Abstracts

Based on previous animal and human observations suggesting involvement of the thalamus in the maintenance and propagation of seizures, thalamic deep brain stimulation (DBS) has been proposed as a treatment for intractable epilepsy. We present long-term follow-up results of a series of patients treated with either anterior nucleus (AN) or centromedian nucleus (CM) DBS for epilepsy. 7 patients with intractable epilepsies of different etiologies, aged 23-51 years, were implanted with either AN or CM electrodes (or both at separate intervals in one case) and received high frequency stimulation beginning 4 weeks after implantation. These patients were followed for a period of 13-66 months (mean 4 years). No change in medication was done in the first year after implantation. Meanwhile, changes in stimulation parameters were done multiple times in all patients, including a 2-month period of single-blinded stimulation OFF. For AN patients, 66% showed [gt]50% seizure reduction at 59, 50, 46 and 45 months. Two patients showed [gt]75% reduction. There were no serious adverse effects. In the [gt]50% good responders group, no change in stimulation parameters (voltages, frequency, bi- or monopolar stimulation) alone or in combination was as effective in reducing the frequency of seizures as simple implantation of the AN electrodes (ie before activation of stimulation). An excellent response to implantation only (91 and 82% reduction from baseline) was a good outcome indicator, while intermediate reductions (27 to 47%) were associated with variable outcomes after the stimulators were turned ON. There was no significant change in seizure frequency during single-blinded stimulation OFF periods in either good or poor responders. The two CM patients showed a poor response (14% or 35% increase from baseline) at 13 and 30 months, although an important reduction in generalized convulsions (from 1-3 per month to 3 in 18 months) was observed in one of the patients. Reversible stimulation dependent CM adverse effects included paresthesias, anorexia and nystagmus. CM stimulation did not reduce the total number of seizures and was associated with some reversible side effects in the two patients studied. AN electrode placement and stimulation in six patients was associated with a [gt]50% long-term seizure reduction in 66% of patients, with no adverse effects. Whether the sustained long-term beneficial response to AN DBS in this small open-label trial represents an effect of microthalamotomy caused by electrode insertion or electrical stimulation through the electrodes, or a combination of these or other factors, remains to be clarified.