Distinctive polysomnographic traits in nocturnal frontal lobe epilepsy

Abstract

To describe the polysomnographic features and distribution of epileptic motor events, in relation to conventional sleep measures and cyclic alternating pattern (CAP) parameters, in 40 untreated patients with nocturnal frontal lobe epilepsy (NFLE). We analyzed the basal polysomnographic recordings of 40 patients (20 male and 20 female; mean age: 31 ± 10 years) with a diagnosis of nocturnal frontal lobe epilepsy. Conventional sleep measures and CAP parameters were assessed. Polysomnographic recordings were subdivided in sleep cycles. The distribution of the epileptic motor events (including minor motor events, paroxysmal arousals, tonic-dystonic, or hyperkinetic seizures and epileptic nocturnal wandering) was analyzed throughout: total sleep time, non-rapid eye movement (NREM) and REM sleep, light sleep (S1 + S2), slow wave sleep (SWS), each sleep cycle, CAP or non-CAP sleep, phase A and phase B of CAP. Only clear epileptic motor events supported by video-polysomnographic evidence were taken into consideration. Polysomnographic findings of patients with NFLE were compared with those of 24 age- and gender-balanced healthy subjects without sleep complaints. Compared to controls, patients with NFLE showed a significant increase in wake after sleep onset, SWS duration, and REM latency, whereas REM sleep duration was significantly lower in NFLE patients. The patients with NFLE showed a significant increase of CAP time, CAP rate (72% vs. 32% in control group), CAP cycles, and mean duration of a CAP sequence. These findings were associated with a significant enhancement of all subtypes of the A phases of CAP (mainly subtype A1). A total of 139 epileptic motor events supported by video-polysomnographic evidence were counted: 98% of all seizures occurred in NREM sleep and 72% of NREM seizures emerged from SWS, the latter being particularly collected in the first sleep cycles and decreasing in frequency together with the progressive decline of deep sleep. Ninety percent of total NREM seizures occurred during a CAP sequence, and CAP-related seizures occurred in association with a phase A. Significant polysomnographic alterations seem to emerge in patients with NFLE (increased REM latency, epileptic fragmentation of SWS, and increase of CAP rate). The analysis of seizure distribution showed that most epileptic events occurred in SWS, with predominance in the first sleep cycle and decreasing in frequency together with the homeostatic decline of SWS across the night. Within the NREM sleep, CAP is a manifestation of unstable sleep and represents a powerful predisposing condition for the occurrence of nocturnal motor seizures, which arise in concomitance with a phase A.