Source localization and possible causes of interictal epileptic activity in tumor-associated epilepsy

Electrophysiological studies in gliomas have demonstrated action potentials in neoplastic cells. These "spiking tumor cells" are, however, an enigma. In attempt to find evidences for spikes within tumoral borders, 21 patients with different intracerebral tumors were preoperatively screened for the o ccurrence of epileptogenic discharges using multichannel MEG and EEG. A cor relation between histopathology and the distance between dipole and tumor b order could be found. Glioma patients showed epileptic activities closer to the border than those with mixed glioneuronal neoplasms and metastases. Fo ur glioma patients demonstrated epileptic activity within the tumor boundar y, however, not in the deep center of the tumor. Patch-clamping of cells fr om acute glioma slices did not yield a correlation between the presence of voltage-gated sodium channels in tumor cells and the MEG/EEG data. Our resu lts demonstrate that the zone with the highest epileptogenic potential is d ifferent in gliomas and other brain tumors. However, our data do not strong ly suggest that glioma cells are directly involved in the generation of tum or-associated epilepsy in vivo via their capability to generate action pote ntials. (C) 2000 Academic Press.