Abstracts

RATIONALE: The chronic electrocorticogram obtained through implanted subdural electrodes is artifact-free and represent an excellent tool for the study of the seizure[ssquote]s onset patterns in patients with extra-temporal epilepsy who usually usually have poorly localizatory scalp ictal EEG recordings.
METHODS: Sixteen patients with extra-temporal epilepsy and normal or non-localizing MRI submitted to extensive coverage of the brain convexity with subdural electrodes were included in the study. The patterns of seizure[ssquote]s onset and the number of electrodes involved on it were studied. Mean follow-up time was 1,9 years.
RESULTS: Seizure[ssquote]s onset included up to 3 electrodes in eight patients, 4 to 6 electrodes in 4 patients and more than 6 electrodes in 4 patients. Seizure-onset patterns included low-amplitude fast activity evolving into a recruiting rhythm (n=9), rhytmic theta activity (n=4) and high amplitude spiking (n=3). A sentinel, more generalized spike, was seen in 6 patients immediately before seizure[ssquote]s onset. Overall, 81% of the patients have been rendered seizure-free after surgery. There was no statistical difference in seizure[ssquote]s outcome related to the pattern of seizure[ssquote]s onset or to the number of electrodes involved at seizure[ssquote]s onset.
CONCLUSIONS: The main seizure[ssquote]s onset pattern found in this study was fast activity evolving into a recruiting rhythm. Surgical outcome in relation to seizures was not different within the different subgroups, but patients with more widespread ictal zones were given considerably bigger cortical resections. The pathophysiological significance of the sentinel spike seen in 37% of the patients remains unclear.
[Supported by: Sao Paulo Secretary of Health]