Abstracts

RATIONALE: Left-sided vagus nerve stimulation (VNS) is an efficacious treatment for patients with refractory epilepsy. The exact mechanism of action remains unknown. In a previous perfusion SPECT activation study of acute, initial stimulation we reported that statistical parametric mapping showed left-sided thalamic deactivation. In this study, we investigated both acute and chronic effects of VNS in patients with refractary complex partial seizures ? secondary generalisation (CPS?SG). METHODS: Fourteen patients, with mean age of 31.7?9.5 years and mean CPS?SG duration of 19.5?8.1 years, received VNS. All patients were considered unsuitable candidates for resective surgery because of non-localizing findings in the presurgical evaluation. All patients underwent a split-dose 99m-Tc ECD activation study before and immediately after their initial stimulation (0.5 mA, 30 Hz). Six of these patients underwent a second activation study 6.3?1.8 months after implantation with an additional 0.25 mA stimulus. Data were acquired on a high-resolution triple-head gammacamera. Stereotactic anatomical normalisation was performed and an automated semiquantitative volume-of-interest analysis was carried out. RESULTS: For the acute activation study, significant deactivation was also found in the right parietal cortex (-3 %, p=0.008). In the chronic activation paradigm a significant ipsilateral thalamic activation was found (5 %, p=0.001). When comparing chronic perfusion to the initial pre-VNS baseline, bilateral mesial temporal perfusion decreases were found bilaterally in the mesial temporal gyrus (-7 %, p=0.02). CONCLUSIONS: Acute VNS stimulation produces different flow changes under initial and chronic conditions. Long-term chronic stimulation results in a relative bilateral mesial temporal lobe hypoperfusion. Supported by grants BOZF-01104495, BOZF-01105399 and BOZF-011A099 from the University of Ghent and by grant 1.5.236.99 from the Fund for Scientific Research-Flanders.