What question did this study set out to answer?

This study aims to investigate the timing of congruent and discordant IEDs to improve EEG recording recommendations.

July 26, 2026Open Access

Timing of congruent and discordant interictal epileptiform EEG discharges in focal epilepsy

KEKatharina ErnstLMU Klinikum MDM DaneshmandEmory University NFNicholas FearnsLMU Klinikum

Key Points

This study aims to investigate the timing of congruent and discordant IEDs to improve EEG recording recommendations.
Analyzed mean latency until first IED in 589 patients with focal epilepsy.
IEDs classified as congruent or discordant based on localization within or outside the epileptogenic zone.
Patients grouped by localization of the epileptogenic zone: frontal, temporal, central, and parieto-occipital.
The first IED was more likely to be congruent with the EZ in temporal lobe epilepsy (p < 0.01).
Mean latency for congruent IEDs was 19.73 h, and for discordant IEDs was 23.27 h.
90% of first IEDs were detected within 49.20 h, with the longest latency observed in frontal lobe epilepsy.

Abstract

OBJECTIVE: Interictal epileptiform discharges (IEDs) can provide additional information for localizing the epileptogenic zone (EZ). However, due to the brevity of routine electroencephalography, IEDs are often not recorded and there is a lack of general recommendation regarding the recording duration METHODS: In our study, we analyzed the mean latency until the first IED was detected in 589 patients with focal epilepsy. IEDs were distinguished as either congruent (occurring within the EZ) or discordant (occurring outside the EZ). Patients were assigned to one of four regional subgroups according to the localization of their EZ: frontal, temporal, central, and parieto-occipital. RESULTS: A total of 50 040 IEDs were analyzed across temporal (n = 252), frontal (n = 127), central (n = 5), and parieto-occipital epilepsy (n = 27). The first IED was significantly more likely to be congruent with the EZ in temporal lobe epilepsy (p < 0.01); otherwise, it was not statistically significant. The mean latency was 19.73 h for congruent IEDs and 23.27 h for discordant IEDs. Overall, 90% of the first IEDs were detected within 49.20 h, with the longest latency observed in frontal lobe epilepsy. SIGNIFICANCE: Our study demonstrates the latency to the first IEDs on EEG, differentiating between IEDs that are congruent and discordant with the EZ. This allows for a more precise estimation of the necessary length of an EEG recording to evaluate the EZ.

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