State of consciousness and interictal epileptiform discharges predict seizure occurrence during routine EEG.

Objective: To identify the patients who are more likely to experience a seizure during routine electroencephalography (EEG) recording.

Methods: We retrospectively reviewed the EEG recordings and medical records of 262 patients, who were admitted in the Neurology Department in Assaf Harofeh Medical Center and referred to the EEG laboratory between October 2006 and 2008 after a seizure.

Results: Eighteen (6.8%) patients had seizures during routine EEG [patients with seizures (PWS)]. The likelihood of seizure occurrence during routine EEG was increased by the presence of interictal epileptiform discharges (odds ratio, 29.85; 95% confidence interval, 6.54-136.21; P=0.001) and abnormal state of consciousness (odds ratio, 9.04; 95% confidence interval, 1.02-80.33; P=0.037). Increased seizure frequency before admission, localization-related epilepsy, and EEG background slowing were significantly more common among PWS compared with patients without seizures on routine EEG (P=0.009, 0.042, and 0.036, respectively).

Conclusions: The presence of interictal epileptiform discharges and decreased state of consciousness increase significantly the likelihood of seizure occurrence during routine EEG. Localization-related epilepsy, increased seizure frequency before admission, and EEG background slowing are more common among PWS.