Abstracts

Rationale: Resective surgery is the most effective treatment of medically refractory epilepsy. In determining the epileptogenic zone, the irritative zone (e.g. electrical field of interictal epileptiform discharges, IED) is often too broad a volume for resection. Although previous studies have suggested that the irritative zone in rapid eye movement (REM) sleep is more localized than in other sleep-wake states (e.g. non-REM sleep), we are not aware of a rigorous set-theoretic comparison of localizing the concordance of irritative zones between sleep-wake states. Our main aim is to determine the degree of concordance between IED fields in REM sleep against NREM sleep and wakefulness. Methods: We examined IEDs from admitted Epilepsy Monitoring Unit (EMU) patients. To determine absolute field size, we visually counted the number of 10-20 electrodes included in IEDs for REM sleep, NREM sleep, and wakefulness. We then treated the ensemble electrode locations in REM sleep, NREM sleep, and wakefulness IEDs as mathematical sets (e.g. A,B). As per Figure 1, we defined discordance as sets with no mathematical intersection (A∩B=Ø), partial concordance as non-empty mathematical intersection (A∩B), and proper concordance as mathematical subset (A⊂B) or superset (A⊃B). In addition to comparing REM sleep to each individual state (e.g. NREM sleep, wakefulness), we also evaluated probabilistic combinations of states: NREM sleep *OR* wakefulness (A+B), NREM sleep *AND* wakefulness (A·B). Results: We analyzed 276 IEDs from 13 epilepsy patients in the Health Sciences Centre Winnipeg EMU. Mean absolute IED field size in REM sleep was 3.04+-0.72 electrodes, awake was 3.57+-0.90 electrodes, and NREM sleep was 4.27+-1.16 electrodes. As per Table 1, there was mostly proper concordance between REM sleep against the state of NREM sleep alone, but mostly partial concordance between REM sleep and the state of wakefulness alone. We also found mostly proper concordance of REM sleep against the probabilistic combination of NREM sleep *OR* wakefulness, but mostly partial concordance of REM sleep against the probabilistic combination of NREM sleep *AND* wakefulness. We only found discordance between REM sleep and the state of NREM sleep alone (n=1 patient), and between REM sleep against the probabilistic combination of NREM sleep *AND* wakefulness (n=2 patients). Conclusions: We confirmed that the irritative zone in REM sleep is smaller than either that of NREM sleep or wakefulness. Although smaller, the IED field in REM sleep mostly overlaps with the field in NREM sleep or wakefulness. However, REM sleep suggests a completely separate novel irritative zone location in a minority of cases (e.g. discordance), or novel extensions of an existing irritative zone in some cases (e.g. partial concordance). Our findings further clarify the previously reported localizing ability of REM sleep, but future research is needed to determine whether novel irritative zones suggested by REM sleep are a valid reflection of the epileptogenic zone. Funding: Winnipeg Health Sciences Centre (HSC) Foundation