Magnetic resonance spectroscopy of the thalamus in patients with typical absence epilepsy

Investigation of Patients With Eye Closure Sensitive Epilepsy With Magnetic Resonance Spectroscopy

Introduction and aim: A proportion of patients diagnosed with genetic generalized epilepsy (GGE) experience eye-closure sensitivity (ECS), the underlying pathogenesis of which is unknown. In this study, we compare magnetic resonance spectroscopy (MRS) findings of healthy volunteers with patients diagnosed with GGE, with and without ECS, to detect possible explanatory differences between groups. Materials and methods: A total of 33 patients diagnosed with GGE: 17 with ECS and 16 without, and 12 healthy volunteers are included. MRS measurements of N-acetyl-aspartate (NAA), choline (Cho), and creatine (Cr) were made of bilateral occipital lobes and thalamus, and values of patients with GGE were compared with those of normal controls, and within subgroups with different clinical variables, using appropriate statistical tests. Results: Left occipital NAA and NAA/Cr levels were found to be significantly higher in the ECS group than in the control group. In the ECS epilepsy group, a significant moderate positive correlation was noted between left thalamic Cr and duration of drug therapy (r = .539, P = .047) and left thalamic Cr and age at epilepsy onset (r = .564, P = .036). Additionally, left thalamic NAA and NAA/Cr levels were observed to be lower in GGE patients compared to healthy subjects, although not to a statistically significant degree. Conclusion:The differences in MRS-measurable metabolites in the left occipital lobe in those with ECS epilepsy suggest an association between the ECS mechanism and the left occipital lobe. Our results also support the multifocal thalamocortical pathway disorder in the pathophysiology of GGE based on the observation of cellular dysfunction in the thalamus.

Metabolic alterations of the dorsolateral prefrontal cortex in sleep-related hypermotor epilepsy: A proton magnetic resonance spectroscopy study

Sleep-related hypermotor epilepsy (SHE) is a focal epilepsy whose neurobiological underpinnings remain poorly understood. The present study aimed to identify possible neurochemical alterations in the dorsolateral prefrontal cortex (DLPFC) in participants with SHE using proton magnetic resonance spectroscopy (¹ H MRS). Thirty-nine participants with SHE (mean age, 30.7 years ± 11.3 [standard deviation], 24 men) and 59 controls (mean age, 29.4 years ± 10.4, 29 men) were consecutively and prospectively recruited and underwent brain magnetic resonance imaging and ¹ H MRS in the bilateral DLPFCs. Brain concentrations of metabolites, including N-acetyl aspartate (NAA), myo-inositol (mI), choline, creatine, the sum of glutamate and glutamine, glutathione (GSH) and γ-aminobutyric acid, were estimated with LCModel and corrected for the partial volume effect of cerebrospinal fluid using tissue segmentation. ANCOVA analyses revealed lower concentration of NAA in the left DLPFC in participants with SHE compared with controls. A significant difference of NAA concentration between DLPFC in the two hemispheres (left > right) was observed only in the control group. We further confirmed a higher GSH concentration in men than in women in SHE participants, which probably indicates that men are more susceptible to this disease. The mI concentration in the right DLPFC was negatively correlated with epilepsy duration. This study demonstrates that DLPFC is an important brain region involved in the pathophysiology of SHE, in which both neurons and astrocytes appear impaired, and the elevated GSH level may suggest an abnormality related to oxidative stress.

Exploring Changes in Thalamus Metabolites as Diagnostic Biomarkers in Idiopathic Generalised Epilepsy Patients Using Magnetic Resonance Spectroscopy

Introduction

Idiopathic generalised epilepsy (IGE) refers to a group of epilepsies resulting from the activation of neurons in the whole brain. This study aimed to evaluate the metabolite changes in thalamus as diagnostic biomarkers in IGE patients compared to healthy individuals using magnetic resonance spectroscopy (MRS) technique.

Methods

The MRS was performed on 35 IGE patients (26 women and 11 men) with average age of 32 (ranged from 18 to 43) and 35 healthy individuals (13 women and 22 men) with average age of 31 (ranged from 21 to 50) as the control group. The levels of N-acetylaspartate (NAA), creatine (Cr) and choline (Cho) were measured using MRS. The NAA/Cr and NAA/Cho ratios were calculated for all participants. These values were statistically compared using t-test between the groups.

Results

The NAA had significant lower values in IGE patients, 9.6 (SD = 0.8) and 9.9 (SD = 0.7) for right and left thalamus, respectively, compared to 10.9 (SD = 0.9) and 10.7 (SD = 0.9) in control group. The Cr values in the left side of thalamus were significantly higher in IGE patients (6.7 [SD = 0.8] versus 5.8 [SD = 0.5]); however, there was no difference in right thalamus. Measurements showed no difference for amounts of Cho between the groups in both sides of thalamus. The NAA/Cr ratio was 1.48 (SD = 0.14) and 1.48 (SD = 0.16) for right and left thalamus, respectively, in IGE patients in comparison with 1.83 (SD = 0.2) and 1.86 (SD = 0.26) in controls. There was no meaningful variation between the NAA/Cho ratio of the right and left thalamus among the groups.

Conclusion

Thalamic NAA, Cr and NAA/Cr ratio values in IGE patients showed statistical differences compared to healthy individuals. Evaluating metabolites variations in thalamus using MRS is suggested for differentiating IGE patients from healthy individuals.

Peripapillary retinal nerve fibre layer thinning in genetic generalized epilepsy

PURPOSE

The purpose of this study was to compare the peripapillary retinal nerve fibre layer (RNFL) between patients with genetic generalized epilepsy (GGE) and healthy controls.

METHODS

This prospective observational study was conducted on adults aged 18-60 years. The study group comprised 26 consecutive patients who met the inclusion criteria and 26 healthy age- and sex-matched healthy adults. Peripapillary RNFL thickness was measured by spectral domain optical coherence tomography.

RESULTS

The average peripapillary RNFL thickness was significantly thinner for GGE patients (98.61 μm) than for healthy controls (104.77 μm) (p = 0.016). Similar results were obtained for the left eye. The peripapillary RFNL thickness of all quadrants was lower for GGE patients than for healthy controls, but it was significant only in the superior (p = 0.009) and inferior (p = 0.024) quadrants for both eyes.

CONCLUSIONS

Our results suggest that the peripapillary RNFL is significantly thinner in GGE patients than in healthy participants. We concluded that this microstructural feature might be an intrinsic feature of GGE.

Proton MR Spectroscopy in Patients With Sleep-Related Hypermotor Epilepsy (SHE): Evidence of Altered Cingulate Cortex Metabolism

Study Objectives

To identify structural and/or metabolic alterations in patients with sleep-related hypermotor epilepsy (SHE) using magnetic resonance imaging (MRI) and proton MR spectroscopy (1H-MRS).

Methods

Nineteen SHE patients (seven males; 34.7 ± 9.7 years, mean age ± standard deviation) and 17 matched healthy volunteers (seven males; 34.0 ± 8.9 years) were included in the study. In all patients, the diagnosis of SHE was confirmed by video-polysomnographic recording of seizures. Semiology, seizure frequency, and therapy were assessed for all patients. For each recruited participant, structural MRI and 1H-MRS sequences were acquired. 1H-MRS was performed on two regions of interest: the medial thalamus and the anterior cingulate gyrus.

Results

At examination, five patients were seizure free. In the remainder, seizure frequency ranged from yearly to multiple episodes per night. Brain MRI was normal in all patients but one. The ratio of N-acetyl-aspartate/Creatine (NAA/Cr) was significantly reduced in the anterior cingulate cortex in patients compared to controls (p < .05). Thalamic NAA/Cr showed no differences between patients and controls. Regression analysis showed that NAA/Cr in the anterior cingulate gyrus correlated with seizure frequency (p < .05), being lower in patients with higher seizure frequency.

Conclusions

Given the absence of structural MR changes, our 1H-MRS data point to a functional NAA reduction in the cingulate cortex of SHE patients, more severe in those patients with higher seizure frequency and thus supporting the involvement of the anterior mesial structures in the pathophysiology of SHE.

The Role of Thalamus Versus Cortex in Epilepsy: Evidence from Human Ictal Centromedian Recordings in Patients Assessed for Deep Brain Stimulation

Background: The onset of generalized seizures is a long debated subject in epilepsy. The relative roles of cortex and thalamus in initiating and maintaining the different seizure types are unclear. Objective: The purpose of the study is to estimate whether the cortex or the centromedian thalamic nucleus is leading in initiating and maintaining seizures in humans. Methods: We report human ictal recordings with simultaneous thalamic and cortical electrodes from three patients without anesthesia being assessed for deep brain stimulation (DBS). Patients 1 and 2 had idiopathic generalized epilepsy whereas patient 3 had frontal lobe epilepsy. Visual inspection was combined with nonlinear correlation analysis. Results: In patient 1, seizure onset was bilateral cortical and the belated onset of leading thalamic discharges was associated with an increase in rhythmicity of discharges, both in thalamus and cortex. In patient 2, we observed bilateral independent interictal discharges restricted to the thalamus. However, ictal onset was diffuse, with discharges larger in the cortex even though they were led by the thalamus. In patient 3, seizure onset was largely restricted to frontal structures, with belated lagging thalamic involvement. Conclusion: In human generalized seizures, the thalamus may become involved early or late in the seizure but, once it becomes involved, it leads the cortex. In contrast, in human frontal seizures the thalamus gets involved late in the seizure and, once it becomes involved, it lags behind the cortex. In addition, the centromedian nucleus of the thalamus is capable of autonomous epileptogenesis as suggested by the presence of independent focal unilateral epileptiform discharges restricted to thalamic structures. The thalamus may also be responsible for maintaining the rhythmicity of ictal discharges.

Altered degree centrality in childhood absence epilepsy: A resting-state fMRI study

Modern network studies have suggested that the pathology of many neurological diseases is in fact not equally distributed over the brain but preferentially affects the hub regions. This study aims to investigate how hub regions were affected in Children with Childhood absence epilepsy (CAE) using resting-state fMRI (rs-fMRI). As one important measures obtained from rs-fMRI, degree centrality (DC) calculates the number of direct connections between a given node and the rest of the brain within the entire connectivity matrix of the brain. In this study, twenty-five CAE children and 25 healthy controls were recruited to investigate the DC changes in CAE patients. Compared with healthy controls, children with CAE showed significantly decreased DC in default mode network (DMN, medial prefrontal cortex, posterior cingulate cortex, precuneus and middle temporal cortex) and increased DC in thalamus. Importantly, significant negative correlation between the epilepsy duration and DC was found in precuneus. Our results suggested selective and specific disruption of hub nodes, especially thalamus and the highly connected brain regions within DMN, might underlie the pathophysiological mechanism of CAE.

Evidencing different neurochemical profiles between thalamic nuclei using high resolution 2D-PRESS semi-LASER (1)H-MRSI at 7 T

OBJECTIVE

To demonstrate that high resolution (1)H semi-LASER MRSI acquired at 7 T permits discrimination of metabolic patterns of different thalamic nuclei.

MATERIALS AND METHODS

Thirteen right-handed healthy volunteers were explored at 7 T using a high-resolution 2D-semi-LASER (1)H-MRSI sequence to determine the relative levels of N-Acetyl Aspartate (NAA), choline (Cho) and creatine-phosphocreatine (Cr) in eight VOIs (volume <0.3 ml) centered on four different thalamic nuclei located on the Oxford thalamic connectivity atlas. Post-processing was done using the CSIAPO software. Chemical shift displacement of metabolites was evaluated on a phantom and correction factors were applied to in vivo data.

RESULTS

The global assessment (ANOVA p < 0.05) of the neurochemical profiles (NAA, Cho and Cr levels) with thalamic nuclei and hemispheres as factors showed a significant global effect (F = 11.98, p < 0.0001), with significant effect of nucleus type (p < 0.0001) and hemisphere (p < 0.0001). Post hoc analyses showed differences in neurochemical profiles between the left and the right hemisphere (p < 0.05), and differences in neurochemical profiles between nuclei within each hemisphere (p < 0.05).

CONCLUSION

For the first time, using high resolution 2D-PRESS semi-LASER (1)H-MRSI acquired at 7 T, we demonstrated that the neurochemical profiles were different between thalamic nuclei, and that these profiles were dependent on the brain hemisphere.

Altered spontaneous activity in treatment-naive childhood absence epilepsy revealed by Regional Homogeneity

PURPOSE

To explore the differences in regional spontaneous activities throughout the whole brain by the Regional Homogeneity (ReHo) method in untreated childhood absence epilepsy (CAE), in order to understand the neuro-pathophysiological mechanism of function impairments in CAE.

METHODS

The rest-functional MRI was used to measure the ReHo in 16 patients with untreated CAE and 16 age- and sex-matched healthy controls. The correlations between the ReHo at each voxel of the whole brain and duration of epilepsy were analyzed.

RESULTS

Compared with healthy controls, we found that ReHo was decreased in bilateral thalamus, caudate, posterior lobe of cerebellum and areas mainly in the default mode network (DMN) (including precuneus and posterior cingulate cortex-PCC, bilateral inferior lateral parietal lobule). The increase of ReHo was found in bilateral insula, left occipital cortex. Moreover, a correlation analysis of the ReHo measurement versus the epilepsy duration was performed, and highly positive correlation was observed in precuneus/PCC and supplementary motor area (SMA).

SIGNIFICANCE

The current findings demonstrated alterations of ReHo in the striato-thalamo-cortical network in drug naïve CAE subjects during interictal resting state. Some regions with decreased ReHo followed the pattern of 'default' state of brain function. In addition, positive correlations between the ReHo values in the precuneus/PCC and SMA and the disease duration were identified. These results indicate that the involvement of these regions may be related to the pathomechanisms of seizure generation and the neurological deficits observed in CAE patients. ReHo has demonstrated the capability to characterize spontaneous brain dysfunction in epilepsy.

Altered functional connectivity within and between brain modules in absence epilepsy: a resting-state functional magnetic resonance imaging study

Functional connectivity has been correlated with a patient's level of consciousness and has been found to be altered in several neuropsychiatric disorders. Absence epilepsy patients, who experience a loss of consciousness, are assumed to suffer from alterations in thalamocortical networks; however, previous studies have not explored the changes at a functional module level. We used resting-state functional magnetic resonance imaging to examine the alteration in functional connectivity that occurs in absence epilepsy patients. By parcellating the brain into 90 brain regions/nodes, we uncovered an altered functional connectivity within and between functional modules. Some brain regions had a greater number of altered connections and therefore behaved as key nodes in the changed network pattern; these regions included the superior frontal gyrus, the amygdala, and the putamen. In particular, the superior frontal gyrus demonstrated both an increased value of connections with other nodes of the frontal default mode network and a decreased value of connections with the limbic system. This divergence is positively correlated with epilepsy duration. These findings provide a new perspective and shed light on how functional connectivity and the balance of within/between module connections may contribute to both the state of consciousness and the development of absence epilepsy.

A case of atypical absence seizures after electroconvulsive treatment in a patient with treatment-resistant depression

Electroconvulsive therapy (ECT) has been used to treat severe treatment-resistant major depressive disorder. Multiple psychotropic medications are usually prescribed in high doses prior to or concomitantly with ECT. Little is known about the interaction of ECT with psychotropic medications. ECT is known to induce seizures, but its tendency to induce absence seizures is not. We present a case of a 44-year-old female, on multiple psychotropic medications, who had frequent atypical absence seizures for many days after ECT. Electroencephalography (EEG) confirmed atypical absence seizures by the presence of typical 2.5 to 3 Hz generalized sharp and slow waves with disorganized background activity.

Functional connectivity changes in patients with absence epilepsy studied using resting-state functional MRI

Functional connectivity is altered in several mental disorders. We used resting-state functional MRI to examine the alterations in functional connectivity that occur in patients with absence epilepsy. We found an altered functional connectivity within and between functional modules in patients with absence epilepsy. Some brain regions had a greater number of altered connections. The functional connectivity within and between modules in absence epilepsy patients showed an increase in the number of positive connections and a decrease in the number of the negative connections. In particular, the superior frontal gyrus demonstrated both an increased number of connections with other nodes of the frontal default mode network and a decreased number of connections with the limbic system. These findings provide a new perspective and shed light on how the balance of connections within and between modules may contribute to the development of absence epilepsy.

Longitudinal ¹H MRS assessment of the thalamus in a Coriaria lactone-induced rhesus monkey status epilepticus model

Neurophysiological, biochemical and anatomical evidence implicates the thalamus as playing a role in epileptic seizures. Until recently, however, longitudinal characterization of in vivo thalamus dynamics had not been reported. In this study, we investigated the metabolism in the thalamus to identify the changes that occur following Coriaria lactone (CL)-induced status epilepticus (SE) and to observe whether the epileptiform discharges could present a difference between the left and right thalami. Five rhesus monkeys underwent whole-brain MRI and single-voxel MRS on a Siemens Trio Tim 3-T MR scanner with a 12-channel head coil. Spectra were processed using LCModel. Scans were performed in five animals before SE and at 1, 7, 21 and 42  days after the onset of SE. Statistical analysis of the data obtained demonstrated no significant difference in the bilateral thalamus of healthy macaques. Our MRS data showed symmetrical distributions of N-acetylaspartate in the right and left thalami after SE (p = 0.003). In addition, this longitudinal study demonstrated elevated glutamate/glutamine (p < 0.05) and reduced myo-inositol (p < 0.05) in the bilateral thalamus 1  day after SE, and all metabolites approached their baseline levels by the fifth scan. Our results demonstrate that metabolic changes occur in the thalamus during CL-induced SE in rhesus monkeys. The various metabolic changes may indicate that the left thalamus is more vulnerable to epileptic strike.

Localization of epileptic foci in Children with childhood absence epilepsy by magnetoencephalography combined with synthetic aperture magnetometry

This present study was aimed to investigate the localizable diagnostic value of magnetoencephalography (MEG) combined with synthetic aperture magnetometry (SAM) in childhood absence epilepsy (CAE). Thirteen CAE patients underwent MEG detection at resting state and after hyperventilation, and then the epileptic foci were located by SAM. In the thirteen CAE patients, epileptic foci were found in five cases (38.5%), and they were all located in the bilateral frontal lobe, suggesting that the frontal lobe in some CAE patients may serve as the epileptic foci. Our findings indicate that MEG combined with SAM could be of diagnostic value in localizing the epileptic foci in certain CAE patients.

Early detection of secondary damage in ipsilateral thalamus after acute infarction at unilateral corona radiata by diffusion tensor imaging and magnetic resonance spectroscopy

Background

Traditional magnetic resonance (MR) imaging can identify abnormal changes in ipsilateral thalamus in patients with unilateral middle cerebral artery (MCA) infarcts. However, it is difficult to demonstrate these early changes quantitatively. Diffusion tensor imaging (DTI) and proton magnetic resonance spectroscopy (MRS) are potentially sensitive and quantitative methods of detection in examining changes of tissue microstructure and metabolism. In this study, We used both DTI and MRS to examine possible secondary damage of thalamus in patients with corona radiata infarction.

Methods

Twelve patients with unilateral corona radiata infarction underwent MR imaging including DTI and MRS at one week (W1), four weeks (W4), and twelve weeks (W12) after onset of stroke. Twelve age-matched controls were imaged. Mean diffusivity (MD), fractional anisotropy (FA), N-acetylaspartate (NAA), choline(Cho), and creatine(Cr) were measured in thalami.

Results

T1-weighted fluid attenuation inversion recovery (FLAIR), T2-weighted, and T2-FLAIR imaging showed an infarct at unilateral corona radiate but no other lesion in each patient brain. In patients, MD was significantly increased at W12, compared to W1 and W4 (all P< 0.05). NAA was significantly decreased at W4 compared to W1, and at W12 compared to W4 (all P< 0.05) in the ipsilateral thalamus. There was no significant change in FA, Cho, or Cr in the ipsilateral thalamus from W1 to W12. Spearman's rank correlation analysis revealed a significant negative correlation between MD and the peak area of NAA, Cho, and Cr at W1, W4, and W12 and a significant positive correlation of FA with NAA at W1.

Conclusions

These findings indicate that DTI and MRS can detect the early changes indicating secondary damage in the ipsilateral thalamus after unilateral corona radiata infarction. MRS may reveal the progressive course of damage in the ipsilateral thalamus over time.

Impaired attention and network connectivity in childhood absence epilepsy

Patients with childhood absence epilepsy (CAE) often demonstrate impaired interictal attention, even with control of their seizures. No previous study has investigated the brain networks involved in this impairment. We used the continuous performance task (CPT) of attentional vigilance and the repetitive tapping task (RTT), a control motor task, to examine interictal attention in 26 children with CAE and 22 matched healthy controls. Each subject underwent simultaneous 3T functional magnetic resonance imaging-electroencephalography (fMRI-EEG) and CPT/RTT testing. Areas of activation on fMRI during the CPT task were correlated with behavioral performance and used as seed regions for resting functional connectivity analysis. All behavioral measures reflecting inattention were significantly higher in patients. Correlation analysis revealed that impairment on all measures of inattention on the CPT task was associated with decreased medial frontal cortex (MFC) activation during CPT. In addition, analysis of resting functional connectivity revealed an overall decrease within an 'attention network' in patients relative to controls. Patients demonstrated significantly impaired connectivity between the right anterior insula/frontal operculum (In/FO) and MFC relative to controls. Our results suggest that there is impaired function in an attention network comprising anterior In/FO and MFC in patients with CAE. These findings provide an anatomical and functional basis for impaired interictal attention in CAE, which may allow the development of improved treatments targeted at these networks.

Functional connectivity in patients with idiopathic generalized epilepsy

PURPOSE

Idiopathic generalized epilepsy (IGE) is characterized by electroencephalography (EEG) recordings with generalized spike wave discharges (GSWDs) arising from normal background activity. Although GSWDs are the result of highly synchronized activity in the thalamocortical network, EEG without GSWDs is believed to represent normal brain activity. The aim of this study was to investigate whether thalamocortical interactions are altered even during GSWD-free EEG periods in patients with IGE.

METHODS

A GSWD-related group analysis was performed in 12 IGE patients to define seeds in areas involved during GSWDs. EEG-functional magnetic resonance imaging (fMRI) datasets from 22 IGE patients without GSWDs during the investigation and 30 age-matched healthy controls were then selected to investigate functional connectivity in GSWD-related areas. Blood oxygen level dependent (BOLD) signal changes were extracted from seeds defined by the GSWD-related group analysis. The averaged time course within each seed was used to detect brain regions with BOLD signal correlated with the seed. Group differences between patients and controls were estimated.

KEY FINDINGS

The GSWD-related group analysis showed BOLD activation in the thalamus, the frontomesial cortex, and the cerebellum and BOLD deactivation in default mode areas. For the connectivity analysis, eight seeds were placed bilaterally in the thalamus, mesial frontal cortex, precuneus, and cerebellum. The functional connectivity analysis of these seeds did not show clearly altered functional connectivity for patients versus controls.

SIGNIFICANCE

The results underscore the paroxysmal nature of GSWDs: Although GSWDs are characterized by highly synchronized activity in the thalamocortical network, the functional connectivity in areas involved during GSWDs does not demonstrate abnormality in GSWD-free periods.

Update on neuroimaging in epilepsy

Neuroimaging in epilepsy is a very large and growing field. Researchers in this area have quickly adopted new methods, resulting in a lively literature. Basic features of common epilepsies are well known, but, outside of the specific area of epilepsy surgery evaluation, new methods evolving in the last few years have had limited new beneficial clinical impact. Here, an overview of the epilepsy neuroimaging literature of the last 5 years, with an emphasis on mesial temporal lobe epilepsy, idiopathic generalized epilepsies, presurgical evaluation and new developments in functional MRI is presented. The need for attention to clinical translation, as well as immediate opportunities and future trends in this field, are discussed.

A proton magnetic resonance spectroscopic study in juvenile absence epilepsy in early stages

PURPOSE

The aim of this study to evaluate the hippocampal, frontal and thalamic lobe functions in the early stage of the juvenile absence epilepsy (JAE) by magnetic resonance proton spectroscopy (MRS).

METHOD

Fourteen patients with juvenile absence epilepsy with typical absence seizures and 10 healthy volunteer controls were included in this study. The diagnosis of the patients was in accordance with EEG findings and seizure semiology. All patients had minimum twice EEG recordings and all had typical 3-Hz generalized spike and slow-wave discharges at least on one EEG. All patients had bilateral MRS of frontal, thalamic and hippocampal regions and NAA, NAA/Cr, NAA/Cho, NAA/Cho+Cr levels were detected.

RESULTS

The mean age was 14.9+/-2.05 and 14.5+/-1.7 of the JAE patients and control subjects, respectively. Mean seizure onset duration were 2.3+/-0.9 years. In patient group the frontal, thalamic and hippocampal NAA/Cr ratios were 1.65, 1.78, 1.47 in right and 1.75, 1.90, 1.42 in left, respectively. While in the control group NAA/Cr ratios were 1.64, 2.42, 1.57 in right and 1.83, 2.44, 1.47 in left, respectively. There weren't any difference in frontal and hippocampal regions, but the bilateral thalamic NAA, NAA/Cr ratios of the patients were significantly lower than control group even in early stages of the disease.

CONCLUSION

The observed reductions in NAA levels and NAA/Cr ratios of bilateral thalamic regions are consistent with epilepsy related excitoxicity as a possible underlying mechanism even in early stage of JAE. However, we believe that to generalize the results of our study a prospective multicenter study is required.

Current themes in neuroimaging of epilepsy: brain networks, dynamic phenomena, and clinical relevance

Brain scanning methods were first applied in patients with epilepsy more than 30years ago. A very substantial literature now exists in this field, which is exponentially increasing. Contemporary neuroimaging studies in epilepsy reflect new concepts in the epilepsies, as well as current methodological developments. In particular, this area is emphasising the role of networks in epileptogenicity, the existence of dynamic phenomena which can be captured by imaging, and is beginning to validate the implementation of neuroimaging in the clinic. Here, recent studies of the last 5years are reviewed, covering the full range of neuroimaging methods with SPECT, PET and MRI in epilepsy.

Multi-voxel magnetic resonance spectroscopy of cerebral metabolites in healthy adults at 3 Tesla

RATIONALE AND OBJECTIVES

The objective of this study was to determine how metabolite values (total N-acetyl aspartate [tNAA], glutamate plus glutamine [Glx], total choline [tCho], myoinositol [mI], and total creatine [tCr]) vary across brain regions in healthy subjects. This study was implemented to create an internal reference database for patients with psychiatric disorders and epilepsy.

MATERIALS AND METHODS

Using the multivoxel technique with a voxelwise phantom calibration on a 3-T magnetic resonance imaging scanner, metabolite levels of 29 healthy controls (13 men, 16 women; average age, 29 years) were obtained from the hippocampi, basal ganglia, insula cortex, cingulum, and precuneus. Additionally, gray and white matter metabolite values were obtained from the frontal and parietal lobes.

RESULTS

No significant effect of gender was noticed. The total magnitude of variation was greatest for Glx, followed by tNAA, mI, tCho, and tCr. Glx/tCr, Glx, and tCr were increased in gray matter, while tNAA/tCr, tCho/tCr, respectively tNAA and tCho, were elevated in white matter. These findings indicate (1) anterior-to-posterior increases of tNAA/tCr and Glx/tCr, respectively tNAA and Glx, along the midline in gray matter (cingulum); (2) increased tNAA/tCr, respectively tNAA, in white matter in the fiber tracts of the precentral region; (3) an accentuated anterior-to-posterior increase of tCr in the insula cortex; and (4) an anterior-to-posterior decrease of tCho/tCr and tCho in white matter.

CONCLUSIONS

There are significant metabolic differences within tissue types and within tissue types at different locations; therefore, the spectra and metabolite values presented should provide a useful internal reference for both clinical and research studies.

Absence seizures: a review of recent reports with new concepts

Absence seizures with bilateral spike-wave (SW) complexes at 3Hz are divided into the childhood form, with onset at around 6 years of age, and the juvenile form, with onset usually at 12 years of age. These seizures typically last 9-12s and, at times, are activated by hyperventilation and occasionally by photic stimulation. Generalized tonic-clonic (GTC) seizures may also occur, especially in the juvenile form. There may be cognitive changes, in addition to linguistic and behavioral problems. Possible mechanisms for epileptogenesis may involve GABAergic systems, but especially T-calcium channels. The thalamus, especially the reticular nucleus, plays a major role, as does the frontal cortex, mainly the dorsolateral and orbital frontal areas, to the extent that some investigators have concluded that absence seizures are not truly generalized, but rather have selective cortical networks, mainly ventromesial frontal areas and the somatosensory cortex. The latter network is a departure from the more popular concept of a generalized epilepsy. Between the "centrencephalic" and "corticoreticular" theories, a "unified" theory is presented. Proposed genes include T-calcium channel gene CACNA1H, likely a susceptible gene in the Chinese Han population and a contributory gene in Caucasians. Electroencephalography has revealed an interictal increase in prefrontal activity, essential for the buildup of the ictal SW complexes maximal in that region. Infraslow activity can also be seen during ictal SW complexes. For treatment, counter to common belief, ethosuximide may not increase GTC seizures, as it reduces low-threshold T-calcium currents in thalamic neurons. Valproic acid and lamotrigine are also first-line medications. In addition, zonisamide and levetiracetam can be very helpful in absence epilepsy.

Correlation study of optimized voxel-based morphometry and (1)H MRS in patients with mesial temporal lobe epilepsy and hippocampal sclerosis

PURPOSE

: To assess whether structural and metabolic brain abnormalities are correlated in MTLE/HS syndrome.

METHODS

: Optimized voxel-based morphometry (VBM) of gray matter concentration (GMC) and gray matter volume (GMV) and proton magnetic resonance spectroscopy measurements from both-sided hippocampal and thalamic regions were performed in 20 MTLE/HS patients and 20 sex- and age-matched healthy controls. The local GMC and GMV values were calculated in both the affected and unaffected hippocampi and ipsilateral and contralateral thalami in patients and healthy subjects, and these were compared. VBM variables and NAA, NAA/Cr and NAA/(Cr+Cho) values from the investigated brain regions were correlated.

RESULTS

: (1) Analysis revealed significantly more extensive GMV reduction than GMC reduction in patients' affected hippocampus. In addition, significant GMV reduction was observed in the ipsilateral thalamus in MTLE/HS patients. (2) Significant decreases in all VBM and MRS variables were revealed in the affected hippocampus. Whilst practically normal GMC values were revealed in patients' both-sided thalamic regions, a significant decrease in local GMV and metabolic measurements were found in the patients' ipsilateral thalamus. (3) Pearson's correlations between structural and metabolic abnormalities were significant for the ipsilateral thalamus only.

CONCLUSION

: Structural and metabolic abnormalities as detected by optimized voxel-based morphometry and (1)H MRS in hippocampal and thalamic regions are only partially correlated in MTLE/HS patients. It seems therefore reasonable that both methods reflect different aspects of brain pathology, which, at least to some degree, might be independently ongoing.

Early treatment suppresses the development of spike-wave epilepsy in a rat model

PURPOSE

Current treatments for epilepsy may control seizures, but have no known effects on the underlying disease. We sought to determine whether early treatment in a model of genetic epilepsy would reduce the severity of the epilepsy phenotype in adulthood.

METHODS

We used Wistar albino Glaxo rats of Rijswijk (WAG/Rij) rats, an established model of human absence epilepsy. Oral ethosuximide was given from age p21 to 5 months, covering the usual period in which seizures develop in this model (age approximately 3 months). Two experiments were performed: (1) cortical expression of ion channels Nav1.1, Nav1.6, and HCN1 (previously shown to be dysregulated in WAG/Rij) measured by immunocytochemistry in adult treated rats; and (2) electroencephalogram (EEG) recordings to measure seizure severity at serial time points after stopping the treatment.

RESULTS

Early treatment with ethosuximide blocked changes in the expression of ion channels Nav1.1, Nav1.6, and HCN1 normally associated with epilepsy in this model. In addition, the treatment led to a persistent suppression of seizures, even after therapy was discontinued. Thus, animals treated with ethosuximide from age p21 to 5 months still had a marked suppression of seizures at age 8 months.

DISCUSSION

These findings suggest that early treatment during development may provide a new strategy for preventing epilepsy in susceptible individuals. If confirmed with other drugs and epilepsy paradigms, the availability of a model in which epileptogenesis can be controlled has important implications both for future basic studies, and human therapeutic trials.