Congratulations to Drs. Michael Okun and Kelly Foote on the publication of “Unilateral Versus Bilateral Ventral Intermediate Nucleus Deep Brain Stimulation for Axial Essential Tremor Symptoms” in the April 24th supplement of Neurology.
Objective: To evaluate effects of unilateral ventral intermediate nucleus (VIM) thalamic deep brain stimulation (DBS) on axial tremor in Essential Tremor (ET). Additionally, we compared the efficacy and tolerability of unilateral versus bilateral stimulation.
Background: Many DBS experts assume that bilateral DBS is necessary for improvement in axial tremor in ET, but with incremental risk for surgical adverse events including speech and gait impairment. In this post hoc analysis from the largest controlled trial to date evaluating the St Jude non-directional lead constant current DBS device for ET (Wharen et al., Parkinsonism Relat Disord, 2017), we sought to either confirm or refute this notion and to better understand the effects of unilateral stimulation on axial tremor.
Design/Methods: Two cohorts were analyzed: patients with unilateral implants (n=119) and those with unilateral implants who underwent a staged second sided implant after six months (n=39). Outcomes included change in Clinical Rating Scale for Tremor (CRST) axial subitems from baseline to 90 and 180 days as well as the on- and off-stimulation conditions at each timepoint and adverse effects. A within subject comparison of the staged cohort of unilateral versus bilateral DBS at 180 days was also performed.
Results: Unilateral stimulation improved head(p<0.001), voice(p<0.001), tongue(p<0.05), face(p<0.05), and trunk tremor(p<0.05) at 90 and 180 days compared to baseline. Change between on- and off-stimulation showed similar results. After bilateral stimulation, further improvement was only seen in head(p<0.05) and face tremor(p<0.001). Among those bilaterally stimulated, 32 additional stimulation and surgery related adverse events occurred after second sided surgery (12 resolved with reprogramming).
Conclusions: Unilateral VIM stimulation for severe ET significantly improved axial ET symptoms, and bilateral stimulation was associated with additional adverse effects. If individual patient expectation is to improve contralateral arm tremor and axial tremor, then unilateral stimulation may be sufficient and could avoid unnecessary morbidity.