EEG-Langzeit-Monitoring - Indikationen und Limitationen im prächirurgischen Monitoring

Abstract

Epilepsy may be difficult to diagnose at first. Video-EEG Monitoring has two main indications: to assure or reject the diagnosis of epilepsy or to localize the seizure onset zone. Interictal epileptiform discharges (IEDs) are essential in classifying epilepsies. However, knowledge on the latency of IEDs is incomplete. The aim of this study was to assess the latency of IEDs and seizures in long-term EEG recordings of patients with epilepsy and therefore shed some light on the limitations of Video-EEG recordings. We analyzed the latency of IEDs and seizures from video-EEGs of 101.5 ± 62.7 hours (median ± SD) duration in 210 consecutive patients (94 male; age 38.6 ± 13.9 years) with active (median 3.5 seizures/month) epilepsy (176 structural-metabolic, 25 genetic, epilepsy duration 16.4 ± 13.7 years). Variables were age, duration of epilepsy, frequency of seizures and medication, the sleep state with IEDs, and their relation to seizures. Findings: Median spike latency was 9.3 ± 23.9 hours (within 20 min, 30 min, 24, 48, and 72 hours in 7.3%, 9.7%, 74.5%, 87.9%, and 98.2% respectively). Frequency of seizures, number of AEDs, etiology, age of onset or duration of epilepsy, and epilepsy syndrome did not correlate with spike latency. Of ninety patients with temporal lobe epilepsy IEDs were present in 95.6%. We did not find IEDs in 21.4% of long-term recorded patients, despite seizures in half of them. In other words, 21 patients with a seizure had no IED. Conclusion: Long-term EEG recordings of 72h in almost all cases should be sufficient to determine the presence of IEDs in patients with unclear paroxysmal events. Still, one in five patients will not have any IEDs even with EEG of long duration. Since IEDs are not uncommon in nonepileptic events and since one in 10 will not have seizures or IEDs, longer lasting EEGs or video records of habitual events should be mandatory in critical patients to minimize false negative studies.