Rationale:
A relationship between sleep, circadian rhythm, and the occurrence of epileptic seizures was first postulated over a hundred years ago. Since then, few studies manly with a small number of seizures were published, most of them focusing on temporal lobe epilepsy. Study results suggest that there is an afternoon peak in the occurrence of seizures in mesial temporal lobe epilepsy. However, various temporal distributions have been reported for other seizure onset zones.
Here we analyzed all partial seizures determined by continuous EEG-monitoring to reevaluate former results and to provide a first step towards creating chronotypes in epilepsy.
Methods:
Data were collected at the epilepsy monitoring unit of the Department of Neurology, LMU University Hospital in Munich between 2004 and 2019 from 715 patients undergoing pre-surgical long-term Video-EEG-monitoring. Only seizures with a single focal seizure onset zone were considered and were divided into five groups: frontal, temporal, parietal, occipital and central seizure onset zone. Temporal distribution was assessed by dividing the seizure frequency in three-hour groups for each brain region.
A cosinor analysis was utilized to model seizure occurrence over a 24 hour interval. Plots of seizure occurrences were created according to the different seizure onset zones to visualize whether the cosinor model would fit the data.
Additionally, the occurrence of seizures from wakefulness or sleep was analyzed.
Results:
A total of 3950 seizures were included in the final analysis (2055 seizures originated from the temporal lobe, 1512 from the frontal lobe, 181 from the central lobe, 90 from the parietal lobe and 112 from the occipital lobe).
The cosinor analysis revealed a periodicity in the occurrence of seizures regarding the temporal (p= 0.019), occipital (p= 0.045) und frontal lobe (p= 0.034). Temporal lobe seizures showed a peak 10am, whereas frontal lobe seizures peaked at 4am and occipital lobe seizures at 4pm.
For seizures arising from the parietal (p= 0.723) or central lobe (p= 0.339) data did not fit the model of cosinor analysis.
Most seizures occurred in the awake state (in total 64.56%) regardless of the seizure onset zone. Especially seizures arising from the parietal and occipital lobe (71.11% and 70.54% respectively) tend to occur in wakefulness.
Conclusions:
Seizure originating from the temporal, frontal or occipital lobe follow a 24h rhythmic whereas parietal and central lobe seizures do not show a 24h periodicity.
By knowing the peaks of seizure occurrence chronotypes can be identified and antiepileptic medication can be adjusted accordingly. This might help to enhance seizure control and reduce seizure associated risk (trauma, drowning).
Funding: None