Deficit di inibizione nel sistema visivo dei pazienti con epilessia generalizzata fotosensibile

Photosensitivity is the propensity to produce epileptic seizures in response to visual stimuli. The most common type of EEG response underlying photosensitivity is the photoparoxysmal response (PPR) to intermittent light stimulation (ILS), that is frequently associated with idiopathic generalized epilepsies. We studied the pathophysiology of photosensitivity by means of paired flash-evoked potentials (F-VEPs), recently revived as powerful tool for detecting excitability changes in the visual system (Cantello et al. 2011). We studied 19 patients with idiopathic generalized epilepsy (IGE) and photosensitivity currently treated with AEDs. Twenty-two age and sex-matched normal subjects acted as controls. We recorded F-VEPs from 3 scalp locations (Oz-Pz; C4-Fz and C3-Fz). Stimuli were single flashes, intermingled at random to flash pairs at the interstimulus interval (ISI) that corresponded to stimuli frequencies of of 8, 16, 20, 30, and 60 Hz, chosen for their interest in the origin of PPR. Patients showed a failure of the normal inhibitory phenomenon on "eyes closed" detected by means of paired F-VEP technique depicting a transient state of hyperexcitable visual cortex. This phenomenon involved even central areas, possibly reflecting direct/indirect projections from visual cortex.