Objective: Thalamic deep brain stimulation (DBS) is commonly used to treat essential tremor, but the optimal lead location within the thalamus has not been systematically evaluated. We examined the relation of lead location to clinical outcome in a series of essential tremor patients treated by thalamic DBS.
Methods: Fifty-seven leads in 37 patients were studied. Lead locations were measured by postoperative magnetic resonance imaging. Contralateral arm tremor was assessed in the DBS-on and DBS-off states using the Fahn-Tolosa-Marin tremor rating scale, with a mean follow-up of 26 months. Lead locations were statistically correlated, using analysis of variance, with percent improvement in tremor resulting from DBS activation.
Results: Improvement in tremor score was significantly correlated with lead location in both the anteroposterior and lateral dimensions. In the plane of the commissures, the optimal electrode location was determined statistically to be 6.3 mm anterior to the posterior commissure and 12.3 mm lateral to the midline, or 10.0 mm lateral to the third ventricle.
Conclusion: Optimal electrode location for thalamic DBS in essential tremor corresponds to the anterior margin of the ventralis intermedius nucleus. Leads located greater than 2 mm (in the plane of the commissures) from the optimal coordinates are more likely to be associated with poor tremor control than leads within 2 mm of the optimal location. The incidence of true physiological tolerance to the antitremor effect of thalamic DBS (defined as poor tremor control in spite of lead location within 2 mm of the optimal site) was found to be 9%.