Unilateral right STN-DBS improves verbal fluency

The decline in verbal fluency in patients with Parkinson’s disease (PD) may be a question of choosing the right side for subthalamic nucleus deep brain stimulation (STN-DBS). Verbal fluency declined after unilateral left STN-DBS verbal fluency while it improved after unilateral right STN-DBS, the SUNDIAL trial suggests.

Verbal fluency often declines after bilateral STN-DBS in patients with PD. “The here presented result is very important because non-motor symptoms in PD are a very important factor for the quality of life,” said Dr Victor del Bene (University of Alabama, AL, USA), who presented the results [1]. He said bilateral STN-DBS is safe and has very positive patient-reported outcomes. However, a common adverse event is a cognitive change, including a decline in verbal fluency and memory. It is unknown if this holds for unilateral STN-DB. Therefore, Dr Del Bene and his group investigated verbal fluency following unilateral STN-DBS in a subcohort of the SUNDIAL trial (NCT03353688). The larger purpose of this randomised, double-blind crossover study is to measure the clinical efficacy of directional versus omnidirectional stimulation in PD and to explore whether electrophysiology biomarkers can rapidly predict effective, well-tolerated contacts for directional DBS therapy. Dr Del Bene and his group enrolled 31 SUNDIAL participants who underwent unilateral STN-DBS. The most symptomatic side was treated resulting in 17 participants treated on their left side and 14 on their right side. At baseline and at 2, 4, and 6 months after surgery, participants underwent verbal fluency and memory assessments and the Stroop test.

At baseline, none of the participants showed signs of cognitive impairment. Verbal fluency scores were significantly lower among participants after left-side STN-DBS (t(20.66)=-2.49; P=0.02). Over 6 months of follow-up, Dr Del Bene and colleagues observed a gradual further decline in verbal fluency in the left STN-DBS group by about 25% (P=0.02). This result was consistent with published data, according to Dr Del Bene. For participants with right-side STN-DBS, verbal fluency improved by about 25% (P<0.001). This group also showed significant improvements in the Stroop test by about 18%.

The results suggest that selecting unilateral right STN-DBS to control left-sided symptoms could reduce the likelihood of verbal fluency declines in patients with PD. Dr Del Bene concluded: “At the very least, there is no evidence of a decline in verbal fluency and response inhibition in the right-side DBS group.”

1. Del Bene VA. Evidence of improved verbal fluency following unilateral right hemisphere subthalamic nucleus deep brain stimulation for Parkinson’s disease. S51.003, AAN 2023 Annual Meeting, 22–27 April, Boston, USA.

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Posted on 26 June, 20238 February, 2024