Which findings on neonatal EEG are characteristic of seizures?

Updated: Oct 03, 2019
  • Author: Rosalia C Silvestri-Hobson, MD; Chief Editor: Selim R Benbadis, MD  more...
  • Print
Answer

Answer

Seizures frequently occur in newborns (14 per 1000), often causing death or permanent neurological sequelae. The prognosis largely depends on etiologic factors and the duration of convulsive activity. It should be noted that generalized tonic-clonic seizures are not seen in the immature brain.

Seizure patterns can be distinguished into subtle, classic, tonic, and myoclonic types. Among these, some have a fairly consistent EEG correlation. For example, tonic spasms, unlike those that occur in older children, are often associated with rhythmic delta wave activity. Clonic seizures frequently correspond to repetitive spike discharges. Myoclonic seizures, which are often erratic or fragmented and which should be distinguished from fragmentary neonatal sleep myoclonus, are often associated with other seizure types (eg, tonic or clonic) and with a burst suppression pattern with or without ictal correlation.

Yoshinaga et al reported abnormal fast activity along with localized occipital spikes at the time of appearance of paroxysmal downward gaze, way before hypsarrhythmia and tonic spasms subsequently appeared with fast activity distribution over the same areas. [10]

Ictal intervals, apnea, or respiratory disturbances often correlate with alphalike EEG patterns. These may be ictal discharges without clinical seizures that are not limited to iatrogenically paralyzed infants (see images below). These occult or electrographic seizures without clinically detectable signs may result from iatrogenic loading, causing serious neurological injury that disables the effector structures or silent cortical areas, which might be more generalized in newborns than in older patients.

Multifocal electrographic seizure in a curarized i Multifocal electrographic seizure in a curarized infant (alphalike pattern).
Infant with L focal paroxysmal temporal discharges Infant with L focal paroxysmal temporal discharges.
Infant with deltalike L-frontal electrographic sei Infant with deltalike L-frontal electrographic seizure.
Infant with L electrographic seizure with multifoc Infant with L electrographic seizure with multifocal L ictal discharges.

Conversely, clinical seizures in the absence of EEG discharges suggest nonepileptic events that should be closely monitored to avoid misdiagnosis. Minimal seizure behavior, uncoupled to ictal EEG patterns, can be seen in healthy neonates and especially in encephalopathic neonates whose brains are seriously compromised by hypoxic-ischemic insults. Severe neurological injury seen in these cases causes severe background EEG abnormalities.

Perinatal asphyxia is still the major cause for the overall incidence of neonatal seizures (44.4%), especially in preterm infants with very low birth weight before 5 days of life. The second major cause is metabolic abnormalities (23.33%). Hypoxic-ischemic encephalopathy, depending on severity, yields the most abnormal results with 66.66% background activity suppression for HIE III. [11]

Several ictal discharge patterns have been identified and reported, including the following patterns:

  • Focal spikes or sharp wave discharges of progressively increasing amplitude over the course of the seizure - These discharges correspond to contralateral jerking and occur predominantly in the rolandic and temporal regions.

  • Multifocal spike and sharp wave discharges, which are often erratic with independent frequencies in multiple foci, are associated with variable seizure types. The underlying cause may range from benign conditions to CNS infection to various hypoxic-ischemic injuries. The prognosis is dependent on the background EEG abnormalities and the specific underlying etiology.

  • Prehypsarrhythmic or hypsarrhythmic patterns can be seen early in compromised newborns, representing the most severe examples of the previous pattern, and are usually associated with anarchic and refractory seizures. A separate group may be the brief ictal discharge pattern and questionable EEG ictal discharges. Decremental discharges, which sometimes accompany neonatal tonic seizures, must be distinguished from the normal arousal response that follows postural change or stimulation.

The expression of ictal activity in relation to sleep stages (REM/NREM) may have age-dependent mechanisms in the developing brain. Schmutzler et al tried to assess the relationship between ictal activity and sleep stages in the newborn EEG, finding the highest association with unrecognizable sleep states where sleep organization is already disrupted. [12] Ictal activity predominates otherwise in REM sleep (p=0.01) with longer duration of discharges, contradicting findings in adults with epilepsy. However, the mechanisms responsible for increased seizures during NREM in adults (synchronous EEG oscillations promoting electrographic seizure propagation and asynchronous discharge patterns reducing seizures during REM sleep) cannot be extrapolated to the immature developing brain.

There is in fact an age-related differential regional distribution of GABA with excitatory and not inhibitory roles [13] in subcortical areas like the substantia nigra that could facilitate the release of focal discharges during REM in newborns. Furthermore, an immaturity of REM-related inhibitory systems at a peripheral level have been shown in infants, which might affect the cortex influencing the frequency of ictal discharges during REM sleep in newborns.

Tekgul et al compared the yielding power of a reduced montage (9 electrodes) with the full 10/20 electrode montage to detect and characterize neonatal seizures and background EEG features. The sensitivity and specificity of the reduced montage for electrographic seizure detection was 96.8% and 100%, respectively, and only in 1 patient's record (over 31 pts) the single seizure was missed altogether. For assessing background abnormalities, the sensitivity and specificity of the reduced montage was 87% and 80%, respectively. The authors conclude that a reduced montage proves to be a sensitive tool for identification of neonatal seizures and grading of background EEG features in newborns. [14]


Did this answer your question?
Additional feedback? (Optional)
Thank you for your feedback!