Assistant Professor Northwestern University Feinberg School of Medicine Chicago, Illinois
Rationale: Ambulatory EEG (aEEG) has emerged as an alternative to prolonged inpatient EEG monitoring in the diagnosis of epilepsy. However, the efficiency of aEEG as compared to epilepsy monitoring unit (EMU) admission has not been well characterized. We aim to directly compare the yield of detecting interictal epileptiform abnormalities (IEA) and capturing habitual events in the aEEG and EMU in the same cohort of patients. Methods: This is a single center retrospective chart review study of patients who had both aEEG evaluation and EMU admission at a level 4 epilepsy center between 1/1/2013 and 3/15/20. Patients’ charts were reviewed, and the following information were extracted for each patient: sex, age at time of seizure onset, age at time of the study, duration of monitoring, clinical diagnosis at the end of EMU admission, and changes to antiseizure drugs (ASD) during EMU. Ambulatory EEG and EMU reports were reviewed to evaluate the yield of capturing IEA, seizures, and habitual nonepileptic events. Results: A total of 343 patients had both aEEG and EMU admission. The average length of aEEG recording was 1.79±0.77 days and the average length of EMU admissions was 4.34±1.13 days. During the EMU admission, 58% of patients had their ASD held, 24.2% had the doses decreased, 12.8% had no changes to their ASD and 5.0% were not on any ASD at the time of admission. The final EMU diagnosis was as follows: 52.2% focal epilepsy, 16.0% generalized epilepsy, 2.3% unlocalizable epilepsy, 5.5% had dual diagnosis of epilepsy and psychogenic non epileptic events (PNES), 9.0% had PNES, 4.1% had physiologic non-epileptic events, and 10.8% had a non-diagnostic EMU admission.
IEA detection: Of the 261 patients diagnosed with epilepsy after their EMU admission, 51% had IEA on both aEEG and EMU studies, 3.1% had IEA on aEEG but not on EMU, 23% had IEA on the EMU study but not on aEEG, and 23% did not have IEAs captured during either study (p< 0.0001).
Electrographic seizure detection: Of the 183 patients who had epileptic seizures, 16.4% of patients had seizures captured on both aEEG and EMU studies, 4.9 % had seizures on aEEG, but not on the EMU, 78.7% had seizures on the EMU study, but not on aEEG (p< 0.0001).
Paroxysmal non-epileptic events: Of the 44 patients who had their habitual PNES events captured during EMU admission, 34.1% also had their events captured on aEEG.
EMU after an inconclusive aEEG evaluation: 195 (56.9%) patients had their aEEG prior to their EMU admission and 97 of these patients (49.7%) had a normal aEEG without habitual events. Of those, 84.5% had a diagnostic EMU admission (44.3% diagnosed with focal epilepsy, 4.1% with generalized epilepsy, 2.1% with unlocalizable epilepsy, 7.2% with epilepsy and PNES, 17.5% with PNES and 9.3% with physiologic non-epileptic events). Conclusions: EMU admissions provide a higher yield, not only for seizure capturing, but also for IEAs detection and capturing non-epileptic events. This could be in part due to ASD withdraw and the longer admission time. In patients with non-diagnostic aEEG, EMU admission should be considered. Funding: Please list any funding that was received in support of this abstract.: none