The background EEG may be normal, or may show focal slowing or attenuation over the region of the leptomeningeal angioma. In the presence of epileptic spasms or generalized seizure types, the background may show widespread slowing or hypsarrhythmia.
Focal interictal spikes or sharp waves may be seen, over the location of the leptomeningeal angioma.
Multi-focal independent spikes or generalized spike-and-wave (usually < 3 Hz) can be seen in those with generalized seizure types.
Hypsarrhythmia can be seen in those with epileptic spasms.
EEG abnormality is enhanced by sleep deprivation and in sleep. Obtaining a sleep EEG is important in infants at risk of epileptic spasms, as the awake EEG may be normal, and abnormality may only be present in sleep.
CAUTION hyperventilation causes cerebral vasoconstriction, which may, in certain circumstances, impair critical cerebral perfusion and cause neurological symptoms. Hyperventilation is best avoided in the presence of intracranial vascular malformations.
Focal rhythmic epileptiform discharges occur during focal seizures, with spatial correlation with the leptomeningeal angioma.