events in the fMRI analysis. Each type of spike was analyzed separately, as one EEG-fMRI study. We determined significant (p < 0.05) positive (activation) and negative (deactivation) BOLD responses for each study.

RESULTS

Twenty-seven patients had spikes during scanning (19 unilateral and eight bilateral). From a total of 35 fMRI studies, 29 (83%) showed BOLD responses: 14 had both activations and deactivations; 12, activations only; and three, deactivations only. Six (17%) showed no responses. Nineteen studies had mainly neocortical TL activation: Sixteen (84%) of 19 concordant with spikes, 12 of 16 with concomitant activation of the contralateral TL, and 16 of 19 with additional extratemporal activation; few showed exclusively mesial TL activation. Seventeen studies showed deactivation, either extratemporal plus temporal (n = 8) or exclusively extratemporal (n = 9).

CONCLUSIONS

BOLD responses to TL spikes occurred in 83% of studies, predominated in the spiking temporal lobe, and manifested as activation or deactivation. Responses often involved the contralateral homologous cortex at the time of unilateral spikes and were frequently observed in extratemporal regions, suggesting that TL epileptic spikes can affect neuronal activity at a distance through synaptic connections.

Metabolism is normal in astrocytes in chronically epileptic rats: a (13)C NMR study of neuronal-glial interactions in a model of temporal lobe epilepsy

The aim of the present work was to study potential disturbances in metabolism and interactions between neurons and glia in the lithium-pilocarpine model of temporal lobe epilepsy. Rats chronically epileptic for 1 month received [1-(13)C]glucose, a substrate for neurons and astrocytes, and [1,2-(13)C]acetate, a substrate for astrocytes only. Analyses of extracts from cerebral cortex, cerebellum, and hippocampal formation (hippocampus, amygdala, entorhinal, and piriform cortices) were performed using (13)C and (1)H nuclear magnetic resonance spectroscopy and HPLC. In the hippocampal formation of epileptic rats, levels of glutamate, aspartate, N-acetyl aspartate, adenosine triphosphate plus adenosine diphosphate and glutathione were decreased. In all regions studied, labeling from [1,2-(13)C]acetate was similar in control and epileptic rats, indicating normal astrocytic metabolism. However, labeling of glutamate, GABA, aspartate, and alanine from [1-(13)C]glucose was decreased in all areas possibly reflecting neuronal loss. The labeling of glutamine from [1-(13)C]glucose was decreased in cerebral cortex and cerebellum and unchanged in hippocampal formation. In conclusion, no changes were detected in glial-neuronal interactions in the hippocampal formation while in cortex and cerebellum the flow of glutamate to astrocytes was decreased, indicating a disturbed glutamate-glutamine cycle. This is, to our knowledge, the first study showing that metabolic disturbances are confined to neurons inside the epileptic circuit.

1H-MRS imaging in intractable frontal lobe epilepsies characterized by depth electrode recording

Presurgical evaluation of frontal lobe epilepsy (FLE) remains a challenging issue and frequently requires invasive depth electrode recording. In this study, we aimed at evaluating the potential usefulness of a non-invasive technique such as proton magnetic resonance spectroscopic imaging ((1)H-MRSI) in the presurgical evaluation of FLE and at investigating the potential electrophysiological correlates of the metabolic disturbances as defined by (1)H-MRSI. We compared the distribution of (1)H-MRSI abnormalities with the electrophysiological abnormalities defined by stereo-electroencephalography (SEEG) recording in 12 patients presenting with several subtypes of FLE. We also used 12 control subjects in order to obtain normative (1)H-MRSI data. We used a multilevel (1)H-MRSI protocol to better sample the principal regions of the frontal lobe. We also applied a metabolic mapping technique allowing a visual display of metabolic data. A significant decrease of both N-acetyl-aspartate/phosphocreatine-creatine and N-acetyl-aspartate/(choline-compounds + phosphocreatine-creatine) ratios was observed in regions involved in the epileptogenic zone (EZ) and/or the irritative zone (IZ) compared to regions without electrical abnormalities in the same patients (P = 0.044 and P = 0.018, respectively), and also compared to controls (P = 0.004 and P = 0.0001, respectively). No significant differences in metabolic ratios were observed between those regions involved in the EZ and those involved in the IZ only. Our results suggest a link between the relative decrease of N-acetyl-aspartate and the EZ as well as the IZ in FLE. Thus, multilevel (1)H-MRSI protocol may add pertinent information during the non-invasive presurgical evaluation of FLE.

Coregistration of quantitative proton magnetic resonance spectroscopic imaging with neuropathological and neurophysiological analyses defines the extent of neuronal impairments in murine human immunodeficiency virus type-1 encephalitis

Relatively few immune-activated and virus-infected mononuclear phagocytes (MP; perivascular macrophages and microglia) may affect widespread neuronal dysfunction during human immunodeficiency virus type 1 (HIV-1)-associated dementia (HAD). Indeed, histopathological evidence of neuronal dropout often belies the extent of cognitive impairment. To define relationships between neuronal function and histopathology, proton magnetic resonance spectroscopic imaging (1H MRSI) and hippocampal long-term potentiation (LTP) were compared with neuronal and glial immunohistology in a murine model of HIV-1 encephalitis (HIVE). HIV-1(ADA)-infected human monocyte-derived macrophages (MDM) were stereotactically injected into the subcortex of severe combined immunodeficient (SCID) mice. Sham-operated and unmanipulated mice served as controls. Seven days after cell injection, brain histological analyses revealed a focal giant cell encephalitis, with reactive astrocytes, microgliosis, and neuronal dropout. Strikingly, significant reductions in N-acetyl aspartate concentration ([NAA]) and LTP levels in HIVE mice were in both injected and contralateral hemispheres and in brain subregions, including the hippocampus, where neuropathology was limited or absent. The data support the importance of 1H MRSI as a tool for assessing neuronal function for HAD. The data also demonstrate that a highly focal encephalitis can produce global deficits for neuronal function and metabolism.

Interictal perceptual function in epilepsy

Epilepsy can affect perception. Ictal perceptual experiences are common, but interictal perceptual function may also be affected. This article reviews the English-language literature on interictal perceptual disturbances in epilepsy. Although most studies report impaired perceptual ability, heightened sensitivity has also been described. There is a compelling, though not absolute, correlation between affected sensory modality and underlying epilepsy syndrome. Olfaction is clearly affected in temporal lobe epilepsy, while visual information processing is disturbed in occipital lobe epilepsy. The cause of interictal perceptual dysfunction is unknown, but propagating epileptiform discharges may play a role. The presence of specific perceptual disturbances in focal epilepsy syndromes is consistent with the view that epilepsy is a network disease, with the potential to affect neural circuits distant from the seizure focus. The use of thoughtfully selected psychophysical perceptual tasks may provide additional insight into the cognitive impact of different epilepsy syndromes and of ablative epilepsy surgery.

Quantitative HMRS and MRI volumetry indicate neuronal damage in the hippocampus of children with focal epilepsy and infrequent seizures

PURPOSE

Seizures induce progressive morphologic and functional changes in particular in the hippocampus, but whether and at what stage the hippocampus is affected in children with focal, temporal, nonintractable epilepsy is poorly known. We have now studied eventual metabolic and volume changes in the hippocampus of children with nonsymptomatic focal epilepsy taking antiepileptic medication (AEDs) but still having infrequent seizures.

METHODS

Quantitative proton magnetic resonance spectroscopy ((1)HMRS) and volumetric MRI were used to study the hippocampal region of 11 pediatric outpatients (age 10 to 17 years) with cryptogenic localization-related epilepsy, and eight healthy volunteers (age 9 to 16 years) served as controls. The spectra were obtained bilaterally from the hippocampi by using the 1.5-T MR imager. The spectral resonance lines of N-acetyl group (NA), creatine and phosphocreatine group (Cr), choline-containing compounds (Cho), and myoinositol (mI) were analyzed quantitatively. The volume of the hippocampus was semiautomatically calculated.

RESULTS

The mean concentration of NA was significantly decreased both in the focus side (9.02 +/- 2.00 mM) and in the nonfocus side (8.88 +/- 2.09 mM) of the patients compared with the controls (10.76 +/- 1.86 mM), in particular if the children had a history of generalized tonic-clonic seizures. The mean concentrations of Cho, Cr, and mI did not differ significantly between the patients and controls. Moreover, the mean hippocampal volume of the focus side of patients was significantly reduced compared with that of the controls.

CONCLUSIONS

Metabolic changes in hippocampi were detected in children with nonsymptomatic localization-related epilepsy and infrequent seizures. Reduced NA could reflect neuronal metabolic dysfunction and/or neuronal damage, as indicated by our volumetric findings.

Postoperative alteration of cerebral glucose metabolism in mesial temporal lobe epilepsy

To investigate postoperative changes in the cerebral glucose metabolism of patients with mesial temporal lobe epilepsy (MTLE), statistical parametric mapping (SPM) analysis was performed on pre- and postoperative (18)F-fluorodeoxyglucose PET (FDG-PET) images. We included 28 patients with MTLE who had undergone surgery and had been seizure-free postoperatively (16 had left MTLE and 12 right MTLE). All patients showed hippocampal sclerosis by pathology or brain MRI. FDG-PET images of the 12 right temporal lobe epilepsy patients were reversed to lateralize the epileptogenic zone to the left side in all patients. Application of the paired t-test in SPM to pre- and postoperative FDG-PETs showed that postoperative glucose metabolism decreased in the caudate nucleus, the pulvinar of the thalamus, fusiform gyrus, lingual gyrus and the posterior region of the insular cortex in the hemisphere ipsilateral to resection, whereas postoperative glucose metabolism increased in the anterior region of the insular cortex, temporal stem white matter, midbrain, inferior precentral gyrus, anterior cingulate gyrus and supramarginal gyrus in the hemisphere ipsilateral to resection. No significant postsurgical changes in cerebral glucose metabolism occurred in the contralateral hemisphere. Subtraction between pre- and postoperative FDG-PET images in individual patients produced similar findings to the SPM results, and additionally showed that postoperative glucose metabolism increased in the anterior thalamus in 12/28 patients (42.8%). SISCOM (subtraction ictal-interictal SPECT co-registered to MRI) performed in 17 patients showed ictal hyperperfusion in the ipsilateral temporal lobe, including the temporal stem white matter, midbrain, insular cortex and cingulate gyrus, bilateral basal ganglia and thalami, and multiple small regions in the frontoparietal lobes during seizures. This study suggests that brain regions showing a postoperative increase in glucose metabolism appear to represent the propagation pathways of ictal and interictal epileptic discharges in MTLE, whereas the postoperative decrease in glucose metabolism may be related to a permanent loss of afferents from resected anterior-mesial temporal structures.

Somatosensory processing is impaired in temporal lobe epilepsy

PURPOSE

Growing evidence suggests that temporal lobe epilepsy (TLE) is a network disease. In this view, the seizure focus may produce measurable deficits in specific cortical functions.

METHODS

A tactile grating orientation (GrOr) discrimination task associated with parietal lobe function was administered at the index fingertip to 15 subjects with medically intractable TLE and to 19 neurologically normal controls. TLE subjects were tested bilaterally at baseline while taking their usual antiepileptic drugs (AEDs), and off AEDs during inpatient video-EEG monitoring (n = 9). Three subjects also were tested after temporal lobectomy. t Tests were used to compare baseline performance between TLE subjects and controls, and between hands ipsilateral and contralateral to side of seizure onset, with Bonferroni correction for multiple comparisons. TLE subjects' baseline thresholds were compared with those obtained off AEDs by using a repeated measures analysis of variance.

RESULTS

TLE subjects were severely impaired bilaterally on the GrOr task, with mean discrimination thresholds nearly twice those of controls (p </= 0.001 for each hand). No significant difference was found in baseline performance between hands (p = 0.37), or between baseline and off-AED testing (p = 0.42). The three subjects tested after temporal lobectomy demonstrated improved performance compared with baseline, but statistics were not performed because of the small subject number.

CONCLUSIONS

Patients with medically intractable TLE have impaired tactile GrOr discrimination bilaterally that is not due to nonspecific effects of AEDs. This impaired perceptual ability may be reversible with surgical removal of the seizure focus.