Relationship between location of epileptic focus and occurrence during sleep versus wakefulness

Different sleep stages exert differential effects on interictal discharges, neural synchrony and seizure threshold. We sought to assess the relationship between localization of the epileptogenic focus and seizure distribution in sleep versus wakefulness among patients with refractory epilepsy. We conducted a retrospective chart review-based study. Video-electroencephalography of patients with refractory epilepsy, planned for resective surgery, were reviewed for seizure localisation and occurrence relative to stage of sleep/wakefulness. Demographic/clinical data, including details of surgery, were also recorded. Bivariate analysis was conducted using the chi-square test for proportions and unpaired t-test/ANOVA to compare the means within groups. We enrolled 175 patients (107 males) with a mean age of 26.1 + 9.8 years (range: 4-53 years). We analysed 1,282 seizures, of which 916 (71.5%) were temporal, 95 (7.4%) frontal, 144 (11.2 %) central/ parietal and 19 (1.5%) arose from the occipital lobe. Temporal lobe onset seizures were more frequent during wakefulness (77.7%) compared to extra-temporal localization (65%) (p<0.0001). Amongst temporal lobe onset seizures, those during wakefulness arose more frequently from the lateral temporal (88.6%) compared to the mesial temporal lobe (75.5%) (p=0.0003). A higher proportion of seizures evolved into secondary generalisation during sleep (23.5%) versus 8.7% during wakefulness (p<0.0001). Our study demonstrates that lobar location of epileptogenic foci is associated with a predilection of seizures to occur, as well as secondarily generalise, during sleep/wakefulness. Seizures with lateral temporal lobe as well as extratemporal lobe onset were more likely to occur during wakefulness. Overall, sleep related seizures were more likely to be of extratemporal lobe onset, though.