Abstracts

Intermittent photic stimulation (IPS) in photosensitive epileptic patients leads to EEG abnormalities, which include generalized discharges with spike and wave activity. However, after treating the patients with sodium valproate (VPA), the generalized spike and wave discharges disappear while the occipital spikes persist. The reasons for the persistence of occipital spikes are not known.
Photosensitive epilepsy - Sodium valproate - Occipital spikes.
Thirty-three PSE patients fourteen (42%) and nineteen (58%) females (M/F ratio of 1:1.14), aged between 8 and 45 years were investigated. All the patients have basic EEG including hyperventilation recorded on 16-channel machine using the International 10-20 electrode placement system. A parasagittal montage was used during photic stimulation provided by a Grass P22 photostimulator at light intensity 2 (1363 cd/m2) with a pattern grid using the 2-second timer if required (3). The patients were tested with their eyes either open or closed. The room light standard was artificial light only. The lamp with grid was placed 30 cm from the face of the patients and they asked to fixate in the centre of the lamp, which subtended a visual angle of 25 degrees. Pattern sensitivity was carried out on the patients with T221 Gratings Generator and Hitachi Monitor at a contrast 90%. Monocular protection was also tested.
All the photosensitive epileptic patients showed occipital origin for EEG spikes preceding a generalized photoparoxysmal response (PPR). Five (15%) of the patients showed occipital spikes in the right occipital region; three (9%) in the left occipital region; nineteen (58%) in both sides of the occipital regions, while only three (9%) was observed in the fronto-occipital derivatives. Two (6%) of the patients presented occipital spikes in the mid-occipito-temporal region. One (3%) patient had ill-defined occipital spikes, which involved all the regions. On a repeat EEG test after treatment with VPA, the generalized spikes were abolished in all the patients while the occipital spikes persisted. That is, after the treatment of the patients with VPA, the EEG examinations showed that the generalized discharges disappear while the occipital spikes persist.
It was concluded that the possible causes of VPA[apos]s inefficacy in abolishing occipital spikes in photosensitive epilepsy was not necessarily due to a failure in IPSP; rather it could be due to a time-dependent failure of certain cells in the visual cortex to respond to the VPA[apos]s modulatory activity, probably involve the ionic channels, neurotransmitters and the second messenger systems.