Presence of interictal epileptiform EEG discharges implies increased risk of recurrence after the first unprovoked seizure: Report of the International League Against Epilepsy and International Federation of Clinical Neurophysiology.

Objective: A joint International Federation of Clinical Neurophysiology-International League Against Epilepsy (IFCN-ILAE) Taskforce was created to explore the published evidence for initial EEG recordings in the evaluation of patients who experienced their first unprovoked seizure, and to determine the diagnostic value of EEG in supporting the diagnosis of epilepsy.

Methods: We conducted a systematic literature review, with two independent authors screening each study. We extracted seizure recurrence data among patients with EEG showing interictal epileptiform discharges (IEDs) vs those with normal or nonspecific-abnormal EEG results. Random-effects meta-analyses of seizure recurrence in relation to IEDs was conducted in the included studies, calculating odds ratios (OR) with confidence intervals (CIs) and diagnostic accuracy.

Results: A total of 4847 patients from 22 studies with variable follow-up durations were analyzed. The random-effects pooled binary estimate of seizure recurrence was 47% (95% CI 40%-55%). The overall proportion with seizure recurrence was higher in patients with IEDs (60%, 95% CI 53%-68%) compared to those without (40%, 95% CI 33%-48%, p < .001). Random-effects meta-analysis showed that the presence of IEDs was associated with seizure recurrence (OR 2.32, 95% CI 1.69-3.17, p < .001). Subgroup analyses of adults and children showed that this difference remained significant in both groups: OR in children of 3.24 (95% CI 2.19-4.79) and in adults of 1.55 (95% CI 1.08-2.21). In eight studies (n = 1209, 923 children) patients remained untreated before the second seizure; the pooled probability of seizure recurrence in those with IED in these studies was no different than in studies in which some patients were treated.

Significance: In conclusion, the presence of IEDs in EEG recordings obtained after the first unprovoked seizure can help clinicians to confirm the clinical diagnosis of epilepsy after a first unprovoked seizure, according to the revised ILAE definition. These results support the relevance of IED detection on EEG as a predictor of seizure recurrence after a first unprovoked seizure. However, its prognostic value is influenced by age and other clinical factors.