Impact of the Length of Study on Event Detection with Video EEG Monitoring
The gold standard of epilepsy diagnosis is the time-locked video EEG recording of the clinical event, with prolonged monitoring providing the greatest advantage over routine studies of 20-30 minutes in duration. Although recording for longer periods of time increases the likelihood of detecting interictal epileptiform abnormalities, most prolonged video EEG monitoring studies are ordered in the hopes of recording at least one of the patient’s typical clinical events. A longstanding question within the epilepsy community is: How much recording time is enough?
Practical limits govern the upper boundary of recording time, namely an increasing risk of scalp skin breakdown beginning at roughly 7 days. Additionally, a minimum boundary of 24 hours is determined by the desire to record a period of nocturnal sleep and sleep-wake transitions that correlate with increased interictal abnormalities and some ictal events. The following studies provide evidence concerning the effectiveness of recording times between these upper and lower boundaries.
Lower Boundary Length of Study
In determining a lower boundary, research from inpatient epilepsy monitoring units (EMU) can provide a sufficient starting point. Todorov et al.(1) examined the necessary length of study to record a sufficient number of seizures for patients undergoing pre-surgical evaluation at Johns Hopkins Hospital. The mean length of study needed to record one seizure was 2.9 to 3.7 days, depending on the recording technique (i.e., scalp versus grid, respectively). This study is particularly notable because these were patients with presumed proven intractable epilepsy where seizure frequency is relatively high.
In assessing whether length of time to first diagnostic event was related to self-reported seizure frequency, Eisenman et al.(2) evaluated 155 patients in the epilepsy monitoring unit (EMU). For patients reporting low, medium, or high seizure frequency, the time to first event was 2.8, 2.1 and 2.1 days, respectively. Differences between the group outcomes were not statistically significant. These results support the conclusion that the average time to first event is between 2-3 days, regardless of self-reported seizure frequency.
Maximum Length of Study
To determine if there is a maximum duration that no longer improved diagnostic utility, Moseley et al.(3) assessed the benefit of prolonged length of study in 446 patients admitted to the EMU, broken down by diagnostic groups. For patients suffering from epilepsy, there did not appear to be a duration of recording beyond which further recording was futile. Patients with psychogenic nonepileptic seizures (PNES) were found more likely to have inconclusive studies overall, and data suggests a cut-off of roughly 5.5 days, though this did not reach statistical significance. The researchers concluded prolonging the length of recording does appear to be clinically useful with no specific cut-off duration. However, more recent results from Celik et al.(4) examining a similar group of 212 patients found that the majority of patients received a diagnosis after two days of recording and that there was limited benefit of prolonging non-surgical video EEG monitoring studies beyond 5 days.
In assessing the diagnostic utility of prolonged EEG in an outpatient setting, Fox et al. (5) evaluated 62 patients (pediatric and adult) who underwent 72-hour ambulatory (non-video) EEG evaluation after a non-diagnostic EMU admission. Roughly half of the ambulatory studies provided sufficient information to make a diagnosis, with the authors acknowledging that the absence of video potentially limited diagnostic distinctions, specifically for non-epileptic events. Though the authors did not specifically state that ambulatory video EEG studies would have produced a higher diagnostic yield, this seems likely from their presented data.
In assessing the existing literature regarding the duration of prolonged VEEG recording and its impact on diagnostic efficacy, the supported conclusion is that an optimal recording time for in- home video EEG monitoring is ~3 days (72 hours) with limited efficacy beyond 5 days.
To learn more about ambulatory video EEG for your patients, check out Stratus’ in home VEEG services.
About the Author
Jeremy Slater, M.D., has worked in the field of epilepsy for more than 27 years and currently serves as the Chief Medical Officer for Stratus. He served as the director of the Texas Comprehensive Epilepsy Program from 2004 through 2017, growing the center from a single neurologist and neurosurgeon to one of the largest epilepsy surgery programs in the country. Dr. Slater earned his medical degree at the University of Pittsburgh School of Medicine, in Pittsburgh, Pa. He completed his residency in neurology followed by a fellowship in epilepsy and clinical neurophysiology at the University of Miami School of Medicine in Miami, Fla.
- Todorov AB, Lesser RP, Uematsu SS, Yankov YA, Todorov AA, Jr. Distribution in time of seizures during presurgical EEG monitoring. Neurology. 1994;44(6):1060-4. doi: 10.1212/wnl.44.6.1060
- Eisenman LN, Attarian H, Fessler AJ, Vahle VJ, Gilliam F. Self-reported seizure frequency and time to first event in the seizure monitoring unit. Epilepsia. 2005;46(5):664-8. doi: 10.1111/j.1528-1167.2005.58004.x
- Moseley BD, Dewar S, Haneef Z, Stern JM. How long is long enough? The utility of prolonged inpatient video EEG monitoring. Epilepsy Res. 2015;109:9-12. doi: 10.1016/j.eplepsyres.2014.10.011
- Celik SY, Headley AJ, Shih JJ. Clinical characteristics of video-EEG patients: Limited utility of prolonging VEEG study duration beyond 5days for spell classification. Epilepsy Behav. 2020;103(Pt A):106827. doi: 10.1016/j.yebeh.2019.106827
- Fox J, Ajinkya S, Chopade P, Schmitt S. The Diagnostic Utility of Ambulatory EEG Following Nondiagnostic Epilepsy Monitoring Unit Admissions. J Clin Neurophysiol. 2019;36(2):146-9. doi: 10.1097/WNP.0000000000000559