Background EEG patterns are very helpful in determining prognosis after neonatal seizures. Electroencephalograms demonstrating isoelectric, low-voltage burst suppression and excessive discontinuity are associated with poor prognoses, whereas records with normal backgrounds are associated with excellent outcomes.
The prognostic value of the EEG improves when similar findings are found on serial studies.

As with older children and adults, interictal spikes are seen more frequently in infants with seizures than in those without seizures. However, differentiating “normal” spikes and sharp waves from those with pathologic significance may be difficult. Strict criteria for differentiating normal sharp waves and spikes from those that are pathologic have yet to be established. For example, frontal sharp waves that shift from hemisphere to hemisphere (often termed “frontal sharp transients”) and multifocal spikes and sharp waves that occur only during the burst phase of quiet sleep (tracé alternant or tracéé discontinue) are considered normal by most electroencephalographers. In addition, normal infants, both term and preterm, may have infrequent, sporadic spikes and sharp waves.

Criteria used to classify spikes and sharp waves as abnormal include spikes and sharp waves that are focal and persist through all sleep states, rolandic-positive sharp waves, and focal or multifocal spikes during the low-amplitude phase of discontinuous sleep. Pathologic spikes often occur in bursts. As with older children, spikes and sharp waves can be seen in neonates who never have detected seizures.

Positive spikes occurring over the rolandic area are often associated with underlying white matter disease, such as periventricular leukomalacia or intraventricular hemorrhages. Positive rolandic spikes typically are not associated with seizures.

Epileptiform activity that is rhythmic and has a distinct beginning and ending is considered an ictal event. In addition, most ictal discharges have some degree of evolution in frequency or morphology of the waveforms. Although no consensus yet exists on the minimal length of time required for the discharge to be considered ictal, we define an EEG ictus as 10 seconds of rhythmic epileptiform activity.

Ictal epileptiform activity can be divided into four basic types: focal spike or sharp-wave discharges, focal low-frequency discharges, focal rhythmic discharges, and multifocal discharges. Although the type of ictal discharge has not been shown to be specific to etiology, this classification system is useful for the purposes of description. Focal spike or sharp-wave discharges consist of rhythmic spikes or sharp waves that originate focally. The frequency of the discharge usually exceeds 2 Hz, and spread of the focal discharge to other regions occasionally occurs. The spread of ictal discharges in the immature brain is usually much slower than in older children and adults. Focal low-frequency discharges consist of focal spikes or sharp waves that occur at a low frequency (approximately 1 Hz). Differentiation of this ictal discharge from periodic lateralized epileptiform discharges is based primarily on evolution and duration. Periodic lateralized epileptiform discharges demonstrate no evolution, typically last longer than 10 minutes, and are considered nonepileptic activity.

Focal low-frequency ictal discharges usually demonstrate an evolution during the discharge in frequency, amplitude, or waveform
morphology (Fig. 4-1). Focal rhythmic patterns consist of rhythmic, monomorphic waves varying from 0.5 to 15.0 Hz. The ictal patterns often vary in frequency during the course of the discharge. In some patients, the ictal discharges “migrate” from one area of the cortex to another. The discharge may have a resemblance to “normal” activity and has been referred to as focal pseudo-beta-alpha-theta-delta discharges. However, unlike the normal background activity seen on the neonatal EEG, ictal betaalpha-theta-delta discharges are paroxysmal, rhythmic, and usually monomorphic in character (Fig. 4-2). Multifocal patterns consist of EEG discharges originating independently or, rarely, simultaneously from two or more foci.

Focal epileptiform activity does not necessarily imply focal pathology. Infants may have focal epileptiform discharges in the face of systemic disorders such as hypoglycemia or hypoxic-ischemic injuries. Cerebral infarctions are frequently associated with focal seizures and lateralized epileptiform discharges in term infants.

Electroencephalographic seizures often occur without any clear clinical accompaniment. In general, EEG seizures without clinical accompaniment have a poorer prognosis than electrical seizures with behavioral changes.