Abstracts

RATIONALE: Consideration of the effects of sleep stage on IED rate and field may enhance the value of IEDs in the epilepsy surgery evaluation. NREM sleep may increase IED rate and field beyond the epileptogenic zone while REM sleep may limit both the frequency and distribution to the region of interest. Therefore the effect of sleep stage on IEDs in the epilepsy surgery evaluation may be useful, confounding or both. The objective of this study was to develop a method of quantifying the frequency and field of IEDs during different stages of sleep in order to better study the effects of sleep on the localizing value of IEDs. The first four subjects in whom this methodology was applied are reported here.
METHODS: Three patients with unilateral temporal lobe IEDs and Engel Class I outcome and one patient unilateral temporal lobe IEDs with class II outcome after anterior temporal lobectomy underwent overnight EEG-polysomnography during their presurgical evaluation. CM visually detected IEDs utilizing referential and bipolar montages while blinded to sleep staging. A second examiner(BAM) reviewed these IEDs. Studies were scored for sleep by MM. IEDs were classified into subtypes based upon distribution of electrode involvement. Each IED subtype was given a variance score based upon distance of involved electrodes from the 3 anterior temporal electrodes (F7/8, Sp1/2 and T3/4), closest to the location of the presumed epileptogenic zone. Rate of each IED subtype in NREM stage 1/2, NREM 3/4 and stage REM sleep was tabulated. Rate-weighted variance in IED field was calculated for NREM1/2, NREM 3/4 and REM sleep by multiplying rates for each IED subtype by their variance score and summing these values for each sleep stage. Paired t-tests were performed comparing rate-weighted IED field variance in NREM 1/2 with that in NREM 3/4 and each of these sleep stages to REM sleep. Statistical significance was set at p[lt].05.
RESULTS: Paired t-tests demonstrated that IED field variance was significantly higher in NREM 3/4 as compared to stage NREM 1/2 sleep (p=.01). IED field variance was higher in NREM 3/4 (p=.04) and NREM 1/2 (p=.04) as compared to REM sleep. Overall, relatively few IEDs were observed during REM sleep. However, when present, they were restricted to the presumed epileptogenic zone. In addition, as compared to stage [onehalf] sleep, NREM stage 3/4 sleep was associated with new IED subtypes with wider distributions and new maxima at frontopolar and posterior temporal electrodes.
CONCLUSIONS: In order to more accurately use the sleep EEG in the epilepsy surgery evaluation we are developing a methodology to quantify IED frequency and distribution. Our preliminary results demonstrate a quantitative difference in IED variance between NREM sleep stages 1/2 and 3/4 and REM sleep. Further directions of this work will be to apply our methodology to larger numbers of patients with both temporal and extra-temporal epilepsy syndromes. In addition we will be compare this method to automated techniques evaluating IED frequency and topography.
At the end of this activity participants should be able to discuss the influence of sleep stage on the expression of interictal epileptiform discharges and the potential role of this effect in the epilepsy surgery evaluation.
[Supported by: NIH/NINDS NRSA NS07222-19 (CM), NINDS KO2 NS02099(BAM)]