A reduction of sleep spindles heralds seizures in focal epilepsy

Sleep has profound effects on epilepsy. It may alter the occurrence of interictal discharges (IEDs) and seizures. Vice versa, an active epilepsy changes sleep. Sleep spindles are typically associated with an increase of IEDs. We examined whether seizures change the number and power of spindles preceding nightly seizures.

We retrospectively examined the nightly EEG recordings of presurgical epilepsy patients from our EEG-video-monitoring unit. We evaluated the 200s before the EEG seizure onset for spindle density (spindles per minute) and spindle power and compared that to the interictal baseline sleep.

The spindle density and the spindle power decreased significantly before the first seizure. The reduction before secondarily generalized seizures (8.7±2.5; p=0.001) was more pronounced than before focal seizures (10.5±2.5; p=0.003) compared to baseline (12.2±2.7). This finding was more pronounced in extratemporal lobe epilepsies than in temporal lobe epilepsies. The reduction of spindle power was also significant and was more pronounced in XTLE. These results were consistent for all other seizures during sleep, the mean spindle density decreased significantly in all focal (10.2±1.9; p=0.001) and generalized preictal period (8.8±2.4; p=0.001) compared to the mean interictal period (12.1±2.1). These were also more significant in XTLE than TLE group.

Our data demonstrate that the occurrence of seizures and propensity of seizure generalisation in focal epilepsy is modulated by specific characteristics of light sleep such as sleep spindles.

This study supports the notion that changes in the epileptic network precede the seizure onset and have an influence on seizure generation and termination.