Latency to first spike in the EEG of epilepsy patients

SummaryBackgroundRoutine EEGs in individuals with epilepsy have interictal spikes in 56% of cases. The availability of prolonged EEG has changed the use of EEG in the assessment of epilepsy.ObjectiveTo determine the time to first epileptiform activity on EEG in patients with epilepsy. This data will help optimize the duration of electrographic assessment for interictal activity in epileptic individuals.Methods46 consecutive patients aged 10 years or older with epilepsy were evaluated. Individuals with seizures in the prior 24 h or with acute symptomatic seizures were excluded. Continuous EEG (for 1–7 days) was analyzed to find the first definite epileptiform activity and the latency assessed.Results37% of the patients had epileptiform activity in the first 20 min of the continuous recording (duration of a routine EEG). 89% had epileptiform activity within 24 h. The yield drops beyond 24 h. 8% of the individuals had no epileptiform activity even after 72 h.ConclusionsThe study suggests the need to consider a change in EEG strategy to assess interictal epileptiform activity. The greatest probability of capturing an interictal abnormality within 20 min was in individuals with generalized epilepsy. In individuals with suspected epilepsy in whom electrographic interictal spike confirmation is deemed necessary, after a first nonspecific or normal routine EEG, a 24 h EEG should be the next step in the electrographic assessment. This study suggests that there may not be much benefit in monitoring for durations longer than 24 h, unless capturing a seizure is the intent.