Effect of deep brain stimulation on nonmotor symptoms in essential tremor.

Objective: Essential tremor (ET) is a prevalent movement disorder that also includes nonmotor symptoms such as anxiety, depression, and cognitive impairment. Deep brain stimulation (DBS) is an established treatment for ET, yet its impact on nonmotor symptoms remains unclear. This study aims to describe neuropsychological outcomes following ventral intermediate nucleus (VIM) DBS in a large cohort of patients with ET and identify factors associated with changes in depression and cognitive function.

Methods: A retrospective cohort study of patients who had undergone VIM DBS was performed. Inclusion criteria were ET diagnosis, surgery between October 2007 and March 2020, and available pre- and post-DBS neuropsychological testing results. Neuropsychological measures included the Beck Depression Inventory-II (BDI-II), Beck Anxiety Inventory (BAI), and cognitive measures assessing attention, executive function, language, memory, and visuospatial function. Post-DBS tremor improvement was graded, and active electrode coordinates and stimulation parameters were identified. Statistical analyses included descriptive statistics, t-tests to compare pre- and postoperative scores at the group level, and one-way analysis of variance to compare variables among patients who improved, were stable, or worsened in psychiatric and cognitive characteristics after DBS.

Results: One hundred thirty-nine patients met the study inclusion criteria. BDI-II scores significantly decreased postoperatively (9.82 ± 6.77 vs 8.29 ± 6.18, p < 0.001, Cohen's d = 0.176), whereas BAI scores remained unchanged. Both language (p = 0.003, Cohen's d = 0.259) and memory (p < 0.001, Cohen's d = 0.336) domains showed statistically significant small-magnitude declines following surgery, whereas attention, executive function, and visuospatial function were unchanged. Patients with improved depression (14.3%) following VIM DBS had significantly higher BDI-II scores preoperatively (p < 0.001, ω2 = 0.226). Patients with worsened language (18.7%) had higher preoperative language scores (p < 0.001, ω2 = 0.058). Patients with worsened memory (15.1%) had higher BAI scores preoperatively (p = 0.002, ω2 = 0.079). Preoperative scores were similar between patients with improved and worsened overall cognition postsurgery. Patients with improved overall cognition had improvements in attention, language, and visuospatial function.

Conclusions: VIM DBS for ET did not result in large-magnitude neuropsychological changes. There were statistically significant, though likely not clinically meaningful, small-magnitude improvements in depression and worsening in language and memory scores. Associations were found between multiple preoperative mood and cognitive scores and post-DBS neuropsychological changes. These findings can help inform clinical decision-making and patient counseling for DBS.