Lateralizing Value of Interictal Spikes on Overnight Sleep‐EEG Studies in Temporal Lobe Epilepsy

Abstract

Summary:Purpose: To determine the lateralizing value of interictal epileptiform discharges (IEDs) recorded during overnight sleep-EEG studies in temporal lobe epilepsy. Because IEDs are more prevalent in non-rapid eye movement (NREM) sleep than in wakefulness, overnight sleep-EEG recordings may contribute additional lateralizing information to the epilepsy surgery evaluation beyond daytime EEGs.Methods: Twenty-four subjects with medically refractory temporal lobe epilepsy underwent continuous overnight sleep-EEG recordings. Subjects were seizure free 2 2 4 h before study and receiving stable doses of medication. The IED foci recorded on overnight studies were compared with daytime EEGs, interictal samples, and ictal recordings during long-term monitoring, brain magnetic resonance images (MRIs), and surgical outcome.Results: (a) In all 24 subjects, including 13 without IEDs on daytime EEGs, temporal IEDs were present during NREM sleep and were exclusively or predominantly (>95%) unilateral in 15 and bitemporal in nine. (b) Unilateral NREM IEDs were concordant with surface or depth ictal-onset regions in 14 subjects, even if MRIs were normal (three subjects) or surface ictal-onset regions were bilateral (five subjects). Eleven of 12 subjects with unilateral concordant NREM IEDs who have undergone surgery are seizure free. (c) Bitemporal IEDs were associated with postoperative seizures in a11 subjects with normal MRIs or widespread MRI abnormalities. However, all subjects with bitemporal IEDs and MRI hippocampal abnormalities concordant with ictal-onset regions had good to excellent surgical outcomes.Conclusions: When combined with other investigations, IEDs recorded on overnight studies add prognostic data to the epilepsy surgery evaluation not provided by daytime EEGs.Key Words: Sleep-Epilepsy-ElectroencephalographyInterictal epileptiform discharges-Surgery.The activating effect of sleep on electroencephalographic (EEG) activity in epilepsy has been established for >50 years (1). Non-rapid eye movement (NREM) sleep increases interictal epileptiform discharges (IEDs) in partial epilepsy (2,3). In contrast, IEDs are relatively suppressed during rapid eye movement (REM) sleep. The activating role of NREM sleep on epileptic cortex has been attributed to increased neuronal synchronization within thalamocortical projection neurons, resulting from the neurochemical and neurophysiologic processes that initiate and maintain NREM sleep (4).Although the usefulness of sleep-EEG recordings for the diagnosis of epilepsy is well established (5) ( 3 ) found that IEDs were more frequent in delta NREM sleep and that NREM sleep extended and REM sleep restricted the IED field in subjects with temporal lobe epilepsy. By using log delta power to measure sleep depth in subjects with partial epilepsy Malow and co-workers (6) showed that the rate of IEDs increased in delta sleep and in deepening NREM sleep. Overnight continuous sleep-EEG studies, therefore, may provide useful information about IED foci that are not provided by daytime E...

Cortical hyperexcitability and epileptogenesis: Understanding the mechanisms of epilepsy - Part 2

“…Furthermore, studies investigating seizure outcome following temporal lobectomy in patients with refractory seizures reported conflicting seizure freedom in patients with contralateral epileptiform discharges and/or seizure propagation. 94,[96][97][98][99] Munari and his co-workers proposed the concept of neocortical secondary epileptogenesis in the development of symptomatic generalised epilepsy associated with focal lesions such as hypothalamic hamartomas. 28 This was later corroborated by Harvey 36 and Freeman 100 and their colleagues based on a series of patients with hypothalamic hamartomas presenting with gelastic seizures, generalised seizures and generalised slow spike-wave discharges on EEG.…”

Sleep-related epileptic behaviors and non-REM-related parasomnias: Insights from stereo-EEG

“…Of clinical importance is the fact that during the phase A of the CAP the interictal discharges can spread ipsilaterally and contralaterally from the primary focus[7], whereas during REM sleep the discharges seem to focalize maximally, especially in TLE [39][40][41]. Moreover, sleep may bring out IEDs that are not present on wake scalp EEG recordings [110][111][112]. Nevertheless, it is imperative to note that most studies assessing the role of sleep on ictal and interictal activity have been performed using scalp EEG and conventional sleep scoring stages.…”

Association of Interictal Epileptiform Discharges with Sleep and Anti-Epileptic Drugs

“…Improved sleep architecture, mainly NREM stages I and II, may increase the frequency of IEDs and may also affect IED distribution pattern [5][6][7][8] . The suggested mechanism of NREM sleep to activate IEDs is the synchronization of neuronal assembly between brainstem, thalamus, and cortex [16][17][18][19] .…”

“…Literature suggest that latent IEDs are mainly activated during non-rapid-eye-movement (NREM) stages I and II sleep and focal IEDs tend to become bilateral and more generalized [5][6][7][8] . Thus, EEG performed during sleep is a standard procedure in the diagnosis of epilepsy.…”