PREDICTIVE VALUE OF INTERICTAL EPILEPTIFORM DISCHARGES DURING NON-REMSLEEP ON SCALP EEG RECORDINGS FOR THE LATERALIZATION OF EPILEPTOGENESIS

Purpose: EEG recording during sleep is widely used in the assessment o f epilepsy, particularly in candidates for surgery, yet the diagnostic value of this procedure is not well established. We evaluated the pre dictive reliability of interictal epileptiform discharges (IEDs) for l ocalization in presurgical patients with temporal lobe epilepsy (TLE) during non-REM sleep. Methods: Preoperative scalp EEG recordings with waking and sleep states were assessed in 83 patients with TLE in whom localization of the epileptogenic zone was subsequently confirmed by s uccessful surgical treatment (patient seizure-free >1 year). Results: The accuracy of EEG recordings for prediction of lateralization signif icantly changed from 51.8% during waking to 78.3% during sleep. After exclusion of patients who showed no discharges, the predictive value c hanged from 74.1 to 86.7%. However, in patients in whom the waking sca lp EEG lateralized incorrectly, no improvement in reliability was achi eved by sleep recording. Conclusions: Our results suggest that IEDs oc curring in non-REM sleep provide more accurate information for lateral ization of epileptogenesis than do those occurring during waking. This gain of diagnostic information was obtained in patients who showed ei ther bilateral or no discharges in waking records, because unilateral discharges arising de novo in sleep were always correctly lateralizing . On the other hand, in patients who showed unilateral discharges in t he awake state, whether ipsilateral or contralateral to the epileptoge nic zone, the findings were generally unchanged during sleep.