OBJECTIVETo investigate spike wave reduction in electrocorticography (EcoG) monitoring for evaluating the outcomes of epilepsy surgery.

METHODSThe epileptogenesis lesions in the target cortex was localized accurately using an EcoG monitoring system in 20 surgical patients with intractable EP. The spike numbers within 60 s were recorded before and after surgical resection of the epileptogenic focus. In cases where the spike number within 60 s was reduced by over 80% after the resection, the surgery was terminated, otherwise extended lesion resection, corpus callosotomy or multiple subpial transection (MST) was carried out with ECoG monitoring, and the spike number within 60 s was recorded. Antiepileptic drugs were routinely prescribed after the operations.

RESULTSTwelve patients exhibited a spike wave reduction by over 80% after resection or extended resection of the lesions, including 4 with cavernomas in the nonfunctional area, who showed a spike wave reduction by over 80% after extended resection of the cortex around the tumor. The reduction was still less than 80% in 4 patients with hippocampal sclerosis and 3 with neurogliocytoma in the functional area after the operations. According to the Engel assessments, 13 cases were in level I, 3 cases in level II, 1 in level III, and 3 in level IV. Seventeen patients responded favorably to the treatment, with a total effective rate of 85%.

CONCLUSIONFor extra-temporal lobe epilepsy, a postoperative spike wave reduction beyond 80% indicate favorable outcome of the surgery, otherwise poor prognosis is expected. But in cases of temporal lobe epilepsy, no direct association is found between spike wave reduction and the prognosis of the patients.