Evidence of Improved Verbal Fluency Following Unilateral Right Hemisphere Subthalamic Nucleus Deep Brain Stimulation for Parkinson’s Disease
Victor Del Bene1, Roy Martin1, Sarah Brinkerhoff2, Joseph Olson1, Matthew Nelson1, Dario Marotta3, Christopher Gonzalez1, Kelly Mills4, Vidyulata Kamath5, Nicole Bentley1, Harrison Walker6
1University of Alabama at Birmingham, 2Auburn University, 3University of Illinois Chicago, 4Neurology, Johns Hopkins University, 5Johns Hopkins University, 6University of Alabama At Birmingham
Objective:
To investigate verbal fluency following unilateral subthalamic nucleus deep brain stimulation (STN-DBS).
Background:
STN-DBS is safe and effective for motor symptoms, but a widely replicated cognitive outcome following bilateral STN-DBS is verbal fluency decline. Since non-motor symptoms, including mild cognitive impairment and dementia are a significant cause of disability in Parkinson’s disease (PD), reducing the risk of DBS-related cognitive decline is important. Compared to bilateral STN-DBS, little is known about unilateral STN-DBS effects on verbal fluency
Design/Methods:
We enrolled 31 PD patients who underwent unilateral STN-DBS in a randomized, cross-over, double-blind study (SUNDIAL). Targets were based on treatment of the most symptomatic side (n = 17 left STN-DBS; 14 right STN-DBS). At 2-, 4-, and 6-months post-surgery, all participants completed a verbal fluency measure (FAS/CFL), and stimulation type (directional versus ring) was randomized. Welch’s two-sample t-test was used to compare verbal fluency baseline scores and the effects of hemisphere and stimulation on cognition were analyzed using linear mixed effects models. Covariates included age, education, and levodopa equivalents at each time point.
Results:
Left STN-DBS patients scored lower on a verbal fluency task than right STN-DBS patients (t(20.66) = -2.49, p = 0.02) at baseline. Following DBS surgery, we observed declines in verbal fluency over the study duration only in the left STN-DBS group (p = 0.02), while the right STN-DBS group improved (p<.001). Stimulation type was not associated with verbal fluency performance.
Conclusions:
After adjusting for age, education, and levodopa equivalent dose, we found group-level verbal fluency declines following unilateral left STN-DBS and improved verbal fluency following unilateral right STN-DBS. In contrast with bilateral STN-DBS where verbal fluency declines are often reported, it is possible that selecting unilateral right STN-DBS to control left-sided symptoms may be a modifiable risk factor to potentially reduce the likelihood of verbal fluency declines in patients with PD.