Time modulation of spike-and-wave activity in generalized epilepsy.

Nineteen patients aged 4 to 44 years with generalized epilepsy and generalized 3 Hz spike-and-wave activity, were monitored for 24 or 36 hours on one to nine occasions to determine the time distribution of ictal and interictal electroencephalographic discharges and the consistency of the time patterns observed. Two patients with a low incidence of spike-and-wave activity had a random pattern of occurrence; the other 17 showed one of three types of time modulation. The latter can be explained by the interaction of two modulative processes, one with a period of about 100 minutes and the other of approximately 24 hours. The pattern observed depends on the phase angle of the two cyclic processes. Treatment with ethosuximide altered the pattern of time modulation, and eventually, when the spike-and-wave activity was reduced to a low level, the time distribution became random.