Seizure 2022, Vol 98, Editor’s Choice: Risk factors for postictal generalized EEG suppression in generalized convulsive seizure: A systematic review and meta-analysis
Epileptic seizures can start and spread through the brain in many ways. This means that there are therefore clear differences between how epilepsy presents in different people. However, bilateral tonic clonic seizures are often treated as an exception to this rule. BTCS are commonly considered as the “final common pathway” of epileptic activity in the brain, and as if they were not only stereotyped in one individual but across all patients with epilepsy. This may be one of the reasons why, in clinical practice and in research studies, the number of bilateral tonic clonic seizures (BTCS) is considered a meaningful measure of the effectiveness of medical or other therapeutic interventions for epilepsy.
In reality, things are more complicated of course. Quite apart from the fact that the subjective impact of BTCS on a person with epilepsy is likely to vary depending on the circumstances in which the seizure has occurred, there are also major objective differences between BTCSs. Some BTCS are associated with injuries or incontinence, others are not. BTCS may only last 30 seconds or continue for over two minutes. What is more, electroclinically definable phases within a single BTCS (including those characterised by the focal build-up of epileptic activity, tonic or clonic manifestations) differ in length intra- and interindividually (1). Last but certainly not least, BTCS differ in terms of the occurrence and duration of postictal generalised EEG suppression (PGES), a recognised risk factor for Sudden Unexplained Death in Epilepsy (SUDEP) (2).
My editor’s choice from the current volume of Seizure is a systematic review and meta-analysis by Yang et al. which examines factors determining the likelihood of PGES development (3). The first finding is that PGES is a common phenomenon, having been identified after 23 to 86% of BTCS across the 15 studies contributing to this meta-analysis. Factors associated with the occurrence of PGES included a longer tonic phase duration, sleep at BTCS onset, and an older age of epilepsy onset. The duration of the whole tonic clonic or clonic phases and the length of the epilepsy history were unassociated with PGES. Another factor which had no impact on the PGES risk was early oxygen – this meta-analysis therefore provided no justification for postictal oxygen administration.
Given that seizure phases have become easier to measure using wearable technology, it should now be technically possible to capture the duration of the tonic phase of BTCS in more naturalistic settings over the longer term. The findings of this study suggest this observation may be a more meaningful objective treatment outcome for future studies than the measures listed above.
(1) Pan S, Wang F, Wang J, Li X, Liu X. Factors influencing the duration of generalized tonic-clonic seizure. Seizure 2016; 34:44-7.
(2) Lhatoo SD, Faulkner HJ, Dembny K, Trippick K, Johnson C, Bird JM. An electroclinical case-control study of sudden unexpected death in epilepsy. Ann Neurol 2010;68:787-96.
(3) Yang X, Yang X, Liu B, Sun A, Zhao X-H. Risk factors for postictal generalized EEG suppression in generalized convulsive seizure: a systematic review and meta-analysis. Seizure 2022;98:19-26.