Time interval required for return to baseline of the background rhythm on electroencephalogram after recorded electrographic seizures

Our objective was to assess the time interval that is required for the return to baseline of the background rhythm in the electroencephalogram (EEG) after ictal electrographic activity. We completed a retrospective EEG review of 28 adults and 13 children admitted to the epilepsy monitoring unit at Massachusetts General Hospital. EEG background rhythm on admission was considered the baseline rhythm per patient. In children the maximum time interval that was required for background rhythm to return to its baseline was 300. min, with average time of 120. min compared to a maximum of 420. min, with average time of 84. min for adults. Background slowing was shorter for frontal lobe seizures and longer for temporal lobe seizures. This study of patients with epilepsy shows that the time required for postictal slowing to resolve is short, and on average background rhythm returns to baseline within 2. h.