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

Abstract

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 1Hz 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 (CCEP ictal-control) at each stimulus intensity, and then normalizing the amplitudes of iCCEP at maximum stimulus intensity by dividing by nCCEP (CCEP ictal/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 (CCEP ictal-control: P<0.01 and CCEP ictal/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. © 2011 International Federation of Clinical Neurophysiology.