Long-term cognitive outcome of bilateral subthalamic deep brain stimulation in Parkinson's disease

The effect of subthalamic deep brain stimulation (STN DBS) on cognition in Parkinson's disease (PD) remains controversial, and it is unclear which factors are related to cognitive decline and dementia after STN DBS, especially over the long term. To this end, we analyzed the cognitive outcome of 103 non-demented patients with PD who were followed-up for at least 12 months after bilateral STN DBS surgery. Preoperatively, the patients were evaluated with the Unified Parkinson's Disease Rating Scale and neuropsychological tests. The rate of global cognitive decline and the incidence of dementia during follow-up for up to 7 years (mean 42.4 ± 24.5 months) were calculated, and preoperative clinical and neuropsychological factors associated with postoperative global cognitive decline or dementia were analyzed. The prevalence of mild cognitive impairment (MCI) and its relation to later cognitive decline or dementia were also evaluated. The annual decline in the mini-mental state examination score was 0.4 ± 1.7 with impaired attention and executive function and a higher levodopa equivalent dose at baseline being the predictors of a faster global cognitive decline after STN DBS. Dementia developed in 13 patients with an incidence rate of 35.7 per 1,000 person-years. Impaired executive function at baseline predicted dementia. At baseline, 63.1 % of the patients had PD-MCI, and these patients were more likely to develop dementia than those without PD-MCI. This study showed that dysfunctions in the frontostriatal circuitry at baseline were associated with a risk of subsequent global cognitive decline and dementia in patients with PD who underwent STN DBS. In addition, preoperative PD-MCI was a risk factor for dementia after STN DBS.