Postictal clinical and electroencephalographic activity following intracranially recorded bilateral tonic–clonic seizures

Abstract

Summary Objective: The dynamics of the postictal period, which may demonstrate such dramatic clinical phenomena as focal neurological deficits, prolonged coma and immobility, and even sudden death, are poorly understood. We sought to classify and characterize postictal phases of bilateral tonic-clonic seizures based on EEG criteria and associated clinical features. Methods: We performed a detailed electroclinical evaluation of the postictal period in a series of 31 bilateral tonic-clonic seizures in 16 patients undergoing epilepsy surgery evaluations for focal pharmacoresistant epilepsy with intracranial electrodes and time-locked video. Results: The postictal EEG demonstrated three clearly differentiated phases: attenuation, a burst-attenuation pattern, and a return to continuous background, with abrupt, synchronized transitions between phases. Postictal attenuation was common, occurring in 84% of seizures in 94% of patients in this study. There was increased power in gamma frequencies (> 25 Hz) during postictal attenuation periods relative to preictal baseline in 88% of seizures demonstrating the attenuation pattern (N=25 seizures, p<0.002). Such increases were seen in more than 90% of channels in 13 seizures (52%), and fewer than 10% of channels in three seizures (12%). Postictal immobility was seen in 87% of seizures, with either a flaccid (58%) or rigid/dystonic (29%) appearance. Clinical motor manifestations, including focal dystonic posturing, automatisms, head and eye deviation, and myoclonic jerking, continued or emerged within the first minute following seizure termination in 48% of seizures, regardless of EEG appearance. Significance: Intracranial postictal attenuation, which may be diffuse or focal, is so common that it should be regarded as an ubiquitous feature of bilateral tonic-clonic seizures, rather than an unusual event. The prominence of high frequency activity coupled with emerging clinical features, including rigid immobility and semiologies such as automatisms, during the postictal period support the presence of ongoing seizure-related neuronal activity in unrecorded brain regions.

Near SUDEP during bilateral stereo‐EEG monitoring characterized by diffuse postictal EEG suppression

“…Prior studies reflect that a prolonged period of PGES is also associated with increasing hypoxemia, both of which are potential biomarkers for SUDEP risk. 12,13 Consistent with findings in MORTEMUS, bradyarrhythmias in our patient were also observed only after preceding periods of apnea and increasing hypoxia. 2 PGES was not seen on any prior scalp EEG recordings that we were able to review.…”

The postictal state — What do we know?

“…6,7,49,67 It has been found in 84% of seizures in 94% of epilepsy patients. 68 Different definitions of postictal EEG suppression have been proposed; for example, EEG attenuation of more than 2 seconds. 49 The underlying mechanism of postictal EEG suppression remains unknown.…”

Characterizing the role of the structural connectome in seizure dynamics

“…In some seizures, there is an initial persistence or increase in SC-FC coupling in the immediate postictal period followed by a decrease, while in some seizures, SC-FC coupling decreases immediately. While the postictal EEG is often characterized by slowing and suppression-particularly in focal to bilateral tonic-clonic seizures-the dynamics of the postictal period are variable, complex, and poorly understood (Kaibara and Blume, 1988;Bateman et al, 2019;Marchi et al, 2019). Additionally, the transition from ictal to postictal is known to be ambiguous, as the end of a seizure is often not well demarcated, neither clinically nor electrophysiologically (Fisher and Engel, 2010).…”