EEG & Clinical Neurophysiology Laboratory, Harborview Medical Center, Box 359722, 325 Ninth Ave, Seattle, Washington, USA.
Purpose. To determine if there is evidence that the left cerebral hemisphere is more prone to epileptogenesis than the right hemisphere.
Methods. We examined 532 patients with localization-related epilepsy, as documented by long-term EEG-video monitor studies. We identified those with interictal epileptiform patterns on EEG confined to one hemisphere, those with clinical seizures that arose only from one side, and individuals with neuropsychological deficits lateralizing more to one cerebral hemisphere than the other. These data were then related to the handedness of the subjects.
Results. For left-handed patients, interictal discharges were significantly more likely to be confined to the left side, seizures more frequently arose from only the left hemisphere, and neuropsychological deficits lateralized more often to the left brain. In contrast, for right-handed subjects, there were no significant differences in unilateral localization of either interictal discharges or of seizure onsets, nor did neuropsychological deficits lateralize more often to one side or the other. Although, as a group, left-handers had an earlier age of onset of epilepsy than right-handers, the lateralizing EEG and neuropsychological patterns seen in left-handers were not related to age of onset of epilepsy, febrile seizures, family history of either epilepsy or left-handedness, or other risk factors.
Conclusion. In localization-related epilepsy, there is a significant association of left-handedness with left hemispheric lateralization of epileptiform EEG patterns and neuropsychological deficits. These findings do not clearly reflect a greater left than right cerebral hemispheric vulnerability to epileptogensis, except possibly in left-handers.