Latency of interictal epileptiform discharges in long-term EEG recordings in epilepsy patients

AbstractPurposeTo assess the latency of interictal epileptiform discharges (IED) and seizures in long-term EEG recordings of patients with epilepsy.MethodIED latency was measured in 210 consecutive patients (mean (SD) age 38.6±13.9 years) with active epilepsy and the relationship to clinical variables was analyzed retrospectively. Median duration of EEG recording was 101.5h (95% confidence interval [CI] 92 to 117h).ResultsIEDs were absent in 45 (21.4%) and present in 165 (78.6%) patients who had a longer duration (p<0.001) and early onset (p<0.01) of epilepsy and more often had IEDs in prior standard EEGs (p<0.01), a structural etiology (OR 2.4, CI: 2.1–2.7), or temporal lobe epilepsy (OR 9.6, CI: 9.0–10.2). IED latency did not correlate with other clinical variables. Median latency to the emergence of the first IED was 9.3h (CI: 7.5–11.4) occurring in 7.3%, 9.7%, 74.6%, 87.9%, and 96.4% within 20min, 30min, 24h, 48h, and 72h, respectively. Seizure frequency was higher in patients with (n=165) than without IEDs (n=45) (72.1% vs. 46.6%, p