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

ObjectiveTo 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).MethodsFourteen 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).ResultsThe 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).ConclusionsPro-epileptic excitability is more accentuated in regions showing an ictal repetitive spiking pattern than a paroxysmal fast pattern.SignificanceThese findings confirm in a new way that cortical excitability varies depending on the ictal onset pattern.

► This study confirms in a new way that cortical excitability varies depending on the ictal onset patterns seen on electrocorticography. ► This is a cortico-cortical evoked potential (CCEP) study to evaluate pathological neuronal excitation in ictal onset regions with different ictal onset patterns. ► This is the first report to evaluate pro-epileptic excitability in regions showing different ictal onset patterns and is useful to better understand pathological neuronal excitation in epilepsy.