Effects of deep brain stimulation on non‑motor symptoms in Parkinson’s disease: insights from longitudinal studies using consistent evaluation scales

Comprehensive Summary

Motor symptoms in Parkinson’s disease have been studied using various models; however, there have been few generalizable studies of non-motor symptoms. Non-motor symptoms are important to study in Parkinson's disease, as they often present prior to motor symptoms. This study used a systematic review following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, registered in the PROSPERO database. A comprehensive review of the literature published from 2007 to June 2024 using various well-established databases was conducted using the inclusion criteria per the researchers. The purpose of the study was to assess the effects of deep brain stimulation on non-motor symptoms in Parkinson’s Disease, while also including depression, sleep quality, apathy, mental health, and QoL, or the Parkinson’s Disease Questionnaire. In addition, the quality of the studies was assessed using the Risk of Bias in Non-Randomized Studies of Interventions tool to determine whether the inclusion criteria were met. Using all of this information, a standardized mean difference with 95% confidence intervals was calculated for the duration of the deep-brain stimulation (DBS) treatment. After thorough evaluation for the meta-analysis, 57 studies were included, with data from over 3,200 patients, after assessing that the studies had a low risk of bias and met all inclusion criteria. The results showed that DBS had significant improvements in non-motor symptoms as well as depression and sleep quality. The quality of life was also significantly improved; however, no improvement was observed in the communication domain. Through the reduction of Levodopa equivalent daily dose (LEDD), there was no significant correlation between LEDD and improvement in quality of life. The authors state that previous studies contain inconsistencies in outcomes, which limit the interpretability of their findings, which led to the purpose of this study. The findings also show that DBS could be beneficial for patients experiencing depressive symptoms or sleep disturbances.

Outcomes and Implications

Parkinson's is a very prevalent neurodegenerative disorder, affecting almost 10 million people worldwide, and can significantly reduce an individual's quality of life. There have been discoveries in the studies surrounding Parkinson's; however, there have been few advancements in preventing the progression, even though many individuals are affected by it worldwide. Therefore, it is extremely important to prevent the onset of Parkinson's, which begins with the non-motor symptoms. It is also crucial to consider what methods would improve non-motor symptoms, which may ultimately slow the progression of Parkinson's. This study highlights the importance of generalizable findings as well as targeting non-motor symptoms when using Parkinson’s disease models.