Ictal dystonia and secondary generalization in temporal lobe seizures: a video-EEG study

Progressive postoperative atrophy of ipsilateral thalamus, putamen, and globus pallidus in patients with temporal lobe epilepsy: A volumetric analysis

OBJECTIVE

Cortical atrophy close to medial temporal structures has been described consistently in patients with temporal lobe epilepsy (TLE). Successful TLE surgery may have a neuroprotective effect preventing further atrophy of temporal and extratemporal cortex. However, the effects of epilepsy surgery on subcortical structures demand additional enlightenment. This work aimed to determine how epilepsy surgery affects volumes of subcortical structures in medically refractory temporal lobe epilepsy patients.

METHODS

We compared MRI volumes of subcortical structures in 62 patients with TLE (36 left, 26 right) before and after anterior temporal lobectomy with 38 TLE patients (20 left, 18 right) who were considered to be good surgical candidates and had at least two brain MRIs.

RESULTS

There were no volume differences in subcortical structures on preoperative and initial MRIs of non-operated TLE patients. At baseline, the ipsilateral thalamus and putamen in TLE patients were marginally smaller than contralateral structures. Operated patients showed a significant postoperative volume reduction in ipsilateral thalamus, putamen, and globus pallidus. In contrast, there were no significant volumetric reductions in non-operated patients longitudinally. There were no volumetric changes associated with different surgical outcomes or different postoperative cognitive outcomes.

SIGNIFICANCE

Our study demonstrated postoperative volume loss of thalamus, putamen and globus pallidus ipsilaterally to the side of resection. Our findings suggest surgery-related changes, likely Wallerian degeneration within subcortical networks not related to seizure or cognitive outcome.

PLAIN LANGUAGE SUMMARY

We studied 100 patients with epilepsy, comparing those who had surgery to those who did not. After surgery, the thalamus, putamen and globus pallidus on the same side as the surgery shrank significantly, but not in non-surgery patients. This suggests surgery-related changes in deeper brain structures, unrelated to seizure freedom or cognitive outcomes. This research sheds additional light on the response of the subcortical structure to epilepsy surgery, highlighting potential areas for further study.

Limited cerebellar gradient extension in temporal lobe epilepsy with dystonic posturing

OBJECTIVE

Dystonic posturing (DP) is a common semiology in temporal lobe epilepsy (TLE). We aimed to explore cerebellar gradient alterations in functional connectivity in TLE patients with and without DP.

METHODS

Resting-state functional MRI data were obtained in 60 TLE patients and 32 matched healthy controls. Patients were further divided into two groups: TLE with DP (TLE + DP, 31 patients) and TLE without DP (TLP-DP, 29 patients). We explored functional gradient alterations in the cerebellum based on cerebellar-cerebral functional connectivity and combined with independent component analysis to evaluate cerebellar-cerebral functional integration and reveal the contribution of the motor components to the gradient.

RESULTS

There were no obvious differences in clinical features and postoperative seizure outcomes between TLE + DP and TLE-DP patients. Patients and controls all showed a clear unimodal-to-transmodal gradient transition in the cerebellum, while TLE patients demonstrated an extended principal gradient in functional connectivity compared to healthy controls, which was more limited in TLE + DP patients. Gradient alterations were more widespread in TLE-DP patients, involving bilateral cerebellum, while gradient alterations in TLE + DP patients were limited in the cerebellum ipsilateral to the seizure focus. In addition, more cerebellar motor components contributed to the gradient alterations in TLE + DP patients, mainly in ipsilateral cerebellum.

SIGNIFICANCE

Extended cerebellar principal gradients in functional connectivity revealed excessive functional segregation between unimodal and transmodal systems in TLE. The functional connectivity gradients were more limited in TLE + DP patients. Functional connectivity in TLE patients with dystonic posturing involved more contribution of cerebellar motor function to ipsilateral cerebellar gradient.

PLAIN LANGUAGE SUMMARY

Dystonic posturing contralateral to epileptic focus is a common symptom in temporal lobe epilepsy, and the cerebellum may be involved in its generation. In this study, we found cerebellar gradients alterations in functional connectivity in temporal lobe epilepsy patients with and without contralateral dystonic posturing. In particular, we found that TLE patients with dystonic posturing may have more limited cerebellar gradient in functional connectivity, involving more contribution of cerebellar motor function to ipsilateral cerebellar gradient. Our study suggests a close relationship between ipsilateral cerebellum and contralateral dystonic posturing.

Mesial temporal lobe spiking reveals distinct patterns of blood oxygen level-dependent functional magnetic resonance imaging activation using simultaneous intracranial electroencephalography-functional magnetic resonance imaging

OBJECTIVE

Temporal lobe epilepsy (TLE) has a high probability of becoming drug resistant and is frequently considered for surgical intervention. However, 30% of TLE cases have nonlesional magnetic resonance imaging (MRI) scans, which is associated with worse surgical outcomes. Characterizing interactions between temporal and extratemporal structures in these patients may help understand these poor outcomes. Simultaneous intracranial electroencephalography-functional MRI (iEEG-fMRI) can measure the hemodynamic changes associated with interictal epileptiform discharges (IEDs) recorded directly from the brain. This study was designed to characterize the whole brain patterns of IED-associated fMRI activation recorded exclusively from the mesial temporal lobes of patients with nonlesional TLE.

METHODS

Eighteen patients with nonlesional TLE undergoing iEEG monitoring with mesial temporal IEDs underwent simultaneous iEEG-fMRI at 3 T. IEDs were marked, and statistically significant clusters of fMRI activation were identified. The locations of IED-associated fMRI activation for each patient were determined, and patients were grouped based on the location and pattern of fMRI activation.

RESULTS

Two patterns of IED-associated fMRI activation emerged: primarily localized (n = 7), where activation was primarily located within the ipsilateral temporal lobe, and primarily diffuse (n = 11), where widespread bilateral extratemporal activation was detected. The primarily diffuse group reported significantly fewer focal to bilateral tonic-clonic seizures and had better postsurgical outcomes.

SIGNIFICANCE

Simultaneous iEEG-fMRI can measure the hemodynamic changes associated with focal IEDs not visible on scalp EEG, such as those arising from the mesial temporal lobe. Significant fMRI activation associated with these IEDs was observed in all patients. Two distinct patterns of IED-associated activation were seen: primarily localized to the ipsilateral temporal lobe and more widespread, bilateral activation. Patients with widespread IED associated-activation had fewer focal to bilateral tonic-clonic seizures and better postsurgical outcome, which may suggest a neuroprotective mechanism limiting the spread of ictal events.

Motor seizure semiology

Motor semiology is a major component of epilepsy evaluation, which provides essential information on seizure classification and helps in seizure localization. The typical motor seizures include tonic, clonic, tonic-clonic, myoclonic, atonic, epileptic spasms, automatisms, and hyperkinetic seizures. Compared to the "positive" motor signs, negative motor phenomena, for example, atonic seizures and Todd's paralysis are also crucial in seizure analysis. Several motor signs, for example, version, unilateral dystonia, figure 4 sign, M2e sign, and asymmetric clonic ending, are commonly observed and have significant clinical value in seizure localization. The purpose of this chapter is to review the localization value and pathophysiology associated with the well-defined motor seizure semiology using updated knowledge from intracranial electroencephalographic recordings, particularly stereoelectroencephalography.

Long-term in vivo application of a potassium channel-based optogenetic silencer in the healthy and epileptic mouse hippocampus

BACKGROUND

Optogenetic tools allow precise manipulation of neuronal activity via genetically encoded light-sensitive proteins. Currently available optogenetic inhibitors are not suitable for prolonged use due to short-lasting photocurrents, tissue heating, and unintended changes in ion distributions, which may interfere with normal neuron physiology. To overcome these limitations, a novel potassium channel-based optogenetic silencer, named PACK, was recently developed. The PACK tool has two components: a photoactivated adenylyl cyclase from Beggiatoa (bPAC) and a cAMP-dependent potassium channel, SthK, which carries a large, long-lasting potassium current in mammalian cells. Previously, it has been shown that activating the PACK silencer with short light pulses led to a significant reduction of neuronal firing in various in vitro and acute in vivo settings. Here, we examined the viability of performing long-term studies in vivo by looking at the inhibitory action and side effects of PACK and its components in healthy and epileptic adult male mice.

RESULTS

We targeted hippocampal cornu ammonis (CA1) pyramidal cells using a viral vector and enabled illumination of these neurons via an implanted optic fiber. Local field potential (LFP) recordings from CA1 of freely moving mice revealed significantly reduced neuronal activity during 50-min intermittent (0.1 Hz) illumination, especially in the gamma frequency range. Adversely, PACK expression in healthy mice induced chronic astrogliosis, dispersion of pyramidal cells, and generalized seizures. These side effects were independent of the light application and were also present in mice expressing bPAC without the potassium channel. Light activation of bPAC alone increased neuronal activity, presumably via enhanced cAMP signaling. Furthermore, we applied bPAC and PACK in the contralateral hippocampus of chronically epileptic mice following a unilateral injection of intrahippocampal kainate. Unexpectedly, the expression of bPAC in the contralateral CA1 area was sufficient to prevent the spread of spontaneous epileptiform activity from the seizure focus to the contralateral hippocampus.

CONCLUSION

Our study highlights the PACK tool as a potent optogenetic inhibitor in vivo. However, further refinement of its light-sensitive domain is required to avoid unexpected physiological changes.

Focal to bilateral motor seizures in temporal lobe epilepsy during video-EEG monitoring: effects on surgical outcome

The aim of this study was to determine whether the occurrence of focal to bilateral motor seizures in the course of partial drug withdrawal during video-EEG monitoring (FTBMS-M) had a predictive value for seizure recurrence in surgically treated patients with mesial temporal lobe epilepsy (MTLE). We analyzed the outcomes of 59 patients who underwent temporal lobe resection at 12 month postoperative follow up. In total, 48 out of 59 patients were rendered seizure free (81.4%). We analyzed seizure recurrence after surgery with reference to: (i) occurrence of seizures after partial drug withdrawal during video-EEG monitoring (FTBMS-M); (ii) history of secondarily generalized seizures during antiepileptic drug treatment prior to presurgical evaluation (FTBMS-H) and (iii) other possible confounding factors (sex, age, epilepsy duration, side of surgery, presence of hippocampal sclerosis, and history of febrile seizures). We found no differences in the frequency of seizure recurrences between patients with FTBMS-M and patients without FTBMS-M (4/20 vs. 7/39; p = 0.848). Conversely, the frequency of seizure recurrence was significantly higher among the patients with FTBMS-H than among the patients without FTBMS-H (7/20 vs. 4/39; p = 0.021). The predictive value of FTBMS-H for postoperative seizure recurrence was confirmed in logistic regression analysis. We found a statistically significant influence of FTBMS-H on poor outcome after surgery, but not of FTBMS-M or other confounding variables, which suggests that withdrawal seizures do not affect postsurgical seizure control.

Disrupted basal ganglia-thalamocortical loops in focal to bilateral tonic-clonic seizures

Focal to bilateral tonic-clonic seizures are associated with lower quality of life, higher risk of seizure-related injuries, increased chance of sudden unexpected death, and unfavourable treatment outcomes. Achieving greater understanding of their underlying circuitry offers better opportunity to control these seizures. Towards this goal, we provide a network science perspective of the interactive pathways among basal ganglia, thalamus and cortex, to explore the imprinting of secondary seizure generalization on the mesoscale brain network in temporal lobe epilepsy. Specifically, we parameterized the functional organization of both the thalamocortical network and the basal ganglia-thalamus network with resting state functional MRI in three groups of patients with different focal to bilateral tonic-clonic seizure histories. Using the participation coefficient to describe the pattern of thalamocortical connections among different cortical networks, we showed that, compared to patients with no previous history, those with positive histories of focal to bilateral tonic-clonic seizures, including both remote (none for >1 year) and current (within the past year) histories, presented more uniform distribution patterns of thalamocortical connections in the ipsilateral medial-dorsal thalamic nuclei. As a sign of greater thalamus-mediated cortico-cortical communication, this result comports with greater susceptibility to secondary seizure generalization from the epileptogenic temporal lobe to broader brain networks in these patients. Using interregional integration to characterize the functional interaction between basal ganglia and thalamus, we demonstrated that patients with current history presented increased interaction between putamen and globus pallidus internus, and decreased interaction between the latter and the thalamus, compared to the other two patient groups. Importantly, through a series of 'disconnection' simulations, we showed that these changes in interactive profiles of the basal ganglia-thalamus network in the current history group mainly depended upon the direct but not the indirect basal ganglia pathway. It is intuitively plausible that such disruption in the striatum-modulated tonic inhibition of the thalamus from the globus pallidus internus could lead to an under-suppressed thalamus, which in turn may account for their greater vulnerability to secondary seizure generalization. Collectively, these findings suggest that the broken balance between basal ganglia inhibition and thalamus synchronization can inform the presence and effective control of focal to bilateral tonic-clonic seizures. The mechanistic underpinnings we uncover may shed light on the development of new treatment strategies for patients with temporal lobe epilepsy.

Focal-to-bilateral motor seizures in temporal lobe epilepsy during video-EEG monitoring: effects on surgical outcome

The aim of this study was to determine whether the occurrence of focal-to-bilateral motor seizures in the course of partial drug withdrawal during video-EEG monitoring (FTBMS-M) had a predictive value for seizure recurrence in surgically treated patients with mesial temporal lobe epilepsy (MTLE). We analyzed the outcomes of 59 patients who underwent temporal lobe resection and had postoperative follow-up from 6 to 58 months. In total, 48 out of 59 patients were rendered seizure free (81.4%). We analyzed seizure recurrence after surgery with reference to: (i) occurrence of seizures after partial drug withdrawal during video-EEG monitoring (FTBMS-M); (ii) history of secondarily generalized seizures during antiepileptic drug treatment prior to presurgical evaluation (FTBMS-H) and (iii) other possible confounding factors (sex, age, epilepsy duration, side of surgery, presence of hippocampal sclerosis, and history of febrile seizures). We found no differences in the frequency of seizure recurrences between patients with FTBMS-M and patients without FTBMS-M (4/20 vs. 7/39; p = 0.848). Conversely, the frequency of seizure recurrence was significantly higher among the patients with FTBMS-H than among the patients without FTBMS-H (7/20 vs. 4/39; p = 0.021). The predictive value of FTBMS-H for postoperative seizure recurrence was confirmed in logistic regression analysis. We found a statistically significant influence of FTBMS-H on poor outcome after surgery, but not of FTBMS-M or other confounding variables, which suggests that withdrawal seizures do not affect post-surgical seizure control.

Localized shape abnormalities in the thalamus and pallidum are associated with secondarily generalized seizures in mesial temporal lobe epilepsy

Mesial temporal lobe epilepsy (mTLE) is a common type of drug-resistant epilepsy and secondarily generalized tonic-clonic seizures (sGTCS) have devastating consequences for patients' safety and quality of life. To probe the mechanism underlying the genesis of sGTCS, we investigated the structural differences between patients with and without sGTCS in a cohort of mTLE with radiologically defined unilateral hippocampal sclerosis. We performed voxel-based morphometric analysis of cortex and vertex-wise shape analysis of subcortical structures (the basal ganglia and thalamus) on MRI of 39 patients (21 with and 18 without sGTCS). Comparisons were initially made between sGTCS and non-sGTCS groups, and subsequently made between uncontrolled-sGTCS and controlled-sGTCS subgroups. Regional atrophy of the ipsilateral ventral pallidum (cluster size=450 voxels, corrected p=0.047, Max voxel coordinate=107, 120, 65), medial thalamus (cluster size=1128 voxels, corrected p=0.049, Max voxel coordinate=107, 93, 67), middle frontal gyrus (cluster size=60 voxels, corrected p<0.05, Max voxel coordinate=-30, 49.5, 6), and contralateral posterior cingulate cortex (cluster size=130 voxels, corrected p<0.05, Max voxel coordinate=16.5, -57, 27) was found in the sGTCS group relative to the non-sGTCS group. Furthermore, the uncontrolled-sGTCS subgroup showed more pronounced atrophy of the ipsilateral medial thalamus (cluster size=1240 voxels, corrected p=0.014, Max voxel coordinate=107, 93, 67) than the controlled-sGTCS subgroup. These findings indicate a central role of thalamus and pallidum in the pathophysiology of sGTCS in mTLE.

Ictal spread of medial temporal lobe seizures with and without secondary generalization: an intracranial electroencephalography analysis

OBJECTIVE

Secondary generalization of seizures has devastating consequences for patient safety and quality of life. The aim of this intracranial electroencephalography (icEEG) study was to investigate the differences in onset and propagation patterns of temporal lobe seizures that remained focal versus those with secondary generalization, in order to better understand the mechanism of secondary generalization.

METHODS

A total of 39 seizures were analyzed in nine patients who met the following criteria: (1) icEEG-video monitoring with at least one secondarily generalized tonic-clonic seizure (GTCS), (2) pathologically proven hippocampal sclerosis, and (3) no seizures for at least 1 year after anteromedial temporal lobe resection. Seizures were classified as focal or secondary generalized by behavioral analysis of video. Onset and propagation patterns were compared by analysis of icEEG.

RESULTS

We obtained data from 22 focal seizures without generalization (FS), and 17 GTCS. Seizure-onset patterns did not differ between FS and GTCS, but there were differences in later propagation. All seizures started with low voltage fast activity, except for seven seizures in one patient (six FS, one GTCS), which started with sharply contoured theta activity. Fifteen of 39 seizures started from the hippocampus, and 24 seizures (including six seizures in a patient without hippocampal contacts) started from other medial temporal lobe areas. We observed involvement or more prominent activation of the posterior-lateral temporal regions in GTCS prior to propagation to the other cortical regions, versus FS, which had no involvement or less prominent activation of the posterior lateral temporal cortex. Occipital contacts were not involved at the time of clinical secondary generalization.

SIGNIFICANCE

The posterior-lateral temporal cortex may serve as an important "gateway" controlling propagation of medial temporal lobe seizures to other cortical regions. Identifying the mechanisms of secondary generalization of focal seizures could lead to improved treatments to confine seizure spread.