Abstracts

Rationale: Slow wave sleep and generalized epileptiform activity are both believed to engage cortico-thalamic circuits. We sought to compare macro-sleep architecture between idiopathic and secondary generalized epilepsy (IGE and SGE), and to compare interactions between sleep stage and epileptic discharges across the two main types of generalized epilepsy. We hypothesized that interictal activity in both generalized epilepsies would be more frequent in 1) sleep than wakefulness, 2) NREM than REM sleep, 3) deep than light sleep and 4) discharges would become fragmentary in sleep. Methods: Ten patients with IGE and eight with SGE underwent overnight video EEG & polysomnography. Exclusion criteria were age <15 years, previous brain surgery, vagal nerve stimulation or known moderate-to-severe obstructive sleep apnea. Sleep stages were manually scored by an experienced sleep technician. Separately, interictal discharges (iEDs) were identified and classified by two neurologists. Results: Mean age was 38.3 years (8 male). SGE subjects tended to spend less time asleep (sleep efficiency: SGE-68.8%; IGE-72.6%, p-NS). Proportion of NREM and REM sleep in IGE were 88.4% and 11.6%, while SGE were 95.7% and 4.3%. REM proportion in SGE was less than IGE, p-0.003. Generalised discharge rate in IGE subjects showed a variable response to sleep. SGE subjects tended to show more discharges in sleep compared to wakefulness (median 204.3 vs 109.5/hour, p-NS) again with some inter-subject variability. In SGE, the number of iEDs per hour (iED rate) was higher in NREM than REM (median 205.5 vs 44.0, p=0.018). There was a similar trend in IGE (median 18.0 vs 1.4/hour, p-NS). SGE subjects had more generalized spike-wave in deep sleep compared with light sleep (iED rate 139.3 vs 106.7, p-0.043), whereas there was no significant difference in IGE subjects (9.2 vs 5.2, p-NS). Generalized paroxysmal fast activity (SGE) occurred only in NREM sleep. In IGE generalized spike-wave discharge trains were shorter in sleep than wakefulness (0.47 vs 0.78 seconds, p-0.025), an effect not seen in SGE. Conclusions: The overall effect of sleep and sleep stage on epileptiform activity was unpredictable in IGE. SGE subjects have disturbed sleep architecture as manifested by reduced REM. In SGE, generalized spike-wave discharges were augmented in deep sleep and rarely occurred in REM, suggesting an inhibitory effect of REM.