Why do seizures in generalized epilepsy often occur in the morning?

Objective: We used transcranial magnetic stimulation to investigate the effect of diurnal variability on cortical excitability in patients with epilepsy. Methods: Thirty drug-naive patients with epilepsy (20 idiopathic generalized epilepsy [IGE], including 10 juvenile myoclonic epilepsy [JME], and 10 focal epilepsy) and 10 control subjects without epilepsy were studied both early in the morning and late in the afternoon. We measured the mean motor thresholds and constructed recovery curves at short (2–15 msec) and long (50–400 msec) interstimulus intervals. Results: An increase in cortical excitability indicated by decreased short and long intracortical inhibition was observed early in the morning compared to the afternoon in patients with JME. In other IGE syndromes, there was decreased long intracortical inhibition only. No effect was found in subjects with focal epilepsy or controls without epilepsy. Conclusion: Cortical excitability measured by transcranial magnetic stimulation increases early in the morning in patients with idiopathic generalized epilepsy, particularly in juvenile myoclonic epilepsy, but not in subjects with focal epilepsy or controls without epilepsy. This may explain the increased seizure susceptibility in this cohort at this time of day.