gms | German Medical Science

Objective: Head tremor may be associated with or the predominant symptom of patients with essential tremor (ET) or dystonia (DT). The globus pallidus internus (GPI) and the ventrolateral thalamus/subthalamic region ("VIM") represent competing targets for deep brain stimulation (DBS). The selection of the most promising target is often based on a symptom-driven decision, not only because the differential diagnosis between ET and DT is often difficult.

Methods: Fourteen patients (8 female; 3 classified as ET and 11 as DT) with predominant head tremor were evaluated. Electrodes were implantated bilaterally into the GPI (4) or VIM (9), and in one patient into both targets in a staged procedure (bilateral GPi stimulation followed by additional unilateral "VIM" stimulation) using microlectrode recording and test stimulation in the awake state or general anesthesia.

Results: In 13 patients, effective (>80–90%) tremor suppression was observed, and in one DT patient treated with GPI stimulation the response on the tremor was only modest. In one DT patient, dystonia had improved following GPI stimulation without affecting positional head tremor, which was then abolished by additional, unilateral "VIM" stimulation performed 12 months later. In one DT patient we observed an ongoing microlesioning effect over >6 months. In one patient, the tremor did not recur following switching off the stimulator for more than 6 months afterwards, whereby a slight tremor recurred without the necessity of reactivating DBS. Notably, an improvement in the cervical dystonia was also noted following "VIM" stimulation. In two patients with a follow-up of >1 year, the Toronto Western Spasmodic Torticollis Rating Scale part I (preoperative scores 8 and 7) was markedly improved (postoperative 2 and 1, respectively) with similar results in patients observed for shorter durations. The location of the active contacts was evaluated, which revealed that most active contacts for GPI and "VIM" stimulation were located within or below the posteroventral pallidum and in the subthalamic region, respectively.

Conclusions: Head tremor in ET and DT patients is efficiently suppressed by DBS applied to the GPI or "VIM." The "VIM" should also be considered in DT patients when tremor is the predominant symptom. Improvement of dystonia with "VIM" stimulation may result from modulation of pallidothalamic in addition to cerebellothalamic projections. Staged procedures addressing both targets may be required in individual cases to obtain adequate results.