Analysis of Ictal Electrocorticographic Features in Nonlesional Neocortical Epilepsy
Journal of Korean Epilepsy Society (대한간질학회지)
Journal of Korean Epilepsy Society (대한간질학회지), Vol.5(1) : 33~40, 2001
Background: To characterize the ictal electrocorticographic features in relation to surgical outcome in nonlesional neocortical epilepsy (NE).
Methods: Seventeen patients with intractable NE underwent surgeries after chronic subdural recordings. All patients did not have any lesions on brain MRI, which was confirmed by pathology postoperatively. One hundred and eighty one ictal EEGs recorded from subdural electrodes were analyzed. Surgical outcome was determined by seizure reduction rate, and free or more than 75% reduction was defined as favorable outcome. The mean duration of follow-up was 55+/-8.7 months.
Results: Reproducible ictal onset zone (IOZ) in more than a half of seizures (p=0.002), and persistent ictal discharges in IOZ from the onset to the end of seizure were found more frequently in the patients with good outcome (p=0.004). Ictal onset patterns consisting of low voltage fast or high amplitude beta spikes predicted a good surgical outcome while rhythmic sinusoidal activity or rhythmic spike/sharp wave were predictive of poor outcome (p=0.01). The ictal onset rhythm consisted of gamma or beta frequencies was more prevalent in the favorable group (p=0.003).
Conclusions: The presence of stable ictal circuit suggested by the consistent earliest activation in more than 50% of seizures and the active participation of IOZ throughout the attack were valuable prognostic factors in addition to the morphology and frequency of ictal onset rhythm.