Personalization of SUDEP risk: A survey of transient subclinical comorbid changes

Sudden Unexpected Death in Epilepsy: A Narrative Review of Mechanism, Risks, and Prevention

Sudden unexpected death in epilepsy (SUDEP) is sudden, unexpected, witnessed or unwitnessed, nontraumatic, non-drowning death that occurs in a person with epilepsy. SUDEP is the leading cause of epilepsy-related death in adults with epilepsy, with an incidence of about 1.2 per 1000 person-years in the general epilepsy population. Recent studies have shown similar prevalence in the pediatric population too. Although the precise mechanism remains unclear, well-documented cases of SUDEP suggest that a generalized tonic clonic seizure-induced, centrally mediated change in cardiorespiratory function leads to terminal apnea and cardiac arrest. Risk factors include generalized tonic clonic seizure frequency, duration of epilepsy, nocturnal seizure, and certain genetic syndromes. Orexin, adenosine, and serotonin neurotransmission have been explored as novel drug targets to mitigate SUDEP risk. Neurostimulation and resective epilepsy surgery have been reported to have beneficial effects on long-term SUDEP risk as well. Future studies may aim to clarify the role of sleep and other comorbidities in SUDEP pathophysiology.

High density probes reveal medullary seizure and rapid medullary shutdown in a model of fatal apnea in seizure

Objective

Sudden unexpected death in epilepsy (SUDEP) is suggested to be a cardiorespiratory collapse that occurs shortly after a seizure. Prior work in rats suggests that reflexive apneas (produced by stimulation of trigeminal or vagal peripheral sensory targets) is highly fatal during seizure but well tolerated otherwise. These reflexes share network connectivity in the medulla, particularly the caudal solitary nucleus (NTS) and ventral respiratory column (VRC), and possibly other intermediate structures. We sought to observe the electrographic activity in these regions.

Methods

We use urethane anesthetized long evans rats. We utilized either 125 μm silver wire in the caudal NTS or a Neuropixel 1.0 probe along a dorsoventral trajectory that spanned the caudal NTS to the VRC. We additionally recorded cardiorespiratory activity via several methods. We induced a reflexive apnea - the diving reflex - by nasal irrigation of cold water for several seconds, which produces a period of apnea, then gasping, and then a gradual return to eupnea. We repeated several trials while the animal was healthy and subsequently induced continuous seizure activity with kainate and repeated the reflexes, which are ultimately fatal during seizure.

Results

Seizure activity confounds many established methods of analyzing high-density single unit data such as provided by Neuropixels probes, and so our analyses focus on averaging responses over larger anatomical regions (120 μm) covering small populations of neurons. Seizure produces broad increases in neuronal activity across the medullary tract, which by itself is not dangerous. Ictal reflexive apneas were broadly more inhibitory (producing a reduction in firing rate) than they were preictally, and fatal ictal responses resulted in a very rapid shutdown of all medullary activity. We only rarely observed ictal central apneas (apneas with no apparent stimuli), but when we did they were apparently safe, always survived, and produced no significant change in network activity (neither increase nor decrease).

Conclusions

These data support the theory that central apnea events in seizure are relatively safe as we observed they produce little change in the medullary tract network, while stimuli-induced-reflexive-apneas are dangerous because they produce profound quieting across respiratory centers. Our data suggest that seizure spreads to this medullary tract at approximately the same rate and intensity as forebrain, as previously described in this model. These data are supportive of SUDEP mechanisms involving brainstem inhibition as a primary cause, such as spreading depolarization waves. These findings likely extend beyond nasal irrigation to any sensory reflexive apnea caused by airway irritation of any kind, and may bear relevance to similar deaths seen in infants.

Dietary and Metabolic Approaches for Treating Autism Spectrum Disorders, Affective Disorders and Cognitive Impairment Comorbid with Epilepsy: A Review of Clinical and Preclinical Evidence

Epilepsy often occurs with other neurological disorders, such as autism, affective disorders, and cognitive impairment. Research indicates that many neurological disorders share a common pathophysiology of dysfunctional energy metabolism, neuroinflammation, oxidative stress, and gut dysbiosis. The past decade has witnessed a growing interest in the use of metabolic therapies for these disorders with or without the context of epilepsy. Over one hundred years ago, the high-fat, low-carbohydrate ketogenic diet (KD) was formulated as a treatment for epilepsy. For those who cannot tolerate the KD, other diets have been developed to provide similar seizure control, presumably through similar mechanisms. These include, but are not limited to, the medium-chain triglyceride diet, low glycemic index diet, and calorie restriction. In addition, dietary supplementation with ketone bodies, polyunsaturated fatty acids, or triheptanoin may also be beneficial. The proposed mechanisms through which these diets and supplements work to reduce neuronal hyperexcitability involve normalization of aberrant energy metabolism, dampening of inflammation, promotion of endogenous antioxidants, and reduction of gut dysbiosis. This raises the possibility that these dietary and metabolic therapies may not only exert anti-seizure effects, but also reduce comorbid disorders in people with epilepsy. Here, we explore this possibility and review the clinical and preclinical evidence where available.