Nocturnal interictal epileptic discharges in adult Lennox-Gastaut syndrome: the effect of sleep stage and time of night
Lennox-Gastaut syndrome (LGS) is characterized by interictal epileptiform discharges (IEDs) occurring during sleep. The aim of this study was to determine whether sleep influences not only the frequency of seizures and IEDs, but also the time-dependent evolution that may support the hypothesis of homeostatic influences on epileptic threshold. Video polysomnography data from our database were reviewed to identify adult LGS patients with at least seven hours of nocturnal recording. Thirteen patients were identified and a second polysomnography was available for nine. The number, duration and index of IEDs, relative to total sleep, sleep stages, and time during the night, were calculated. The majority of IEDs occurred during non-rapid eye movement sleep, mainly in stage 2 and slow-wave sleep. Adjusting for time spent in each sleep stage, we found 45 IEDs/hour in stage 1, 123/hour in stage 2, 106/hour in slow-wave sleep, and 26/hour in rapid eye movement sleep. The temporal distribution of IEDs showed a significant rise in the first three hours of sleep, followed by a progressive decrease at the end of the night (F=85.6; p<0.0001). Interictal epileptiform discharges occurrence in adult LGS is facilitated by non-rapid eye movement sleep with an evident effect of stage 2 and slow-wave sleep. The significant IED occurrence in the first part of the night and the subsequent decline suggests a link between epileptic threshold and homeostatic sleep mechanisms. The latter should be considered regarding choice of therapy.