Impact of Hyperventilation and Sleep Deprivation Upon Visual Evoked Potentials in Patients with Epilepsy

The diagnosis of epilepsy can cause many problems, especially when the routine electrophysiological tests are inconclusive. The aim of the present study was to assess the visual evoked potential (VEP) in patients with epilepsy using various kinds of stimulation and activation tests. The VEP parameters were also presented with reference to the type of seizure and abnormalities in electroencephalogram (EEG), including the response to the activation tests.

This study comprised 81 patients with newly diagnosed epilepsy of unknown etiology before initiation of the treatment. The VEP tests were performed at rest, after hyperventilation, and deprivation of sleep. Visual stimulation included an alternating checkerboard pattern and a uniform flash light (FL) with a frequency of 1.88 and 15 Hz.

The VEP parameters obtained with the stimulation of a checkerboard pattern did not differ significantly between the patients and controls. Neither the presence of seizure activity in EEG nor the type of seizure significantly affected the VEP parameters. Using the FL stimulation, a significantly prolonged VEP latency was found at the FL frequency of 1.88 Hz and shortened at the frequency of 15 Hz. These changes were augmented after activation tests. In case of the patients with positive intermittent photic stimulation response in EEG, a significant prolongation of P100 latency was shown at rest and after FL stimulation at the frequency of 1.88 Hz.

Standard activation methods significantly affect the VEP parameters in patients with epilepsy. Changes in the VEP parameters depend on the frequency and the type of the stimulus, as well as the activation method used. These findings suggest a disturbed balance between the glutamatergic and GABAergic systems in the visual excitability of neuronal networks in case of patients with epilepsy.