Magnetic resonance spectroscopy and imaging of the thalamus in idiopathic generalized epilepsy

Prevalence of clinical electroencephalography findings in stroke patients with delirium

OBJECTIVE

Delirium is an acute cognitive disorder associated with multiple electroencephalographic (EEG) abnormalities in non-neurological patients, though specific EEG characteristics in patients with stroke remain unclear. We aimed to compare the prevalence of EEG abnormalities in stroke patients during delirium episodes with periods that did not correspond to delirium.

METHODS

We retrospectively analyzed clinical EEG reports for stroke patients who received daily delirium assessments as part of a prospective study. We compared the prevalence of EEG features corresponding to patient-days with vs. without delirium, including focal and generalized slowing, and focal and generalized epileptiform abnormalities (EAs).

RESULTS

Among 58 patients who received EEGs, there were 192 days of both EEG and delirium monitoring (88% [n = 169] corresponding to delirium). Generalized slowing was significantly more prevalent on days with vs. without delirium (96% vs. 57%, p = 0.03), as were bilateral or generalized EAs (38% vs. 13%, p = 0.03). In contrast, focal slowing (53% vs. 74%, p = 0.11) and focal EAs were less prevalent on days with delirium (38% vs. 48%, p = 0.37), though these differences were not statistically significant.

CONCLUSIONS

We found a higher prevalence of generalized but not focal EEG abnormalities in stroke patients with delirium.

SIGNIFICANCE

These findings may reinforce the diffuse nature of delirium-associated encephalopathy, even in patients with discrete structural lesions.

Effect of vagus nerve stimulation against generalized seizure and status epilepticus recurrence

Objective

Vagus nerve stimulation (VNS) is a palliative surgery for drug-resistant epilepsy. The two objectives of this study were to (1) determine the seizure type most responsive to VNS and (2) investigate the preventive effect on status epilepticus (SE) recurrence.

Methods

We retrospectively reviewed 136 patients with drug-resistant epilepsy who underwent VNS implantation. We examined seizure outcomes at 6, 12, and 24 months following implantation of VNS as well as at the last visit to the Juntendo Epilepsy Center. Univariate analysis and multivariate logistic regression models were used to estimate the prognostic factors.

Results

125 patients were followed up for at least 1 year after VNS implantation. The percentage of patients with at least a 50% reduction in seizure frequency compared with prior to VNS implantation increased over time at 6, 12, and 24 months after VNS implantation: 28, 41, and 52%, respectively. Regarding overall seizure outcomes, 70 (56%) patients responded to VNS. Of the 40 patients with a history of SE prior to VNS implantation, 27 (67%) showed no recurrence of SE. The duration of epilepsy, history of SE prior to VNS implantation and seizure type were correlated with seizure outcomes after VNS implantation in univariate analysis (p = 0.05, p < 0.01, and p = 0.03, respectively). In multivariate logistic regression analysis, generalized seizure was associated with VNS response [odds ratio (OR): 4.18, 95% CI: 1.13-15.5, p = 0.03]. A history of SE prior to VNS implantation was associated with VNS non-responders [(OR): 0.221, 95% CI: 0.097-0.503, p < 0.01]. The duration of epilepsy, focal to bilateral tonic-clonic seizure and epileptic spasms were not significantly associated with VNS responders (p = 0.07, p = 0.71, and p = 0.11, respectively).

Conclusion

Following 125 patients with drug-resistant epilepsy for an average of 69 months, 56% showed at least 50% reduction in seizure frequency after VNS implantation. This study suggests that generalized seizure is the most responsive to VNS, and that VNS may reduce the risk of recurrence of SE. VNS was shown to be effective against generalized seizure and also may potentially influence the risk of further events of SE, two marker of disease treatment that can lead to improved quality of life.

Thalamostriatal disconnection underpins long-term seizure freedom in frontal lobe epilepsy surgery

Around 50% of patients undergoing frontal lobe surgery for focal drug-resistant epilepsy become seizure free post-operatively; however, only about 30% of patients remain seizure free in the long-term. Early seizure recurrence is likely to be caused by partial resection of the epileptogenic lesion, whilst delayed seizure recurrence can occur even if the epileptogenic lesion has been completely excised. This suggests a coexistent epileptogenic network facilitating ictogenesis in close or distant dormant epileptic foci. As thalamic and striatal dysregulation can support epileptogenesis and disconnection of cortico-thalamostriatal pathways through hemispherotomy or neuromodulation can improve seizure outcome regardless of focality, we hypothesize that projections from the striatum and the thalamus to the cortex may contribute to this common epileptogenic network. To this end, we retrospectively reviewed a series of 47 consecutive individuals who underwent surgery for drug-resistant frontal lobe epilepsy. We performed voxel-based and tractography disconnectome analyses to investigate shared patterns of disconnection associated with long-term seizure freedom. Seizure freedom after 3 and 5 years was independently associated with disconnection of the anterior thalamic radiation and anterior cortico-striatal projections. This was also confirmed in a subgroup of 29 patients with complete resections, suggesting these pathways may play a critical role in supporting the development of novel epileptic networks. Our study indicates that network dysfunction in frontal lobe epilepsy may extend beyond the resection and putative epileptogenic zone. This may be critical in the pathogenesis of delayed seizure recurrence as thalamic and striatal networks may promote epileptogenesis and disconnection may underpin long-term seizure freedom.

Could thalamic biochemical changes correlate to cognitive impairment in idiopathic generalized epilepsy?

Background

The thalamus is crucial in the development of idiopathic generalized epilepsy (IGE), which could lead to cognitive dysfunctions, according to data from neuropsychology and advanced neuroimaging investigations. This research aimed to measure the metabolic changes in the thalamus and to assess if could be contributed to cognitive impairment in IGE patients. Thirty IGE patients and thirty healthy volunteers with matched ages, genders, and educational levels participated in this cross-sectional case–control research. The IGE patients and controls were evaluated neuropsychologically using Intelligence Quotient (IQ) to assess general cognitive ability, Digit span for attention, Wechsler memory scale (WMS) for verbal memory, cube drawing test for visuospatial memory, Trail making test for executive functions, and Controlled Oral Word Association test (COWAT) for verbal fluency and quantitative multi-voxel MR spectroscopy (MRS) measurements of N-acetyl aspartate (NAA), choline (Cho), creatine (Cr), NAA/Cr, NAA/Cho and Cho/Cr ratios at 1.5 T scanner. The voxels were located over the right and left thalamus.

Results

The IGE patients showed worse cognitive performance in IQ, attention, executive function, and verbal and visuospatial memory domains compared to the controls. The IGE patients exhibited a significantly decrease NAA in the right thalamus (p = 0.004) and a lower NAA/Cr ratio in the left thalamus (p = 0.01). the mean thalamus NAA level exhibited a positive correlation with CDT (r = 0.45, p = P = 0.01), and WMS-R (r = 0.39, p = 0.03) and a negative correlation with trail-making A test (r = 0.42, P = 0.01).

Conclusions

it was concluded that IGE patients exhibited poor cognition which could be attributed to thalamic neurometabolic changes due to impaired thalamic cortical circuits.

Neurostimulation in generalized epilepsy: A systematic review and meta-analysis

OBJECTIVE

There are three neurostimulation devices available to treat generalized epilepsy: vagus nerve stimulation (VNS), deep brain stimulation (DBS), and responsive neurostimulation (RNS). However, the choice between them is unclear due to lack of head-to-head comparisons. A systematic comparison of neurostimulation outcomes in generalized epilepsy has not been performed previously. The goal of this meta-analysis was to determine whether one of these devices is better than the others to treat generalized epilepsy.

METHODS

Following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, a systematic review of PubMed, Embase, and Web of Science was performed for studies reporting seizure outcomes following VNS, RNS, and DBS implantation in generalized drug-resistant epilepsy between the first pivotal trial study for each modality through August 2022. Specific search criteria were used for VNS ("vagus", "vagal", or "VNS" in the title and "epilepsy" or "seizure"), DBS ("deep brain stimulation", "DBS", "anterior thalamic nucleus", "centromedian nucleus", or "thalamic stimulation" in the title and "epilepsy" or "seizure"), and RNS ("responsive neurostimulation" or "RNS" in the title and "epilepsy" or "seizure"). From 4409 articles identified, 319 underwent full-text reviews, and 20 studies were included. Data were pooled using a random-effects model using the meta package in R.

RESULTS

Sufficient data for meta-analysis were available from seven studies for VNS (n = 510) and nine studies for DBS (n = 87). Data from RNS (five studies, n = 18) were insufficient for meta-analysis. The mean (SD) follow-up durations were as follows: VNS, 39.1 (23.4) months; DBS, 23.1 (19.6) months; and RNS, 22.3 (10.6) months. Meta-analysis showed seizure reductions of 48.3% (95% confidence interval [CI] = 38.7%-57.9%) for VNS and 64.8% (95% CI = 54.4%-75.2%) for DBS (p = .02).

SIGNIFICANCE

Our meta-analysis indicates that the use of DBS may lead to greater seizure reduction than VNS in generalized epilepsy. Results from RNS use are promising, but further research is required.

Ketamine administration in idiopathic epileptic and healthy control dogs: Can we detect differences in brain metabolite response with spectroscopy?

Introduction

In recent years ketamine has increasingly become the focus of multimodal emergency management for epileptic seizures. However, little is known about the effect of ketamine on brain metabolites in epileptic patients. Magnetic resonance spectroscopy (MRS) is a non-invasive technique to estimate brain metabolites in vivo. Our aim was to measure the effect of ketamine on thalamic metabolites in idiopathic epileptic (IE) dogs using 3 Tesla MRS. We hypothesized that ketamine would increase the glutamine-glutamate (GLX)/creatine ratio in epileptic dogs with and without antiseizure drug treatment, but not in control dogs. Furthermore, we hypothesized that no different responses after ketamine administration in other measured brain metabolite ratios between the different groups would be detected.

Methods

In this controlled prospective experimental trial IE dogs with or without antiseizure drug treatment and healthy client-owned relatives of the breeds Border Collie and Greater Swiss Mountain Dog, were included. After sedation with butorphanol, induction with propofol and maintenance with sevoflurane in oxygen and air, a single voxel MRS at the level of the thalamus was performed before and 2 min after intravenous administration of 1 mg/kg ketamine. An automated data processing spectral fitting linear combination model algorithm was used to estimate all commonly measured metabolite ratios. A mixed ANOVA with the independent variables ketamine administration and group allocation was performed for all measured metabolites. A p < 0.05 was considered statistically significant.

Results

Twelve healthy control dogs, 10 untreated IE and 12 treated IE dogs were included. No significant effects for GLX/creatine were found. However, increased glucose/creatine ratios were found (p < 0.001) with no effect of group allocation. Furthermore, increases in the GABA/creatine ratio were found in IEU dogs.

Discussion

MRS was able to detect changes in metabolite/creatine ratios after intravenous administration of 1 mg/kg ketamine in dogs and no evidence was found that excitatory effects are induced in the thalamus. Although it is beyond the scope of this study to investigate the antiseizure potential of ketamine in dogs, results of this research suggest that the effect of ketamine on the brain metabolites could be dependent on the concentrations of brain metabolites before administration.

Centromedian thalamic neuromodulation for the treatment of idiopathic generalized epilepsy

Idiopathic generalized epilepsy (IGE) is a common type of epilepsy and despite an increase in the number of available anti-seizure medications, approximately 20–30% of people with IGE continue to experience seizures despite adequate medication trials. Unlike focal epilepsy, resective surgery is not a viable treatment option for IGE; however, neuromodulation may be an effective surgical treatment for people with IGE. Thalamic stimulation through deep brain stimulation (DBS) and responsive neurostimulation (RNS) have been explored for the treatment of generalized and focal epilepsies. Although the data regarding DBS and RNS in IGE is limited to case reports and case series, the results of the published studies have been promising. The current manuscript will review the published literature of DBS and RNS within the centromedian nucleus of the thalamus for the treatment of IGE, as well as highlight an illustrative case.

Structural network alterations in focal and generalized epilepsy assessed in a worldwide ENIGMA study follow axes of epilepsy risk gene expression

Epilepsy is associated with genetic risk factors and cortico-subcortical network alterations, but associations between neurobiological mechanisms and macroscale connectomics remain unclear. This multisite ENIGMA-Epilepsy study examined whole-brain structural covariance networks in patients with epilepsy and related findings to postmortem epilepsy risk gene expression patterns. Brain network analysis included 578 adults with temporal lobe epilepsy (TLE), 288 adults with idiopathic generalized epilepsy (IGE), and 1328 healthy controls from 18 centres worldwide. Graph theoretical analysis of structural covariance networks revealed increased clustering and path length in orbitofrontal and temporal regions in TLE, suggesting a shift towards network regularization. Conversely, people with IGE showed decreased clustering and path length in fronto-temporo-parietal cortices, indicating a random network configuration. Syndrome-specific topological alterations reflected expression patterns of risk genes for hippocampal sclerosis in TLE and for generalized epilepsy in IGE. These imaging-transcriptomic signatures could potentially guide diagnosis or tailor therapeutic approaches to specific epilepsy syndromes.

Single-Voxel Proton Magnetic Resonance Spectroscopy of the Thalamus in Idiopathic Epileptic Dogs and in Healthy Control Dogs

The role of magnetic resonance spectroscopy (MRS) in the investigation of brain metabolites in epileptic syndromes in dogs has not been explored systematically to date. The aim of this study was to investigate metabolites in the thalamus in dogs affected by idiopathic epilepsy (IE) with and without antiepileptic drug treatment (AEDT) and to compare them to unaffected controls. Our hypothesis is that similar to humans with generalized epilepsy and loss of consciousness, N-acetyl aspartate (NAA) would be reduced, and glutamate–glutamine (Glx) would be increased in treated and untreated IE in comparison with the control group. In this prospective case–control study, Border Collie (BC) and Greater Swiss Mountain dog (GSMD) were divided into three groups: (1) healthy controls, IE with generalized tonic–clonic seizures with (2) and without (3) AEDT. A total of 41 BC and GSMD were included using 3 Tesla single-voxel proton MRS of the thalamus (PRESS localization, shortest TE, TR = 2000 ms, NSA = 240). After exclusion of 11 dogs, 30 dogs (18 IE and 12 healthy controls) remained available for analysis. Metabolite concentrations were estimated with LCModel using creatine as reference and compared using Kruskal–Wallis and Wilcoxon rank-sum tests. The Kruskal–Wallis test revealed significant differences in the NAA-to-creatine (p = 0.04) and Glx-to-creatine (p = 0.03) ratios between the three groups. The Wilcoxon rank-sum test further showed significant reduction in the NAA/creatine ratio in idiopathic epileptic dogs under AEDT compared to epileptic dogs without AEDT (p = 0.03) and compared to healthy controls (p = 0.03). In opposite to humans, Glx/creatine ratio was significantly reduced in dogs with IE under AEDT compared to epileptic dogs without AEDT (p = 0.03) and controls (p = 0.02). IE without AEDT and healthy controls did not show significant difference, neither in NAA/creatine (p = 0.60), nor in Glx-to-creatine (p = 0.55) ratio. In conclusion, MRS showed changes in dogs with IE and generalized seizures under AEDT, but not in those without AEDT. Based upon these results, MRS can be considered a useful advanced imaging technique for the evaluation of dogs with IE in the clinical and research settings.

Neuroimaging and thalamic connectomics in epilepsy neuromodulation

Neuromodulation is an increasingly utilized therapy for the treatment of people with drug-resistant epilepsy. To date, the most common and effective target has been the thalamus, which is known to play a key role in multiple forms of epilepsy. Neuroimaging has facilitated rapid developments in the understanding of functional targets, surgical and programming techniques, and the effects of thalamic stimulation. In this review, the role of neuroimaging in neuromodulation is explored. First, the structural and functional changes of the thalamus in common epilepsy syndromes are discussed as the rationale for neuromodulation of the thalamus. Next, methods for imaging different thalamic nuclei are presented, as well as rationale for the need of direct surgical targeting rather than reliance on traditional stereotactic coordinates. Lastly, we discuss the potential role of neuroimaging in assessing the effects of thalamic stimulation and as a potential biomarker for neuromodulation outcomes.

Seizures initiate in zones of relative hyperexcitation in a zebrafish epilepsy model

Seizures are thought to arise from an imbalance of excitatory and inhibitory neuronal activity. While most classical studies suggest excessive excitatory neural activity plays a generative role, some recent findings challenge this view and instead argue that excessive activity in inhibitory neurons initiates seizures. We investigated this question of imbalance in a zebrafish seizure model with two-photon imaging of excitatory and inhibitory neuronal activity throughout the brain using a nuclear-localized calcium sensor. We found that seizures consistently initiated in circumscribed zones of the midbrain before propagating to other brain regions. Excitatory neurons were both more prevalent and more likely to be recruited than inhibitory neurons in initiation as compared with propagation zones. These findings support a mechanistic picture whereby seizures initiate in a region of hyper-excitation, then propagate more broadly once inhibitory restraint in the surround is overcome.

Quantifying seizure termination patterns reveals limited pathways to seizure end

OBJECTIVE

Despite their possible importance in the design of novel neuromodulatory approaches and in understanding status epilepticus, the dynamics and mechanisms of seizure termination are not well studied. We examined intracranial recordings from patients with epilepsy to differentiate seizure termination patterns and investigated whether these patterns are indicative of different underlying mechanisms.

METHODS

Seizures were classified into one of two termination patterns: (a) those that end simultaneously across the brain (synchronous), and (b) those whose termination is piecemeal across the cortex (asynchronous). Both types ended with either a burst suppression pattern, or continuous seizure activity. These patterns were quantified and compared using burst suppression ratio, absolute energy, and network connectivity.

RESULTS

Seizures with electrographic generalization showed burst suppression patterns in 90% of cases, compared with only 60% of seizures which remained focal. Interestingly, we found similar absolute energy and burst suppression ratios in seizures with synchronous and asynchronous termination, while seizures with continuous seizure activity were found to be different from seizures with burst suppression, showing lower energy during seizure and lower burst suppression ratio at the start and end of seizure. Finally, network density was observed to increase with seizure progression, with significantly lower densities in seizures with continuous seizure activity compared to seizures with burst suppression.

SIGNIFICANCE

Based on this spatiotemporal classification scheme, we suggest that there are a limited number of seizure termination patterns and dynamics. If this bears out, it would imply that the number of mechanisms underlying seizure termination is also constrained. Seizures with different termination patterns exhibit different dynamics even before their start. This may provide useful clues about how seizures may be managed, which in turn may lead to more targeted modes of therapy for seizure control.

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.

Magnetic resonance imaging (MRI) volumetry in children with nonlesional epilepsy, does it help?

Background

Epilepsy is a chronic condition characterized by repeated spontaneous seizures. It affects up to 1% of the population worldwide. Children with magnetic resonance imaging (MRI) negative (or “nonlesional”) focal epilepsy constitute the most challenging pharmacoresistant group undergoing pre-neurosurgical evaluation. Volumetric magnetic resonance imaging (VMRI) is a non-invasive brain imaging technique done to measure the volume and structure of specific regions of the brain. It is useful for many things, but primarily for discovering atrophy (wasting away of body tissue) and measuring its progression. The aim of this study is to assess role of volumetric magnetic resonance imaging in evaluation of nonlesional childhood epilepsy in which no specific findings detected in conventional MRI.

Results

There were 20 children with normal MRI brain volumetry (33.3%) and 40 children (66.6%) with abnormal MRI brain volumetry.

Grey matter volume in the abnormal group was significantly higher (P value was 0.001*) than the normal group (mean ± S.D 934.04 ± 118.12 versus 788.57 ± 57.71 respectively). White matter volume in the abnormal group was significantly smaller (P value was < 0.0001*) than in the normal group (mean ± S.D 217.79 ± 65.22 versus 418.07 ± 103.76 respectively). Right hippocampus CA4-DG volume in the abnormal volume group was found to be significantly smaller (P value < 0.0001*) than that of the normal group volume (mean ± S.D 0.095 ± 0.04 versus 0.32 ± 0.36 respectively). Right hippocampus subiculum volume in the abnormal volume group were found to be significantly smaller (P value was < 0.0001*) than that of the normal group volume (mean ± S.D 0.42 ± 0.11 versus 0.84 ± 0.09 respectively). Thalamus volume in the abnormal group was significantly smaller (P value 0.048*) than in the normal group (mean ± S.D 10.235 ± 3.22 versus 11.82 ± 0.75 respectively). Right thalamus was significantly smaller (P value was 0.028*) than in the normal group (mean ± S.D 5.01 ± 1.62 versus 5.91 ± 0.39 respectively). The sensitivity of the right hippocampus subiculum volume and right hippocampus CA4-DG was 100%. The sensitivity of white matter volume and grey matter volume and thalamus was 85% and 75% and 55% respectively. The specificity of the right hippocampus subiculum volume and right hippocampus CA4-DG was 90% and 90% respectively. The specificity of the right hippocampus subiculum volume and right hippocampus CA4-DG and grey matter volume and white matter volume and total hippocampus and thalamus was 100%. The specificity of brain volume was 60%. The accuracy of the right hippocampus subiculum volume and right hippocampus CA4-DG was 100%. The specificity of white matter volume, grey matter volume, thalamus, total hippocampus, and brain volume was 97%, 87%, 65%, 61%, and 57% respectively.

Conclusion

Volumetric magnetic resonance imaging is a promising imaging technique that can provide assistance in evaluation of nonlesional pharmacoresistant childhood epilepsy.

A systematic review of resting-state and task-based fmri in juvenile myoclonic epilepsy

Functional neuroimaging modalities have enhanced our understanding of juvenile myoclonic epilepsy (JME) underlying neural mechanisms. Due to its non-invasive, sensitive and analytical nature, functional magnetic resonance imaging (fMRI) provides valuable insights into relevant functional brain networks and their segregation and integration properties. We systematically reviewed the contribution of resting-state and task-based fMRI to the current understanding of the pathophysiology and the patterns of seizure propagation in JME Altogether, despite some discrepancies, functional findings suggest that corticothalamo-striato-cerebellar network along with default-mode network and salience network are the most affected networks in patients with JME. However, further studies are required to investigate the association between JME's main deficiencies, e.g., motor and cognitive deficiencies and fMRI findings. Moreover, simultaneous electroencephalography-fMRI (EEG-fMRI) studies indicate that alterations of these networks play a role in seizure modulation but fall short of identifying a causal relationship between altered functional properties and seizure propagation. This review highlights the complex pathophysiology of JME, which necessitates the design of more personalized diagnostic and therapeutic strategies in this group.

Electrical status epilepticus in sleep: The role of thalamus in etiopathogenesis

PURPOSE

In patients diagnosed with epilepsy, decreased ratio of N-acetyl aspartate to creatine (NAA/Cr) measured in magnetic resonance spectroscopy (MRS) has been accepted as a sign of neuronal cell loss or dysfunction. In this study, we aimed to determine whether a similar neuronal cell loss is present in a group of encephalopathy with electrical status epilepticus in sleep (ESES) patients METHODS: We performed this case-control study at a tertiary pediatric neurology center with patients with ESES. Inclusion criteria for the patient group were as follows: 1) a spike-wave index of at least 50%, 2) acquired neuropsychological regression, 3) normal cranial MRI. Eventually, a total of 21 patients with ESES and 17 control subjects were enrolled in the study. MRI of all control subjects was also within normal limits. 3D Slicer program was used for the analysis of thalamic and brain volumes. LCModel spectral fitting software was used to analyze single-voxel MRS data from the right and left thalamus of the subjects.

RESULTS

The mean age was 8.0 ± 1.88 years and 8.3 ± 1.70 years in ESES patients and the control subjects. After correcting for the main potential confounders (age and gender) with a linear regression model, NAA/Creatine ratio of the right thalamus was significantly lower in the ESES patient group compared to the healthy control group (p = 0.026). Likewise, the left thalamus NAA/Cr ratio was significantly lower in the ESES patient group than the healthy control group (p = 0.007). After correcting for age and gender, right thalamic volume was not statistically significantly smaller in ESES patients than in healthy controls (p = 0.337), but left thalamic volume was smaller in ESES patients than in healthy controls (p = 0.024).

CONCLUSION

In ESES patients, the NAA/Creatine ratio, which is an indicator of neuronal cell loss or dysfunction in the right and left thalamus, which appears regular on MRI, was found to be significantly lower than the healthy control group. This metabolic-induced thalamic dysfunction, which was reported for the first time up to date, may play a role in ESES epileptogenesis.

Automated subcortical volume estimation from 2D MRI in epilepsy and implications for clinical trials

Purpose

Most techniques used for automatic segmentation of subcortical brain regions are developed for three-dimensional (3D) MR images. MRIs obtained in non-specialist hospitals may be non-isotropic and two-dimensional (2D). Automatic segmentation of 2D images may be challenging and represents a lost opportunity to perform quantitative image analysis. We determine the performance of a modified subcortical segmentation technique applied to 2D images in patients with idiopathic generalised epilepsy (IGE).

Methods

Volume estimates were derived from 2D (0.4 × 0.4 × 3 mm) and 3D (1 × 1x1mm) T1-weighted acquisitions in 31 patients with IGE and 39 healthy controls. 2D image segmentation was performed using a modified FSL FIRST (FMRIB Integrated Registration and Segmentation Tool) pipeline requiring additional image reorientation, cropping, interpolation and brain extraction prior to conventional FIRST segmentation. Consistency between segmentations was assessed using Dice coefficients and volumes across both approaches were compared between patients and controls. The influence of slice thickness on consistency was further assessed using 2D images with slice thickness increased to 6 mm.

Results

All average Dice coefficients showed excellent agreement between 2 and 3D images across subcortical structures (0.86–0.96). Most 2D volumes were consistently slightly lower compared to 3D volumes. 2D images with increased slice thickness showed lower agreement with 3D images with lower Dice coefficients (0.55–0.83). Significant volume reduction of the left and right thalamus and putamen was observed in patients relative to controls across 2D and 3D images.

Conclusion

Automated subcortical volume estimation of 2D images with a resolution of 0.4 × 0.4x3mm using a modified FIRST pipeline is consistent with volumes derived from 3D images, although this consistency decreases with an increased slice thickness. Thalamic and putamen atrophy has previously been reported in patients with IGE. Automated subcortical volume estimation from 2D images is feasible and most reliable at using in-plane acquisitions greater than 1 mm x 1 mm and provides an opportunity to perform quantitative image analysis studies in clinical trials.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00234-021-02811-x.

Atrophy in the Left Amygdala Predicted Drug Responses in Idiopathic Generalized Epilepsy Patients With Tonic-Clonic Seizures

We aimed to determine the alterations in the subcortical structures of patients with idiopathic generalized epilepsy with tonic-clonic seizures (IGE-GTCS) via MRI volumetry and vertex-based shape analysis and to evaluate the relationships between MRI measures and drug responses. In a follow-up sample of 48 patients with IGE-GTCS and 48 matched normal controls (NCs), high-resolution 3D T1WI was performed at baseline. After 1 year of follow-up, 31 patients were classified as seizure free (SF) and 17 as drug resistant (DR). The volumes of subcortical structures were extracted, and vertex-based shape analysis was performed using FSL-Integrated Registration and Segmentation Toolbox (FSL-FIRST). Comparisons among groups were calculated adjusting for covariates [age, sex, and intracranial volume (ICV)]. Analysis of the relationships among imaging biomarkers along with frequency and duration was assessed using partial correlations. The differential imaging indicators were used as features in a linear support vector machine (LSVM). The DR group displayed significant regional atrophy in the volume of the left amygdala compared with NCs (p = 0.004, false discovery rate corrected) and SF patients (p = 0.029, uncorrected). Meanwhile, vertex-based shape analysis showed focal inward deformation in the basolateral subregion of the left amygdala in DR compared with the results for SF and NC (p < 0.05, FWE corrected). There were significant correlations between the volume changes and seizure frequency (r = -0.324, p = 0.030) and between shape (r = -0.438, p = 0.003) changes and seizure frequency. Moreover, the volume of the left thalamus in the DR group was significantly correlated with seizure frequency (r = -0.689, p = 0.006). The SVM results revealed areas under the receiver operating characteristic curve of 0.82, 0.68, and 0.88 for the classification between SF and DR, between SF and NC, and between DR and NC, respectively. This study indicates the presence of focal atrophy in the basolateral region of the left amygdala in patients with IGE drug resistance; this finding may help predict drug responses and suggests a potential therapeutic target.

Systematically disrupted functional gradient of the cortical connectome in generalized epilepsy: Initial discovery and independent sample replication

Genetic generalized epilepsy is a network disorder typically involving distributed areas identified by classical neuroanatomy. However, the finer topological relationships in terms of continuous spatial arrangement between these systems are still ambiguous. Connectome gradients provide the topological representations of human macroscale hierarchy in an abstract low-dimensional space by embedding the functional connectome into a set of axes. Leveraging connectome gradients, we systematically scrutinized abnormalities of functional connectome gradient in patients with genetic generalized epilepsy with tonic-clonic seizure (GGE-GTCS, n = 78) compared to healthy controls (HC, n = 85), and further examined the reproducibility across multiple processing configurations and in an independent validation sample (patients with GGE-GTCS, n = 28; HC, n = 31). Our findings demonstrated an extended principal gradient at different spatial scales, network-level and vertex-level, in patients with GGE-GTCS. We found consistent results across processing parameters and in validation sample. The extended principal gradient revealed the excessive functional segregation between unimodal and transmodal systems associated with duration of epilepsy and age at seizure onset in patients. Furthermore, the connectivity profile of regions with abnormal principal gradients verified the disrupted functional hierarchy revealed by gradients. Together, our findings provided a novel view of functional system hierarchy alterations, which facilitated a continuous spatial arrangement of macroscale networks, to increase our understanding of the functional connectome hierarchy in generalized epilepsy.

Structural Brain Network Abnormalities and the Probability of Seizure Recurrence After Epilepsy Surgery

OBJECTIVE

We assessed preoperative structural brain networks and clinical characteristics of patients with drug-resistant temporal lobe epilepsy (TLE) to identify correlates of postsurgical seizure recurrences.

METHODS

We examined data from 51 patients with TLE who underwent anterior temporal lobe resection (ATLR) and 29 healthy controls. For each patient, using the preoperative structural, diffusion, and postoperative structural MRI, we generated 2 networks: presurgery network and surgically spared network. Standardizing these networks with respect to controls, we determined the number of abnormal nodes before surgery and expected to be spared by surgery. We incorporated these 2 abnormality measures and 13 commonly acquired clinical data from each patient into a robust machine learning framework to estimate patient-specific chances of seizures persisting after surgery.

RESULTS

Patients with more abnormal nodes had a lower chance of complete seizure freedom at 1 year and, even if seizure-free at 1 year, were more likely to relapse within 5 years. The number of abnormal nodes was greater and their locations more widespread in the surgically spared networks of patients with poor outcome than in patients with good outcome. We achieved an area under the curve of 0.84 ± 0.06 and specificity of 0.89 ± 0.09 in predicting unsuccessful seizure outcomes (International League Against Epilepsy [ILAE] 3-5) as opposed to complete seizure freedom (ILAE 1) at 1 year. Moreover, the model-predicted likelihood of seizure relapse was significantly correlated with the grade of surgical outcome at year 1 and associated with relapses up to 5 years after surgery.

CONCLUSION

Node abnormality offers a personalized, noninvasive marker that can be combined with clinical data to better estimate the chances of seizure freedom at 1 year and subsequent relapse up to 5 years after ATLR.

CLASSIFICATION OF EVIDENCE

This study provides Class II evidence that node abnormality predicts postsurgical seizure recurrence.

Neurochemicals of limbic system and thalamofrontal cortical network: Are they different between patients with idiopathic generalized epilepsy and psychogenic nonepileptic seizure?

OBJECTIVE

Thalamofrontal cortical network and limbic system are proposed to be involved in psychogenic nonepileptic seizure (PNES) and idiopathic generalized epilepsy (IGE). This study aimed to investigate neurochemical changes in prefrontal cortex, thalamus, and limbic circuits in patients with PNES and IGE. We also analyzed the interaction between cognitive functions and neurochemical changes in both groups.

METHODS

Hydrogen proton magnetic resonance spectroscopy (1H-MRS) was used to measure N-acetyl aspartate (NAA), choline (Cho), creatine (Cr), glutamate-glutamine (Glx), and myo-inositol (MI). The voxels were placed on the bilateral dorsolateral prefrontal cortex (DLPFC), dorsomedial prefrontal cortex (DMPFC), anterior cingulate cortex (ACC), and thalamus. Attention and inhibitory control, as well as general intelligence status, were investigated using the Integrated Visual and Auditory Continuous Performance Test (IVA-CPT) and the Wechsler Adult Intelligence Scale (WAIS), respectively, in patients with PNES and IGE, as well as healthy volunteers.

RESULTS

The 1H-MRS showed a decreased ratio of NAA/Cr in the right and left thalamus, right DMPFC, and right ACC in patients with IGE and PNES. Furthermore, a decrease of the NAA/Cr ratio in the left DMPFC and an increase of NAA/Cr ratio in the right DLPFC were observed in patients with PNES compared with the controls. The patient groups had a decreased ratio of Cho/Cr in right ACC compared with the healthy subjects. Moreover, the NAA/Cr ratio in the left thalamus and left DMPFC was correlated with seizure frequency in patient groups. Reduced NAA/Cr ratio in the right ACC and left DLPFC were also correlated with poor IVA-CPT scores.

CONCLUSION

This study highlighted the dysfunction in prefrontal-thalamic-limbic circuits and impairment in neurocognition in patients with PNES and IGE.

Network-based atrophy modeling in the common epilepsies: A worldwide ENIGMA study

Epilepsy is increasingly conceptualized as a network disorder. In this cross-sectional mega-analysis, we integrated neuroimaging and connectome analysis to identify network associations with atrophy patterns in 1021 adults with epilepsy compared to 1564 healthy controls from 19 international sites. In temporal lobe epilepsy, areas of atrophy colocalized with highly interconnected cortical hub regions, whereas idiopathic generalized epilepsy showed preferential subcortical hub involvement. These morphological abnormalities were anchored to the connectivity profiles of distinct disease epicenters, pointing to temporo-limbic cortices in temporal lobe epilepsy and fronto-central cortices in idiopathic generalized epilepsy. Negative effects of age on atrophy further revealed a strong influence of connectome architecture in temporal lobe, but not idiopathic generalized, epilepsy. Our findings were reproduced across individual sites and single patients and were robust across different analytical methods. Through worldwide collaboration in ENIGMA-Epilepsy, we provided deeper insights into the macroscale features that shape the pathophysiology of common epilepsies.

Macroscale and microcircuit dissociation of focal and generalized human epilepsies

Thalamo-cortical pathology plays key roles in both generalized and focal epilepsies, but there is little work directly comparing these syndromes at the level of whole-brain mechanisms. Using multimodal imaging, connectomics, and computational simulations, we examined thalamo-cortical and cortico-cortical signatures and underlying microcircuits in 96 genetic generalized (GE) and 107 temporal lobe epilepsy (TLE) patients, along with 65 healthy controls. Structural and functional network profiling highlighted extensive atrophy, microstructural disruptions and decreased thalamo-cortical connectivity in TLE, while GE showed only subtle structural anomalies paralleled by enhanced thalamo-cortical connectivity. Connectome-informed biophysical simulations indicated modest increases in subcortical drive contributing to cortical dynamics in GE, while TLE presented with reduced subcortical drive and imbalanced excitation-inhibition within limbic and somatomotor microcircuits. Multiple sensitivity analyses supported robustness. Our multiscale analyses differentiate human focal and generalized epilepsy at the systems-level, showing paradoxically more severe microcircuit and macroscale imbalances in the former.

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.

Subtle Brain Developmental Abnormalities in the Pathogenesis of Juvenile Myoclonic Epilepsy

Juvenile myoclonic epilepsy (JME), a lifelong disorder that starts during adolescence, is the most common of genetic generalized epilepsy syndromes. JME is characterized by awakening myoclonic jerks and myoclonic-tonic-clonic (m-t-c) grand mal convulsions. Unfortunately, one third of JME patients have drug refractory m-t-c convulsions and these recur in 70-80% who attempt to stop antiepileptic drugs (AEDs). Behavioral studies documented impulsivity, but also impairment of executive functions relying on organization and feedback, which points to prefrontal lobe dysfunction. Quantitative voxel-based morphometry (VBM) revealed abnormalities of gray matter (GM) volumes in cortical (frontal and parietal) and subcortical structures (thalamus, putamen, and hippocampus). Proton magnetic resonance spectroscopy (MRS) found evidence of dysfunction of thalamic neurons. White matter (WM) integrity was disrupted in corpus callosum and frontal WM tracts. Magnetic resonance imaging (MRI) further unveiled anomalies in both GM and WM structures that were already present at the time of seizure onset. Aberrant growth trajectories of brain development occurred during the first 2 years of JME diagnosis. Because of genetic origin, disease causing variants were sought, first by positional cloning, and most recently, by next generation sequencing. To date, only six genes harboring pathogenic variants (GABRA1, GABRD, EFHC1, BRD2, CASR, and ICK) with Mendelian and complex inheritance and covering a limited proportion of the world population, are considered as major susceptibility alleles for JME. Evidence on the cellular role, developmental and cell-type expression profiles of these six diverse JME genes, point to their pathogenic variants driving the first steps of brain development when cell division, expansion, axial, and tangential migration of progenitor cells (including interneuron cortical progenitors) sculpture subtle alterations in brain networks and microcircuits during development. These alterations may explain "microdysgenesis" neuropathology, impulsivity, executive dysfunctions, EEG polyspike waves, and awakening m-t-c convulsions observed in JME patients.

Neuroimaging of Sudden Unexpected Death in Epilepsy (SUDEP): Insights From Structural and Resting-State Functional MRI Studies

The elusive nature of sudden unexpected death in epilepsy (SUDEP) has led to investigations of mechanisms and identification of biomarkers of this fatal scenario that constitutes the leading cause of premature death in epilepsy. In this short review, we compile evidence from structural and functional neuroimaging that demonstrates alterations to brain structures and networks involved in central autonomic and respiratory control in SUDEP and those at elevated risk. These findings suggest that compromised central control of vital regulatory processes may contribute to SUDEP. Both structural changes and dysfunctional interactions indicate potential mechanisms underlying the fatal event; contributions to individual risk prediction will require further study. The nature and sites of functional disruptions suggest potential non-invasive interventions to overcome failing processes.

Alterations in Brain Metabolites in Patients with Epilepsy with Impaired Consciousness: A Case-Control Study of Interictal Multivoxel 1H-MRS Findings

BACKGROUND AND PURPOSE

Previous studies have shown perfusion abnormalities in the thalamus and upper brain stem in patients with epilepsy with impaired consciousness. We hypothesized that these areas associated with consciousness will also show metabolic abnormalities. However, metabolic abnormalities in those areas correlated with consciousness has not been characterized with multiple-voxel ¹H-MRS. In this study, we investigated the metabolic alterations in these brain regions and assessed the correlation between seizure features and metabolic alterations.

MATERIALS AND METHODS

Fifty-seven patients with epilepsy and 24 control subjects underwent routine MR imaging and 3D multiple-voxel ¹H-MRS. Patients were divided into 3 subgroups: focal impaired awareness seizures (n = 18), primary generalized tonic-clonic seizures (n = 19), and secondary generalized tonic-clonic seizures (n = 20). The measured metabolite alterations in NAA/Cr, NAA/(Cr + Cho), and Cho/Cr ratios in brain regions associated with the consciousness network were compared between the patient and control groups. ROIs were placed in the bilateral inferior frontal gyrus, supramarginal gyrus, cingulate gyrus, precuneus, thalamus, and upper brain stem. Correlations between clinical parameters (epilepsy duration and seizure frequency) and metabolite alterations were analyzed.

RESULTS

Significantly lower NAA/Cr and NAA/(Cho + Cr) ratios (P < .05 and < .01, respectively) were observed in the bilateral thalamus and upper brain stem in all experimental groups, and significantly high Cho/Cr ratios (P < .05) were observed in the right thalamus in the focal impaired awareness seizures group. There were no significant differences in metabolite ratios among the 3 patient groups (P > .05). The secondary generalized tonic-clonic seizures group showed a negative correlation between the duration of epilepsy and the NAA/(Cr + Cho) ratio in the bilateral thalamus (P < .05).

CONCLUSIONS

Metabolic alterations were observed in the brain stem and thalamus in patients with epilepsy with impaired consciousness.

Grey and White Matter Alterations in Juvenile Myoclonic Epilepsy: A Comprehensive Review

Juvenile myoclonic epilepsy (JME) has been classified as a syndrome of idiopathic generalized epilepsy and is characterized by a strong genetic basis, age-specific onset of seizures, specific types of seizures, generalized spike-wave discharges on electroencephalography, and a lack of focal abnormality on magnetic resonance imaging (MRI). Recently, a wide range of advanced neuroimaging techniques have been utilized to elucidate the neuroanatomical substrates and pathophysiological mechanisms underlying JME. Specifically, a number of quantitative MRI studies have reported focal or regional abnormalities of the subcortical and cortical grey matter, particularly the thalamus and frontal cortex, in JME patients. In addition, diffusion tensor imaging studies have pointed to disrupted microstructural integrity of the corpus callosum and multiple frontal white matter tracts as well as thalamofrontal dysconnectivity in JME patients. Converging evidence from neuroimaging studies strongly suggests that JME is a predominantly thalamofrontal network epilepsy, challenging the traditional concept of JME as a generalized epilepsy. There is also limited evidence indicating extrafrontal and extrathalamic involvement in JME. This systematic review outlines the main findings from currently available MRI studies focusing on grey and white matter alterations, and discusses their contributions to the etiology and pathophysiology of JME. The clinical utility, advantages, and drawbacks of each imaging modality are briefly described as well.

Spectral decomposition for resolving partial volume effects in MRSI

PURPOSE

Estimation of brain metabolite concentrations by MR spectroscopic imaging (MRSI) is complicated by partial volume contributions from different tissues. This study evaluates a method for increasing tissue specificity that incorporates prior knowledge of tissue distributions.

METHODS

A spectral decomposition (sDec) technique was evaluated for separation of spectra from white matter (WM) and gray matter (GM), and for measurements in small brain regions using whole-brain MRSI. Simulation and in vivo studies compare results of metabolite quantifications obtained with the sDec technique to those obtained by spectral fitting of individual voxels using mean values and linear regression against tissue fractions and spectral fitting of regionally integrated spectra.

RESULTS

Simulation studies showed that, for GM and the putamen, the sDec method offers < 2% and 3.5% error, respectively, in metabolite estimates. These errors are considerably reduced in comparison to methods that do not account for partial volume effects or use regressions against tissue fractions. In an analysis of data from 197 studies, significant differences in mean metabolite values and changes with age were found. Spectral decomposition resulted in significantly better linewidth, signal-to-noise ratio, and spectral fitting quality as compared to individual spectral analysis. Moreover, significant partial volume effects were seen on correlations of neurometabolite estimates with age.

CONCLUSION

The sDec analysis approach is of considerable value in studies of pathologies that may preferentially affect WM or GM, as well as smaller brain regions significantly affected by partial volume effects. Magn Reson Med 79:2886-2895, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Subcortical grey matter changes in juvenile myoclonic epilepsy

Recent neuroimaging studies have provided converging evidence of structural and functional abnormalities of the thalamus in patients with juvenile myoclonic epilepsy (JME). There has also been limited evidence indicating involvement of the subcortical grey matter structures other than thalamus in JME, but with inconsistent findings across the studies. In the present study, we combined volumetric MRI and diffusion tensor imaging analyses to investigate macrostructural and microstructural alterations of the subcortical grey matter in 64 JME patients compared to 58 matched control subjects. Raw volume, fractional anisotropy (FA), and mean diffusivity (MD) of 6 subcortical grey matter structures (amygdala, hippocampus, caudate, pallidum, putamen, thalamus) were measured in both hemispheres. Between-group (controls versus patients) comparisons of normalized volume, FA, and MD, as well as within-group (patients) correlation analyses between structural changes and clinical variables were carried out. Compared to controls, JME patients exhibited significant volume reductions in left pallidum and bilateral putamen and thalamus. Duration of epilepsy negatively correlated with bilateral putamen volumes. Patients and controls did not differ in FA values of all structures. Compared to controls, JME patients showed significant MD increases in left pallidum and bilateral hippocampus, putamen, and thalamus. Significant positive correlations were found between duration of epilepsy and MD values of bilateral hippocampus and thalamus. We have provided evidence that macrostructural and microstructural abnormalities may not only be confined to the thalamus but also affect basal ganglia and hippocampus in JME. Our findings could further support the pathophysiological hypothesis of striato-thalamo-frontal network abnormality underlying JME, and may implicate disease progression.

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Reduced volumes of left pallidum and bilateral putamen and thalamus in JME patients

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Negative correlation between disease duration and putamen volumes

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Increased MD of left pallidum and bilateral hippocampus, putamen, and thalamus in JME patients

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Positive correlation between disease duration and MD of bilateral hippocampus and thalamus

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Structural changes may not only be confined to the thalamus but also affect basal ganglia and hippocampus in JME.

Proton spectroscopy of the thalamus in a homogeneous sample of patients with easy-to-control juvenile myoclonic epilepsy

Objective

Juvenile myoclonic epilepsy (JME) is a subtype of genetically determined generalized epilepsy that does not present abnormalities on conventional magnetic resonance imaging. The aim of this study was to identify metabolic alterations in the thalamus in a clinically homogeneous sample of patients with easy-to-control JME, using short-echo time proton magnetic resonance spectroscopy (MRS).

Materials and Methods

We performed single-voxel (2 cm × 2 cm × 2 cm), short-echo time (TE = 35 ms) proton MRS of the thalamus in 21 patients with JME and in 14 healthy age-matched controls. We quantified N-acetylaspartate (NAA), total NAA, creatine (Cr), choline, and myo-inositol (MI), as well as the sum of glutamate and glutamine signals, all scaled to internal water content, and we calculated metabolite ratios using Cr as a reference. Values of p < 0.05 were considered significant.

Results

The MI level and the MI/Cr ratio were significantly lower in the thalami of patients diagnosed with JME than in those of the controls. Other metabolites and their ratios did not differ significantly between the two groups.

Conclusion

In our sample of 21 JME patients, we identified lower levels of MI in the thalamus. No significant abnormalities were observed in the concentrations or ratios of other metabolites.

Thalamic hypoperfusion and disrupted cerebral blood flow networks in idiopathic generalized epilepsy: Arterial spin labeling and graph theoretical analysis

PURPOSE

The aim of this study was to investigate interictal cerebral blood flow (CBF) distributions and graph theoretical networks in idiopathic generalized epilepsy (IGE) using arterial spin labeling (ASL) imaging and anatomical covariance methods of graph theoretical analysis.

MATERIAL AND METHODS

We recruited 19 patients with IGE and 19 age-/gender-matched healthy controls. Their CBF images were obtained by pseudo-continuous ASL imaging and compared using statistical parametric mapping 8 software (SPM8) and Graph Analysis Toolbox (GAT).

RESULTS

The ASL imaging could detect interictal hypoperfusion in the thalamus, upper midbrain, and left cerebellum in IGE. Additionally, the graph theoretical analyses revealed characteristic findings of the CBF network of IGE, including significantly reduced resilience to attacks and changes of regional clustering especially in the bilateral temporo-occipital areas and lateral frontal lobes. There was no significance in the comparisons of network metrics.

CONCLUSION

These findings could contribute to a better understanding of the pathophysiology of IGE.

Clinico-radiological profile and outcome of dengue patients with central nervous system manifestations: A case series in an Eastern India tertiary care hospital

BACKGROUND AND OBJECTIVE

Dengue, an acute viral disease, transmitted by Aedes mosquitoes, has a variable clinical spectrum ranging from asymptomatic infection to life-threatening dengue hemorrhagic fever and dengue shock syndrome. However, neurological complications, in general, are unusual but have been observed more frequently in the recent past, and some studies highlighted varied neurological complications during the course of illness. Although dengue is classically considered a nonneurotropic virus, there is increasing evidence for dengue viral neurotropism. In this study, we have evaluated clinico-radiological profile and outcome of nine serologically confirmed dengue patients having varied manifestations of central nervous system (CNS) involvement.

MATERIALS AND METHODS

All the consecutive patients presented with neurological complications with positive serology for dengue infection (IgM positivity) in Department of Medicine, in a tertiary care hospital in Eastern India from August 2013 to October 2014 were included in the study. These patients were subjected to a detailed clinical evaluation, laboratory assessment including complete hemogram, coagulation profile, liver function test, serum electrolytes, and routine CSF (Cerebrospinal Fluid) study with the exclusion of other common neuroinvasive pathogens.

RESULTS

Out of 9 patients with neurological complications associated with confirmed dengue infection, 2 (22%) patients had dengue encephalopathy, 5 (56%) patients have dengue encephalitis, 1 (11%) patient had dengue meningitis, and 1 (11%) patient had postdengue immune-mediated CNS involvement.

CONCLUSION

This case series reaffirms the occurrence of varied CNS manifestations in dengue virus infection and underlines the importance of inclusion of dengue in the differential diagnosis of acute encephalitis syndrome.

Does the Thalamo-Cortical Synchrony Play a Role in Seizure Termination?

The mechanisms underlying seizure termination are still unclear despite their therapeutic importance. We studied thalamo-cortical connectivity and synchrony in human mesial temporal lobe seizures in order to analyze their role in seizure termination. Twenty-two seizures from 10 patients with drug-resistant mesial temporal lobe epilepsy undergoing pre-surgical evaluation were analyzed using intracerebral recordings [stereoelectroencephalography (SEEG)]. We performed a measure of SEEG signal interdependencies (non-linear correlation), to estimate the functional connectivity between thalamus and cortical regions. Then, we derived synchronization indices, namely global, thalamic, mesio-temporal, and thalamo-mesio temporal index at the onset and the end of seizures. In addition, an estimation of thalamic “outputs and inputs” connectivity was proposed. Thalamus was consistently involved in the last phase of all analyzed seizures and thalamic synchronization index was significantly more elevated at the end of seizure than at the onset. The global synchronization index at the end of seizure negatively correlated with seizure duration (p = 0.045) and in the same way the thalamic synchronization index showed an inverse tendency with seizure duration. Six seizures out of twenty-two displayed a particular thalamo-cortical spike-and-wave pattern at the end. They were associated to higher values of all synchronization indices and outputs from thalamus (p = 0.0079). SWP seizures displayed a higher and sustained increase of cortical and thalamo-cortical synchronization with a stronger participation of thalamic outputs. We suggest that thalamo-cortical oscillations might contribute to seizure termination via modulation of cortical synchronization. In the subgroup of SWP seizures, thalamus may exert a control on temporal lobe structures by inducing a stable hypersynchronization that ultimately leads to seizure termination.

BOLD responses related to focal spikes and widespread bilateral synchronous discharges generated in the frontal lobe

OBJECTIVE

To investigate whether specific frontal regions have a tendency to generate widespread bilateral synchronous discharges (WBSDs) and others focal spikes and to determine the regions most involved when WBSDs occur; to assess the relationships between the extent of electroencephalography (EEG) discharges and the extent of metabolic changes measured by EEG/functional magnetic resonance imaging (fMRI).

METHODS

Thirty-seven patients with interictal epileptic discharges (IEDs) with frontocentral predominance underwent EEG/fMRI. Patients were divided into a Focal (20 patients) group with focal frontal spikes and a WBSD group (17 patients). Maps of hemodynamic responses related to IEDs were compared between the two groups.

RESULTS

The mean number ± SD of IEDs in the Focal group was 137.5 ± 38.1 and in the WBSD group, 73.5 ± 16.6 (p = 0.07). The volume of hemodynamic responses in the WBSD group was significantly larger than in the Focal group (mean, 243.3 ± 41.1 versus 114.8 ± 27.4 cm(3), p = 0.01). Maximum hemodynamic responses occurred in both groups in the following regions: dorsolateral prefrontal, mesial prefrontal, cingulate, and supplementary motor cortices. Maxima in premotor and motor cortex, frontal operculum, frontopolar, and orbitofrontal regions were found only in the Focal group, and maxima in thalamus and caudate only occurred in the WBSD group. Thalamic responses were significantly more common in the WBSD group (14/17) than in the Focal group (7/20), p = 0.004. Deactivation in the default mode network was significantly more common in the WBSD group (14/17) than in the Focal group (10/20), p = 0.04.

SIGNIFICANCE

The spatial distribution and extent of blood oxygen level-dependent (BOLD) responses correlate well with electrophysiologic changes. Focal frontal spikes and WBSDs are not region specific in the frontal lobe, and the same frontal region can generate focal and generalized discharges. This suggests that widespread discharges reflect widespread epileptogenicity rather than a focal discharge located in a region favorable to spreading. The thalamus plays an important role in bilateral synchronization.

Functional neuroimaging abnormalities in idiopathic generalized epilepsy

Magnetic resonance imaging (MRI) techniques have been used to quantitatively assess focal and network abnormalities. Idiopathic generalized epilepsy (IGE) is characterized by bilateral synchronous spike–wave discharges on electroencephalography (EEG) but normal clinical MRI. Dysfunctions involving the neocortex, particularly the prefrontal cortex, and thalamus likely contribute to seizure activity. To identify possible morphometric and functional differences in the brains of IGE patients and normal controls, we employed measures of thalamic volumes, cortical thickness, gray–white blurring, fractional anisotropy (FA) measures from diffusion tensor imaging (DTI) and fractional amplitude of low frequency fluctuations (fALFF) in thalamic subregions from resting state functional MRI. Data from 27 patients with IGE and 27 age- and sex-matched controls showed similar thalamic volumes, cortical thickness and gray–white contrast. There were no differences in FA values on DTI in tracts connecting the thalamus and prefrontal cortex. Functional analysis revealed decreased fALFF in the prefrontal cortex (PFC) subregion of the thalamus in patients with IGE. We provide minimum detectable effect sizes for each measure used in the study. Our analysis indicates that fMRI-based methods are more sensitive than quantitative structural techniques for characterizing brain abnormalities in IGE.

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People with idiopathic generalized epilepsy show no brain abnormalities on visual inspection of clinical images.

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Quantitative MRI measures can be deployed to detect structural and functional aberrancies

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Fractional amplitude of low frequency fluctuations (fALFF) from resting state fMRI is decreased in the anterior thalamus in patients with IGE

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We were unable to detect structural differences in the cortex or thalami in IGE compared to controls.

Neuroimaging the epileptogenic process

Epilepsy is one of the most common chronic neurological conditions worldwide. Anti-epileptic drugs (AEDs) can suppress seizures, but do not affect the underlying epileptic state, and many epilepsy patients are unable to attain seizure control with AEDs. To cure or prevent epilepsy, disease-modifying interventions that inhibit or reverse the disease process of epileptogenesis must be developed. A major limitation in the development and implementation of such an intervention is the current poor understanding, and the lack of reliable biomarkers, of the epileptogenic process. Neuroimaging represents a non-invasive medical and research tool with the ability to identify early pathophysiological changes involved in epileptogenesis, monitor disease progression, and assess the effectiveness of possible therapies. Here we will provide an overview of studies conducted in animal models and in patients with epilepsy that have utilized various neuroimaging modalities to investigate epileptogenesis.

Altered thalamocortical functional connectivity in idiopathic generalized epilepsy

OBJECTIVE

Aberrant thalamocortical network has been hypothesized to play a crucial role in the fundamental pathogenesis underlying idiopathic generalized epilepsy (IGE). We aimed to investigate alterations of thalamocortical functional network in patients with IGE using thalamic seed-based functional connectivity (FC) analysis, and their relationships with frontal cognitive functions and clinical characteristics.

METHODS

Forty-nine IGE patients (31 with juvenile myoclonic epilepsy, 17 with IGE with generalized tonic-clonic seizures only, one with juvenile absence epilepsy) and 42 control subjects were prospectively recruited. Voxel-based morphometry (VBM) was first performed to detect thalamic region of gray matter (GM) reduction in patients compared to controls. Between-group comparison of thalamocortical FC was then carried out using resting-state functional magnetic resonance imaging (MRI) analysis seeding at thalamic region of volume difference. In addition, thalamocortical FC was correlated with frontal cognitive performance and clinical variables.

RESULTS

Neuropsychological assessment revealed that patients with IGE had poorer performance than controls on most of the frontal cognitive functions. VBM detected a reduction in GM in the anteromedial thalamus in patients relative to controls. FC analysis seeding at the anteromedial thalamus revealed a reduction of thalamocortical FC in the bilateral medial prefrontal cortex and precuneus/posterior cingulate cortex in patients with IGE compared to controls. Thalamocortical FC strength of bilateral medial prefrontal cortex correlated negatively with disease duration, but did not correlate with seizure frequency or frontal cognitive functions in patients with IGE.

SIGNIFICANCE

Our results indicate that IGE is associated with decreased thalamocortical FC between anteromedial thalamus and medial prefrontal cortex and precuneus/posterior cingulate cortex. Our finding of greater reduction of medial prefrontal FC in relation to increasing disease duration suggests that thalamoprefrontal network abnormality, the proposed pathophysiologic mechanism underlying IGE, may be the consequence of the long-standing burden of the disease.

Longitudinal absolute metabolite quantification of white and gray matter regions in healthy controls using proton MR spectroscopic imaging

The purpose of this study was to evaluate quality parameters, metabolite concentrations and concentration ratios, and to investigate the reproducibility of quantitative proton magnetic resonance spectroscopic imaging ((1)H-MRSI) of selected white and gray matter regions of healthy adults. 2D-quantitative short-TE (1)H-MRSI spectra were obtained at 1.5T from the healthy human brain. Subjects (n = 12) were scanned twice with an interval of six months. Absolute metabolite concentrations were obtained based on coil loading, taking into account differences in sensitivity of the phased-array head coil. Spectral quality parameters, absolute metabolite concentrations, concentration ratios, and their reproducibility were determined and compared between time-points using a repeated measures general linear model. The quality of the spectra of selected brain areas was good, as determined by a mean spectral linewidth between 4.8 and 7.3 Hz (depending on the region). No significant differences between the two time-points were observed for spectral quality, concentrations, or concentration ratios. The mean intrasubject coefficient of variation (CoV) varied between 4.0 and 8.5% for total N-acetylaspartate, 7.2 and 10.8% for total creatine, 5.9 and 9.8% for myo-inositol, and 8.0 and 13.3% for choline, and remained below 20% for glutamate. CoV was generally lower when concentration ratios were considered. The study shows that longitudinal quantitative short-TE (1)H-MRSI generates reproducible absolute metabolite concentrations in healthy human white and gray matter. This may serve as a background for longitudinal clinical studies in adult patients.

Hippocampal atrophy and memory dysfunction in patients with juvenile myoclonic epilepsy

Juvenile myoclonic epilepsy (JME) is a well-defined idiopathic generalized epilepsy (IGE) syndrome, being the most common IGE in adults and accounting for 5-11% of patients with epilepsy. While neuropsychological and neuroimaging studies have discussed the thalamofrontal dysfunction as the major pathophysiologic mechanism of JME, investigation on memory is scarce in patients with JME, with lack of objective assessments addressing common complaints and daily difficulties such as recalling telephone numbers, messages to pass on, and taking antiepileptic drugs regularly. The aim of this study was to objectively assess memory deficits in a group of patients with JME using neuropsychological examination combined with structural MRI of the hippocampi. After informed consent, a cohort of 56 consecutive patients with JME (29 males; mean age ± SD = 26.5 ± 9.01 years; range = 14.0-55.0 years) was included. The control group consisted of 42 healthy volunteers (18 males; mean age ± SD = 31.0 ± 8.54 years; range=20.0-56.0 years) without a family history of neuropsychiatric disorders. Patients and controls were submitted to a MRI and to a neuropsychological assessment, and comparisons between groups were performed, as well as a correlation study between hippocampal atrophy and neuropsychological performance in a group of patients with JME. The level of statistical significance was set at p<0.05. Significant hippocampal atrophy among patients with JME was observed, which was correlated with memory dysfunctions. The present findings reinforce the existence of functional-anatomic ictogenic networks that are not limited to frontal lobes, providing further support towards the concept of 'system epilepsies' in JME.

Juvenile myoclonic epilepsy--neuroimaging findings

Juvenile myoclonic epilepsy (JME) has been classified as a syndrome of idiopathic generalized epilepsy and is characterized by specific types of seizures, showing a lack of pathology using magnetic resonance imaging (MRI) and computed tomography scanning. However, JME is associated with a particular personality profile, and behavioral and neuropsychological studies have suggested the possible involvement of frontal lobe dysfunction. The development of highly sensitive neuroimaging techniques has provided a means of elucidating the underlying mechanisms of JME. Positron emission tomography demonstrated metabolic and neurotransmitter changes in the dorsolateral prefrontal cortex reflecting the particular cognitive and behavioral profile of JME patients. (1)H-magnetic resonance spectroscopy has shown evidence of thalamic dysfunction, which appears to be progressive. Such techniques provide evidence of multi-focal disease mechanisms, suggesting that JME is a frontal lobe variant of a multi-regional, thalamocortical 'network' epilepsy, rather than a generalized epilepsy syndrome. Quantitative MRI revealed significant abnormalities of cortical gray matter in medial frontal areas close to the supplementary motor area and diffusion abnormalities with increased functional coupling between the motor and prefrontal cognitive systems. This altered structural connectivity of the supplementary motor area provides an explanatory framework for the particular imaging findings, seizure type, and seizure-provoking mechanisms in JME.

Personality traits in juvenile myoclonic epilepsy: evidence of cortical abnormalities from a surface morphometry study

Cluster B personality disorders (PD), characterized as emotional instability, immaturity, lack of discipline, and rapid mood changes, have been observed among patients with juvenile myoclonic epilepsy (JME) and have been associated with a worse seizure outcome. Proper understanding of the neurobiology of PD associated with JME could contribute to understanding the basis for earlier and more effective interventions. In the present study, volumetric and geometric features of cortical structure were assessed through an automated cortical surface reconstruction method aiming to verify possible structural cortical alterations among patients with JME. Twenty-two patients with JME with cluster B PD, 44 patients with JME without psychiatric disorders, and 23 healthy controls were submitted to a psychiatric evaluation through SCID I and SCID II and to an MRI scan. Significant cortical alterations in mesiofrontal and frontobasal regions, as well as in other limbic and paralimbic regions, were observed mainly in patients with JME with PD. The present study adds evidence to the hypothesis of frontal and limbic involvement in the pathophysiology of cluster B PD in JME, regions linked to mood and affective regulation, as well as to impulsivity and social behavior. Moreover, a multidimensional pattern of frontal, limbic, and paralimbic changes was observed through a method of structural analysis which offers different and simultaneous geometric features, allowing the elaboration of important pathophysiologic insights about cluster B PD in JME.

Volumetric and shape analysis of thalamus in idiopathic generalized epilepsy

Previous studies using voxel-based morphometry (VBM) provided emerging evidence of structural changes of the thalamus in idiopathic generalized epilepsy (IGE). However, the location of atrophy within the thalamus in IGE has been somewhat inconsistent across the studies. We, therefore, examined the location of thalamic atrophy and its relationship with clinical factors in IGE, using multiple analytic methods. Fifty IGE patients and 50 controls were scanned on a 3T MRI. Structural evaluation consisted of automated thalamic volumetry, VBM, and thalamic shape analysis. Group comparison between patients and controls was made to assess thalamic atrophy. Within-group correlations between thalamic atrophy and clinical variables were further performed in patients. Both thalamic volumes were reduced in IGE patients, and were negatively correlated with disease duration. The VBM showed a significant regional grey matter volume reduction in bilateral anterior-medial thalami in patients compared to controls. Voxel values extracted from the anterior-medial thalamic cluster were negatively correlated with disease duration. Vertex-based shape analysis revealed regional atrophy on the anterior-medial and posterior-dorsal aspects of thalamus bilaterally in patients compared to controls. Correlation analysis showed that anterior-medial and posterior-dorsal aspects of bilateral thalami were negatively correlated with disease duration. Combining multiple analyses, we demonstrated regional atrophy of anterior-medial and posterior-dorsal thalamus in patients with IGE. Given the anatomical connection of these thalamic regions with the frontal lobe, our finding of greater thalamic atrophy in relation to increasing disease duration further supports the pathophysiological concept of thalamo-frontal network abnormality underlying IGE, and may implicate frontal cognitive dysfunctions and disease progression.

Subcortical structural abnormalities in juvenile myoclonic epilepsy (JME): MR volumetry and vertex based analysis

PURPOSE

Imaging studies in juvenile myoclonic epilepsy (JME) have shown abnormalities of the thalamus and frontal cortex. The purpose of this study was to systematically investigate the morphological changes in the deep gray matter (GM) structures using techniques of voxel based morphometry (VBM), MR volumetry and shape analysis.

METHODOLOGY

The study included 40 patients with JME (M:F=21:19; age 22.8±5.3 years) and 19 matched controls (M:F=13:6; age 24.5±4.2 years). All subjects underwent MRI using standard protocol that included T1-3D TFE (Turbo Field Echo) images with 1mm thickness. VBM analysis and MR volumetry were performed. The volumes of deep subcortical GM structures were extracted and vertex-wise shape analysis was performed using FSL-FIRST (FSL-Integrated Registration and Segmentation Toolbox) software.

RESULTS

VBM analysis with a thalamic mask revealed focal thalamic alterations in the anteromedial aspect of the thalamus (p<0.05, false discovery rate (FDR) corrected) which remained significant after adjusting for age, gender and intracranial volume (ICV). Significant volume loss was noted in both the thalami. Vertex-wise shape analysis showed significant focal surface reductions in the thalami bilaterally in patients that were predominantly seen in the medial as well as lateral aspects of the thalamus (p<0.05, FDR corrected). The disease duration correlated with left hippocampus volume while age of onset correlated with right hippocampus volume.

CONCLUSIONS

This study confirms the presence of thalamic alterations in patients with JME. Shape analysis technique provided complementary information and disclosed the presence of focal atrophic changes in patients' thalami. The striatum and hippocampus did not show any significant alterations.

Microstructural white matter abnormality and frontal cognitive dysfunctions in juvenile myoclonic epilepsy

PURPOSE

Previous neuroimaging studies provide growing evidence that patients with juvenile myoclonic epilepsy (JME) have both structural and functional abnormalities of the thalamus and frontal lobe gray matter. However, limited data are available regarding the issue of white matter (WM) involvement, making the microstructural WM changes in JME largely unknown. In the present study we investigated changes of WM integrity in patients with JME, and their relationships with cognitive functions and epilepsy-specific clinical factors.

METHODS

We performed diffusion tensor imaging (DTI) and neuropsychological assessment in 25 patients with JME and 30 control subjects matched for age, gender, and education level. Between-group comparisons of fractional anisotropy (FA) and mean diffusivity (MD) were carried out in a whole-brain voxel-wise manner by using tract-based spatial statistics (TBSS). In addition, both FA and MD were correlated with cognitive performance and epilepsy-specific clinical variables to investigate the influence of these clinical and cognitive factors on WM integrity changes.

KEY FINDINGS

Neuropsychological evaluation revealed that patients with JME had poorer performance than control subjects on most of the frontal function tests. TBSS demonstrated that, compared to controls, patients with JME had significantly reduced FA and increased MD in bilateral anterior and superior corona radiata, genu and body of corpus callosum, and multiple frontal WM tracts. Disease severity, as assessed by the number of generalized tonic-clonic seizures in given years, was negatively correlated with FA and positively correlated with MD extracted from regions of significant differences between patients and controls in TBSS.

SIGNIFICANCE

Our findings of widespread disturbance of microstructural WM integrity in the frontal lobe and corpus callosum that interconnects frontal cortices could further support the pathophysiologic hypothesis of thalamofrontal network abnormality in JME. These WM abnormalities may implicate frontal cognitive dysfunctions and disease progression in JME.