Characteristics of visual evoked potentials related to the electro-clinical expression of reflex seizures in photosensitive patients with idiopathic occipital lobe epilepsy

Seizures provoked by visual stimuli may be induced by abnormal responses to light (photosensitivity) and structured patterns (patternsensitivity). In this study, we analysed visual evoked potentials (VEPs) in three different samples: i) 38 photosensitive patients (21 males, 17 females; mean age 10.0 +/- 2.9 years) with idiopathic occipital lobe epilepsy and reflex seizures (RS); ii) 13 non-photosensitive patients (6 males, 7 females; mean age 11.7 +/- 5.3) with idiopathic occipital lobe epilepsy; 20 healthy controls (12 males, 8 females; mean age 10.0 +/- 3.4). After written informed consent, all subjects underwent a standard procedure of visual stimulation with intermittent light and pattern stimulation, under digital video-EEG recording. The EEG signal was processed off-line by averaging analysis for each stimulus to obtain the corresponding VEP. Comparisons among groups showed no significant differences for P100 latency. Higher P100 amplitude as well as higher afterdischarge (AD) were found in photosensitive patients with RS. Thirty-seven of these patients had one or more RS during the procedure of stimulation for a total of 66 episodes. Significant increases of P100 amplitude and higher values of AD amplitude were found in relation to the occurrence of photoparoxysmal response (PPR) and/or seizures during full-field pattern stimulation. The increase in amplitude of the AD was higher when PPR was associated with seizures. The high amplitude of early VEP components confirms the abnormal hyperexcitability in the cortex of photosensitive patients with occipital lobe epilepsy. Moreover, the AD amplitude appears to be related to electro-clinical expression, being greater when PPR evolves into clinically evident seizures.