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 (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.