Approximately one third of patients with focal epilepsy exhibit bilateral, mainly homotopic, apparently independent, epileptiform electroencephalographic (EEG) abnormalities in scalp-recorded tracings under normal physiologic recording conditions.1-4 Although this finding is well established, its significance with respect to pathophysiology is unclear. For example, does it mean that both hemispheres contain an epileptogenic lesion that is at least potentially clinically significant? Do these bilateral discharges imply that there are multiple primary foci and, if so, why are they so often symmetrical? Or, is it possible that one epileptogenic lesion may give rise to another? Equally obscure is the meaning of such bilateral epileptiform discharge with respect to the outcome of surgical treatment. Does the presence of an active spike focus contralateral to an intended excision afford a warning that the operative intervention is unlikely to result in cure? Is it rather a warning that operative intervention is needed more quickly? Or,
Morrell F. The Role of Secondary Epileptogenesis in Human Epilepsy. Arch Neurol. 1991;48(12):1221–1224. doi:10.1001/archneur.1991.00530240025011
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