Latency to the first epileptiform activity in the EEG of epileptic patients

Abstract

Background: Approximately 56% of patients with epilepsy have interictal discharges. Increasing the diagnostic value of interictal electroencephalography (EEG) may help in increasing the ability to diagnose epilepsy especially in patients with low incidence of interictal discharges. Objective: To determine the latency of the epileptic activity on EEG in epileptic patients. Methods: Two hundred patients with epilepsy of different age groups were recruited in this study. We excluded those who had a definite seizure within the last 24 h and those with acute symptomatic seizures. Continuous EEG (for 2 h up to 24 h) was analyzed to find out the latency of the first clear epileptic activity. Results: Epileptiform activity was detected in 45.45% of the patients in the first 20 min of EEG recording. This percentage increases to 55% after 1 h and 64% after 2 h of recording EEG trace. After 24 h, 85.45% had epileptiform activity. Conclusions: Diagnostic yield of digital EEG increases steeply with increasing the duration of the trace and hence the time of routine EEG should be increased to 1–2 h. A 24 h EEG is of utmost value in diagnosis of epilepsy if the routine EEG is not helpful in this task.