Abstracts

Rationale: : Video EEG monitoring is an invaluable tool in pre-surgical epilepsy evaluation. A definitive localization of seizure onset zone by EEG is needed for pre-surgical planning. Some patients may have inconclusive studies for a variety of reasons, and the value of repeat monitoring in these cases is uncertain. Methods: We reviewed reports for 119 adult patients admitted to the NIH epilepsy monitoring unit (EMU) from September 2010 to June 2013 for pre-surgical evaluation. We identified 20 patients who had more than one monitoring session during that period. EEG was reviewed daily for the entire 24 hours of recording. Interictal discharges and all ictal episodes were identified. Monitoring was continued until at least 3 typical events were captured or up to a maximum of 14 days. AEDs typically were tapered during the EMU stay.Results: 20 patients (9 males) had repeat monitoring. Sixteen had 2 sessions, and two had 3 sessions. One patient each had 4 and 5 sessions respectively. The average duration of monitoring was 7.62 days. The reasons for repeating monitoring included incongruent EEG findings (three), non localizable seizure onset (four), no seizure captured in initial recording (four), only one seizure captured in initial monitoring (two),initial monitoring done in another hospital (one), greater than 12 months interval from initial monitoring to presentation for surgery (three) and bi-temporal epilepsy cases (three). In 13/20 patients there was no difference in the results between initial and repeat monitoring. Four patients with no seizures captured initially had seizures on a subsequent recording. In all three of the patients with incongruent EEG and MRI findings, repeat EEG clarified the presurgical plan. In one case, MRI showed right mesial temporal sclerosis but seizures on initial monitoring were of left frontal onset. Subsequent monitoring revealed a second seizure type of right temporal onset. In the second case with left mesial temporal sclerosis, in addition to left temporal discharges and seizures of left temporal onset, generalized spike wave discharges were noted on EEG. Subsequent monitoring revealed a second seizure type with diffuse onset.Conclusions: In our series, repeat monitoring increased diagnostic yield in 35% of pre-surgical cases, particularly in cases with incongruent EEG findings or low yield on initial monitoring. This is in contrast to yields of 81% (1) and 55% (2) in previous studies. The different patient population (pre-surgical vs all EMU) could account for the difference in results. Repeat monitoring did not change the plan in patients with bitemporal epilepsy, non-localizable seizure onset and greater than 12 months between initial monitoring and presentation for surgery. References: 1. Muniz J, Benbadis SR. Repeating video/EEG monitoring: why and with what results? Epilepsy Behav 2010 Aug:18(4):472-473 2. Elgavish R, Cabaniss W. What is the diagnostic value of repeating a nondiagnostic Video-EEG study? J Clin Neurophysiol 2011 Jun;28 (3):311-3