The evolution of neurophysiological features in holoprosencephaly.

The evolution of EEG, visual and auditory evoked responses (VER and AER) and sleep is described in three cases of semilobar holoprosencephaly. During the neonatal period, the waking EEG was characterized by almost continuous high amplitude rhythmic alpha-theta activity in case 1 and 2, which became discontinuous during quiet sleep. Moderate amplitude rhythmic alpha-theta waves were seen in case 3. This rhythmic alpha-theta activity gradually disappeared with increasing age, being replaced by non-specific slow dysrhythmia. In case 3, the subsequent EEGs were characterized by focal spikes at 4 months, multifocal spikes at 5 and 6 months, hypsarrhythmia at 8 months and bisynchronous diffuse sharp and slow wave discharges at 2 years and 7 months. Ictal EEGs were characterized by desynchronization and/or rapid synchronization, epileptic recruiting rhythm and postical high amplitude slow waves. Definite but mostly abnormal VERs or AERs were obtained in all three cases. In two cases, the evoked responses showed a progressive decrease in amplitude and VERs were abolished finally. No sleep cycle could be identified during the neonatal period probably because of frequent seizures. In two cases no circadian rhythm of sleep developed, although almost normal REM-NREM sleep cycle was present.