Introduction: New targets for Deep Brain Stimulation (DBS) for tremor control have recently gained popularity. Modulation of the cerebello-thalamo-cortical circuit via the dentato-rubro-thalamic tract (DRTt) has been recognized as effective for tremor suppression (1,2). Our prospective observational study analyzed outcomes after using direct targeting of the DRTt.

Methods: 20 consecutively enrolled intention tremor patients obtained pre-operative 3T MRI with diffusion tensor (dTi) sequences. The DRTt was drawn for each individual patient on StealthViz dTi software (Medtronic) using the dentate nucleus as the seed region and the ipsilateral pre-central gyrus as the end region (1), which was then directly targeted during DBS surgery. Intraoperative testing confirmed successful tremor control. Post-operative analysis of electrode contact (EC) position as seen on CT relative to the DRTt was performed. The volume of tissue activated (VTA) was estimated using therapeutic EC parameters and an isotropic model (3). Post-operative clinical evaluations were performed at 6 months.

Results: The mean age of patients was 65.3 years; mean duration of tremor was 12.6 years. Most patients (95%) had distal upper extremity tremor; 1 patient (5%) had proximal bilateral upper extremity tremor. Head tremor was seen in 7/20 (35%). Mean voltage for the L electrode = 3.35 V; R = 2.6 V. Mean distance from the center of the active EC to the DRTt was 0.90 mm on the L, and 0.82 mm on the R. After calculating the estimated VTA for each therapeutic EC, only 1 (2.5%) VTA fell outside the respective targeted DRTt, although the patient reported 90% tremor improvement. Overall, there was 93% tremor control. All patients self-reported improved quality of life.

Conclusions: Direct targeting of the DRTt is effective in tremor suppression. Accounting for both model and software limitations, electrode placement directly affecting these fiber tracts reproducibly produced tremor control; it is our preferred target.

Patient Care: By directly targeting the DRT tract, we have been able to improve tremor control by over 90% in our patients. This was superior to choosing indirect targeting of the VIM, which may not provide as consistently good tremor control.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of using diffusion tensor imaging for direct targeting of tracts in DBS 2) Discuss, in small groups, how individual patients’ outcomes for tremor control may improve through direct targeting of the DRTt over indirectly targeting the VIM thalamus 3) Identify other novel targets for modulation using dTi tractography as a tool

References: 1. Coenen VA, Allert N, Mädler B. A role of diffusion tensor imaging fiber tracking in deep brain stimulation surgery: DBS of the dentato-rubro-thalamic tract (drt) for the treatment of therapy-refractory tremor. Acta Neurochir (Wien). 2011 Aug;153(8):1579-85; discussion 1585. 2. Coenen VA, Allert N, Paus S, Kronenbürger M, Urbach H, Mädler B. Modulation of the cerebello-thalamo-cortical network in thalamic deep brain stimulation for tremor: a diffusion tensor imaging study. Neurosurgery. 2014 Dec;75(6):657-69; discussion 669-70. 3. Butson CR, Cooper SE, Henderson JM, McIntyre CC. Patient-specific analysis of the volume of tissue activated during deep brain stimulation. Neuroimage. 2007 Jan 15;34(2):661-70.