Annual variations of quantitative EEG in patients with chronic epilepsy

Annual changes in powers of the close-eyed EEG were measured over 12 months in 12 patients with epilepsy.

The present study included 12 patients aged 14.6+/-2.7 years with chronic epilepsy, suffering for 6-14 years. EEGs were recorded every month between 9 and 11 a.m. Five patients had generalized seizures and 7 partial complex seizures secondarily generalized. Visual analysis of EEG was performed before the quantitative assessment. The signals were recorded using a set of 14 (F3, F4, F7, F8, C3, C4, P3, P4, 01, 02, T3, T4, T5, T6) scalp electrodes. For each patient, 20 artifact-free EEG epochs, each of 2 s. duration were selected for spectral analysis to calculate spectral power. The sampling frequency was 240 Hz. Frequencies below 1 Hz and above 70 Hz were eliminated by digital filtering. The channels were recorded relative to a vertex reference. A fast Fourier transformation algorithm of signal processing was used to obtain the power spectrum of each lead. Absolute power spectrum was calculated within 4 frequency bands: delta (1-3.99 Hz), theta (4-7.99 Hz), alpha (8-12.99 Hz), and beta (13-30.99 Hz).

We found the abnormalities to be predominantly focal in EEG. None of the EEG recordings were normal, and the power spectra differed over the year. A statistically significant increase of delta and theta bands in May and a decrease of alpha bands in September was found. We did not find positive correlations between the changes in the quantitative EEG analysis and the number of seizures in patients.

These findings suggest the annual variations of EEG in patients with chronic epilepsy. Furthermore studies are needed to clarify the annual variations of EEG among healthy volunteers.