High Frequency Thalamic Stimulation for Inoperable Mesial Temporal Epilepsy

Purpose: To assess the safety, tolerability and efficacy of high-frequency periodic thalamic stimulation in inoperable mesial temporal epilepsy and the usefulness of intracranially evoked responses for assessment of anatomical uniformity of lead placement.

Methods: Four subjects were implanted with leads aimed at the anterior thalamic nuclei. Six weeks later, Soletra IPGs were activated using parameters similar to the closed-loop trial's (mean: 175 Hz; 4.1 V; 90 mus; 1 min ON, 5 min OFF). Efficacy was assessed by comparing percentage change in seizure frequency over a 6-month baseline versus a 36-month treatment period, using a within-subjects repeated measures design. Tolerability and safety were similarly monitored. Evoked responses elicited by thalamic stimulation were recorded from depth electrodes in the amygdalo-hippocampal regions and compared intra and interindividually.

Results: All subjects completed the study, tolerated stimulation and had no serious adverse effects. Mean reduction in seizure frequency was 75.6% (t =-8.24; p < or = 0.01) (range: 92% to 53%). Quality of life improved in all. Verification of electrode placement with a software function indicated that stimulated structures were presumably, Anterior thalami, Latero-polaris, Reticulatus Polaris, Ventro-oralis Internus, and Campus Forelii. Evoked responses from stimulated sites were heterogeneous, intra and interindividually, also suggesting a lack of uniformity in lead placement.

Conclusions: High-frequency, periodic, round-the-clock thalamic stimulation seems safe, well tolerated and efficacious for inoperable mesial temporal epilepsy. Identification of clinically useful parameters may be facilitated by brief closed-loop trials. Selective stimulation of a single structure may not be feasible at certain intensities, nor required for efficacy. Evoked responses may be useful for verification of uniformity of target acquisition.