The background EEG is normal.
CAUTION Focal slowing consistently over one area is not seen consider structural brain abnormality.
CAUTION Generalized slowing is not seen except in post-ictal periods.
A single routine EEG is normal in 10% of patients. Multifocal high voltage repetitive spikes or sharp and slow-waves are seen in 90% of patients, these often are present in different focal areas on sequential EEGs. All focal brain regions may be affected but abnormality in posterior regions is common, with occipital spikes seen on EEG in 60% of patients. Low voltage spikes and generalized discharges may be seen in a minority of cases.
Example of multifocal spikes in Panayiotopoulos syndrome.
Example of occipital (left) spikes of high amplitude in Panayiotopoulos syndrome.
Eye closure (elimination of central vision and fixation off sensitivity) may activate occipital spikes. EEG abnormality is enhanced by sleep deprivation and by sleep, when discharges often have a wilder field and may be bilaterally synchronous.
Ictal patterns are unilateral, often having posterior onset, with rhythmic slow (theta or delta) activity intermixed with small spikes.