Mild cognitive impairment is not predictive of dementia up to 15 years after subthalamic deep brain stimulation in Parkinson's disease

Background Cognitive impairment and dementia are common findings in patients with Parkinson's disease (PD). However, the long-term effects of subthalamic deep brain stimulation (STN-DBS) on cognition remain unclear. Objective We report short- and long-term effects of STN-DBS on cognition in PD. Methods We analyzed neuropsychological data before STN-DBS surgery, 3-month post-surgery, 1-year post-surgery and in a long-term follow-up (8-15 years post-surgery) to examine the effects of STN-DBS on cognition. Results 81 patients with a mean disease duration of 13.0 years were examined before surgery. 50.6% were identified with mild cognitive impairment (MCI), having a mean disease duration of 14.2 years. Pre-surgical PD-MCI was not associated with clinically diagnosed dementia (PD-D) before death or before long-term follow-up (OR 0.8, 95% CI 0.3-2.2, p = 0.714), but disease duration at the time of surgery was associated with development of PD-D (OR 1.2, 95% CI 1.1-1.3, p = 0.005). Verbal fluency declined significantly 3 months after surgery, while other domains remained unaffected. In neuropsychological testing at long-term follow-up (N = 29), global cognitive impairment or dementia was found in 19 patients. The presence of depressive symptoms before surgery was associated to PD-D at long-term follow-up. Death before long-term follow-up was more common in patients with pre-surgical MCI than in patients with normal cognition. Conclusions Influence on cognition was described in a short- and long-term follow-up study up to 15 years after STN-DBS surgery in PD. Disease duration, but not pre-surgical MCI was associated with development of dementia. Impaired verbal fluency was observed both in a short- and long-term follow-up.