Abstracts

Rationale: Ambulatory electroencephalography (aEEG) is a useful tool for differentiating epileptic versus nonepileptic attacks and is a good alternative to inpatient video EEG. It is a cost-effective technique with high diagnostic yield for quantifying seizure activity. In recent years with the advent of more electronic storage, the duration of aEEG recordings can be increased to 72 hours. The diagnostic yield of 24-72 hour aEEG has rarely been analyzed. Our primary aim is to measure the overall capture rate of aEEG to detect epileptiform discharges or seizures at 1, 2, or 3 days of recording. Our secondary aim is to determine how frequently positive aEEGs led to a confirmation of diagnosis or change in management at each time interval. We suspect that the yield of aEEG declines after 2 days of recording.  Methods: At the Stanford Comprehensive Epilepsy Center, a total of 361 adult aEEG procedure notes were identified by a software program and retrospectively analyzed. AEEGs were conducted using the standard 10-20 electrode placement and recorded for at least 20 hours. If a patient had multiple aEEG, only the first study was analyzed. We categorized the aEEGs into 3 durations: 1 day (20-30 hours), 2 days (30-50 hours), and 3 days (50-76 hours). For each of the intervals, we determined the proportion of the studies which detected epileptic seizures or discharges. An additional chart review was performed on positive records (n=101). For the secondary aim, we counted cases of positive aEEG which led to a direct confirmation of diagnosis (i.e., new diagnosis of epilepsy in a patient who was not suspected of having epilepsy or detection of events of interest).  We also counted cases of positive aEEG which led to direct change in management (i.e., increased current medication dosages, starting new anti-seizure medications, hospital admission, or changed the presurgical workup).  The Cochran-Armitage Linear Trend Test was used to ascertain significant trends with the increasing duration of the recordings. Results: Among 361 consecutive adult patients who underwent aEEG between 2010 - 2017, epileptiform discharges or seizures were detected in 101 records (28% positive). The yield of epileptiform discharges for each time interval was 22%, 17%, and 18% for 20-30 hour (n=142 studies), 30-50 (n=123), and 50-76 (n=96) respectively. Seizures were detected in 11%, 7%, and 8% for 20-30 hour (n=142 studies), 30-50 (n=123), and 50-76 (n=96) respectively. There were no significant differences in the detection of epileptiform abnormalities or seizures between the 3 categories of duration. There was a significantly decreasing trend in detection of newly diagnosed epilepsy (p<0.016) in longer recordings: 18%, 14%, and 0% for 20-30 hour (n=142 studies), 30-50 (n=123), and 50-76 (n=96) respectively. A positive aEEG directly led to a change in management in 50%, 28%, and 64% of 20-30 hour (n=142 studies), 30-50 (n=123), and 50-76 (n=96) respectively, but did not reach statistical significance. Longer recordings were associated with a statistically significant increasing trend in detecting nonepileptic events (p<0.0087) and increasing anti-seizure medication dosages (p<0.0063). Longer recordings were not associated with any trends of starting new anti-seizure medications.  Conclusions: This study confirmed that the yield for epileptic discharges or seizures did not increase nor decrease with longer recordings over 24 hours.  AEEGs that recorded over 24 hours have a higher probability of detecting nonepileptic events and are associated with increasing the anti-seizure medication dosages. Limits of the study include the retrospective design and lack of chart review on 260 patients with a negative aEEG.  Funding: none