Abstracts

RATIONALE: Sleep state may facilitate seizures due to increased thalamocortical synchronizing mechanisms. Seizures are believed to be more common in non-rapid eye movement (NREM) sleep, especially NREM stage 2 sleep, than in rapid eye movement (REM) sleep, although studies have not adjusted for the amount of time spent in specific sleep stages. We determined seizure rate for NREM vs. REM sleep and for NREM sleep stages in epilepsy patients with seizures during sleep who underwent overnight polysomnography (PSG). METHODS: We reviewed PSGs performed over the last 13 years in our Sleep Laboratory and video-EEG-PSGs performed over the last 2 years in our Epilepsy Laboratory to identify patients with recorded seizures during sleep. Patients were excluded if they had only electrographic seizures or if the diagnosis of epileptic events was uncertain. A total of 29 patients having 58 seizures were identified, 17 of whom were presurgical candidates. Their age ranged from 4-72 years. RESULTS: 93% of seizures occurred in NREM (56% in stage 2, 20% in stage 1, 17% in delta (stage 3 and 4 combined) and 7% in REM sleep. The ratio of seizures to stage of sleep in minutes was higher in NREM sleep (0.193 for NREM and 0.044 for REM; p < 0.0001; paired t-test). Within NREM sleep, ratios were 0.164 for stage 1, 0.222 for stage 2, 0.155 for delta; no statistically significant difference; p >0.1). The majority of seizures (55%) occurred after 3.5 hours of sleep onset, a time of the night when NREM stage 2 sleep predominates. CONCLUSIONS: After adjusting for time in sleep stage, seizures were more frequent during NREM than REM sleep. The highest rate of seizures occurred during NREM stage 2 sleep, although this result did not reach statistical significance. These findings support the role of NREM sleep in facilitating seizures. Further basic and clinical neurophysiological studies are necessary to characterize the mechanisms underlying sleep-related facilitation of seizures. Study supported by NINDS K02 NS02099