Authors :
Presenting Author: Olivia Marais, MD – Stanford University
Spencer Nam, MD – Brooke Army Medical Center
Manveer Dilts-Garcha, MD – Touro University Medical Group Stockton
Alexandria Jensen, PhD – Stanford University School of Medicine
Fanglin Zhang, MD, PhD – Stanford University
Robert Fisher, MD, PhD – Stanford University
Rationale:
Identification of interictal epileptiform discharges in the scalp electroencephalogram (EEG) is a central component of confirming a clinical diagnosis of epilepsy. Discharge duration might reflect important underlying physiological processes or clinical features. Distinction of spikes from sharp waves, depends on “pointiness” and duration (under 70 ms for a spike, and 70-200 ms for a sharp). However, the specified limits of duration for spikes versus sharp waves has varied and been difficult to justify.Methods:
We received IRB approval for a retrospective de-identified data review to examine spike and sharp wave duration in 100 patients referred for routine EEGs, ambulatory EEGs, and epilepsy monitoring unit admissions. We selected for EEGs with at least three interictal spike or sharp waves. We excluded records with generalized spikes, spike-waves, polyspikes, discharges during electrographic seizures, and those from patients with skull breaches, or periodic discharges. The goal was to determine whether duration was consistent in patients with multiple discharges and whether seizure frequency was different for patients with discharge duration above or below 70 ms. The most recent clinic note was obtained to extract age, age of onset, seizure type, seizure frequency, etiology, and number of anti-seizure medicines.
Results:
We measured 882 interictal discharges in 100 patients. The patients included 57 males and 43 females (biological sex). Epileptiform discharges were unilateral in 64 patients and bilateral or multifocal in 36 patients. Each record presented 3-10 interictal discharges. The mean number of discharges per patient was 8.8 (standard deviation 2.2). The mean discharge duration was 71.9 ms (standard deviation 31.4 ms). The discharge durations ranged from 15 to 200 ms. A plot of the distribution of all discharge durations is shown in Figure 1. The majority of patients (87%) had mixed sharps and spikes, with 6% having only sharps and 7% having only spikes. A plot of the distribution of all discharge durations for each patient is shown in Figure 2 to highlight the variation of discharge durations within an individual patient. Mean discharge durations were poorly correlated both with seizure frequencies and number of anti-seizure medications taken at the time of the EEG, with respective Pearson correlation coefficients of -0.023 (p=0.82) and -0.027 (p=0.80).
Conclusions:
In our series of 882 discharges in 100 consecutive patients we observed no correlation of discharge duration with seizure frequency or number of anti-seizures medicines. Among the 100 patients, only 13% had exclusive spikes or sharp waves. The high prevalence of mixed discharges in the majority of patients suggests that duration of an individual discharge is not a defining characteristic of that person’s epilepsy. While this study is small and preliminary, it suggests that the distinction between spike and sharp waves at 70 ms may not be clinically relevant and perhaps both these discharges could be called spikes.
Funding:
RSF was supported by the James and Carrie Anderson Chair and the Steve Chen Funds for Epilepsy Research. No industry, governmental or foundation funding was used for this study.