Refuting a Temporal Correlation: Interictal Epileptic Discharges Do Not Preferentially Occur During Respiratory Events in Patients With Sleep‐Related Breathing Disorder and Epilepsy

The bidirectional interaction between sleep and epilepsy is well known. In particular, it has been established that sleep apnea can worsen epilepsy, whereas sleep apnea (SA) treatment has a beneficial effect on seizure control. However, the exact mechanisms whereby SA promotes epileptic seizures are unknown. We set out to examine whether interictal epileptic discharges (IED), one of the hallmarks of epilepsy, occur predominantly during respiratory events (RE, apnea or hypopnea) or desaturations in patients with obstructive SA (OSA) and epilepsy. Adult patients (> 18) who underwent a video-polysomnography at the Bern University Hospital between 2012 and 2020 with an apnea-hypopnea-index (AHI) ≥ 10/h and IED were included in this retrospective study. IED density (per hour) was computed during and outside RE and oxygen desaturations (3%) using the AASM criteria and an extended definition. A total of 27 patients (9 females) met the inclusion criteria. The median age was 49 years and the median AHI was 17.4/h. There was no statistically significant difference in IED density in phases of sleep with RE compared to sleep without (median 3.6 [IQR 0.2-8.0] vs. 6.3 [3.7-19.7], p = 0.055). In the extended definition of RE, IED density was significantly lower during RE: 2.6 [0.3-6.6] versus 6.7 [3.9-20.5], p = 0.017. Desaturations were similarly associated with lower IED density in both analyses: 2.2 [0-7.4] versus 6.4 [3.4-18.4], p = 0.009 and 2.6 [0-6.7] versus 6.8 [3.4-18.5], p = 0.012. Our study shows that the influence of OSA on epileptic activity is probably indirect and does not result solely from immediate hypoxemia.