Does the interval between the first unprovoked seizure and EEG influence the diagnostic yield?

Objective: There is no consensus on the optimum time for an EEG after the first seizure. We sought to investigate whether the timing of an EEG after a first unprovoked seizure influences its diagnostic yield. Methods: A retrospective analysis was conducted at a tertiary hospital in Australia. Adult patients who presented with a first unprovoked seizure were studied. Using multivariable logistic regression, we investigated the association of EEG timing, seizure presentation, and risk factors for epilepsy with the presence of interictal epileptiform discharges (IED) in the EEG as the outcome. The chi-square test compared EEG yields across each week after the seizure. Results: Among 452 patients, the time from seizure to EEG did not show a statistically significant impact on the presence of IEDs (OR = 1, 95 % CI 0.99-1, p = 0.095). The yield of epileptiform abnormalities generally declined over time but was not statistically significant across weeks (p = 0.40). A modest but significant relationship was found between age and the likelihood of detecting IEDs, with older age associated with a lower yield of abnormalities (OR = 0.98, 95 % CI 0.973-0.997, p = 0.016). Conclusion: Our results suggest that the timing of the EEG following the first unprovoked seizure does not significantly impact the diagnostic yield.