Effect of deep brain stimulation on patients with Parkinson's disease with mild cognitive impairment

Cognitive deficits are prevalent in Parkinson's disease (PD), often progressing to PD dementia (PDD). Deep brain stimulation (DBS) is an established treatment for PD motor symptoms, but its effects on patients with mild cognitive impairment (PD-MCI) remain unclear. While MCI is a relative contraindication for DBS, evidence regarding its impact on post-operative outcomes is limited. This systematic review aims to assess the post-operative cognitive and functional outcomes of DBS in patients with PD and MCI.

A comprehensive literature search was conducted across PubMed, Scopus, PsycInfo and Embase following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Studies published by February 2024 that evaluated DBS outcomes in patients with PD-MCI were included. Data extraction focused on cognitive assessments, quality of life and clinical outcomes.

Eight studies comprising 984 patients met inclusion criteria. Six studies identified PD-MCI as a potential risk factor for developing PDD post-DBS, though only two demonstrated statistically significant cognitive decline post-DBS. Five studies found no differences in outcomes post-DBS, between patients with PD-MCI and PD without cognitive impairment.

DBS does not appear to significantly worsen cognitive decline in patients with PD-MCI beyond the expected disease progression. However, certain cognitive domains, particularly visuospatial impairments, may increase the risk of adverse outcomes. Standardised cognitive screening is necessary for optimal patient selection for future research to refine clinical guidelines for DBS eligibility.