Diagnostic yield of sequential routine EEG and extended outpatient video-EEG monitoring

Objective: To investigate the diagnostic yield of outpatient video-EEG monitoring (OVEM) in patients with suspected but unconfirmed epilepsy. Methods: OVEM data, comprised of 20-min video-EEG (REEG) followed by 4 h of video-EEG monitoring (EXM), from 179 consecutive patients were retrospectively analyzed. Three diagnostic categories were defined: localization-related epilepsy (LRE), generalized epilepsy (GE), and nonepileptic seizures (NES). Outcome measures were: frequency of events; diagnostic yield of entire OVEM; relative yields of REEG alone and EXM after nondiagnostic REEG; EXM diagnostic rate (yield of EXM after nondiagnostic REEG/yield of entire OVEM). Results: Habitual events occurred in 14 (8%) and 25 (15%) patients during REEG and EXM, respectively. Overall, OVEM was diagnostic in 90/179 patients (50%): LRE 21%; GE 15%; NES 15%. REEG alone was diagnostic in 49/179 patients (27%): LRE 7%; GE 13%; NES 7%. After nondiagnostic REEG, the subsequent EXM was diagnostic in 41/130 patients (32%): LRE (n = 24); GE (n = 2); NES (n = 15). The EXM diagnostic rate (95% confidence interval) was 0.65 (0.47-0.80) for LRE, 0.08 (0.01-0.25) for GE, and 0.56 (0.35-0.75) for NES. Conclusions: OVEM is useful in establishing and classifying epilepsy. Compared to REEG, EXM is relatively more beneficial in the diagnosis of LRE and NES rather than GE. Significance: This study outlines the benefits of extended outpatient video-EEG monitoring after nondiagnostic routine EEG.