Abstracts

Deep brain stimulation (DBS) of the thalamic and sub-thalamic nuclei have been explored in recent years for possible therapeutic effects in epilepsy. The centro-lateral (CL) thalamic nuclei are a key element in a hypothesized pathophysiology called thalamocortical dysrhythmia (TCD) associated with several neuropsychiatric conditions including epilepsy. Lesioning of the CL nuclei has been reported to produce seizure reduction in a few cases of epilepsy. We report preliminary observations on physiological responses to DBS of this thalamic target in a patient with treatment-resistant partial epilepsy., Bilateral DBS electrodes were placed stereotactically in the CL nuclei in a 27 year old male with debilitating treatment-resistant partial epilepsy who had failed left parietal resective surgery and Vagus Nerve Stimulation therapy. A Kinetra Pulse Generator (Medtronic, Inc) was implanted in the subclavicular region. Intraoperative microelectrode recordings were performed prior to implantation of DBS electrodes. EEG responses to bilateral and unilateral CL stimulation were recorded intraoperatively and one month after implantation. EEG data were subjected to power spectral analysis using custom software written in SCILAB., DBS Electrode locations were confirmed by MRI to be within 1 mm of the stereotactic targets in the axial plane. Intraoperative microelectrode recordings showed spike bursts with the characteristics of low-threshold spikes (LTS bursts) in the left CL nucleus. These were far less abundant on the right. The burst frequency of approximately 5 Hz, coincided with a large theta peak in the patient[apos]s baseline EEG power spectrum. High frequency (130 Hz) stimulation of the CL nuclei with a pulse-width of 90 microseconds, produced a non-linear, voltage-dependent decrease in theta power, which reached statistical significance above 2.5 volts (p[lt]0.01 based on a 2-sided Wilcoxon test applied to log EEG spectral power), and saturated by 7.5V. Unlike this response which was bilateral on unilateral stimulation, a drop in beta-range EEG power was noted to occur ipsilaterally on unilateral CL stimulation., The EEG response to high frequency DBS of the CL thalamic nuclei are consistent with prior observations based on lesioning this target. The asymmetry in the abundance of LTS bursts in the CL thalamic nuclei was consistent with the laterality of the patient[apos]s epileptogenic zone. The thalamocortical dysrhythmia (TCD) hypothesis predicts these effects, and deserves further evaluation. Acute stimulation of the CL nuclei appears to be well tolerated. Tolerability of chronic stimulation and efficacy in seizure reduction remain to be determined.,