Prognostic value of interictal epileptiform discharges on routine EEG in adults with epilepsy

To determine whether interictal epileptiform discharges (IEDs) on routine electroencephalography (EEG) predict seizure recurrence in adults with established epilepsy.

We conducted a retrospective survival analysis of consecutive adults with epilepsy undergoing routine EEG at a tertiary center between 2018 and 2019. Using multivariate Cox proportional hazards models guided by a directed acyclic graph and adjusted for confounders including past seizure frequency and duration of epilepsy, we estimated the association between the presence of IEDs and time to next seizure, stratified by epilepsy type.

We included 488 consecutive routine EEG studies from 438 patients. Over a median follow-up of 124.5 weeks, seizures recurred in 50.4% of cases. The presence of IEDs was associated with increased seizure risk in both focal (adjusted hazard ratio [aHR] = 1.47, 95% confidence interval [CI]: 1.01-2.15, p = .043) and generalized epilepsy (aHR = 1.82, 95% CI: 1.08-3.06, p = .024).

IEDs on routine EEG independently predict increased seizure risk in adults with epilepsy, with a stronger effect in generalized epilepsies. This suggests that routine EEG may have prognostic value during epilepsy follow-up and warrant further investigations as a potential prognostic biomarker to help inform clinical decision-making.