Diagnosis

The clinical recognition of neonatal seizures may be difficult or inaccurate (35, 57). Clinical manifestations may consist of generalized fragmentary clonic movements, focal clonic activity, myoclonic jerks, tonic extension, or subtle aberrations of behavioral patterns. Generalized synchronous clonic jerking is rare. Generalized fragmentary seizures are rhythmic clonic movements that migrate rapidly and randomly in a nonjacksonian fashion from one body part to another. Tonic seizures consist of spells resembling decerebrate rigidity and are seen almost exclusively in infants with structural brain disease. Electrographic seizures are more common than clinical events in both term and preterm infants (49). It is becoming quite evident that the reliable diagnosis of neonatal seizures requires electrical confirmation of suspected clinical spells (10, 35). The issue is further complicated, however, by the phenomenon of electroclinical dissociation (61). Neonates may manifest dramatic clinical events that are at times associated with electrographic epileptic discharges and at times are not. Subtle seizures with brain stem signatures are more often associated with electroclinical dissociation compared to clonic extremity movements. Nevertheless, the electroencephalograph (EEG) is the ideal tool with which to assess the severity of neonatal seizures and the response to anticonvulsant treatment (10).

EEG Indications

The EEG is of greatest prognostic value if obtained within the first day of life because unfavorable diagnostic patterns tend to disappear thereafter. The EEG tends to become normal even in infants who will develop severe neurologic sequelae. A normal EEG within the first week of life has been correlated with a normal outcome in 85% of patients (17, 46). Our data on 71 infants with neonatal seizures showed that 75% of those with normal EEGs had a normal outcome. A grave prognosis accompanies an initial EEG showing a flat record with low-voltage patterns (5–15µV during the waking state and 10–15µV during the sleep state) or burst suppression patterns; these infants die or are severely impaired at follow-up. Low-voltage patterns beyond the second week of life, rhythmic bursts of alpha or theta activity superimposed on low-voltage activity, and abnormalities in spatial and temporal organization of the background are also ominous.