Chronotopographical potential distribution of some SSEP components in cerebrovascular insufficiency

In 7 patients with symptoms of cerebrovascular diseases a somatosensory evoked potential (SSEP) chronotopogram was constructed after median nerve stimulation of seven different EP components: N20, P25, P45, P100, N140, P200 and P300. We examined only a limited number of patients (and controls) because the methodology is very time-consuming. We analyzed the topography in these patients in order to obtain insight in the effect of this disease on EP distributions and to find arguments in favor of the use of this methodology in clinical examination. These chronotopographical maps were constructed on the basis of the localization of maximal amplitude of the different components and their dipole counterparts (if present). 3 patients showed a delay of the specific components, and in 1 patient most of the non-specific components were delayed. The chronotopographical representation in most patients was abnormal. Relations with clinical state and computer tomography (CT) are described. Focal hypodensity on the CT gives rise to a large extension of the area of the specific component N20, overruling the dipole counterpart P20. Slight cortical atrophy in 4 patients causes abnormalities in the P300/N300 dipole direction. Chronotopograms give new information. Therefore, it seems justified to improve the method and implement it for clinical use in the near future.