Clinical relevance of quantified intracranial interictal spike activity in presurgical evaluation of epilepsy.

PURPOSE: Electrocorticograms of 32 patients with medically intractable seizures, recorded through intracranial electrodes, were retrospectively analyzed. The objective was to assess whether quantitative analysis of interictal spikes may be used for delineation of the epileptogenic zone.
METHODS: We used a newly developed computer program for automatic detection of interictal spikes and averaging procedures. This allowed determination of the earliest spike of each spike cluster, the maximal averaged spike amplitude, the highest spike frequency, and the shortest averaged spike duration at each recording site.
RESULTS: The following results were obtained: (a) Within a zone </=2 cm from the site of seizure origin, we localized the averaged earliest spike of a spike cluster in 27 (84%) of 32 patients, the highest averaged spike amplitude in 24 (75%) of 32, the shortest averaged spike duration in 22 (69%) of 32, and the maximal spike frequency in 17 (53%) of 32; (b) No correlation was found between spike occurrence and histopathology; (c) No evidence was found for decreased postoperative seizure control in patients with several multilobar or bihemispheric occurrence of spike clusters.
CONCLUSIONS: The zones of the earliest spike and seizure origin demonstrate a high correlation that favors a common epileptic generator. Removal of all brain areas demonstrating spike clusters is unnecessary to achieve seizure control. Quantification of interictal spike activity is a valuable tool for localization of the seizure generator.