Objective: This study aimed at identifying the characteristics - especially the duration - of rhythmic discharges in neonatal EEG, and their association with clinical neonatal problems. Specifically, we aimed at testing the diagnostic and prognostic validity of using 10 s as minimal duration for defining electroencephalographic seizures.
Design and methods: The polysomnographies of 340 neonates were reviewed, and episodes of rhythmic discharges were identified, analyzed, and quantified. The study sample was divided into 3 groups: one in which the maximal duration of rhythmic discharges was shorter than 10 s (brief rhythmic discharges, BRD), a second one in which there were rhythmic discharges longer than 10 s (long rhythmic discharges, LRD), and finally a group in which no rhythmic discharge was found (No-RD). These 3 groups of subjects were compared for the baseline and outcome clinical data.
Results: From the 340 neonates studied, 210 did not present any form of rhythmic discharge, 67 (19. 7%) had only BRD episodes, and 63 (18.5%) had at least one LRD episode. Prevalence of rhythmic discharges was low among healthy full term newborns, and was significantly higher among preterm and high-risk newborns. Electrophysiological characteristics of rhythmic discharges did not differ between healthy neonates and high-risk ones. Accompanying clinical manifestations were present in 26.3% of the LRD group, but also in 15.9% of the BRD group. The presence of BRD was significantly associated with leukomalacia and with hypoglycemia in the cross-sectional analysis of baseline data, and with an increased risk for abnormal neurodevelopmental outcome after a mean follow-up period of 47 months (adjusted relative risk=4.90, P<0.01).
Conclusions: The present data demonstrate an association between BRD and clinical history of hypoxic-ischemic encephalopathy, especially when complicated by leukomalacia, and also with a prognosis of increased risk for abnormal neurodevelopmental outcome. The clinical and prognostic significance of isolated BRD justifies the need to include these brief episodes in future studies of neonatal seizures.