Do nonspecific focal EEG slowing and epileptiform abnormalities favor one hemisphere?
OBJECTIVE
Several EEG-based studies suggest that epileptiform activity originates from the left more than the right hemisphere. In contrast, other pathophysiologies such as stroke lateralize relatively symmetrically. Study of focal slowing and other EEG abnormalities allows assessment of favoring as well as referral and interpretation bias.


METHODS
The 1,331 consecutive adult EEG reports were reviewed for epileptiform discharges (EDs) and nonepileptiform focal slowing. Side of slowing or EDs, interpreting electoencephalographer, and whether the patient was undergoing long-term monitoring or routine EEG were tallied. Results were statistically analyzed.


RESULTS
Focal slowing occurred symmetrically; EDs favored the left hemisphere (p < 0.01).


CONCLUSIONS
The left hemisphere may be more prone to epileptiform abnormalities in adults, but not to the nonspecific pathophysiologic processes that cause slowing. These findings suggest that potential interpretation bias does not influence left hemispheric favoring of EDs and instead may implicate a biologic etiology.
Doherty
Michael J
MJ
Department of Neurology and Regional Epilepsy Center, University of Washington, Seattle, Washington 98195, USA. mdoherty@u.washington.edu
Walting
Paul J
PJ
Morita
Denise C
DC
Peterson
Rich A
RA
Miller
John W
JW
Holmes
Mark D
MD
Watson
Nathaniel F
NF
D000328:Adult; D015982:Bias; D002540:Cerebral Cortex / Q000503:physiopathology; D004292:Dominance, Cerebral / Q000502:physiology*; D004569:Electroencephalography / Q000706:statistics & numerical data; D004829:Epilepsy, Generalized / Q000175:diagnosis* / Q000503:physiopathology; D005071:Evoked Potentials / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D015588:Observer Variation; D012189:Retrospective Studies