Mc. Salinsky et al., INTRAINDIVIDUAL ANALYSIS OF ANTIEPILEPTIC DRUG EFFECTS ON EEG BACKGROUND RHYTHMS, Electroencephalography and clinical neurophysiology, 90(3), 1994, pp. 186-193
Antiepileptic drug (AED) therapy with either phenytoin or carbamazepin
e has been associated with generalized slowing of EEG background rhyth
ms. These effects have been seen in groups of patients undergoing AED
manipulation, although the background slowing has been highly variable
from patient to patient. Background slowing may represent an objectiv
e physiologic measure of drug impact on cerebral function and could be
useful in monitoring for AED neurotoxicity in individual patients. Th
is would require an intraindividual analysis of AED effects on EEG bac
kground rhythms. The present study was designed to develop a methodolo
gy for intraindividual analysis of EEG background changes and to apply
this methodology to patients beginning or ending chronic AED therapy.
EEG recordings were obtained under controlled conditions in 31 health
y subjects and were repeated after an interval of 12-16 weeks. EEG bac
kground rhythms from each record were analyzed using the fast Fourier
transform, and test-retest differences for several quantitative measur
es were calculated from each subject's paired recordings. EEG recordin
gs were also obtained in 6 patients beginning or ending chronic AED th
erapy. Test-retest differences for each patient's quantitative EEG mea
sures were statistically compared with the distributions of test-retes
t measures obtained from the healthy controls. AED therapy was associa
ted with an increase in absolute delta and/or theta power and a slowin
g of the dominant posterior rhythm; however, these EEG background chan
ges varied widely in degree from patient to patient. Intraindividual a
nalysis revealed that 5 patients had statistically significant slowing
relative to the control group on at least 1 of the 9 target quantitat
ive EEG measures, as well as a composite measure. Statistically signif
icant slowing was also seen as a group effect. The results suggest tha
t among patients undergoing chronic therapy with phenytoin or carbamaz
epine there are widely different degrees of EEG background slowing, of
ten significantly beyond that expected on the basis of test-retest var
iability. Intraindividual analysis of the EEG background may be a prac
tical objective measure of a patients unique response to chronic AED t
herapy.