Temporal association of interictal discharges with respiratory events in patients with sleep-disordered breathing and epilepsy

<bold>Background:</bold> Sleep-disordered breathing is a common co-morbidity in individuals with epilepsy, which has been shown to worsen seizure control. The pathophysiological mechanisms remain elusive. <bold>Objective:</bold> We hypothesized that there is a temporal association of respiratory events (RE) – apneas and hypopnoeas (AH), oxygen desaturations (3%) and the interictal epileptic discharge (IED). <bold>Methods:</bold> Retrospective single center study of adults (≥ 18 years) referred routinely to the Sleep-Wake-Epilepsy Center (Inselspital Bern, Switzerland) who had a polysomnography (PSG), an AHI ≥10/h and epileptiform activity in the PSG. We compared the IED density in sleep with and sleep without RE (multiplied by 100), first during RE and second an extended definition for RE starting 5 seconds before the start and 10 seconds after the end of the RE. <bold>Results:</bold> We included 28 patients (10 female, 35%), median age was 50 years [interquartile range (IQR) 40-59] and the AHI was 17.4 (IQR 13.9-25.1). There was no statistically significant difference in IED density in phases of sleep with AH compared to sleep without 5.94 (0.32-13.9) vs 10.54 (6.23-29.57), p=0.054. In the extended definition of RE, IED density was significantly lower during AH: 4.31 (0.42-10.98) vs 11.16 (6.51-29.94), p=0.017. Desaturations were similarly associated with lower IED density in both analyses: 3.70 (0.00-16.17) vs 10.74 (5.65-30.06), p=0.009 and 4.40 (0.00-11.11) vs 11.26 (5.66-30.25), p=0.012. <bold>Conclusion:</bold> There is no increase of IED during RE, suggesting that the link between sleep apnea and worsening of epilepsy is indirect and not due to respiratory events and hypoxia triggering epileptic activity.