The Effect of Deep Brain Stimulation on Swallowing Function in Parkinson's Disease: A Narrative Review

Unlike appendicular motor symptoms, such as bradykinesia and rigidity, in Parkinson's disease (PD), which have already been reported to respond well to deep brain stimulation (DBS), there is limited literature on the effects of DBS on swallowing function in patients with PD. The field lacks consensus as there are conflicting reports among existing studies regarding whether swallowing function improves or declines following DBS implantation. This narrative review aims to summarize and analyze the studies published on the effect of DBS on swallowing function in patients with PD. We collated studies published up to February 2020 using a comprehensive electronic database search of PubMed, SCOPUS, EMBASE, and the Cochrane Library. Two reviewers independently assessed the studies using strict inclusion and exclusion criteria. The primary literature search yielded 529 relevant papers. After reading their titles and abstracts and assessing their eligibility based on the full-text, we finally included and reviewed 14 publications. Nine of these studies reported positive effects of DBS on swallowing function and four studies showed no significant positive results. The remaining study showed decreased swallowing function after unilateral subthalamic nucleus-DBS surgery. In conclusion, we found that DBS has the potential to improve swallowing function in patients with PD. However, high-quality evidence is lacking. To clearly elucidate the effect of DBS on swallowing function in patients with PD, high-quality randomized controlled trials should be conducted in the future.