Annual variations of quantitative EEG in patients with chronic epilepsy

Purpose: Annual changes in powers of the close-eyed EEG were measured over 12 months in 12 patients with epilepsy. Material and Methods: 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 alogorithm 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). Results: 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. Conclusions: 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.