Ictal scalp EEG recording during sleep and wakefulness: diagnostic implications for seizure localization and lateralization.

To determine the localizing value of electroencephalography (EEG) for seizures during sleep versus seizures during wakefulness, we compared scalp EEG for 58 seizures that occurred during sleep with 76 seizures during wake in 28 consecutive patients with temporal lobe epilepsy. Regression analysis showed that seizures during sleep are 2.5 times more likely to have focal EEG onset (p = 0.01) and 4 times more likely to correctly localize seizure onset (p = 0.04) than seizures during wake. EEG seizure onset preceded clinical onset by a longer duration in sleep seizures (mean, 4.69 s) than in wake seizures (mean, 1.23 s; p < 0.01). Sleep seizures showed fewer artifacts, but the difference was not significant (p = 0.07). For temporal lobectomy candidates undergoing video-EEG monitoring, the recording of seizures during sleep may be favored.