Neocortical Slow Oscillations Implicated in the Generation of Epileptic Spasms

Electroclinical Landscape of Infantile Epileptic Spasms Syndrome

OBJECTIVES

To elucidate the electroclinical characteristics of infantile epileptic spasms syndrome (IESS) and to determine any potential association among these with underlying etiologies and response to therapy.

METHODS

Sixty-eight, treatment-naive children with IESS underwent long-term video electroencephalogram (EEG) recording, which was used to characterize the semiology, ictal, and inter-ictal EEG patterns. Children were further followed up to assess electroclinical predictors of etiologies and short-term therapeutic response.

RESULTS

Of 68 children enrolled (69% boys), the median age at enrollment was 10.5 mo (IQR-8). Eighty-eight percent of children had flexor spasms, followed by mixed (7%) and extensor (4.4%). Asymmetrical spasms were noted in 17.6% children, and all of them had underlying structural etiology. Two children had the status of epileptic spasms. In the present cohort, authors recognized five distinct ictal EEG correlates of epileptic spasms; the frontocentral dominant slow wave was the most prevalent (32%), followed by the generalized slow-wave complex with superimposed fast rhythm in 29.4%. The occipital dominant slow wave complex was a peculiar pattern in 16%. The major underlying etiologies were hypoxic-ischemic brain injuries (36.7%) and neonatal hypoglycemic brain injuries (22%). Besides asymmetric spasms, authors could not identify any significant association among electroclinical characteristics, underlying etiologies and response to therapy in this study.

CONCLUSIONS

The electroclinical landscape of IESS is peculiar and diverse in developing countries. The presence of asymmetrical spasms indicated underlying structural etiology.

Neurobehavioral deficits and a progressive ictogenesis in the tetrodotoxin model of epileptic spasms

OBJECTIVE

Our goal was to determine whether animals with a history of epileptic spasms have learning and memory deficits. We also used continuous (24/7) long-term electroencephalographic (EEG) recordings to evaluate the evolution of epileptiform activity in the same animals over time.

METHODS

Object recognition memory and object location memory tests were undertaken, as well as a matching to place water maze test that evaluated working memory. A retrospective analysis was undertaken of long-term video/EEG recordings from rats with epileptic spasms. The frequency and duration of the ictal events of spasms were quantified.

RESULTS

Rats with a history of epileptic spasms showed impairment on the three behavioral tests, and their scores on the object recognition memory and matching to place water maze tests indicated neocortical involvement in the observed impaired cognition. Analysis of EEG recordings unexpectedly showed that the ictal events of spasms and their accompanying behaviors progressively increased in duration over a 2-week period soon after onset, after which spasm duration plateaued. At the same time, spasm frequency remained unchanged. Soon after spasm onset, ictal events were variable in wave form but became more stereotyped as the syndrome evolved.

SIGNIFICANCE

Our EEG findings are the first to demonstrate progressive ictogenesis for epileptic spasms. Furthermore, in demonstrating cognitive deficits in the tetrodotoxin model, we have met a criterion for an animal model of West syndrome. Animal models will allow in-depth studies of spasm progression's potential role in cognitive regression and may elucidate why early treatment is considered essential for improved neurodevelopmental outcomes in children.

Lesional Intractable Epileptic Spasms in Children: Electroclinical Localization and Postoperative Outcomes

To analyze the influence of seizure semiology, electroencephalography (EEG) features and magnetic resonance imaging (MRI) change on epileptogenic zone localization and surgical prognosis in children with epileptic spasm (ES) were assessed. Data from 127 patients with medically intractable epilepsy with ES who underwent surgical treatment were retrospectively analyzed. ES semiology was classified as non-lateralized, bilateral asymmetric, and focal. Interictal epileptiform discharges were divided into diffusive or multifocal, unilateral, and focal. MRI results showed visible local lesions for all patients, while the anatomo-electrical-clinical value of localization of the epileptogenic zone was dependent on the surgical outcome. During preoperative video EEG monitoring, among all 127 cases, 53 cases (41.7%) had ES only, 46 (36.2%) had ES and focal seizures, 17 (13.4%) had ES and generalized seizures, and 11 (8.7%) had ES with focal and generalized seizures. Notably, 35 (27.6%) and 92 cases (72.4%) showed simple and complex ES, respectively. Interictal EEG showed that 22 cases (17.3%) had bilateral multifocal discharges or hypsarrhythmia, 25 (19.7%) had unilateral dominant discharges, and 80 (63.0%) had definite focal or regional discharges. Ictal discharges were generalized/bilateral in 71 cases (55.9%) and definite/lateralized in 56 cases (44.1%). Surgically resected lesions were in the hemisphere (28.3%), frontal lobe (24.4%), temporal lobe (16.5%), temporo-parieto-occipital region (14.2%), and posterior cortex region (8.7%). Seizure-free rates at 1 and 4 years postoperatively were 81.8 and 72.7%, respectively. There was no significant difference between electroclinical characteristics of ES and seizure-free rate. Surgical treatment showed good outcomes in most patients in this cohort. Semiology and ictal EEG change of ES had no effect on localization, while focal or lateralized epileptiform discharges of interictal EEG may affect lateralization and localization. Complete resection of epileptogenic lesions identified via MRI was the only factor associated with a positive surgical outcome.

Brain state-dependent high-frequency activity as a biomarker for abnormal neocortical networks in an epileptic spasms animal model

OBJECTIVE

Epileptic spasms are a hallmark of a severe epileptic state. A previous study showed neocortical up and down states defined by unit activity play a role in the generation of spasms. However, recording unit activity is challenging in clinical settings, and more accessible neurophysiological signals are needed for the analysis of these brain states.

METHODS

In the tetrodotoxin model, we used 16-channel microarrays to record electrophysiological activity in the neocortex during interictal periods and spasms. High-frequency activity (HFA) in the frequency range of fast ripples (200-500 Hz) was analyzed, as were slow wave oscillations (1-8 Hz), and correlated with the neocortical up and down states defined by multiunit activity (MUA).

RESULTS

HFA and MUA had high temporal correlation during interictal and ictal periods. Both increased strikingly during interictal up states and ictal events but were silenced during interictal down states and preictal pauses, and their distributions were clustered at the peak of slow oscillations in local field potential recordings. In addition, both HFA power and MUA firing rates were increased to a greater extent during spasms than interictal up states. During non-rapid eye movement sleep, the HFA rhythmicity faithfully followed the MUA up and down states, but during rapid eye movement sleep when MUA up and down states disappeared the HFA rhythmicity was largely absent. We also observed an increase in the number of HFA down state minutes prior to ictal onset, consistent with the results from analyses of MUA down states.

SIGNIFICANCE

This study provides evidence that HFA may serve as a biomarker for the pathological up states of epileptic spasms. The availability of HFA recordings makes this a clinically practical technique. These findings will likely provide a novel approach for localizing and studying epileptogenic neocortical networks not only in spasms patients but also in other types of epilepsy.

Using the TTX Model to Better Understand the Pathophysiology of a DREADDed Epilepsy-Infantile (Epileptic) Spasms

Neocortical Slow Oscillations Implicated in the Generation of Epileptic Spasms

Lee CH, Le JT, Ballester-Rosado CJ, et al. Ann Neurol. 2020;89(2):226-241. doi:10.1002/ana.25935

Objective:

Epileptic spasms are a hallmark of severe seizure disorders. The neurophysiological mechanisms and the neuronal circuit(s) that generate these seizures are unresolved and are the focus of studies reported here.

Methods:

In the tetrodotoxin model, we used 16-channel microarrays and microwires to record electrophysiological activity in neocortex and thalamus during spasms. Chemogenetic activation was used to examine the role of neocortical pyramidal cells in generating spasms. Comparisons were made to recordings from infantile spasm patients.

Results:

Current source density and simultaneous multiunit activity analyses indicate that the ictal events of spasms are initiated in infragranular cortical layers. A dramatic pause of neuronal activity was recorded immediately prior to the onset of spasms. This preictal pause is shown to share many features with the down states of slow-wave sleep. In addition, the ensuing interictal up states of slow-wave rhythms are more intense in epileptic than control animals and occasionally appear sufficient to initiate spasms. Chemogenetic activation of neocortical pyramidal cells supported these observations, as it increased slow oscillations and spasm numbers and clustering. Recordings also revealed a ramp-up in the number of neocortical slow oscillations preceding spasms, which was also observed in infantile spasm patients.

Interpretation:

Our findings provide evidence that epileptic spasms can arise from the neocortex and reveal a previously unappreciated interplay between brain state physiology and spasm generation. The identification of neocortical up states as a mechanism capable of initiating epileptic spasms will likely provide new targets for interventional therapies.