INTERICTAL INDEXES OF TEMPORAL SEIZURE ORIGIN

Two studies assessed the value of temporal lobe interictal electroence phalographic (EEG) spikes and delta in indicating side of temporal epi leptogenesis. The first study determined laterality of spikes/delta in awake recordings of 56 patients whose seizures all began unilaterally as proven by (1) EEG-recorded seizures and (2) >90% improvement after lobectomy. Spikes of 52 (93%) and delta of 46 (82%) patients predomin ated or appeared exclusively ipsilateral to seizure origin. Neither pr edominated contralaterally in any patient. The second study investigat ed laterality of temporal seizures in a separate group of 156 patients with various side vs side spike or delta ratios on 1 to greater-than- or-equal-to 4 awake recordings. Ninety-nine of 104 patients (95%) with temporal spikes on four or more awake recordings had most or all seiz ures ipsilateral to most spikes, including 79 of 80 (99%) of those wit h greater-than-or-equal-to 3 side vs side spike ratios. Among the 120 patients with high (greater-than-or-equal-to 3) side vs side spike rat ios, most or all seizures of 118 (98%) originated ipsilateral to most spikes. Predominant seizure origin also correlated with lateralized ar rhythmic delta-from 90% ipsilateral seizures of those with one EEG wit h delta to 100% with greater-than-or-equal-to 4 such EEGs. Data from t hese two studies using opposite directions of analysis (seizures --> s pikes/delta and spikes/delta --> seizures) demonstrate high correlatio ns between laterality of interictal and ictal entities, particularly i f temporal spikes clearly predominate on one side and if unilateral te mporal delta activity persists over several recordings. Such correlati ons suggest that the awake interictal scalp EEG cannot be ignored when assessing laterality of temporal epileptogenesis.