Quantitative Evaluation of Medial Temporal Lobe Morphology in Children with Febrile Status Epilepticus: Results of the FEBSTAT Study

Hippocampal sclerosis and temporal lobe epilepsy following febrile status epilepticus: The FEBSTAT study

OBJECTIVE

This study was undertaken to determine whether hippocampal T2 hyperintensity predicts sequelae of febrile status epilepticus, including hippocampal atrophy, sclerosis, and mesial temporal lobe epilepsy.

METHODS

Acute magnetic resonance imaging (MRI) was obtained within a mean of 4.4 (SD = 5.5, median = 2.0) days after febrile status on >200 infants with follow-up MRI at approximately 1, 5, and 10 years. Hippocampal size, morphology, and T2 signal intensity were scored visually by neuroradiologists blinded to clinical details. Hippocampal volumetry provided quantitative measurement. Upon the occurrence of two or more unprovoked seizures, subjects were reassessed for epilepsy. Hippocampal volumes were normalized using total brain volumes.

RESULTS

Fourteen of 22 subjects with acute hippocampal T2 hyperintensity returned for follow-up MRI, and 10 developed definite hippocampal sclerosis, which persisted through the 10-year follow-up. Hippocampi appearing normal initially remained normal on visual inspection. However, in subjects with normal-appearing hippocampi, volumetrics indicated that male, but not female, hippocampi were smaller than controls, but increasing hippocampal asymmetry was not seen following febrile status. Forty-four subjects developed epilepsy; six developed mesial temporal lobe epilepsy and, of the six, two had definite, two had equivocal, and two had no hippocampal sclerosis. Only one subject developed mesial temporal epilepsy without initial hyperintensity, and that subject had hippocampal malrotation. Ten-year cumulative incidence of all types of epilepsy, including mesial temporal epilepsy, was highest in subjects with initial T2 hyperintensity and lowest in those with normal signal and no other brain abnormalities.

SIGNIFICANCE

Hippocampal T2 hyperintensity following febrile status epilepticus predicted hippocampal sclerosis and significant likelihood of mesial temporal lobe epilepsy. Normal hippocampal appearance in the acute postictal MRI was followed by maintained normal appearance, symmetric growth, and lower risk of epilepsy. Volumetric measurement detected mildly decreased hippocampal volume in males with febrile status.

A Pediatric Rat Model of Organophosphate-Induced Refractory Status Epilepticus: Characterization of Long-Term Epileptic Seizure Activity, Neurologic Dysfunction and Neurodegeneration

Children are highly vulnerable to the neurotoxic effects of organophosphates (OPs), which can cause neuronal developmental defects, including intellectual disability, autism, epilepsy, and related comorbidities. Unfortunately, no specific pediatric OP neurotoxicity model currently exists. In this study, we developed and characterized a pediatric rat model of status epilepticus (SE) induced by the OP diisopropylfluorophosphate (DFP) and examined its impact on long-term neurological outcomes. Postnatal day 21 rats were exposed to a DFP regimen with standard antidotes. Progressive behavioral deteriorations were assessed over a three-month period. Development of epileptic seizures, ictal discharges, high-frequency oscillations (HFOs), and interictal spikes were monitored by video-electroencephalography recordings. Histology-stereology analysis was performed to assess neurodegeneration, neuroinflammation, and morphologic abnormalities. DFP-exposed, post-SE animals exhibited significantly elevated levels of anxiety and depression than age-matched controls at 1, 2, and 3 months post-exposure. DFP-exposed animals displayed aggressive behavior and a marked decline in object recognition memory, as well as prominent impairment in spatial learning and memory. DFP-exposed animals had striking electrographic abnormalities with the occurrence of displayed epileptic seizures, ictal discharges, HFOs, and interictal spikes, suggesting chronic epilepsy. Neuropathological analysis showed substantially fewer principal neurons and inhibitory interneurons with a marked increase in reactive microglia and neuroinflammation in the hippocampus and other brain regions. DFP-exposed animals also exhibited mossy fiber sprouting indicating impaired network formations. Long-term epileptic seizures and neuropsychiatric functional deficits induced by DFP were consistent with neuropathological defects. Collectively, this pediatric model displays many hallmarks of chronic sequelae reminiscent of children exposed to OPs, suggesting that it will be a valuable tool for investigating pathologic mechanisms and potential treatment strategies to attenuate long-term OP neurotoxicity. SIGNIFICANCE STATEMENT: Millions of children are exposed to organophosphates (OPs) used in agriculture or chemical incidents. This study investigated the long-term impact of neonatal exposure to the OP chemical diisopropylfluorophosphate (DFP) on neurobehavioral and neurodevelopmental outcomes in adulthood. DFP exposure caused long-lasting behavioral abnormalities, epileptic seizures, and bilateral brain defects with an array of neurological sequelae seen in children's OP neurotoxicity. Thus, this model provides a novel tool to explore therapeutic interventions that mitigate long-term neurotoxic effects of children exposed to OP-induced seizures and status epilepticus.

Molecular Mechanisms in the Genesis of Seizures and Epilepsy Associated With Viral Infection

Seizures are a common presenting symptom during viral infections of the central nervous system (CNS) and can occur during the initial phase of infection ("early" or acute symptomatic seizures), after recovery ("late" or spontaneous seizures, indicating the development of acquired epilepsy), or both. The development of acute and delayed seizures may have shared as well as unique pathogenic mechanisms and prognostic implications. Based on an extensive review of the literature, we present an overview of viruses that are associated with early and late seizures in humans. We then describe potential pathophysiologic mechanisms underlying ictogenesis and epileptogenesis, including routes of neuroinvasion, viral control and clearance, systemic inflammation, alterations of the blood-brain barrier, neuroinflammation, and inflammation-induced molecular reorganization of synapses and neural circuits. We provide clinical and animal model findings to highlight commonalities and differences in these processes across various neurotropic or neuropathogenic viruses, including herpesviruses, SARS-CoV-2, flaviviruses, and picornaviruses. In addition, we extensively review the literature regarding Theiler's murine encephalomyelitis virus (TMEV). This picornavirus, although not pathogenic for humans, is possibly the best-characterized model for understanding the molecular mechanisms that drive seizures, epilepsy, and hippocampal damage during viral infection. An enhanced understanding of these mechanisms derived from the TMEV model may lead to novel therapeutic interventions that interfere with ictogenesis and epileptogenesis, even within non-infectious contexts.

Status epilepticus and early development: neuronal injury, neurodegeneration, and their consequences

Evidence showing that the immature brain is vulnerable to seizure-induced damage has been accumulating for decades. Clinical data have always suggested that some early-life seizures are associated with negative sequelae, but clinical observations are frequently obscured by multiple uncontrolled contributing factors and can rarely establish causality. Determining with certainty that seizures, per se, can cause neuronal death and can irreversibly disrupt critical developmental processes, required the development of suitable model systems. Several experimental seizure models clearly show that the immature brain can sustain neuronal injury as a result of uncontrolled seizure activity and that even in the absence of observable neuronal death, the developing brain is selectively vulnerable to interruptions of required growth programs. Severe early-life seizures inhibit DNA, RNA, and protein synthesis, and they can reduce the accumulation of myelin and synaptic markers in the developing nervous system, leading to functional delays in development. Depending on the seizure pathway involved, and the developmental period under study, classic neurodegeneration, excitotoxicity, and apoptosis can result in permanent damage to critical neural networks in the temporal lobe and in many other brain regions. This conclusion is further supported by recent clinical studies showing that prolonged febrile status epilepticus can lead to hippocampal injury, which evolves into hippocampal atrophy and hippocampal sclerosis. A growing body of experimental data demonstrates that the metabolic compromise and cellular loss produced by seizures during critical phases of brain development negatively affect later hippocampal physiology including learning and memory functions in maturity.

Human Herpesviruses 6A and 6B in Brain Diseases: Association versus Causation

Human herpesvirus 6A (HHV-6A) and human herpesvirus 6B (HHV-6B), collectively termed HHV-6A/B, are neurotropic viruses that permanently infect most humans from an early age. Although most people infected with these viruses appear to suffer no ill effects, the viruses are a well-established cause of encephalitis in immunocompromised patients. In this review, we summarize the evidence that the viruses may also be one trigger for febrile seizures (including febrile status epilepticus) in immunocompetent infants and children, mesial temporal lobe epilepsy, multiple sclerosis (MS), and, possibly, Alzheimer's disease. We propose criteria for linking ubiquitous infectious agents capable of producing lifelong infection to any neurologic disease, and then we examine to what extent these criteria have been met for these viruses and these diseases.

Acute Seizures-Work-Up and Management in Children

Seizures are common in the pediatric population; however, most children do not go on to develop epilepsy later in life. Selecting appropriate diagnostic modalities to determine an accurate diagnosis and appropriate treatment as well as with counseling families regarding the etiology and prognosis of seizures, is essential. This article will review updated definitions of seizures, including provoked versus unprovoked, as well as the International League Against Epilepsy operational definition of epilepsy. A variety of specific acute symptomatic seizures requiring special consideration are discussed, along with neonatal seizures and seizure mimics, which are common in pediatric populations.

Genetic Contributions to Acquired Epilepsies

Whether genetic factors contribute to acquired epilepsies has long been controversial. Supporters observe that, among individuals exposed to seemingly the same brain insult, only a minority develops unprovoked seizures. Yet, only in relatively recent years have studies started to build a case for genetic contributions. Here, we appraise this emerging evidence, by providing a critical review of studies published in the field.

Looking for indicative magnetic resonance imaging signs of hippocampal developmental abnormalities in patients with mesial temporal lobe epilepsy and healthy controls

OBJECTIVE

To evaluate the frequency of qualitative features for hippocampal developmental abnormalities (HiDeA) definition on magnetic resonance imaging (MRI) in mesial temporal lobe epilepsy (MTLE) patients and healthy controls, highlighting which were more sensitive and specific to the epileptic syndrome.

METHODS

We enrolled 93 healthy controls and 187 MTLE patients. Among patients, 133 were MRI-negative and 54 had hippocampal sclerosis (HS). Two blinded, trained investigators defined HiDeA if three signs were present, including at least one of the following: (1) globular hippocampal shape (HCS), (2) verticalized collateral sulcus, and (3) medial positioning of hippocampus (HCP). After evaluating the prevalence of HiDeA in MTLE and controls, we assessed the frequency of each sign. Then, we classified differences in type or number of HiDeA diagnostic features, calculating their sensitivity and specificity. Fisher exact test was used to assess statistical significance.

RESULTS

HiDeA was detected in 36 of 187 MTLE cases (19.25%) and in eight of 93 (8.6%) controls. In particular, HiDeA was present in 25 of 133 (18.8%) patients with MRI-negative MTLE. Among all visual criteria here considered, HCS showed higher sensitivity both in the MRI-negative MTLE group (88%) and in the HS-MTLE group (91%). HCP, thickened subiculum, and reduction of the upper horizontal portion of the parahippocampal gyrus (HCTH) signs demonstrated a 100% specificity in both groups. In healthy controls, HCS was confirmed to have the highest sensitivity (100%), whereas HCP showed the highest specificity (98.8%). All these criteria were statistically associated with HiDeA. Electroencephalographic focus was concordant with the HiDeA side in 52.2% of MTLE patients. An association was not found among signs of HiDeA and treatment responsiveness.

SIGNIFICANCE

We identified characteristic signs of HiDeA, such as HCTH or HCP, differentiating HiDeA features between MTLE and healthy controls. The identification of sensitive and, more importantly, specific criteria of HiDeA could be helpful to make a more confident visual diagnosis.

The Genetics of Epilepsy

Epilepsy encompasses a group of heterogeneous brain diseases that affect more than 50 million people worldwide. Epilepsy may have discernible structural, infectious, metabolic, and immune etiologies; however, in most people with epilepsy, no obvious cause is identifiable. Based initially on family studies and later on advances in gene sequencing technologies and computational approaches, as well as the establishment of large collaborative initiatives, we now know that genetics plays a much greater role in epilepsy than was previously appreciated. Here, we review the progress in the field of epilepsy genetics and highlight molecular discoveries in the most important epilepsy groups, including those that have been long considered to have a nongenetic cause. We discuss where the field of epilepsy genetics is moving as it enters a new era in which the genetic architecture of common epilepsies is starting to be unraveled.

Hippocampal morphometry in sudden and unexpected death in epilepsy

OBJECTIVE

To determine hippocampal morphometric measures, including granule cell dispersion and features of malrotation, as potential biomarkers for sudden unexpected death in epilepsy (SUDEP) from an archival postmortem series.

METHODS

In a retrospective study of 187 archival postmortems from 3 groups, SUDEP (68; 14 with hippocampal sclerosis [HS]), non-SUDEP epilepsy controls (EP-C = 66; 25 with HS), and nonepilepsy controls (NEC = 53), Nissl/hematoxylin & eosin-stained sections from left and right hippocampus from 5 coronal levels were digitized. Image analysis was carried out for granule cell layer (GCL) thickness and measurements of hippocampal dimensions (HD) for shape (width [HD1], height [HD2]) and medial hippocampal positioning in relation to the parahippocampal gyrus (PHG) length (HD3). A qualitative evaluation of hippocampal malrotational (HMAL) features, dentate gyrus invaginations (DGI), and subicular/CA1 folds (SCF) was also made.

RESULTS

GCL thickness was increased in HS more than those without (p < 0.001). In non-HS cases, increased GCL thickness was noted in EP-C compared to NEC (p < 0.05) but not between SUDEP and NEC. There was no difference in the frequency of DGI, SCF, measurements of hippocampal shape (HD1, HD2, or ratio), or medial positioning among SUDEP, EP-C, and NEC groups, when factoring in HS, coronal level, and age at death. Comparison between left and right sides within cases showed greater PHG lengths (HD3) on the right side in the SUDEP group only (p = 0.018).

CONCLUSIONS

No hippocampal morphometric features were identified in support of either excessive granule cell dispersion or features of HMAL as definitive biomarkers for SUDEP. Asymmetries in PHG measurements in SUDEP warrant further investigation as they may indicate abnormal central autonomic networks.

Review: The past, present and future challenges in epilepsy-related and sudden deaths and biobanking

Awareness and research on epilepsy-related deaths (ERD), in particular Sudden Unexpected Death in Epilepsy (SUDEP), have exponentially increased over the last two decades. Most publications have focused on guidelines that inform clinicians dealing with these deaths, educating patients, potential risk factors and mechanisms. There is a relative paucity of information available for pathologists who conduct these autopsies regarding appropriate post mortem practice and investigations. As we move from recognizing SUDEP as the most common form of ERD toward in-depth investigations into its causes and prevention, health professionals involved with these autopsies and post mortem procedure must remain fully informed. Systematizing a more comprehensive and consistent practice of examining these cases will facilitate (i) more precise determination of cause of death, (ii) identification of SUDEP for improved epidemiological surveillance (the first step for an intervention study), and (iii) biobanking and cell-based research. This article reviews how pathologists and healthcare professionals have approached ERD, current practices, logistical problems and areas to improve and harmonize. The main neuropathology, cardiac and genetic findings in SUDEP are outlined, providing a framework for best practices, integration of clinical, pathological and molecular genetic investigations in SUDEP, and ultimately prevention.