Abstracts

Rationale: To compare frequency of respiratory events between two groups of generalized epilepsies with frequent epileptic discharges overnight, and to determine the temporal association between interictal discharges (iEDs) and respiratory events. We hypothesized that hypoventilation may trigger generalized discharges. Methods: Ten patients with IGE and eight patients with SGE underwent overnight video EEG & polysomnography (male-8, mean age-38.3). Exclusion criteria were age <15 years, previous brain surgery, vagal nerve stimulation or known history of moderate-to-severe obstructive sleep apnea. Sleep stages and respiratory events were scored by an experienced sleep scientist using standard criteria. Separately, iEDs were identified and classified by two neurologists. Respiratory events included hypopnea (based on at least 10 seconds 50% nasal pressure amplitude reduction, or discernable reduction breathing with arousal or at least 3% oxygen saturation reduction from pre-event baseline), apneas and desaturation. Temporal association was defined as an iED occurring during or up to 60 seconds after a respiratory event, to ensure capture of even delayed effects of hypoventilation. Results: Overall, average arousal index was 10.4 (IGE-12.2 and SGE-8, p-NS). Average apnea-hypopnea index (AHI, events per hour) was 15.2 (IGE-12.5 and SGE-18.5, p-NS). Moderate-to-severe sleep apnea (AHI >15) was detected in three IGE patients (30.0%) and four SGE patients (50%), p=0.4. Hypoventilation events were mostly ‘obstructive’. Central apnea was detected in two IGE and four SGE subjects. Average body mass index was 29.1 Kg/m2 (IGE-30.8 and SGE-27.0, p=0.2). There was no significant difference in oxygen saturation, awake versus asleep in IGE and SGE. Across both epilepsy groups, most iEDs (80.7%) were not associated with respiratory events (p=0.002). Conclusions: A large proportion of patients with typical SGE had overnight hypoventilation events, despite BMIs in the non-obese range. A similar, but milder effect was observed in this group of IGE patients with frequent interictal discharges. Contrary to our hypothesis, IEDs were not temporally related to hypoventilation. This raises the possibility that generalized epileptic processes or treatments interfere with mechanisms sustaining upper airway muscle tone.