Properties of afterdischarges from electrical stimulation in patients with epilepsy.

OBJECTIVE: To investigate the properties of afterdischarges (ADs) from intracerebral electrical stimulation (ES) in patients with epilepsy who underwent stereotactic electroencephalography (SEEG) and determine the relationship between epileptogenic zone (EZ) or irritative zone (IZ) and ADs. METHODS: We retrospectively analyzed 10 patients with intractable epilepsy who underwent SEEG. ESs were delivered following the given parameters: bipolar, biphasic, 50Hz, 0.2ms pulse duration, 0.5-10mA. The properties of ADs were documented, including their incidence, location, threshold, morphology and evolution. RESULTS: A total of 213 ADs (5%) were elicited by 4701 trains of ES. Stimulation through contacts implanted in the hippocampus (59%) generally evoked more ADs than contacts elsewhere (19%). AD thresholds for hippocampal stimulation were significantly lower than those for stimulation in grey matter. Polyspikes (58%) were the most common AD morphology. Evolution occurred more commonly with sequential spikes (47%) than with other AD morphologies (14%). There was no significant correlation between the location of ADs and EZ. However, ADs were significantly more frequently localized to IZ than areas outside IZ (P<0.05). CONCLUSIONS: There seemed to be a lack of correlation between the location of ADs and EZ. However, ADs were more likely to be elicited in IZ.