Abstracts

Rationale: VNS has been used as a palliative procedure for the treatment of refractory focal and generalized epilepsy, in both adults and children. On the other hand, its mechanism of action remains poorly understood. Methods: A 14 years old girl presented with refractory secondary generalized epilepsy since the age of 6 years and mental retardation. Her EEG showed diffuse polispike and wave discharges. MRI showed double-cortex syndrome. She was submitted to extended callosal section at the age of 10 years which yielded 50% seizure frequency reduction. She was submitted to VNS by the age of 12 years, and to thalamic centro-median deep brain stimulation (DBS) at the age of 13 years. Results: As VNS stimulation intensity was increased (> 1mA), there was appearance of extra-pyramidal symptoms (2 days latency): she developed bilateral tremor and rigidity, and gait and postural disturbance. All symptoms were levodopa-responsive and disappeared 7-10 days after VNS was turned off. Several attempts to reactivate VNS led to the same results. During the periods when VNS was on she presented with marked seizure frequency reduction. Thalamic centro-median DBS was turned on after VNS was turned off. The child developed exactly the same symptoms and obtained a similar seizure control after increasing DBS voltage (> 1V). Conclusions: This is the first report of a clinically evident direct effect of VNS on the basal ganglia. The same adverse reaction was noted after centro-median DBS, suggesting that the anticonvulsant effect (and the side effect) of both VNS and DBS were mediated by the modulation of basal ganglia and non-specific thalamic nuclei. Both structures are interconnected to the nigro-striatal anticonvulsant system.