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Background/Interictal EEG

The background EEG is abnormal in all states, with a suppression-burst pattern. High voltage bursts (150-300uV) of spikes or sharp and slow waves, lasting 1-3 seconds are seen with inter-burst intervals of 3-5 seconds.

The EEG may evolve to a hypsarrhythmia pattern in children who evolve to have West syndrome.


With tonic seizures there is diffuse attenuation of the suppression-burst background pattern with emergence of low-voltage, high frequency activity. Focal ictal rhythms may be seen if there are focal motor seizures.

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