The EEG background may show a discontinuous pattern or may be normal.
The interictal EEG may show a theta pointu alternant pattern (seen in half of cases) or there may be focal or multi-focal epileptiform abnormalities. The interictal EEG is normal in around 10% of cases. The theta pointu alternant pattern may continue for up to two weeks after cessation of seizures.
NOTE A theta pointu alternant pattern consists of runs of theta activity intermixed with sharp waves, seen in awake and asleep states, that often alternates sides and does not change in response to various stimuli.
CAUTION A theta pointu alternant pattern is not specific for this syndrome (it can be seen in neonatal seizures due to a range of other causes).
The EEG abnormality may be enhanced in sleep.
Rhythmic spikes or slow waves are seen with ictal events. These may be focal (mainly seen in the centro-temporal regions, although other focal areas may be affected) or generalized. Subclinical ictal discharges can continue for long periods after the clinical seizure.