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Patients with progressed Essential Tremor (ET) treated with deep brain stimulation (DBS) of the ventral intermediate nucleus (VIM) can experience reduced tremor control with progression of their disease. Initially, tremor improvement can be obtained by increasing the stimulation. Eventually, this can cause side effects as the standard lead causes unwanted stimulation of adjacent regions (e.g. internal capsule). In this study, we replaced the standard leads (sDBS, Medtronic) with directional leads (dDBS, Boston Scientific) in a cohort of patients with progressed ET and insufficient tremor control. This prospective trial was designed to evaluate the clinical benefits and complications of directional leads in this cohort of patients.
Six patients with progressed ET and bilateral DBS with standard leads in the VIM were entered into the study. Patients must have initially experienced optimal tremor control but later developed tremor, which could only be controlled with concurrent unwanted side effects. Leads must have been optimally placed (post-operative CT fusion). Patients then had their standard DBS system replaced with directional leads. Tremor rating scale (TRS) and quality of life tests were performed before and after replacement surgery. The primary endpoint was the degree of tremor reduction with no side effect for the standard and directional lead systems. The secondary endpoints were improvements in quality of life measures e.g. QUEST.
When comparing the amount of tremor (OFF-ON) with no side effects before (sDBS) and after replacement (dDBS), there is a statistically significant improvement (Wilcoxon Signed- Rank Test: p< 0.02) in favour of the dDBS system. The results of the QUEST (Quality of Life in Essential Tremor Questioner) and VHI (Voice Handicap Index) show a significant improvement. The amount of hours needed to program the directional leads, reflect a learning curve. There were no complications from surgery.
Directional DBS can significantly improve tremor without additional side effects in progressed ET patients with VIM DBS when compared to standard DBS. This can improve patients’ quality of life related to their tremor and voice. Replacement surgery is a feasible and safe option for progressed ET patients. Furthermore our data supports the up-front implantation of dDBS to improve patients’ tremor without side effects in less severely affected patients at an earlier stage.