Epileptiform abnormalities during sleep in Rett syndrome.

We recorded all-night electroencephalograms (EEGs)/polysomnograms on 2 consecutive nights from 4 children (ages 4-11 years) with Rett syndrome. The first 10 sec of each 60 sec epoch were analyzed with counts of left and right hemisphere spikes and correlated with sleep stage. Spike counts were lowest during wakefulness. Spikes were most frequent over parasagittal regions during all sleep stages and varied from 0.28 +/- 0.03 to 40.4 +/- 0.7 (mean +/- S.E.M.) spikes/hemisphere/min. Spike counts were 51-109% higher during NREM sleep than during REM sleep. In 3 of 4 subjects, spikes were most frequent during light NREM sleep. Spikes increased in frequency during the second half of the night. We conclude that in Rett syndrome, epileptiform activity is maximally expressed in stage 1-2 NREM sleep and during the early morning hours. Sleep EEG features may be useful in the diagnosis of Rett syndrome.