Periictal cerebral tissue hypoxemia: A potential marker of SUDEP risk

Challenges and future directions of SUDEP models

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death among patients with epilepsy, causing a global public health burden. The underlying mechanisms of SUDEP remain elusive, and effective prevention or treatment strategies require further investigation. A major challenge in current SUDEP research is the lack of an ideal model that maximally mimics the human condition. Animal models are important for revealing the potential pathogenesis of SUDEP and preventing its occurrence; however, they have potential limitations due to species differences that prevent them from precisely replicating the intricate physiological and pathological processes of human disease. This Review provides a comprehensive overview of several available SUDEP animal models, highlighting their pros and cons. More importantly, we further propose the establishment of an ideal model based on brain-computer interfaces and artificial intelligence, hoping to offer new insights into potential advancements in SUDEP research. In doing so, we hope to provide valuable information for SUDEP researchers, offer new insights into the pathogenesis of SUDEP and open new avenues for the development of strategies to prevent SUDEP.

The influence of biological rhythms on the initial onset of status epilepticus in critically ill inpatients and the study of its predictive Model

This study aims to explore the relationship between the circadian rhythms of critically ill patients and the incidence of Status Epilepticus (SE), and to develop a predictive model based on circadian rhythm indicators and clinical factors. We conducted a diurnal rhythm analysis of vital sign data from 4413 patients, discovering significant differences in the circadian rhythms of body temperature, blood oxygen saturation, and heart rate between the SE and non-SE groups, which were correlated with the incidence of SE. We also employed various machine learning algorithms to identify the ten most significant variables and developed a predictive model with strong performance and clinical applicability. Our research provides a new perspective and methodology for the study of biological rhythms in critically ill patients, offering new evidence and tools for the prevention and treatment of SE. Our findings are consistent or similar to some in the literature, while differing from or supplementing others. We observed significant differences in the vital signs of epileptic patients at different times of the day across various diagnostic time groups, reflecting the regulatory effects of circadian rhythms. We suggest heightened monitoring and intervention of vital signs in critically ill patients, especially during late night to early morning hours, to reduce the risk of SE and provide more personalized treatment plans.

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.

Relation of Brain Perfusion Patterns to Sudden Unexpected Death Risk Stratification: A Study in Drug Resistant Focal Epilepsy

To explore the role of the interictal and ictal SPECT to identity functional neuroimaging biomarkers for SUDEP risk stratification in patients with drug-resistant focal epilepsy (DRFE). Twenty-nine interictal-ictal Single photon emission computed tomography (SPECT) scans were obtained from nine DRFE patients. A methodology for the relative quantification of cerebral blood flow of 74 cortical and sub-cortical structures was employed. The optimal number of clusters (K) was estimated using a modified v-fold cross-validation for the use of K means algorithm. The two regions of interest (ROIs) that represent the hypoperfused and hyperperfused areas were identified. To select the structures related to the SUDEP-7 inventory score, a data mining method that computes an automatic feature selection was used. During the interictal and ictal state, the hyperperfused ROIs in the largest part of patients were the bilateral rectus gyrus, putamen as well as globus pallidus ipsilateral to the seizure onset zone. The hypoperfused ROIs included the red nucleus, substantia nigra, medulla, and entorhinal area. The findings indicated that the nearly invariability in the perfusion pattern during the interictal to ictal transition observed in the ipsi-lateral putamen F = 12.60, p = 0.03, entorhinal area F = 25.80, p = 0.01, and temporal middle gyrus F = 12.60, p = 0.03 is a potential biomarker of SUDEP risk. The results presented in this paper allowed identifying hypo- and hyperperfused brain regions during the ictal and interictal state potentially related to SUDEP risk stratification.

Risk of sudden unexpected death in people with epilepsy and obstructive sleep apnea

This study aimed to determine whether severity of newly diagnosed obstructive sleep apnea (OSA) in people with epilepsy is associated with elevated sudden unexpected death in epilepsy (SUDEP) risk as calculated by the revised SUDEP-7 Inventory (rSUDEP-7). To this aim, a retrospective cross-sectional study was conducted at a single academic center. Adults ≥18 years of age with epilepsy and newly diagnosed OSA were retrospectively identified via electronic health records. Analysis was performed for subjects with confirmed epilepsy, OSA, and complete diagnostic PSG and rSUDEP-7 data. OSA severity was categorized as mild, moderate or severe. Logistic regression analysis was used to determine the association between OSA severity and rSUDEP-7 scores, adjusting for significantly different baseline characteristics. Of 86 subjects, OSA severity was classified as mild 38(44.2 %), moderate 25(29.1 %), and severe 23(26.7 %). Multivariate logistic regression demonstrated that severe OSA was significantly associated with rSUDEP-7 ≥ 5 after adjusting for congestive heart failure and diabetes (OR:4.08,p = 0.046,CI:1.04-16.28), but was attenuated when male gender was added to the model (OR:3.91,p = 0.067,CI:0.91-16.77). In conclusion, severe OSA is associated with elevated SUDEP risk. As a treatable disorder, OSA may thus represent a modifiable SUDEP risk factor. However, future confirmatory studies involving the prospective, longitudinal evaluation of SUDEP from broader populations are required.

Improving prediction of sudden unexpected death in epilepsy: From SUDEP-7 to SUDEP-3

OBJECTIVE

Sudden unexpected death in epilepsy (SUDEP) is a significant cause of mortality in epilepsy. The aim of this study is to evaluate the validity of the SUDEP-7 inventory and its components as tools for predicting SUDEP risk, and to develop and validate an improved inventory.

METHODS

The study included 28 patients who underwent video-electroencephalography (EEG) monitoring and later died of SUDEP, and 56 age- and sex-matched control patients with epilepsy. The SUDEP-7 score, its individual components, and an alternative inventory were examined as predictors of SUDEP.

RESULTS

SUDEP-7 scores were significantly higher among SUDEP patients compared with controls, both at time of admission (p = 0.024) and most recent follow-up (p = 0.016). SUDEP-7 scores declined only among controls, who demonstrated reduced seizure frequency. Seizure freedom after epilepsy surgery was also associated with survival. Several components of the SUDEP-7 inventory were independently associated with higher risk of SUDEP, including more than three generalized tonic-clonic (GTC) seizures (p = 0.002), one or more GTC seizures (p = 0.001), or one or more seizures of any type within the last year (p = 0.013), and intellectual disability (p = 0.031). In stepwise regression models, SUDEP-7 scores did not enhance the prediction of SUDEP over either GTC seizure frequency or seizure frequency alone. A novel SUDEP-3 inventory comprising GTC seizure frequency, seizure frequency, and intellectual disability (p < 0.001) outperformed the SUDEP-7 inventory (p = 0.010) in predicting SUDEP.

SIGNIFICANCE

Our findings demonstrate the limitations of the SUDEP-7 inventory. We propose a new three-item SUDEP-3 inventory, which predicts SUDEP better than the SUDEP-7.

Hemispheric Cerebral Oximetry Monitoring During Pediatric Seizure Activity in a Pediatric Emergency Department

BACKGROUND

Sustained neuronal activity during seizures causes cellular perturbations, alterations in cerebral physiology, and potentially neurological injury, a neurological emergency. With variable clinical manifestations of seizures, frequent failure of seizure recognition by providers in pediatric and developmentally challenged patients can increase seizure complications. Neuroresuscitation should include rapid cerebral physiology assessment for increased seizure recognition and optimal neurological outcomes. In neurological emergencies, cerebral oximetry has demonstrated its utility in altered cerebral physiology and a standard combat neurological assessment tool. During adult seizures, cerebral oximetry (regional cerebral oxygen saturation [rcSO2]) has been shown as a useful neurological assessment tool, but research is lacking in pediatric emergency department (PED) seizure patients.

OBJECTIVE

The aim of this study was to identify trends in rcSO2 readings for patients presenting to the PED with seizure activity and in the postseizure state in order to evaluate usefulness of rcSO2 as a neurological assessment tool in pediatric seizure patients.

METHODS

This was a PED observational case series comparing hemispheric rcSO2 readings in first-time clinically evident generalized and focal seizure patients to first-time postseizure patients with no PED seizures.

RESULTS

Generalized or focal seizure (n = 185) hemispheric rcSO2 revealed significant differences compared with nonseizure and controls' rcSO2 readings (n = 115) (P < 0.0001). Generalized and focal seizure rcSO2's were either less than 60% or greater than 80% compared with nonseizure rcSO2 (P < 0.0001). Ipsilateral focal seizure rcSO2 correlated to seizure side (P < 0.0001) and was less than the contralateral rcSO2 (P < 0.0001), with interhemispheric rcSO2 discordance greater than 16 (P < 0.0001). Seizure to preseizure rcSO2 discordance was as follows: generalized 15.2, focal: left 19.8, right 20.3 (P < 0.0001).

CONCLUSIONS

Hemispheric during-seizure rcSO2 readings significantly correlated with generalized and focal seizures and reflected altered cerebral physiology. Ipsilateral focal seizure rcSO2 readings correlated to the focal side with wide interhemispheric rcSO2 discordance. All postseizure rcSO2 readings returned to preseizure readings, showing altered cerebral physiology resolution. Overall, in generalized or focal seizure, rcSO2 readings were less than 60% or greater than 80%, and in focal seizure, interhemispheric rcSO2 discordance was greater than 10. During seizures, hemispheric rcSO2 readings demonstrated its potential pediatric seizure utility. Utilizing rcSO2 readings related to seizure activity could expedite pediatric and developmentally challenged patients' seizure recognition, cerebral assessment, and interventions especially in pharmacoresistant seizures.

Seizures in patients with respiratory disease - a retrospective single center study

OBJECTIVE

Seizures are a neurological condition commonly experienced during the follow-up period after systemic or metabolic disorders. The aim of the present study was to determine the etiological factors of seizures in patients at a tertiary care chest clinic.

METHODS

We reviewed all neurology consultations that were requested due to seizures in inpatient clinics in a tertiary care hospital specializing in respiratory disorders between January 2011 and January 2018 were retrospectively reviewed.

RESULTS

The present study included 705 of 2793 (25.2%) patients who requested consultations for seizures during the study period. The mean age of the sample was 64.05±17.19 years. Of the 705 patients, 307 (43.5%) had a previous history of epilepsy (Group I) and 398 (56.5%) had a first-time seizure and were considered to have symptomatic seizures (Group II). Multiple factors played roles in the development of seizures in 54.8% of the patients. In most patients, metabolic causes, systemic infections, and drug use were identified and an intracranial metastatic mass lesion was the major cause in patients with lung cancer. Rates of hypoxemia and respiratory acidosis were significantly higher in patients with symptomatic seizures (Group II) than in patients with primary epilepsy (Group I).

CONCLUSIONS

Blood gas changes such as hypoxemia and respiratory acidosis were among the factors statistically associated with the development of symptomatic seizures in patients with respiratory diseases. Additionally, hypoxemia, hypercapnia, and respiratory acidosis were correlated with mortality in patients hospitalized for respiratory system diseases who requested consultations for seizures.

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.

Obstructive sleep apnea in refractory epilepsy: A pilot study investigating frequency, clinical features, and association with risk of sudden unexpected death in epilepsy

OBJECTIVE

We aimed to determine the frequency of probable obstructive sleep apnea (pOSA) in refractory epilepsy monitoring unit inpatients and clinical features associated with pOSA, including risk for sudden unexpected death in epilepsy (SUDEP).

METHODS

We prospectively recruited 49 consecutive adult patients admitted to the Mayo Clinic Epilepsy Monitoring Unit with focal, generalized, or unclassified epilepsy syndromes. pOSA was identified using oximetric oxyhemoglobin desaturation index (ODI) and the Sleep Apnea-Sleep Disorders Questionnaire (SA-SDQ) and STOP-BAG screening tools. Revised SUDEP Risk Inventory (rSUDEP-7) scores were calculated, and epilepsy patients with and without pOSA were compared with Wilcoxon signed-rank tests. Correlation and regression analyses were utilized to determine relationships between pOSA and rSUDEP-7 scores.

RESULTS

Thirty-five percent of patients had pOSA, with a mean ODI of 11.3 ± 5.1/h (range = 5.1-22.8). Patients with pOSA were older and heavier, and more frequently had a focal epilepsy syndrome and longer epilepsy duration, with higher SA-SDQ and STOP-BAG scores (all P < 0.05). Median rSUDEP-7 score was 3 ± 1.4 (range = 0-6). Higher rSUDEP-7 scores were positively correlated with higher ODI (P = 0.036). rSUDEP-7 score ≥ 5 was associated with pOSA by ODI, SA-SDQ, and STOP-BAG questionnaire criteria (P < 0.05).

SIGNIFICANCE

Our pilot study identified a high frequency of pOSA in refractory epilepsy monitoring patients, finding that pOSA patients were older and heavier, with higher screening symptoms for sleep apnea and more frequent focal seizures with a longer epilepsy duration. We also found a possible association between OSA and SUDEP risk. Identification and treatment of OSA in patients with epilepsy could conceivably provide a novel approach toward preventing the risk of SUDEP. Future studies with polysomnography are needed to confirm predictive features for OSA in epilepsy populations, and to determine whether OSA is associated with SUDEP risk.

Sudden unexpected death in epilepsy, periictal physiology, and the SUDEP-7 Inventory

Sudden unexpected death in epilepsy (SUDEP) is a significant public health burden. Epidemiological studies have identified clinical SUDEP risk factors across large populations, but the means to apply this information to individual patients are lacking. The SUDEP-7 Inventory was developed as a marker of clinical SUDEP risk and has been used in studies of potential SUDEP biomarkers. We retrospectively reviewed clinical data from 16 patients dying of SUDEP and 48 matched living epilepsy controls to determine whether individuals succumbing to SUDEP could be distinguished from living epilepsy controls using the revised SUDEP-7 Inventory, the absolute number of clinical risk factors as identified by an International League Against Epilepsy meta-analysis (ILAE score), and physiological characteristics previously associated with SUDEP risk. Mean revised SUDEP-7 Inventory score was 3.3 ± 2.0 in SUDEP cases and 3.8 ± 2.3 in controls (P = 0.39). Mean ILAE score was 2.4 ± 1.1 in SUDEP cases and 2.6 ± 1.4 in controls (P = 0.62). There were no significant differences in interictal heart rate variability (measured by the root mean square of differences of successive RR intervals), periictal cardiorespiratory dysfunction, and postictal generalized electroencephalographic suppression between the groups. This demonstrates that a reliable instrument for individual SUDEP risk stratification is lacking and highlights the need for improved understanding of SUDEP pathophysiology and individual risk determination.

Assessment of brain oxygenation imbalance following soman exposure in rats

Nerve agents (NAs) are potent organophosphorus (OP) compounds with applications in chemical warfare. OP compounds act by inhibiting acetylcholinesterase (AChE). Soman (O-pinacolyl methylphosphonofluoridate) is one of the most potent NAs. It is well known that small doses of NAs can be lethal, and that even non-lethal exposure leads to long-term mental debilitation/neurological damage. However, the neuropathology following exposure to sub-lethal nerve agents is not well understood. In this study, we examined changes in tissue oxygenation (pO₂) in the cortex and hippocampus after a sub-lethal dose of soman [80-90 μg/kg; subcutaneous]. pO₂ changes can provide information regarding oxygen delivery and utilization and may be indicative of a disruption in cerebral blood flow and/or metabolism. Changes in oxygenation were measured with chronically implanted oxygen sensors in awake and freely moving rats. Measurements were taken before, during, and after soman-induced convulsive seizures. Soman exposure resulted in an immediate increase in pO₂ in the cortex, followed by an even greater increase that precedes the onset of soman-induced convulsive seizures. The rise in hippocampus pO₂ was delayed relative to the cortex, although the general pattern of brain oxygenation between these two regions was similar. After convulsive seizures began, pO₂ levels declined but usually remained hyperoxygenated. Following the decline in pO₂, low frequency cycles of large amplitude changes were observed in both the cortex and hippocampus. This pattern is consistent with recurring seizures. Measuring real-time changes in brain pO₂ provides new information on the physiological status of the brain following soman exposure. These results highlight that the measurement of brain oxygenation could provide a sensitive marker of nerve agent exposure and serve as a biomarker for treatment studies.

From unwitnessed fatality to witnessed rescue: Nonpharmacologic interventions in sudden unexpected death in epilepsy

Sudden unexpected death in epilepsy (SUDEP) risk reduction remains a critical aim in epilepsy care. To date, only aggressive medical and surgical efforts to control seizures have been demonstrated to be of benefit. Incomplete understanding of SUDEP mechanisms limits the development of more specific interventions. Periictal cardiorespiratory dysfunction is implicated in SUDEP; postictal electroencephalography (EEG) suppression, coma, and immobility may also play a role. Nocturnal supervision is protective against SUDEP, presumably by permitting intervention in the case of a life-threatening event. Resuscitative efforts were implemented promptly in near-SUDEP cases but delayed in SUDEP deaths in the Mortality in Epilepsy Monitoring Unit Study (MORTEMUS) study. Nursing interventions--including repositioning, oral suctioning, and oxygen administration--reduce seizure duration, respiratory dysfunction, and EEG suppression in the epilepsy monitoring unit (EMU), but have not been studied in outpatients. Cardiac pacemakers or cardioverter-defibrillator devices may be of benefit in a few select individuals. A role for implantable neurostimulators has not yet been established. Seizure detection devices, including those that monitor generalized tonic-clonic seizure-associated movements or cardiorespiratory parameters, may provide a means to permit timely periictal intervention. However, these and other devices, such as antisuffocation pillows, have not been adequately investigated with respect to SUDEP prevention.

Postictal generalized EEG suppression after generalized convulsive seizures: A double-edged sword

OBJECTIVE

The aim of this study is to investigate the key facilitating factors for postictal generalized EEG suppression (PGES) in a large cohort of patients with generalized convulsive seizures (GCSs).

METHODS

We retrospectively reviewed the data of consecutive patients who had GCSs in the epilepsy monitoring units of two epilepsy centers. Statistical analysis was performed to assess specific variables as potential risk factors for PGES.

RESULTS

Among the 208 enrolled patients with 366 seizures, PGES was observed in 109 (51.9%) patients and 168 (45.9%) GCSs. The mean duration of PGES was 33.2 ± 12.0 s (34 s, 3-70 s). PGES or severe PGES (>20 s) was associated with more severe postictal coma and temporal lobe epilepsy. Moreover, PGES was independently associated with a longer tonic duration, shorter total seizure duration, and lower habitual seizure frequency.

CONCLUSIONS

PGES is strongly correlated not only with longer tonic duration, but also with shorter total seizure duration and lower habitual seizure frequency.

SIGNIFICANCE

PGES may represent a switch-off inhibitory mechanism in seizure termination; moreover, it may indicate the efficacy of a long-lasting inhibitory network that suppresses GCS ictogenesis.

Periictal autonomic dysfunction and generalized postictal EEG suppression in convulsive seizures arising from sleep and wakefulness

Sleep appears to be an independent risk factor of sudden unexpected death in epilepsy (SUDEP). We retrospectively determined the periictal electrophysiological characteristics of nocturnal and diurnal generalized convulsive seizures (GCSs) in 109 patients. Our data showed that preictal heart rate (HR) was significantly lower in 46 patients with nocturnal GCSs than in 63 patients with diurnal GCSs (p=0.002). However, there was no significant difference in postictal HR and respiratory rate (RR), total seizure duration, total convulsive phase, tonic phase, and clonic phase. Meanwhile, postictal generalized EEG suppression (PGES) was observed in 52.4% of the patients with diurnal GCSs and 67.4% of the patients with nocturnal GCSs. Duration of PGES was 38.2±17.3s in patients with diurnal GCSs and 49.5±21.7s in patients with nocturnal GCSs. There was also no significant difference in the prevalence (p=0.118) and duration (p=0.044, Bonferroni-corrected significant level: α=0.00625) of PGES in the two patient groups. Therefore, there is no clear evidence to attribute the SUDEP risk associated with sleep to postictal autonomic dysfunction and PGES, as compared to wakefulness.