Cortical excitability varies upon ictal onset patterns in neocortical epilepsy: A cortico-cortical evoked potential study

Objective: To better understand pathological neuronal excitation in epilepsy by comparing cortico-cortical evoked potential (CCEP) responses in regions with different ictal onset patterns: focal paroxysmal fast (PF) and repetitive spiking (RS). Methods: Fourteen patients undergoing invasive monitoring (six patients with PF and eight with RS) were studied with CCEPs. A repetitive 1 Hz bipolar electrical stimulus was applied to both the ictal onset region (iCCEP) and to a control region (nCCEP) and CCEPs were recorded from the surrounding electrodes. The two groups were compared by subtracting the amplitude of nCCEP from that of iCCEP (CCEPictal (control)) at each stimulus intensity, and then normalizing the amplitudes of iCCEP at maximum stimulus intensity by dividing by nCCEP (CCEPictal/control). Results: The CCEP response to stimulation in the ictal onset region was significantly larger than to control stimulation for both ictal patterns (paroxysmal fast: P = 0.02, repetitive spiking: P < 0.01), with repetitive spiking group amplitudes higher than the paroxysmal fast group (CCEPictal (control): P < 0.01 and CCEPictal/control: P = 0.04). Conclusions: Pro-epileptic excitability is more accentuated in regions showing an ictal repetitive spiking pattern than a paroxysmal fast pattern. Significance: These findings confirm in a new way that cortical excitability varies depending on the ictal onset pattern. (C) 2011 Published by Elsevier Ireland Ltd. on behalf of International Federation of Clinical Neurophysiology.