Rapidly progressive hippocampal atrophy: evidence for a seizure-induced mechanism

Progressive alterations in electrophysiological and epileptic network properties during the development of temporal lobe epilepsy in rats

OBJECTIVE

Refractory temporal lobe epilepsy (TLE) with recurring seizures causing continuing pathological changes in neural reorganization. There is an incomplete understanding of how spatiotemporal electrophysiological characteristics changes during the development of TLE. Long-term multi-site epilepsy patients' data is hard to obtain. Thus, our study relied on animal models to reveal the changes in electrophysiological and epileptic network characteristics systematically.

METHODS

Long-term local field potentials (LFPs) were recorded over a period of 1 to 4 months from 6 pilocarpine-treated TLE rats. We compared variations of seizure onset zone (SOZ), seizure onset pattern (SOP), the latency of seizure onsets, and functional connectivity network from 10-channel LFPs between the early and late stages. Moreover, three machine learning classifiers trained by early-stage data were used to test seizure detection performance in the late stage.

RESULTS

Compared to the early stage, the earliest seizure onset was more frequently detected in hippocampus areas in the late stage. The latency of seizure onsets between electrodes became shorter. Low-voltage fast activity (LVFA) was the most common SOP and the proportion of it increased in the late stage. Different brain states were observed during seizures using Granger causality (GC). Moreover, seizure detection classifiers trained by early-stage data were less accurate when tested in late-stage data.

SIGNIFICANCE

Neuromodulation especially closed-loop deep brain stimulation (DBS) is effective in the treatment of refractory TLE. Although the frequency or amplitude of the stimulation is generally adjusted in existing closed-loop DBS devices in clinical usage, the adjustment rarely considers the pathological progression of chronic TLE. This suggests that an important factor affecting the therapeutic effect of neuromodulation may have been overlooked. The present study reveals time-varying electrophysiological and epileptic network properties in chronic TLE rats and indicates that classifiers of seizure detection and neuromodulation parameters might be designed to adapt to the current state dynamically with the progression of epilepsy.

Toward individualized prediction of seizure recurrence: Hippocampal neuroimaging features in a cohort of patients from a first seizure clinic

PURPOSE

We performed an exploratory analysis of electroencephalography (EEG) and neuroimaging data from a cohort of 51 patients with first seizure (FS) and new-onset epilepsy (NOE) to identify variables, or combinations of variables, that might discriminate between clinical trajectories over a one-year period and yield potential biomarkers of epileptogenesis.

METHODS

Patients underwent EEG, hippocampal and whole brain structural magnetic resonance imaging (MRI), diffusion tensor imaging (DTI), and magnetic resonance spectroscopy (MRS) within six weeks of the index seizure, and repeat neuroimaging one year later. We classified patients with FS as having had a single seizure (FS-SS) or having converted to epilepsy (FS-CON) after one year and performed logistic regression to identify combinations of variables that might discriminate between FS-SS and FS-CON, and between FS-SS and the combined group FS-CON + NOE. We performed paired t-tests to assess changes in quantitative variables over time.

RESULTS

Several combinations of variables derived from hippocampal structural MRI, DTI, and MRS provided excellent discrimination between FS-SS and FS-CON in our sample, with areas under the receiver operating curve (AUROC) ranging from 0.924 to 1. They also provided excellent discrimination between FS-SS and the combined group FS-CON + NOE in our sample, with AUROC ranging from 0.902 to 1. After one year, hippocampal fractional anisotropy (FA) increased bilaterally, hippocampal radial diffusivity (RD) decreased on the side with the larger initial measurement, and whole brain axial diffusivity (AD) increased in patients with FS-SS; hippocampal volume decreased on the side with the larger initial measurement, hippocampal FA increased bilaterally, hippocampal RD decreased bilaterally and whole brain AD, FA and mean diffusivity increased in the combined group FS-CON + NOE (corrected threshold for significance, q = 0.017).

CONCLUSION

We propose a prospective, multicenter study to develop and test models for the prediction of seizure recurrence in patients after a first seizure, based on hippocampal neuroimaging. Further longitudinal neuroimaging studies in patients with a first seizure and new-onset epilepsy may provide clues to the microstructural changes occurring at the earliest stages of epilepsy and yield biomarkers of epileptogenesis.

Symptomatic developmental venous anomalies

Cerebral developmental venous anomalies (DVAs) are variations of venous vascular anatomy related to an underdevelopment of either the superficial or deep venous emissary system, resulting in a dilated transmedullary vein fed by multiple smaller venous radicles responsible for drainage of normal brain parenchyma. While typically benign and found incidentally on imaging studies, DVAs can rarely be symptomatic. The radiographic appearance of DVAs, as well as their symptomatic manifestations, is diverse. Herein, we will discuss the pathophysiology of symptomatic DVAs while providing illustrative case examples depicting each of their pathogenic mechanisms.

Avoiding complacency when treating uncontrolled seizures: why and how?

Introduction: Despite the advances in the diagnosis and treatment of epilepsy, approximately 30% of the patients remain intractable. Uncontrolled seizures have deleterious consequences, including brain damage, cognitive decline, decreased quality of life, and increased mortality.Areas covered: In this article, the authors discuss the treatment gap in patients with intractable epilepsy and the possible mechanisms of drug resistance. The authors provide a treatment algorithm for patients with intractable epilepsy, including non-pharmacological treatment options, such as diet, neurostimulation (vagus nerve stimulation, responsive neurostimulation, and deep brain stimulation), curative surgeries, and palliative surgeries.Expert opinion: There are currently several gaps in the management of seizures. Thirty percent of the 1% of the population with epilepsy is drug resistant. Non-pharmacologic treatments have improved in the last 30 years and continue to do so, but epilepsy surgery in general is still vastly under-utilized. Resective surgery is the only potentially curative procedure. Neurostimulation is generally palliative and is also improving, with smarter types of neurostimulation and paradigms.

Neurodegeneration and Pathology in Epilepsy: Clinical and Basic Perspectives

Epilepsy is commonly associated with a number of neurodegenerative and pathological alterations in those areas of the brain that are involved in repeated electrographic seizures. These most prominently include neuron loss and an increase in astrocyte number and size but may also include enhanced blood-brain barrier permeability, the formation of new capillaries, axonal sprouting, and central inflammation. In animal models in which seizures are either repeatedly elicited or are self-generated, a similar set of neurodegenerative and pathological alterations in brain anatomy are observed. The primary causal agent responsible for these alterations may be the cascade of events that follow a seizure and lead to an hypoperfusion/hypoxic episode. While epilepsy has long and correctly been considered an electrical disorder, the vascular system likely plays an important causal role in the neurodegeneration and pathology that occur as a consequence of repeated seizures.

Epilepsy as progressive disorders: what is the evidence that can guide our clinical decisions and how can neuroimaging help?

There is evidence that some types of epilepsy progress over time, and an important part of this knowledge has derived from neuroimaging studies. Different authors have demonstrated structural damage more pronounced in individuals with a longer duration of epilepsy, and others have been able to quantify this progression over time. However, others have failed to demonstrate progression possibly due to the heterogeneity of individuals evaluated. Currently, temporal lobe epilepsy associated with hippocampal sclerosis is regarded as a progressive disorder. Conversely, for other types of epilepsy, the evidence is not so clear. The causes of this damage progression are also unknown although there is consistent evidence that seizure is one of the mechanisms. The conflicting data about epilepsy progression can be a challenge for clinical decisions for an individual patient. Studies with homogenous groups and longer follow-up are necessary for appropriate conclusions about the real burden of damage progression in epilepsies, and neuroimaging will be essential in this context.

Histamine 1 receptor knock out mice show age-dependent susceptibility to status epilepticus and consequent neuronal damage

The central histaminergic neuron system is an important regulator of activity stages such as arousal and sleep. In several epilepsy models, histamine has been shown to modulate epileptic activity and histamine 1 (H1) receptors seem to play a key role in this process. However, little is known about the H1 receptor-mediated seizure regulation during the early postnatal development, and therefore we examined differences in severity of kainic acid (KA)-induced status epilepticus (SE) and consequent neuronal damage in H1 receptor knock out (KO) and wild type (WT) mice at postnatal days 14, 21, and 60 (P14, P21, and P60). Our results show that in P14 H1 receptor KO mice, SE severity and neuronal damage were comparable to those of WT mice, whereas P21 KO mice had significantly decreased survival, more severe seizures, and enhanced neuronal damage in various brain regions, which were observed only in males. In P60 mice, SE severity did not differ between the genotypes, but in KO group, neuronal damage was significantly increased. Our results suggest that H1 receptors could contribute to regulation of seizures and neuronal damage age-dependently thus making the histaminergic system as a challenging target for novel drug design in epilepsy.

Mesial temporal sclerosis after posterior reversible encephalopathy syndrome

Neither intrathecal methotrexate nor posterior reversible encephalopathy syndrome has previously been reported to result in mesial temporal sclerosis. Described here is the case of a boy with no risk factors for mesial temporal sclerosis who presented with posterior reversible encephalopathy syndrome and partial complex seizures 8 days after initiation of intrathecal methotrexate for treatment of Burkitt lymphoma, and who ultimately progressed to intractable temporal lobe epilepsy due to left mesial temporal sclerosis.

DEVELOPMENTAL VENOUS ANOMALIES

DEVELOPMENTAL VENOUS ANOMALIES (DVAs), formerly known as venous angiomas, have become the most frequently diagnosed intracranial vascular malformation. DVAs are currently considered congenital cerebrovascular anomalies with mature venous walls that lack arterial or capillary elements. They are composed of radially arranged medullary veins, which converge in an enlarged transcortical or subependymal collector vein, and have characteristic appearances (caput medusae) on magnetic resonance imaging and angiography. DVAs were once thought to be rare lesions with substantial potential for intracerebral hemorrhage and considerable morbidity. The prevalence of incidental and asymptomatic DVAs has been more apparent since the advent of magnetic resonance imaging; recent cohort studies have challenged the once-held view of isolated DVAs as the cause of major neurological complications. The previously reported high incidence of intracerebral hemorrhage associated with DVAs is currently attributed to coexistent, angiographically occult cavernous malformations. Some patients may still have noteworthy neurological morbidity or die as a result of acute infarction or hemorrhage directly attributed to DVA thrombosis. DVAs can coexist with cavernous malformations and arteriovenous malformations. Such combination or transitional forms of malformations might suggest common pathways in pathogenesis. Recent data support a key role for DVAs in the pathogenesis of mixed vascular malformations.

Childhood status epilepticus and excitotoxic neuronal injury

This report describes the case of an 11-year-old girl with a prior history of epilepsy and multiple episodes of status epilepticus who presented with generalized convulsive status epilepticus and left hemiclonic seizures. Magnetic resonance imaging, including diffusion-weighted sequences and spectroscopy, and neuropathology at autopsy were consistent with excitotoxic neuronal injury to the hippocampus, cortex, thalamus, mammillary bodies, and cerebellum. Review of the literature revealed 11 similar cases that support the hypothesis of excitotoxic neuronal cell death after status epilepticus.

Cognitive effects of seizures

We aimed to review recent prospective and cross-sectional studies regarding the gradual and chronic effects of (cumulative) seizures on cognition. In contrast with the increasing evidence of structural changes in the brain associated with repeated seizures, its functional repercussions remain unclear. Methodological difficulties of cross-sectional and prospective studies are addressed. It appears that all but one of the prospective studies available on children are limited to measures of intelligence. Most studies revealed no significant adverse effects, although there appears to be a subgroup of about 10-25% of children that shows a clinically significant intellectual decline. Children with generalized symptomatic epilepsies, frequent seizures, high antiepileptic drug use, and early onset of epilepsy appear at risk, although psychosocial factors may also play an important role. Five of the six prospective studies on adults report evidence of a mild decline in cognition in patients with a (longstanding) history of pharmacoresistant epilepsy. The adverse effect on cognitive abilities, memory in particular, seems somewhat more robust than that on measures of intelligence. A significant association between cognitive decline and seizure related variables is rarely substantiated in prospective research and cross-sectional studies show contradicting results. Taken together, the data suggest a mild but measurable decline of intellectual performance in children and adults. Decline of specific cognitive abilities in children is impossible to evaluate given the very little data available. In adults, memory appears to be the most vulnerable cognitive function. Due to many confounding variables, the effect of seizures per se is difficult to estimate, but appears limited.

Transient and permanent magnetic resonance imaging abnormalities after complex partial status epilepticus

Epileptic seizures, especially status epilepticus can produce MRI changes. In contrast to convulsive status epilepticus (CSE), permanent parenchymal loss is not well documented with nonconvulsive status epilepticus (NCSE) and the observed MRI changes are transient. We describe a patient with non-lesional right-sided temporal lobe epilepsy with complex partial seizures and repeated episodes of untreated complex partial status epilepticus (CPSE). Diffusion-weighted MRI exhibited marked and extended signal changes within the right temporal, frontal, insular and cingulate regions. The affected areas are considered propagation pathways of temporal lobe epilepsies. After admission, the patient was treated with i.v. antiepileptic drugs. Behavioral, EEG and MRI signal changes resolved. An atrophy of the right temporal lobe not seen in the pre-status MRI examinations was observed 6 weeks after the resolution of MRI hyperintensities. Prior episodes of CPSE had been correctly treated and remained without permanent brain damage. This case report is in favour of immediate and aggressive treatment of partial NCSE in order to avoid irreversible parenchymal loss.

Quantitative measurement of cortical surface features in localization-related temporal lobe epilepsy

Differences in cortical surface features between healthy controls (n = 48) and patients with temporal lobe epilepsy (n = 46), ages 14-59, were characterized by means of advanced quantitative MRI processing techniques. Cortical surface features of interest included gyral and sulcal curvature, cortical depth, and total cortical surface area. Epilepsy patients and controls differed on measures of gyrification; the abnormalities generalized despite the focal nature of the primary epileptic process. Changes in cortical surface features were associated with increasing chronological age in both groups. Abnormalities in gyrification were associated with cognitive performance and with other morphometric measurements (e.g., surface cerebral spinal fluid). These findings are related to the literature regarding morphometric changes associated with temporal lobe epilepsy and normal aging.

Serial imaging of the brain

Epilepsy is a heterogeneous condition and it is likely that susceptibility factors and genetic predisposition interact with acquired influences such as seizures, AEDs, cerebral insults, subclinical seizures,and ongoing neurodegenerative processes to render certain individuals selectively vulnerable to cerebral damage. There is currently in substantial evidence to suggest that neuroprotective treatments that rely entirely on their anticonvulsant properties are sufficient to prevent the development of cerebral atrophy. The development of postprocessing techniques in serial imaging studies have allowed the detection of subtle changes, and it is likely that development of more sensitive imaging techniques with higher-strength MR magnets and novel MR contrasts will expand our understanding of the factors that render an individual susceptible to hippocampal and extratemporal atrophy. This will allow a more informed assessment of the role required of neuroprotective agents in arresting the progression of cerebral damage and dysfunction.

Persistent severe amnesia due to seizure recurrence after unilateral temporal lobectomy

Anterograde amnesia is a severely disabling state which has been reported as a consequence of bilateral mesiotemporal lesions in humans. In the present paper, recurrent epileptic seizures after temporal lobectomy are described as a rare cause of severe amnesia in two patients. Diffusion-weighted MRI in one patient showed cytotoxic edema during a nonconvulsive status epilepticus and subsequent progressive hippocampal atrophy within the following month. In the other patient, repeated conventional MRI revealed no structural abnormalities in the contralateral temporal lobe.

Hippocampal sclerosis is a progressive disorder: a longitudinal volumetric MRI study

Twelve patients with refractory temporal lobe epilepsy and unilateral hippocampal sclerosis had repeat volumetric magnetic resonance imaging scans after a mean of 3.4 years to determine whether progressive hippocampal volume loss occurred. Seizure-free patients showed no change in hippocampal volume. Patients with continuing seizures had a decline in ipsilateral hippocampal volume that correlated with seizure frequency. Patients with medically refractory temporal lobe epilepsy and unilateral hippocampal sclerosis have progressive hippocampal atrophy.