Abstracts

Rationale: The objective of this study was to (1) assess practice patterns in the utilization of ambulatory EEGs (aEEG) for spell characterization, (2) quantify the diagnostic yield of these studies for capturing epileptic and non-epileptic spells, and (3) examine demographic and clinical characteristics associated with capturing an event. Methods: We abstracted data on patients who received an aEEG for spell characterization between 8/2018 and 11/2018 (n=62). We assessed the distribution of patient characteristics overall and stratified by aEEG duration time (≤24 hours, >24 to ≤48 hours, and >48 hours). Characteristics assessed included age, gender, and medical history prior to aEEG. We also quantified the frequency of epileptic and non-epileptic spell capture, as well as the median time to spell capture. To determine if certain patient characteristics were associated with capturing a spell, we used log-binomial regression to estimate prevalence ratios (PR’s) and 95% confidence intervals (CI’s). Results: Patients were a median of 12 years (IQR: 7-28 years) and 54% were female (Table 1). Over half of patients (63%) had a prior history of epilepsy, 54% previously had an abnormal MRI, and 70% had a prior abnormal EEG study. Median aEEG duration was 47 hours (IQR: 24-71). Those prescribed longer aEEG durations were older, more likely to have had a previous abnormal MRI, and less likely to have a history of epilepsy. Additionally, patients with longer aEEG durations were less likely to have prior EEG showing diffuse slowing and/or interictal discharges. Less than half of patients (46%) had a spell captured on aEEG, with only 6 patients (10%) having an epileptic spell captured. Longer aEEG duration did not result in a higher prevalence of having an event captured (Figure 1), and median time to event captured was similar among those who had the shortest aEEG duration compared to those who had the longest aEEG durations (median event time: 3 vs. 4 hours, Table 1). The prevalence of having a spell captured was higher among females (PR: 1.5; 95% CI: 0.8, 2.7), and those whose prior EEGs showed diffuse slowing (PR: 1.4; 95% CI 0.8, 2.4) or ESES (PR: 1.5; 95% CI: 0.6, 3.5), but these associations were not statistically significant. Conclusions: There is substantial variation in practice patterns in utilizing aEEG for spell characterization. Longer aEEG duration does not appear to improve the likelihood of event capture. Ambulatory EEG may be a useful diagnostic tool to distinguish between epileptic and non-epileptic spells, but the probability of capturing epileptic events is low. Funding: No funding