Short and Long-Term Cognitive Effects of Subthalamic Deep Brain Stimulation in Parkinson’s Disease and Identification of Relevant Factors

Background: Subthalamic nucleus deep brain stimulation (STN-DBS) successfully controls the motor symptoms of Parkinson’s disease (PD) but has associated cognitive side-effects. Objective: Establish the short- and long-term cognitive effects of STN-DBS in PD. Methods: Both the short-term and long-term effects of STN-DBS on cognition were examined through evaluation of the controlled studies that compared patients with STN-DBS to unoperated PD patients, thus controlling for illness progression. We also reviewed the literature to identify the factors that influence cognitive outcome of STN-DBS in PD. Results: The meta-analysis of the short-term cognitive effects of STN-DBS revealed moderate effect sizes for semantic and phonemic verbal fluency and small effect sizes for psychomotor speed and language, indicating greater decline in the STN-DBS operated than the unoperated patients in these cognitive domains. The longer-term STN-DBS results from controlled studies indicated rates of cognitive decline/dementia up to 32%; which are no different from the rates from the natural progression of PD. Greater executive dysfunction and poorer memory pre-operatively, older age, higher pre-operative doses of levodopa, and greater axial involvement are some of the factors associated with worse cognition after STN-DBS in PD. Conclusion: This evidence can be used to inform patients and their families about the short-term and long-term risks of cognitive decline following STN-DBS surgery and aid the team in selection of suitable candidates for surgery.