Characterization and classification of neonatal seizures.

To characterize and classify neonatal seizures, we studied 349 neonates, using a portable, cribside EEG/polygraphic/video monitoring system. We recorded 415 clinical seizures in 71 infants; 11 other infants had electrical seizure activity without clinical accompaniments. Each seizure was analyzed in terms of its clinical character and its relationship to the presence of EEG seizure activity. Focal clonic seizures, some forms of myoclonic seizures, and focal tonic seizures were consistently associated with electrical seizure activity. Most "subtle" seizures, all generalized tonic seizures, and some forms of myoclonic seizures were either not associated with EEG seizure activity or had an inconsistent relationship with such activity. Seizures that were consistently and coherently related to focal EEG seizure activity had a high correlation with focal brain lesions and a favorable short-term outcome. Seizures with no relationship or an inconsistent relationship to EEG seizure activity were correlated with diffuse processes such as hypoxic-ischemic encephalopathy and a poor short-term outcome. The clinical and background EEG features of infants whose seizures were not accompanied by EEG seizure activity suggest that these seizures may not be epileptic in character.