Abstracts

The value of interictal epileptiform discharges (IEDs) in the epilepsy surgery evaluation may be enhanced by consideration of the sleep stage in which they are observed. Rapid eye movement (REM) sleep may limit IED field and may be of particular use in localization of the epileptogenic zone. However, REM sleep may also limit IED frequency and contain fewer IEDs. Furthermore, medically refractory epilepsy and the video-EEG monitoring environment may contribute to sleep disruption and limit REM sleep available for study. These factors may hinder the use of IEDs during REM sleep in the pre-surgical evaluation. The objective of this study was to determine prevalence of and factors associated with IEDs during REM sleep in patients with medically refractory epilepsy.
This sample was derived from patients admitted for presurgical video-EEG monitoring between July, 1998 and June, 2000 and participating in a protocol examining the relationship of IEDs and seizures to sleep. They were monitored with continuous overnight EEG-polysomnography. Only the first night of sleep was used for analysis to avoid the confounding variables of antiepileptic drug withdrawal, epileptic seizures, and sleep deprivation. Patients were excluded from study if they had seizures during this first night. Studies were scored for sleep-stage by MM. CM and BAM visually detected IEDs during NREM and REM sleep using bipolar and referential montages. IED rate per hour was calculated for REM and NREM sleep. To approximate the overall NREM IED rate, NREM sleep one hour prior to the first REM epoch was used. Independent samples two-tailed t-tests and Chi-Square tests were performed with statistical significance set at p[lt].05.
In 38 of 55 patients (73%) there was at least 30 minutes REM sleep during the first night. In 12 of these 38 patients (32%), IEDs were present during stage REM sleep. In all cases the IED rate was lower in REM as compared to NREM sleep. The presence of IEDs during REM sleep was significantly associated with both NREM IED frequency (p = .01) and the presence of a localizing ictal EEG (p[lt].001). Greater NREM IED frequency was also associated with the presence of a localizing ictal EEG (p=.03). The presence of IEDs during REM sleep was not significantly associated with patient age, age at seizure onset, gender, baseline seizure frequency, extra-temporal onset seizures, the presence of mesial temporal sclerosis, the presence of lesions other that mesial temporal sclerosis, subsequent epilepsy surgery or epilepsy surgery outcome.
The majority of patients had sufficient REM sleep to evaluate for IEDs during this sleep stage. A significant number of patients had IEDs during REM sleep. Both REM sleep IEDs and frequent NREM sleep IEDs were associated with a localizing ictal EEG. These findings are of potential importance in the epilepsy surgery evaluation and will require further confirmation in larger datasets.
[Supported by: AAN Clinical Research Training Fellowship(CM) NINDS K02 NS02099 (BAM)]