Ictal-interictal continuum: a review of recent advancements
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Tao et al. Acta Epileptologica (2020) 2:13 https://doi.org/10.1186/s42494-020-00021-1
REVIEW
Open Access
Ictal-interictal continuum: a review of recent advancements James X. Tao1*, Xiaoxiao Qin2,3 and Qun Wang2,3
Abstract Continuous electroencephalogram (cEEG) has become an indispensable technique in the management of critically ill patients for early detection and treatment of non-convulsive seizures (NCS) and non-convulsive status epilepticus (NCSE). It has also brought about a renaissance in a wide range of rhythmic and periodic patterns with heterogeneous frequency and morphology. These patterns share the rhythmic and sharp appearances of electrographic seizures, but often lack the necessary frequency, spatiotemporal evolution and clinical accompaniments to meet the definitive criteria for ictal patterns. They may be associated with cerebral metabolic crisis and neuronal injury, therefore not clearly interictal either, but lie along an intervening spectrum referred to as ictal-interictal continuum (IIC). Generally speaking, rhythmic and periodic patterns are categorized as interictal patterns when occurring at a rate of 2.5 Hz with spatiotemporal evolution. As such, IIC commonly includes the rhythmic and periodic patterns occurring at a rate of 1–2.5 Hz without spatiotemporal evolution and clinical correlates. Currently there are no evidence-based guidelines on when and if to treat patients with IIC patterns, and particularly how aggressively to treat, presenting a challenging electrophysiological and clinical conundrum. In practice, a diagnostic trial with preferably a non-sedative anti-seizure medication (ASM) can be considered with the end point being both clinical and electrographic improvement. When available and necessary, correlation of IIC with biomarkers of neuronal injury, such as neuronal specific enolase (NSE), neuroimaging, depth electrode recording, cerebral microdialysis and oxygen measurement, can be assessed for the consideration of ASM treatment. Here we review the recent advancements in their clinical significance, risk stratification and treatment algorithm. Keywords: Periodic discharges, Critical care, Continuous EEG, Ictal-interictal continuum, Nonconvulsive seizures
Background Periodic discharges were initially described by Cobb and Hill in patients with subacute progressive encephalitis in 1950 [1]. Chatrian and colleagues later described periodic lateralized epileptiform discharges (PLEDs) in patients with acute focal brain lesions in 1964 [2]. In the light of widespread use of continuous EEG monitoring for critically ill patients in the last several decades, a spectrum of rhythmic and periodic patterns have been described. The American Clinical Neurophysiology Society (ACNS) has created a uniform EEG terminology for * Correspondence: [email protected] 1 Department of Neurology, The University of Chicago, 5841 South Maryland Ave. MC2030, Chicago, IL 6063, U.S.A. Full list of author information is available at the end of the article
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