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The background EEG is abnormal, and may show widespread high amplitude fast activity (alpha and beta frequencies), widespread slowing, high amplitude spike or sharp activity (with or without subsequent EEG attenuation) or hypsarrhythmia (seen in those with epileptic spasms).

Specific genetic etiologies may have preferential EEG patterns, children with anterior agyria-pachygyria with DCX mutations may have diffuse moderate amplitude alpha activity, whereas those with posterior predominant cortical abnormality and LIS1 mutations may have bursts of sharp and slow waves with periods of attenuation.


EEG abnormality is enhanced by sleep deprivation and in sleep. Obtaining a sleep EEG is important in infants at risk of epileptic spasms, as epileptic spasms may only be demonstrated from sleep or on wakening.


Ictal EEG reflects the types of seizures that are present. When epileptic spasms or generalized seizures are present, the ictal EEG associated with these seizure types is seen.

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