From unwitnessed fatality to witnessed rescue: Pharmacologic intervention in sudden unexpected death in epilepsy

Repeated seizures lead to progressive ventilatory dysfunction in SSKcnj16-/- rats

Patients with uncontrolled epilepsy experience repeated seizures putting them at increased risk for sudden unexpected death in epilepsy (SUDEP). Data from human patients have led to the hypothesis that SUDEP results from severe cardiorespiratory suppression after a seizure, which may involve pathological deficiencies in the brainstem serotonin (5-HT) system. Rats with a genomic Kcnj16 mutation (SSKcnj16-/- rats) are susceptible to sound-induced generalized tonic-clonic seizures (GTCS) which, when repeated once daily for up to 10 days (10-day seizure protocol), increased mortality, particularly in male rats. Here, we test the hypothesis that repeated seizures across the 10-day protocol will cause a progressive ventilatory dysfunction due to time-dependent 5-HT deficiency. Initial severe seizures led to ictal and postictal apneas and transient decreases in breathing frequency, ventilatory drive, breath-to-breath variability, and brief hypoventilation. These seizure-induced effects on ventilation were exacerbated with increasing seizures and ventilatory chemoreflexes became further impaired after repeated seizures. Tissue analyses of key brainstem regions controlling breathing showed time-dependent 5-HT system suppression and increased immunoreactivity for IBA-1 (microglial marker) without changes in overall cell counts at 3, 7, and 10 days of seizures. Fluoxetine treatment in SSKcnj16-/- rats prevented repeated seizure-induced progressive respiratory suppression but failed to prevent seizure-related mortality. We conclude that repeated seizures cause a progressive compromise of ventilatory control in the immediate postictal period largely mediated by serotonin system suppression in brainstem regions of respiratory control. However, other unknown factors contribute to overall survival following repeated seizures in this model.NEW & NOTEWORTHY This study demonstrated that repeated seizures in a novel rat model (SSKcnj16-/- rats) caused a progressively greater ventilatory dysfunction in the immediate postictal period associated with brainstem serotonin (5-HT) suppression. Augmenting brain 5-HT with a selective serotonin reuptake inhibitor prevented the progressive ventilatory dysfunction induced by repeated seizures but failed to prevent seizure-related mortality, suggesting that repeated seizures may lead to cardiorespiratory suppression and failure through multiple mechanisms.

Sudden unexpected death in epilepsy: A critical view of the literature

Sudden unexpected death in epilepsy (SUDEP) is a sudden, unexpected, witnessed or unwitnessed, non-traumatic and non-drowning death, occurring in benign circumstances, in an individual with epilepsy, with or without evidence for a seizure and excluding documented status epilepticus in which postmortem examination does not reveal other causes of death. Lower diagnostic levels are assigned when cases met most or all of these criteria, but data suggested more than one possible cause of death. The incidence of SUDEP ranged from 0.09 to 2.4 per 1000 person-years. Differences can be attributed to the age of the study populations (with peaks in the 20-40-year age group) and the severity of the disease. Young age, disease severity (in particular, a history of generalized TCS), having symptomatic epilepsy, and the response to antiseizure medications (ASMs) are possible independent predictors of SUDEP. The pathophysiological mechanisms are not fully known due to the limited data available and because SUDEP is not always witnessed and has been electrophysiologically monitored only in a few cases with simultaneous assessment of respiratory, cardiac, and brain activity. The pathophysiological basis of SUDEP may vary according to different circumstances that make that particular seizure, in that specific moment and in that patient, a fatal event. The main hypothesized mechanisms, which could contribute to a cascade of events, are cardiac dysfunction (included potential effects of ASMs, genetically determined channelopathies, acquired heart diseases), respiratory dysfunction (included postictal arousal deficit for the respiratory mechanism, acquired respiratory diseases), neuromodulator dysfunction, postictal EEG depression and genetic factors.

A unified hypothesis of SUDEP: Seizure-induced respiratory depression induced by adenosine may lead to SUDEP but can be prevented by autoresuscitation and other restorative respiratory response mechanisms mediated by the action of serotonin on the periaqueductal gray

Sudden unexpected death in epilepsy (SUDEP) is a major cause of death in people with epilepsy (PWE). Postictal apnea leading to cardiac arrest is the most common sequence of terminal events in witnessed cases of SUDEP, and postconvulsive central apnea has been proposed as a potential biomarker of SUDEP susceptibility. Research in SUDEP animal models has led to the serotonin and adenosine hypotheses of SUDEP. These neurotransmitters influence respiration, seizures, and lethality in animal models of SUDEP, and are implicated in human SUDEP cases. Adenosine released during seizures is proposed to be an important seizure termination mechanism. However, adenosine also depresses respiration, and this effect is mediated, in part, by inhibition of neuronal activity in subcortical structures that modulate respiration, including the periaqueductal gray (PAG). Drugs that enhance the action of adenosine increase postictal death in SUDEP models. Serotonin is also released during seizures, but enhances respiration in response to an elevated carbon dioxide level, which often occurs postictally. This effect of serotonin can potentially compensate, in part, for the adenosine-mediated respiratory depression, acting to facilitate autoresuscitation and other restorative respiratory response mechanisms. A number of drugs that enhance the action of serotonin prevent postictal death in several SUDEP models and reduce postictal respiratory depression in PWE. This effect of serotonergic drugs may be mediated, in part, by actions on brainstem sites that modulate respiration, including the PAG. Enhanced activity in the PAG increases respiration in response to hypoxia and other exigent conditions and can be activated by electrical stimulation. Thus, we propose the unifying hypothesis that seizure-induced adenosine release leads to respiratory depression. This can be reversed by serotonergic action on autoresuscitation and other restorative respiratory responses acting, in part, via the PAG. Therefore, we hypothesize that serotonergic or direct activation of this brainstem site may be a useful approach for SUDEP prevention.

Drug-resistant epilepsy and mortality-Why and when do neuromodulation and epilepsy surgery reduce overall mortality

Patients with drug-resistant epilepsy have an increased mortality rate, with the majority of deaths being epilepsy related and 40% due to sudden unexpected death in epilepsy (SUDEP). The impact of epilepsy surgery on mortality has been investigated since the 1970s, with increased interest in this field during the past 15 years. We systematically reviewed studies investigating mortality rate in patients undergoing epilepsy surgery or neuromodulation therapies. The quality of available evidence proved heterogenous and often limited by significant methodological issues. Perioperative mortality following epilepsy surgery was found to be <1%. Meta-analysis of studies that directly compared patients who underwent surgery to those not operated following presurgical evaluation showed that the former have a two-fold lower risk of death and a three-fold lower risk of SUDEP compared to the latter (odds ratio [OR] 0.40, 95% confidence interval [CI]: 0.29-0.56; p < .0001 for overall mortality and OR 0.32, 95% CI: 0.18-0.57; p < .001 for SUDEP). Limited data are available regarding the risk of death and SUDEP in patients undergoing neuromodulation therapies, although some evidence indicates that vagus nerve stimulation might be associated with a lower risk of SUDEP. Several key questions remain to be addressed in future studies, considering the need to better inform patients about the long-term benefit-risk ratio of epilepsy surgery. Dedicated long-term prospective studies will thus be required to provide more personalized information on the impact of surgery and/or neuromodulation on the risk of death and SUDEP.

Sudden unexpected death in epilepsy: Respiratory mechanisms

Epilepsy is one of the most common chronic neurologic diseases, with a prevalence of 1% in the US population. Many people with epilepsy live normal lives, but are at risk of sudden unexpected death in epilepsy (SUDEP). This mysterious comorbidity of epilepsy causes premature death in 17%-50% of those with epilepsy. Most SUDEP occurs after a generalized seizure, and patients are typically found in bed in the prone position. Until recently, it was thought that SUDEP was due to cardiovascular failure, but patients who died while being monitored in hospital epilepsy units revealed that most SUDEP is due to postictal central apnea. Some cases may occur when seizures invade the amygdala and activate projections to the brainstem. Evidence suggests that the pathophysiology is linked to defects in the serotonin system and central CO₂ chemoreception, and that there is considerable overlap with mechanisms thought to be involved in sudden infant death syndrome (SIDS). Future work is needed to identify biomarkers for patients at highest risk, improve ascertainment, develop methods to alert caregivers when SUDEP is imminent, and find effective approaches to prevent these fatal events.

Coffee consumption and seizure frequency in patients with drug-resistant focal epilepsy

OBJECTIVE

To assess the relation between coffee consumption and seizure frequency in patients with drug-resistant focal epilepsy.

METHODS

Cross-sectional analysis of data collected in the SAVE study, which included patients with drug-resistant focal epilepsy during long-term EEG monitoring. Patients in whom both coffee consumption and data about seizure frequency, including focal to bilateral tonic-clonic seizures (FBTCS), were available were selected. Coffee consumption was collected using a standardized self-report questionnaire and classified into four groups: none, rare (from less than 1 cup/week to up 3 cups/week), moderate (from 4 cups/week to 3 cups/day), and high (more than 4 cups/day).

RESULTS

Six hundred and nineteen patients were included. There was no relation between coffee consumption and total seizure frequency (p = 0.902). In contrast, the number of FBTCS reported over the past year was significantly associated with usual coffee consumption (p = 0.029). Specifically, number of FBCTS in patients who reported moderate coffee consumption was lower than in others. In comparison with patients with moderate coffee consumption, the odds ratio (95%CI) for reporting at least 1 FBTCS per year was 1.6 (1.03-2.49) in patients who never take coffee, 1.62 (1.02-2.57) in those with rare consumption and 2.05 (1.24-3.4) in those with high consumption. Multiple ordinal logistic regression showed a trend toward an association between coffee consumption and number of FBTCS (p = 0.08).

CONCLUSIONS AND RELEVANCE

Our data suggest that effect of coffee consumption on seizures might depend on dose with potential benefits on FBTCS frequency at moderate doses. These results will have to be confirmed by prospective studies.

Review: Neuropathology findings in autonomic brain regions in SUDEP and future research directions

Autonomic dysfunction is implicated from clinical, neuroimaging and experimental studies in sudden and unexpected death in epilepsy (SUDEP). Neuropathological analysis in SUDEP series enable exploration of acquired, seizure-related cellular adaptations in autonomic and brainstem autonomic centres of relevance to dysfunction in the peri-ictal period. Alterations in SUDEP compared to control groups have been identified in the ventrolateral medulla, amygdala, hippocampus and central autonomic regions. These involve neuropeptidergic, serotonergic and adenosine systems, as well as specific regional astroglial and microglial populations, as potential neuronal modulators, orchestrating autonomic dysfunction. Future research studies need to extend to clinically and genetically characterized epilepsies, to explore if common or distinct pathways of autonomic dysfunction mediate SUDEP. The ultimate objective of SUDEP research is the identification of disease biomarkers for at risk patients, to improve post-mortem recognition and disease categorisation, but ultimately, for exposing potential treatment targets of pharmacologically modifiable and reversible cellular alterations.

Serotonin 5-HT4 receptors play a critical role in the action of fenfluramine to block seizure-induced sudden death in a mouse model of SUDEP

RATIONALE

Our previous study showed that the recently approved anticonvulsant drug, fenfluramine, which enhances the release of serotonin (5-hydroxytryptamine, 5-HT) in the brain, prevents seizure-induced respiratory arrest (S-IRA) in the DBA/1 mouse model of sudden unexpected death in epilepsy (SUDEP). The present study examined the role of 5-HT receptor subtypes in mediating the effect of this agent by combined administration of fenfluramine with selective 5-HT receptor antagonists prior to seizure in DBA/1 mice.

METHODS

Fenfluramine (15 mg/kg, i.p.) was administered to primed DBA/1 mice, and audiogenic seizure (Sz) was induced 16 h later. Thirty min prior to Sz induction a selective antagonist acting on 5-HT_1A, 5-HT₂, 5-HT₃ 5-HT₄, 5-HT_5A, 5-HT₆ or 5-HT₇ receptors at a sub-toxic dose was administered, and changes in seizure-induced behaviors were evaluated. Follow-up studies examined the effect of administration of a 5-HT₄ receptor agonist, BIMU 8, as well as the effect of co-administration of ineffective doses of fenfluramine and BIMU-8 on Sz behaviors.

RESULTS

The 5-HT₄ antagonist (GR125487) was the only 5-HT receptor antagonist that was able to reverse the action of fenfluramine to block Sz and S-IRA. Treatment with the 5-HT₄ receptor agonist (BIMU-8), or co-administration of ineffective doses of BIMU-8 and fenfluramine significantly reduced the incidence of S-IRA and tonic Sz in DBA/1 mice. The antagonists for 5-HT₃, 5-HT_5A 5-HT₆, and 5-HT₇ receptors did not significantly affect the action of fenfluramine. However, the 5-HT_1A and the 5-HT₂ antagonists enhanced the anticonvulsant effects of fenfluramine.

CONCLUSIONS

These findings suggest that the action of fenfluramine to prevent seizure-induced sudden death in DBA/1 mice is mediated primarily by activation of 5-HT₄ receptors. These studies are the first to indicate the therapeutic potential of 5-HT₄ receptor agonists either alone or in combination with fenfluramine for preventing SUDEP. Enhancement of the anticonvulsant effect of fenfluramine by 5-HT_1A and 5-HT₂ antagonists may involve presynaptic actions of these antagonists. Thus, the Sz and S-IRA blocking actions of fenfluramine involve complex interactions with several 5-HT receptor subtypes. These data also provide further support for the serotonin hypothesis of SUDEP.

Suppression of phrenic nerve activity as a potential predictor of imminent sudden unexpected death in epilepsy (SUDEP)

Sudden unexpected death in epilepsy (SUDEP) is a leading cause of death in patients with refractory epilepsy. Centrally-mediated respiratory dysfunction has been identified as one of the principal mechanisms responsible for SUDEP. Seizures generate a surge in adenosine release. Elevated adenosine levels suppress breathing. Insufficient metabolic clearance of a seizure-induced adenosine surge might be a precipitating factor in SUDEP. In order to deliver targeted therapies to prevent SUDEP, reliable biomarkers must be identified to enable prompt intervention. Because of the integral role of the phrenic nerve in breathing, we hypothesized that suppression of phrenic nerve activity could be utilized as predictive biomarker for imminent SUDEP. We used a rat model of kainic acid-induced seizures in combination with pharmacological suppression of metabolic adenosine clearance to trigger seizure-induced death in tracheostomized rats. Recordings of EEG, blood pressure, and phrenic nerve activity were made concomitant to the seizure. We found suppression of phrenic nerve burst frequency to 58.9% of baseline (p < 0.001, one-way ANOVA) which preceded seizure-induced death; importantly, irregularities of phrenic nerve activity were partly reversible by the adenosine receptor antagonist caffeine. Suppression of phrenic nerve activity may be a useful biomarker for imminent SUDEP. The ability to reliably detect the onset of SUDEP may be instrumental in the timely administration of potentially lifesaving interventions.

Disordered autonomic function during exposure to moderate heat or exercise in a mouse model of Dravet syndrome

OBJECTIVE

To examine autonomic regulation of core body temperature, heart rate (HR), and breathing rate (BR) in response to moderately elevated ambient temperature or moderate physical exercise in a mouse model of Dravet syndrome (DS).

METHODS

We studied video-EEG, ECG, respiration, and temperature in mice with global heterozygous Scn1a knockout (KO) (DS mice), interneuron specific Scn1a KO, and wildtype (WT) mice during exposure to increased environmental temperature and moderate treadmill exercise.

RESULTS

Core body temperatures of WT and DS mice were similar during baseline. After 15 mins of heat exposure, the peak value was lower in DS than WT mice. In the following mins of heat exposure, the temperature slowly returned close to baseline level in WT, whereas it remained elevated in DS mice. KO of Scn1a in GABAergic neurons caused similar thermoregulatory deficits in mice. During exercise, the HR increase was less prominent in DS than WT mice. After exercise, the HR was significantly more suppressed in DS. The heart rate variability (HRV) was lower in DS than WT mice during baseline and higher in DS during exercise-recovery periods.

SIGNIFICANCE

We found novel abnormalities that expand the spectrum of interictal, ictal, and postictal autonomic dysregulation in DS mice. During mild heat stress, there was a significantly blunted correction of body temperature, and a less suppression of both HR and respiration rate in DS than WT mice. These effects were seen in mice with selective KO of Scn1A in GABAergic neurons. During exercise stress, there was diminished increase in HR, followed by an exaggerated HR suppression and HRV elevation during recovery in DS mice compared to controls. These findings suggest that different environmental stressors can uncover distinct autonomic disturbances in DS mice. Interneurons play an important role in thermoregulation. Understanding the spectrum and mechanisms of autonomic disorders in DS may help develop more effective strategies to prevent seizures and SUDEP.

Neonatal Seizures and Purinergic Signalling

Neonatal seizures are one of the most common comorbidities of neonatal encephalopathy, with seizures aggravating acute injury and clinical outcomes. Current treatment can control early life seizures; however, a high level of pharmacoresistance remains among infants, with increasing evidence suggesting current anti-seizure medication potentiating brain damage. This emphasises the need to develop safer therapeutic strategies with a different mechanism of action. The purinergic system, characterised by the use of adenosine triphosphate and its metabolites as signalling molecules, consists of the membrane-bound P1 and P2 purinoreceptors and proteins to modulate extracellular purine nucleotides and nucleoside levels. Targeting this system is proving successful at treating many disorders and diseases of the central nervous system, including epilepsy. Mounting evidence demonstrates that drugs targeting the purinergic system provide both convulsive and anticonvulsive effects. With components of the purinergic signalling system being widely expressed during brain development, emerging evidence suggests that purinergic signalling contributes to neonatal seizures. In this review, we first provide an overview on neonatal seizure pathology and purinergic signalling during brain development. We then describe in detail recent evidence demonstrating a role for purinergic signalling during neonatal seizures and discuss possible purine-based avenues for seizure suppression in neonates.

Role of Adenosine in Epilepsy and Seizures

Adenosine is an endogenous anticonvulsant and neuroprotectant of the brain. Seizure activity produces large quantities of adenosine, and it is this seizure-induced adenosine surge that normally stops a seizure. However, within the context of epilepsy, adenosine plays a wide spectrum of different roles. It not only controls seizures (ictogenesis), but also plays a major role in processes that turn a normal brain into an epileptic brain (epileptogenesis). It is involved in the control of abnormal synaptic plasticity and neurodegeneration and plays a major role in the expression of comorbid symptoms and complications of epilepsy, such as sudden unexpected death in epilepsy (SUDEP). Given the important role of adenosine in epilepsy, therapeutic strategies are in development with the goal to utilize adenosine augmentation not only for the suppression of seizures but also for disease modification and epilepsy prevention, as well as strategies to block adenosine A_2A receptor overfunction associated with neurodegeneration. This review provides a comprehensive overview of the role of adenosine in epilepsy.

Adenosine kinase and adenosine receptors A1 R and A2A R in temporal lobe epilepsy and hippocampal sclerosis and association with risk factors for SUDEP

OBJECTIVE

The "adenosine hypothesis of SUDEP" (sudden unexpected death in epilepsy) predicts that a seizure-induced adenosine surge combined with impaired metabolic clearance can foster lethal apnea or cardiac arrest. Changes in adenosine receptor density and adenosine kinase (ADK) occur in surgical epilepsy patients. Our aim was to correlate the distribution of ADK and adenosine A_2A and A₁ receptors (A_2A R and A₁ R) in surgical tissue from patients with temporal lobe epilepsy and hippocampal sclerosis (TLE/HS) with SUDEP risk factors.

METHODS

In 75 cases, patients were stratified into high-risk (n = 16), medium-risk (n = 11) and low-risk (n = 48) categories according to the frequency of generalized seizures before surgery. Using whole-slide scanning Definiens image analysis we quantified the labeling index (LI) for ADK, A_2A R, and A₁ R in seven regions of interest: temporal cortex, temporal lobe white matter, CA1, CA4, dentate gyrus, subiculum, and amygdala and relative to glial and neuronal densities with glial fibrillary acidic protein (GFAP) and neuronal nuclear antigen (NeuN).

RESULTS

A₁ R showed predominant neuronal, A_2A R astroglial, and ADK nuclear labeling in all regions but with significant variation. Compared with the low-risk group, the high-risk group had significantly lower A_2A R LI in the temporal cortex. In HS cases with severe neuronal cell loss and gliosis predominantly in the CA1 and CA4 regions, significantly higher A₁ R was present in the amygdala in high-risk than in low-risk cases. There was no significant difference in neuronal loss or gliosis between the risk groups or differences for ADK labeling.

SIGNIFICANCE

Reduced cortical A_2A R suggests glial dysfunction and impaired adenosine modulation in response to seizures in patients at higher risk for SUDEP. Increased neuronal A₁ R in the high-risk group could contribute to periictal amygdala dysfunction in SUDEP.

Scurrying to Understand Sudden Expected Death in Epilepsy: Insights From Animal Models

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in patients with refractory epilepsy, accounting for up to 17% of deaths in patients with epilepsy. The pathophysiology of SUDEP has remained unclear, largely because it is unpredictable and commonly unwitnessed. This poses a great challenge to studies in patients. Recently, there has been an increase in animal studies to try to better understand the pathophysiology of SUDEP. In this current review, we focus on developments through seizure-induced death models and the preventative strategies they may reveal.

The Purinome and the preBötzinger Complex - A Ménage of Unexplored Mechanisms That May Modulate/Shape the Hypoxic Ventilatory Response

Exploration of purinergic signaling in brainstem homeostatic control processes is challenging the traditional view that the biphasic hypoxic ventilatory response, which comprises a rapid initial increase in breathing followed by a slower secondary depression, reflects the interaction between peripheral chemoreceptor-mediated excitation and central inhibition. While controversial, accumulating evidence supports that in addition to peripheral excitation, interactions between central excitatory and inhibitory purinergic mechanisms shape this key homeostatic reflex. The objective of this review is to present our working model of how purinergic signaling modulates the glutamatergic inspiratory synapse in the preBötzinger Complex (key site of inspiratory rhythm generation) to shape the hypoxic ventilatory response. It is based on the perspective that has emerged from decades of analysis of glutamatergic synapses in the hippocampus, where the actions of extracellular ATP are determined by a complex signaling system, the purinome. The purinome involves not only the actions of ATP and adenosine at P2 and P1 receptors, respectively, but diverse families of enzymes and transporters that collectively determine the rate of ATP degradation, adenosine accumulation and adenosine clearance. We summarize current knowledge of the roles played by these different purinergic elements in the hypoxic ventilatory response, often drawing on examples from other brain regions, and look ahead to many unanswered questions and remaining challenges.

The ventrolateral medulla and medullary raphe in sudden unexpected death in epilepsy

Sudden unexpected death in epilepsy (SUDEP) is a leading cause of premature death in patients with epilepsy. One hypothesis proposes that sudden death is mediated by post-ictal central respiratory depression, which could relate to underlying pathology in key respiratory nuclei and/or their neuromodulators. Our aim was to investigate neuronal populations in the ventrolateral medulla (which includes the putative human pre-Bötzinger complex) and the medullary raphe. Forty brainstems were studied comprising four groups: 14 SUDEP, six epilepsy controls, seven Dravet syndrome cases and 13 non-epilepsy controls. Serial sections through the medulla (from obex 1 to 10 mm) were stained for Nissl, somatostatin, neurokinin 1 receptor (for pre-Bötzinger complex neurons) and galanin, tryptophan hydroxylase and serotonin transporter (neuromodulatory systems). Using stereology total neuronal number and densities, with respect to obex level, were measured. Whole slide scanning image analysis was used to quantify immunolabelling indices as well as co-localization between markers. Significant findings included reduction in somatostatin neurons and neurokinin 1 receptor labelling in the ventrolateral medulla in sudden death in epilepsy compared to controls (P < 0.05). Galanin and tryptophan hydroxylase labelling was also reduced in sudden death cases and more significantly in the ventrolateral medulla region than the raphe (P < 0.005 and P < 0.05). With serotonin transporter, reduction in labelling in cases of sudden death in epilepsy was noted only in the raphe (P ≤ 0.01); however, co-localization with tryptophan hydroxylase was significantly reduced in the ventrolateral medulla. Epilepsy controls and cases with Dravet syndrome showed less significant alterations with differences from non-epilepsy controls noted only for somatostatin in the ventrolateral medulla (P < 0.05). Variations in labelling with respect to obex level were noted of potential relevance to the rostro-caudal organization of respiratory nuclear groups, including tryptophan hydroxylase, where the greatest statistical difference noted between all epilepsy cases and controls was at obex 9-10 mm (P = 0.034), the putative level of the pre-Bötzinger complex. Furthermore, there was evidence for variation with duration of epilepsy for somatostatin and neurokinin 1 receptor. Our findings suggest alteration to neuronal populations in the medulla in SUDEP with evidence for greater reduction in neuromodulatory neuropeptidergic and mono-aminergic systems, including for galanin, and serotonin. Other nuclei need to be investigated to evaluate if this is part of more widespread brainstem pathology. Our findings could be a result of previous seizures and may represent a pathological risk factor for SUDEP through impaired respiratory homeostasis during a seizure.

Neural activity in the periaqueductal gray and other specific subcortical structures is enhanced when a selective serotonin reuptake inhibitor selectively prevents seizure-induced sudden death in the DBA/1 mouse model of sudden unexpected death in epilepsy

OBJECTIVE

Sudden unexpected death in epilepsy (SUDEP) is a critical issue in epilepsy, and DBA/1 mice are a useful animal model of this devastating epilepsy sequela. The serotonin hypothesis for SUDEP proposes that modifying serotonergic function significantly alters susceptibility to seizure-induced respiratory arrest (S-IRA). Agents that enhance serotonergic function, including a selective serotonin reuptake inhibitor, fluoxetine, selectively prevent S-IRA in DBA/1 mice. This study examined fluoxetine-induced changes in brain activity using manganese-enhanced magnetic resonance imaging (MEMRI) to reveal sites in the DBA/1 mouse brain where fluoxetine acts to prevent S-IRA.

METHODS

DBA/1 mice were subjected to audiogenic seizures (Sz) after saline or fluoxetine (45 mg/kg, intraperitoneal) administration. Control DBA/1 mice received fluoxetine or saline, but Sz were not evoked. A previous MEMRI study established the regions of interest (ROIs) for Sz in the DBA/1 mouse brain, and the present study examined MEMRI differences in the ROIs of these mouse groups.

RESULTS

The neural activity in several ROIs was significantly increased in fluoxetine-treated DBA/1 mice that exhibited Sz but not S-IRA when compared to the saline-treated mice that exhibited both Sz and respiratory arrest. These structures included the periaqueductal gray (PAG), amygdala, reticular formation (sensorimotor-limbic network), Kölliker-Fuse nucleus, facial-parafacial group (respiratory network), and pontine raphe. Of these ROIs, only the PAG showed significantly decreased neural activity with saline pretreatment when seizure-induced respiratory arrest occurred as compared to saline treatment without seizure.

SIGNIFICANCE

The PAG is known to play an important compensatory role for respiratory distress caused by numerous exigent situations in normal animals. The pattern of fluoxetine-induced activity changes in the present study suggests that PAG may be the most critical target for fluoxetine's action to prevent seizure-induced sudden death. These findings have potential clinical importance, because there is evidence of anomalous serotonergic function and PAG imaging abnormalities in human SUDEP.

Don’t Just Stand There: Do Something! The Case for Peri-Ictal Intervention

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Time of Day and a Ketogenic Diet Influence Susceptibility to SUDEP in Scn1a R1407X/+ Mice

Sudden unexpected death in epilepsy (SUDEP) is a major cause of mortality in patients with drug-resistant epilepsy. Most SUDEP cases occur in bed at night and are preceded by a generalized tonic-clonic seizure (GTCS). Dravet syndrome (DS) is a severe childhood-onset epilepsy commonly caused by mutations in the SCN1A gene. Affected individuals suffer from refractory seizures and an increased risk of SUDEP. Here, we demonstrate that mice with the Scn1a^R1407X/+ loss-of-function mutation (DS) experience more spontaneous seizures and SUDEP during the early night. We also evaluate effects of long-term ketogenic diet (KD) treatment on mortality and seizure frequency. DS mice showed high premature mortality (44% survival by P60) that was associated with increased spontaneous GTCSs 1–2 days prior to SUDEP. KD treated mice had a significant reduction in mortality (86% survival by P60) compared to mice fed a control diet. Interestingly, increased survival was not associated with a decrease in seizure frequency. Further studies are needed to determine how KD confers protection from SUDEP. Moreover, our findings implicate time of day as a factor influencing the occurrence of seizures and SUDEP. DS mice, though nocturnal, are more likely to have SUDEP at night, suggesting that the increased incidence of SUDEP at night in may not be solely due to sleep.

SUDEP and Grief: Overview and Current Issues

The medical community and the general public are aware of sudden deaths in apparently healthy infants (SIDS) and in cases of cardiac arrest (SCD). However, there is a third, less-well known, form of sudden death that occurs in persons with epilepsy (SUDEP). This paper provides a detailed overview what is known about SUDEP, including the current important, unresolved issues being considered in the field (research, education, informed consent). This paper also includes an overview of the grieving process common to all three conditions. Again, the current issues being considered in the field of grieving are presented (major depression, posttraumatic stress disorder). It is written for physicians, including psychiatrists, and for the health community beyond neurologists and serves as a provider resource for persons with epilepsy, their families, and for the general public. This information about SUDEP and grief becomes also additionally important as national health care moves toward an interdisciplinary primary care model of service delivery.

Fenfluramine, a serotonin-releasing drug, prevents seizure-induced respiratory arrest and is anticonvulsant in the DBA/1 mouse model of SUDEP

OBJECTIVE

Prevention of sudden unexpected death in epilepsy (SUDEP) is a critical goal for epilepsy therapy. The DBA/1 mouse model of SUDEP exhibits an elevated susceptibility to seizure-induced death in response to electroconvulsive shock, hyperthermia, convulsant drug, and acoustic stimulation. The serotonin hypothesis of SUDEP is based on findings that treatments which modify serotonergic function significantly alter susceptibility to seizure-induced sudden death in several epilepsy models, including DBA/1 mice. Serotonergic abnormalities have also recently been observed in human SUDEP. Fenfluramine is a drug that enhances serotonin release in the brain. Recent studies have found that the addition of fenfluramine improved seizure control in patients with Dravet syndrome, which has a high incidence of SUDEP. Therefore, we investigated the effects of fenfluramine on seizures and seizure-induced respiratory arrest (S-IRA) in DBA/1 mice.

METHODS

The dose and time course of the effects of fenfluramine (i.p.) on audiogenic seizures (Sz) induced by an electric bell in DBA/1 mice were determined. Videos of Sz-induced behaviors were recorded for analysis. Statistical significance (P < 0.05) was evaluated using the chi-square test.

RESULTS

Sixteen hours after administration of 15 mg/kg of fenfluramine, a high incidence of selective block of S-IRA susceptibility (P < 0.001) occurred in DBA/1 mice without blocking any convulsive behavior. Thirty minutes after 20-40 mg/kg of fenfluramine, significant reductions of seizure incidence and severity, as well as S-IRA susceptibility occurred, which were long-lasting (≥48 hours). The median effective dose (ED₅₀ ) of fenfluramine for significantly reducing Sz at 30 minutes was 21 mg/kg.

SIGNIFICANCE

This study presents the first evidence for the effectiveness of fenfluramine in reducing seizure incidence, severity, and S-IRA susceptibility in a mammalian SUDEP model. The ability of fenfluramine to block S-IRA selectively suggests the potential usefulness of fenfluramine in prophylaxis of SUDEP. These results further confirm and extend the serotonin hypothesis of SUDEP.

Hypoxemia following generalized convulsive seizures

Objective

To analyze the factors that determine the occurrence or severity of postictal hypoxemia in the immediate aftermath of a generalized convulsive seizure (GCS).

Methods

We reviewed the video-EEG recordings of 1,006 patients with drug-resistant focal epilepsy included in the REPO2MSE study to identify those with ≥1 GCS and pulse oximetry (SpO2) measurement. Factors determining recovery of SpO2 ≥ 90% were investigated using Cox proportional hazards models. Association between SpO2 nadir and person- or seizure-specific variables was analyzed after correction for individual effects and the varying number of seizures.

Results

A total of 107 GCS in 73 patients were analyzed. A transient hypoxemia was observed in 92 GCS (86%). Rate of GCS with SpO2 <70% dropped from 40% to 21% when oxygen was administered early (p = 0.046). Early recovery of SpO2 ≥90% was associated with early administration of oxygen (p = 0.004), absence of postictal generalized EEG suppression (PGES) (p = 0.014), and extratemporal lobe epilepsy (p = 0.001). Lack of early administration of O2 (p = 0.003), occurrence of PGES (p = 0.018), and occurrence of ictal hypoxemia during the focal phase (p = 0.022) were associated with lower SpO2 nadir.

Conclusion

Postictal hypoxemia was observed in the immediate aftermath of nearly all GCS but administration of oxygen had a strong preventive effect. Severity of postictal hypoxemia was greater in temporal lobe epilepsy and when hypoxemia was already observed before the onset of secondary GCS.

Deficient post-ictal cardiorespiratory compensatory mechanisms mediated by the periaqueductal gray may lead to death in a mouse model of SUDEP

Post-ictal cardiorespiratory failure is implicated as a major cause of sudden unexpected death in epilepsy (SUDEP) in patients. The DBA/1 mouse model of SUDEP is abnormally susceptible to fatal seizure-induced cardiorespiratory failure (S-CRF) induced by convulsant drug, hyperthermia, electroshock, and acoustic stimulation. Clinical and pre-clinical studies have implicated periaqueductal gray (PAG) abnormalities in SUDEP. Recent functional neuroimaging studies observed that S-CRF resulted in selective changes in PAG neuronal activity in DBA/1 mice. The PAG plays a critical compensatory role for respiratory distress caused by numerous physiological challenges in non-epileptic individuals. These observations suggest that abnormalities in PAG-mediated cardiorespiratory modulation may contribute to S-CRF in DBA/1 mice. To evaluate this, electrical stimulation (20 Hz, 20-100 μA, 10 s) was presented in the PAG of anesthetized DBA/1 and C57BL/6 (non-epileptic) control mice, and post-stimulus changes in respiration [inter-breath interval (IBI)] and heart rate variability (HRV) were examined. The post-stimulus period was considered analogous to the post-ictal period when S-CRF occurred in previous DBA/1 mouse studies. PAG stimulation caused significant intensity-related decreases in IBI in both mouse strains. However, this effect was significantly reduced in DBA/1 vis-a-vis C57BL/6 mice. These changes began immediately following cessation of stimulation and remained significant for 10 s. This time period is critical for initiating resuscitation to successfully prevent seizure-induced death in previous DBA/1 mouse experiments. Significant post-stimulus increases in HRV were also seen at ≥60 μA in the PAG in C57BL/6 mice, which were absent in DBA/1 mice. These data along with previous neuroimaging findings suggest that compensatory cardiorespiratory modulation mediated by PAG is deficient, which may be important to the susceptibility of DBA/1 mice to S-CRF. These observations suggest that correcting this deficit pharmacologically or by electrical stimulation may help to prevent S-CRF. These findings further support the potential importance of PAG abnormalities to human SUDEP.

Circumstances of SUDEP: A nationwide population-based case series

OBJECTIVE

Given the increasing attention being paid to potential strategies for sudden unexpected death in epilepsy (SUDEP) prevention, we analyzed the circumstances of SUDEP and its incidence in relation to time of year, week, and day.

METHODS

Prospective case-series based on persons with an International Classification of Diseases (ICD-10) code for epilepsy in the Swedish Patient Registry 1998-2005, who were alive on June 30, 2006 (n = 60 952). Linkage to the National Cause-of-Death Registry identified all deaths from July 2006 through December 2011, with epilepsy mentioned on death certificate, together with all deaths during 2008 (n = 3166). Death certificates, medical charts, autopsy, and police reports were reviewed to identify SUDEP cases and related circumstances. Autopsied non-SUDEP deaths (n = 60) from the study population served as a reference.

RESULTS

There were 329 SUDEPs (63% men) of which 167 were definite, 89 probable, and 73 possible. SUDEP cases were younger at death (50.8 years) than non-SUDEP deaths (73.3 years) (P < .001) and more likely to be male (63% vs 55%, P = .0079). Most SUDEP cases died at night (58%), at home (91%), and 65% were found dead in bed. When documented, 70% were found in prone position. In 17%, death was witnessed and in 88% of these, a seizure was observed. Of the 329 SUDEP cases, 71% were living alone and 14% shared a bedroom. Compared to an autopsied non-SUDEP reference group, definite SUDEPs were more likely to die at home, during the night, unwitnessed, in the prone position, to live alone, and more often with a preceding seizure.

SIGNIFICANCE

SUDEP cases live alone, die unwitnessed at home at night, with indication of a preceding seizure, supporting the critical role of lack of supervision. These facts need to be considered in the development of preventive strategies.

Association of sleep with sudden unexpected death in epilepsy

OBJECTIVE

The objective of this study was to determine the association of sleep with sudden unexpected death in epilepsy (SUDEP).

METHODS

We conducted a systematic review and meta-analysis based on literature search from databases PubMed, Web of Science, and Scopus using keywords "SUDEP", or "sudden unexpected death in epilepsy", or "sudden unexplained death in epilepsy". Sudden unexpected death in epilepsy was considered to occur during sleep if the patient was found in bed, if the SUDEP cases were documented as in sleep, or if the patient was found at bedside on the bedroom floor.

RESULTS

Circadian pattern was documented in 880 of the 1025 SUDEP cases in 67 studies meeting the inclusion and exclusion criteria. Of the 880 SUDEP cases, 69.3% occurred during sleep and 30.7% occurred during wakefulness. Sudden unexpected death in epilepsy was significantly associated with sleep as compared to wakefulness (P<0.001). In the subgroup of 272 cases in which circadian pattern and age were documented, patients 40years old or younger were more likely to die in sleep than those older than 40years (OR: 2.0; 95% CI=1.0, 3.8; P=0.05). In the subgroup of 114 cases in which both circadian pattern and body position at the time of death were documented, 87.6% (95% CI=81.1%, 94.2%) of patients who died during sleep were in the prone position, whereas 52.9% (95% CI=24.7%, 81.1%) of patients who died during wakefulness were in the prone position. Patients with nocturnal seizures were 6.3 times more likely to die in a prone position than those with diurnal seizures (OR: 6.3; 95% CI=2.0, 19.5; P=0.002).

CONCLUSIONS

There is a strong association of SUDEP with sleep, suggesting that sleep is a significant risk factor for SUDEP. Although the risks of SUDEP associated with sleep are unknown and likely multifactorial, the prone position might be an important contributory factor.

The effect of atomoxetine, a selective norepinephrine reuptake inhibitor, on respiratory arrest and cardiorespiratory function in the DBA/1 mouse model of SUDEP

Sudden unexpected death in epilepsy (SUDEP) is a significant public health burden. The mechanisms of SUDEP are elusive, although cardiorespiratory dysfunction is a likely contributor. Clinical and animal studies indicate that seizure-induced respiratory arrest (S-IRA) is the primary event leading to death in many SUDEP cases. Our prior studies demonstrated that intraperitoneal (IP) injection of atomoxetine, a norepinephrine reuptake inhibitor (NRI) widely used to treat attention deficit hyperactivity disorder, suppresses S-IRA in DBA/1 mice. In the current study, we injected atomoxetine intracerebroventricularly (ICV) and measured its effect on S-IRA in DBA/1 mice to determine its central effects. Additionally, to test our hypothesis that atomoxetine reduces S-IRA via altering cardiorespiratory function, we examined the effect of atomoxetine on respiratory and cardiac function using non-invasive plethysmography and ECG in anesthetized DBA/1 mice, and on blood pressure and heart rate using a tail-cuff system in conscious DBA/1 mice. ICV administration of atomoxetine at 200-250nmol significantly reduced S-IRA evoked by acoustic stimulation in DBA/1 mice, consistent with a central atomoxetine effect on S-IRA. Peripheral atomoxetine administration at a dosage that reduces S-IRA (15mg/kg, IP) slightly increased basal ventilation and the ventilatory response to 7% CO₂, but exerted no effect on heart rate in anesthetized DBA/1 mice. IP injection of atomoxetine produced no effect on the heart rate and blood pressures in conscious mice. These data suggest that atomoxetine suppresses S-IRA through direct effects on the CNS and potentially through enhanced lung ventilation in DBA/1 mice.

Atomoxetine, a norepinephrine reuptake inhibitor, reduces seizure-induced respiratory arrest

Sudden unexpected death in epilepsy (SUDEP) is a devastating epilepsy complication, and no effective preventive strategies are currently available for this fatal disorder. Clinical and animal studies of SUDEP demonstrate that seizure-induced respiratory arrest (S-IRA) is the primary event leading to death after generalized seizures in many cases. Enhancing brain levels of serotonin reduces S-IRA in animal models relevant to SUDEP, including the DBA/1 mouse. Given that serotonin in the brain plays an important role in modulating respiration and arousal, these findings suggest that deficits in respiration and/or arousal may contribute to S-IRA. It is well known that norepinephrine is an important neurotransmitter that modulates respiration and arousal in the brain as well. Therefore, we hypothesized that enhancing noradrenergic neurotransmission suppresses S-IRA. To test this hypothesis, we examined the effect of atomoxetine, a norepinephrine reuptake inhibitor (NRI), on S-IRA evoked by either acoustic stimulation or pentylenetetrazole in DBA/1 mice. We report the original observation that atomoxetine specifically suppresses S-IRA without altering the susceptibility to seizures evoked by acoustic stimulation, and atomoxetine also reduces S-IRA evoked by pentylenetetrazole in DBA/1 mice. Our data suggest that the noradrenergic signaling is importantly involved in S-IRA, and that atomoxetine, a medication widely used to treat attention deficit hyperactivity disorder (ADHD), is potentially useful to prevent SUDEP.

Understanding Death in Children With Epilepsy

Death in children with epilepsy is profoundly disturbing, with lasting effects on the family, community, and health care providers. The overall risk of death for children with epilepsy is about ten times that of the general population. However, the risk of premature death for children without associated neurological comorbidities is similar to that of the general population, and most deaths are related to the cause of the epilepsy or associated neurological disability, not seizures. The most common cause of seizure-related death in children with epilepsy is sudden unexpected death in epilepsy (SUDEP). SUDEP is relatively uncommon in childhood, but the risk increases if epilepsy persists into adulthood. Although the direct cause of SUDEP remains unknown, most often death follows a generalized convulsive seizure and the risk of SUDEP is strongly related to drug-resistant epilepsy and frequent generalized tonic-clonic seizures. The most effective SUDEP prevention strategy is to reduce the frequency of seizures, although a number of seizure detection devices are under development and in the future may prove to be useful for seizure detection for those at particularly high risk. There are distinct benefits for health care professionals to discuss mortality with the family soon after the diagnosis of epilepsy. An individual approach is appropriate. When a child with epilepsy dies, particularly if the death was unexpected, family grief may be profound. Physicians and other health care professionals have a critical role in supporting families that lose a child to epilepsy. This review will provide health care providers with information needed to discuss the risk of death in children with epilepsy and support families following a loss.

Efficacy of naloxone in reducing postictal central respiratory dysfunction in patients with epilepsy: study protocol for a double-blind, randomized, placebo-controlled trial

Background

Generalized tonic-clonic seizures (GTCSs) are the main risk factor for sudden unexpected death in epilepsy (SUDEP). Experimental and clinical data strongly suggest that the majority of SUDEP results from a postictal respiratory dysfunction progressing to terminal apnea. Postictal apnea could partly derive from a seizure-induced massive release of endogenous opioids. The main objective of this study is to evaluate the efficacy of an opioid antagonist, naloxone, administered in the immediate aftermath of a GTCS, in reducing the severity of the postictal central respiratory dysfunction.

Methods/design

The Efficacy of Naloxone in Reducing Postictal Central Respiratory Dysfunction in Patients with Epilepsy (ENALEPSY) study is a multicenter, double-blind, randomized, placebo-controlled trial conducted in patients with drug-resistant focal epilepsy who are undergoing long-term video-electroencephalogram (EEG) monitoring (LTM) in an epilepsy monitoring unit (EMU). We plan to randomize 166 patients (1:1) to receive intravenous naloxone (0.4 mg) or placebo in the immediate aftermath of a GTCS. Because inclusion in the study needs to take place prior to the occurrence of the GTCS, and because such occurrence is observed in about one-fourth of patients undergoing LTM, we plan to include a maximum of 700 patients upon admission in the EMU. The primary endpoint will be the proportion of patients whose oxygen saturation is <90 % between 1 and 3 min after the end of a GTCS. Secondary outcomes will include the following: the proportion of patients who show postictal apnea, the occurrence and duration of postictal generalized EEG suppression, the total duration of the postictal coma, postictal pain, and the number of patients who have a second GTCS within 120 min after the intravenous injection.

Discussion

The demonstration of naloxone’s efficacy on the severity of postictal hypoxemia will have two primary consequences. First, naloxone would be the first and only therapeutic approach that could be delivered immediately to reverse postictal apnea. Second, demonstration that an opioid antagonist can effectively reduce postictal apnea would pave the way for an assessment of a preventive therapy for SUDEP targeting the same pathophysiological pathway using oral administration of naltrexone.

Trial registration

ClinicalTrials.gov identifier: NCT02332447. Registered on 5 January 2015.

Electronic supplementary material

The online version of this article (doi:10.1186/s13063-016-1653-1) contains supplementary material, which is available to authorized users.

Serotonergic agents act on 5-HT3 receptors in the brain to block seizure-induced respiratory arrest in the DBA/1 mouse model of SUDEP

Drugs that enhance the action of serotonin (5-hydroxytrypamine, 5-HT), including several selective serotonin reuptake inhibitors (SSRIs), reduce susceptibility to seizure-induced respiratory arrest (S-IRA) that leads to death in the DBA/1 mouse model of sudden unexpected death in epilepsy (SUDEP). However, it is not clear if specific 5-HT receptors are important in the action of these drugs and whether the brain is the major site of action of these agents in this SUDEP model. The current study examined the actions of agents that affect the 5-HT₃ receptor subtype on S-IRA and whether intracerebroventricular (ICV) microinjection of an SSRI would reduce S-IRA susceptibility in DBA/1 mice. The data indicate that systemic administration of SR 57227, a 5-HT₃ agonist, was effective in blocking S-IRA in doses that did not block seizures, and the S-IRA blocking effect of the SSRI, fluoxetine, was abolished by coadministration of a 5-HT₃ antagonist, ondansetron. Intracerebroventricular administration of fluoxetine in the present study was also able to block S-IRA without blocking seizures. These findings suggest that 5-HT₃ receptors play an important role in the block of S-IRA by serotonergic agents, such as SSRIs, which is consistent with the abnormal expression of 5-HT₃ receptors in the brainstem of DBA mice observed previously. Taken together, these data indicate that systemically administered serotonergic agents act, at least, in part, in the brain, to reduce S-IRA susceptibility in DBA/1 mice and that 5-HT₃ receptors may be important to this effect.