Object. The tremor-suppression effect resulting from long-term stimulation of the thalamic nucleus ventralis intermedius (Vim) and the nucleus ventralis oralis posterior (Vop) was examined in the treatment of parkinsonian, essential, and poststroke tremor.
Methods. After identifying the accurate anterior border of the nucleus ventrocaudalis (Vc), deep brain stimulation (DBS) electrodes with four contacts were inserted into the Vim—Vop region at an angle of between 40 and 50° from the horizontal plane of the anterior commissure—posterior commissure line. Two distal contacts were placed on the Vim side and two proximal contacts on the Vop side. The best sites of stimulation and parameters of bipolar stimulation were selected in each case and follow-up examinations were conducted for at least 2 years.
In all 15 cases of parkinsonian tremor (18 sides) and in 14 of 15 cases of essential tremor (24 of 25 sides), cathodal stimulation of the Vim side with anodal stimulation of the Vop side was determined to be the best choice to suppress the tremor. In poststroke tremor, however, six of 12 cases (six of 12 sides) were selected for cathodal stimulation of the Vop side with anodal stimulation of the Vim side. The average stimulation intensity 1 month after initiation of DBS was 1.61 V in cases of parkinsonian tremor, 1.99 V in cases of essential tremor, and 2.39 V in cases of poststroke tremor. A comparison of stimulation intensities required at 1 and 24 months after initiation of DBS revealed that the lowest effective stimulation intensity increased 24.2% in cases of parkinsonian tremor, 21% in cases of poststroke tremor, and 46.9% in cases of essential tremor. Suppression of tremor was achieved in all cases (42 cases, 55 sides) during a period of 2 years. Nevertheless, two cases of poststroke tremor required dual-lead stimulation at the unilateral Vim—Vop region from the start of DBS, and two cases of essential tremor and one case of poststroke tremor required a stimulation intensity that was high enough to evoke unpleasant paresthesia and slight motor contraction during the follow-up period.
Conclusions. Effective stimulation sites and stimulation intensities differ in different kinds of tremor; Vim and Vop stimulation is necessary in many cases. Interactions of the Vim and Vop under the control of interconnected areas of the motor circuitry may play an important role in both the development and DBS-induced suppression of tremor.