Abstracts

RATIONALE: In medically refractory epileptic patients who cannot be treated by resective surgery, alternative methods such as chronic neurostimulation are under development. We considered subthalamic nucleus high frequency stimulation (STN HFS), on the basis that the nigral system exerts inhibitory control in various animal models of epilepsy. We were encouraged by the known relationship between the STN and the nigral system, by the effects of pharmacological or electrical inhibition of the STN on different seizure types in rats, and by our experience with STN HFS in parkinsonian patient.
METHODS: From 1998, STN HFS was performed in 3 patients suffering from medically intractable seizures involving the sensori-motor cortex, and who were considered unsuitable for resective surgery. Two (Pt1: 5 yrs, Pt3: 8 yrs) had focal cortical dysplasia with hemiparesia and were treated with polytherapy. The remaining patient (Pt2: 19 yrs) suffered from severe myoclonic epilepsy treated by valproate. Electrodes were stereotactically implanted in STN unilaterally (Pt1) or bilaterally (Pt2, Pt3), according to the method used in movement disorders. STN and scalp EEG activity was temporarily recorded, and electrodes were then connected to an implantable programmable generator. Stimulation frequency was set at 130 Hz, pulse width at 90 microsec, and the voltage was progressively increased according to patients tolerance and clinical response.
RESULTS: In all patients, interictal spikes, as well as ictal discharges, were recorded simultaneously from scalp and STN electrodes. Results of STN HFS was assessed after a follow-up of 2 yrs (Pt1), 18 months (Pt2), and 8 months (Pt3). The number of seizures/month has significantly decreased in all cases, with a seizure reduction of 80% in Pt1 (66 vs 336, p[lt]0.01), 40% in Pt2 (10 vs 16, p[lt]0.01), and 71% in Pt3 (79 vs 270, p[lt]0.01). In Pt1, the effect was more prominent on seizures occurring in series (-89%) and during the day (-88%) than on those occurring during sleep (-53%). Hemiparesis resolved in Pt1 and motor function slightly improved in Pt3. AEDs remained unchanged (Pt2) or has been slightly reduced (Pt1, Pt3).
CONCLUSIONS: The present study provides evidence that STN HFS may induce a long lasting (up to 2 yrs) significant reduction of seizure frequency (40-80%) in cases of intractable epileptic seizures involving the sensori-motor cortex. These findings open up new therapeutical perspectives for intractable epilepsies considered unsuitable for resective surgery. Clinical trials will be necessary to further document and prove the validity of this method, to identify the best candidates, and to better define the stimulation parameters.