Abstracts

Rationale: Cyclic alternating pattern (CAP) is a normal sleep phenomenon characterized by periodic higher amplitude EEG activity (CAP-A phase) alternating with a background phase (CAP-B). It is seen across the NREM stages. We studied CAP index (total CAP duration/NREM duration) in idiopathic and secondary generalized epilepsy (IGE and SGE). We hypothesized that the frequency of generalized discharges in both IGE and SGE will be highest in periods of CAP-A. 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 moderate-to-severe obstructive sleep apnea. Sleep stages were manually scored by an experienced sleep scientist. Separately, interictal discharges (iEDs) were identified and classified by two neurologists. CAP was scored according to established criteria (Terzano et al, Sleep Medicine, 2002). Results: Overall average CAP rate was 56%. There was no significant difference between CAP rate in IGE (57%) and SGE (54%). CAP rate was highest in slow wave sleep (63%), followed by in NREM-2 (56%) and least in NREM-1 (26%). In IGE, the number of iEDs per hour (iED rate) was higher in CAP-A than CAP-B (median 37.5 vs 1.0/hour, p-0.005) and higher than in non-CAP (17.5/hour, p-0.022). In SGE, a similar potent effect was seen, with iED rate higher in CAP-A than CAP-B (median 474.5 vs 30.0/hour, p-0.018) and higher than non-CAP (165.5/hour, p-0.036). Conclusions: We found no difference in CAP rate between IGE and SGE, but observed rates higher than the 30% reported in normal subjects. CAP-A, the phenomenon of phasic higher amplitude activity, appears strongly associated with generalized epileptiform activity in IGE and SGE. Cerebral circuits sustaining CAP-A appear to facilitate generalized epileptiform activity.