The relationship between ictal activity and sleep stages in the newborn EEG.

OBJECTIVE: To verify the relationship of ictal activity and sleep organization (REM/NREM stages) in the neonatal EEG.

METHODS: A retrospective study was developed with 41 high-risk newborns, with clinical history suggestive of seizures and ictal activity identified by the EEG. In each EEG, sleep organization and number/duration of sleep stages were determined. Sleep stages (REM, NREM) were scored following behavior and EEG activity. When it was impossible to recognize stages the epoch was classified as unrecognizable sleep stages (UNSS). Ictal activity was classified according to morphology and correlated with sleep epochs. Density of ictal activity was calculated as the duration of the discharge divided by the duration of the sleep epoch.

RESULTS: Unrecognizable sleep stages were observed in 21 EEGs (51.2%). Comparing NREM X REM states there was a significant predominance of ictal activity in REM sleep (P = 0.01). Duration of discharges was longer on REM epochs; however, differences were not significant. Considering the type of discharges there was a predominance of monomorphic rhythmic discharges in all sleep epochs.

CONCLUSIONS: In this sample, epileptogenic activity occurred more frequently in UNSS, where sleep organization was already disrupted. When it was possible to recognize sleep stages, ictal activity was more frequently during REM sleep.

SIGNIFICANCE: This study speculates the relationship between sleep organization and ictal activity and raises the hypothesis that the expression of ictal activity in relation to sleep stages (REM/NREM) may have age-dependent mechanisms in the developing brain.