Abstracts

Rationale: Epileptic seizures occur at different times of the 24-hour day, possibly under the influence of cerebral (circadian) rhythms. Up to now, human studies in this respect are limited to the dichotomy: sleep/wake or at best mention the time of the day or sleepstage in which the seizures were seen. More detailed studies were done in animals, but gave different results. Modern methods of assessing the phase of the human circadian rhythm were not used up to now. The aims of our study are two-fold: 1) to describe the time of the 24 hr. day on which seizures occur and 2) to provide ideas and if possible guidelines, how to investigate the influence of the biological clock on seizures. Methods: Consecutive patients were included (children 2-15 yrs. or adults) with focal seizures (clinical and EEG event for at least 5 seconds) during longterm EEG and video recording. The latter method provided the exact time of the epileptic events and the (sleep) stage the seizure occurred in. As methods to evaluate the biological clock we assessed: 1) simple clocktime, 2) questionnaires and actigraphy, 3) continuous core body temperature measurement, 4) melatonin curves, 5)manipulation of the biological clock.Results: In total 870 seizures were assessed. Nearly half occurred when the patient was awake; the others preferentially during NREM I-II sleep. The period 2-8 pm was over represented in the prevalence of seizures. This holds for adults and children and all types of seizures with the exception of frontal seizures in adults which were seen mostly at the end of the sleep period. For the second aim of the study we had the following considerations. The results from simple methods for assessment of the influence of the biological clock (real clock time, questionnaires, actigraphy, melatonin curves and temperature measurement)are often interrelated. To delineate the real contribution of the biological clock, it is necessary to rule out factors which may be circadian as well (light/dark, meals,etc.). Constant routine procedures do so, but introduce sleepdeprivation and give again a potential bias, in particular in patients with epilepsy. The most plausible way to reach our aims is to manipulate the biological clock by changes in behaviour and using light and melatonin as tools for changing the phase of the circadian rhythm (forced desynchrony). Conclusions: Correlation of simple clocktime and the moment a seizure occurs gives some insight in (circadian) rhythms in epilepsy. These measurements may be biased through other interfering circumstances. In order to have more precise information, new methods for the assessment of the biological clock are necessary. Melatonin curves, continuous core body temperature measurement in combination with forced desynchrony of the biological clock, are the methods of choice.