Factors correlated with intracranial interictal epileptiform discharges in refractory epilepsy

Objective: This study was undertaken to evaluate the influence that subject-specific factors have on intracranial interictal epileptiform discharge (IED) rates in persons with refractory epilepsy. Methods: One hundred fifty subjects with intracranial electrodes performed multiple sessions of a free recall memory task; this standardized task controlled for subject attention levels. We utilized a dominance analysis to rank the importance of subject-specific factors based on their relative influence on IED rates. Linear mixed-effects models were employed to comprehensively examine factors with highly ranked importance. Results: Antiseizure medication (ASM) status, time of testing, and seizure onset zone (SOZ) location were the highest-ranking factors in terms of their impact on IED rates. The average IED rate of electrodes in SOZs was 34% higher than the average IED rate of electrodes outside of SOZs (non-SOZ; p <.001). However, non-SOZ electrodes had similar IED rates regardless of the subject's SOZ location (p =.99). Subjects on older generation (p <.001) and combined generation (p <.001) ASM regimens had significantly lower IED rates relative to the group taking no ASMs; newer generation ASM regimens demonstrated a nonsignificant association with IED rates (p =.13). Of the ASMs included in this study, the following ASMs were associated with significant reductions in IED rates: levetiracetam (p <.001), carbamazepine (p <.001), lacosamide (p =.03), zonisamide (p =.01), lamotrigine (p =.03), phenytoin (p =.03), and topiramate (p =.01). We observed a nonsignificant association between time of testing and IED rates (morning–afternoon p =.15, morning–evening p =.85, afternoon–evening p =.26). Significance: The current study ranks the relative influence that subject-specific factors have on IED rates and highlights the importance of considering certain factors, such as SOZ location and ASM status, when analyzing IEDs for clinical or research purposes.