Effect of Anti-Seizure Medications on Interictal Epileptiform Discharges in Focal Epilepsy

The purpose of this study was to assess the change in frequency and distribution of focal interictal epileptiform discharges (IEDs) as measured on scalp EEG after anti-seizure medications (ASMs) were weaned in the epilepsy monitoring unit. We retrospectively reviewed the EEG of patients with focal epilepsy on a single ASM. A two-hour EEG epoch was selected at sleep onset during the first day of admission and defined as the high-ASM epoch. This was compared to a two-hour low-ASM epoch at sleep onset after the ASM was weaned, at least 6 h before or after a seizure. IEDs were manually counted and characterized. A total of 115 patients were included. For those on levetiracetam, there was a significant increase in IED quantity when comparing the high-ASM to the low-ASM epoch (mean 40.6 to 71.4, p < 0.001). For those on sodium channel blockers, there was a non-significant trend towards a decrease in IED quantity as the ASM dose was decreased (p = 0.065). There was no statistically significant change found for other individual ASMs. For the cohort, 12 patients had IED observed only on the low-ASM epoch (which were not present on the high-ASM epoch), 6 of which were treated with levetiracetam. In summary, our findings showed weaning of levetiracetam was associated with a significant increase in IEDs whereas other ASMs were not. Some populations of IEDs were only seen after ASMs were weaned. These findings suggest that different ASMs may have unique effects on IEDs when weaned.