Abstracts

Rationale: A common impression among clinicians is that patients undergoing workup for epilepsy surgery have fewer seizures during intracranial video/EEG monitoring than during scalp video/EEG monitoring. The possible transient decrease in seizures may be an immediate effect of anesthesia, pain medication, or the implant surgery. The objective of this study was to examine the changes in seizure frequency during scalp and intracranial video/EEG monitoring and to identify reasons for the differences. Methods: Retrospective review of 193 patients with intractable epilepsy with both inpatient scalp video/EEG monitoring and intracranial video/EEG monitoring in a comprehensive epilepsy program between 1992 and 2009. Number of seizures per day during each monitoring period, number of days to first seizure, AED, pain medications, types of implanted electrodes, and anesthesia agents were reviewed. Linear regression and t-test were performed for statistical analysis. Results: During scalp video/EEG monitoring, patients experienced an average of 1.38 0.85 seizures/day and an average of 1.467 0.123 seizures/day during intracranial monitoring (p>0.05). Patients were off all AED for a mean of 1.27 0.152 days during scalp and 3.00 0.312 days during intracranial monitoring (p<0.0001). Patients experienced their first seizure after an average of 1.78 0.104 days during scalp and after 2.30 0.227 days during intracranial monitoring. The number of days to first seizure was significantly longer during intracranial monitoring (p=0.018). Fifty patients (25.9%) had no seizures until the fourth day or later of intracranial monitoring. Four patients had no seizures during their entire admission for intracranial monitoring, despite extending the monitoring period up to 21 days in one patient. 118/193 (61.1%) of patients received grid implants, while the remaining patients received a combination of depth and strip electrodes. Patients with grids experienced a significantly greater decrease in mean seizure frequency as compared to patients with depth and strip electrodes (p=0.005). Patients received a mean of 33.4 milligrams of morphine equivalents during intracranial monitoring. Seizure frequency during intracranial monitoring was inversely related to total morphine equivalents received. Location or pathology did not influence the occurrence of first seizure or change in seizure frequency during intracranial monitoring (p>