Cognitive functioning and psychiatric symptoms in parkinson’s disease

Parkinson’s disease (PD) is characterized by motor symptoms as well as non-motor symptoms, such as (but not limited to) cognitive impairment and psychiatric symptoms. Deep brain stimulation (DBS) is one of the treatment options for patients experiencing medication related motor response fluctuations. The Netherlands SubThalamic And Pallidal Study (NSTAPS), a randomized controlled trial, was initiated to compare the two main DBS targets: the globus pallidus internal segment (GPi) and the subthalamic nucleus (STN). In this thesis, we report that STN DBS showed more improvement in off-drug phase motor symptoms and disability than GPi DBS up to 5 years after surgery. In addition, cognitive, psychiatric, and psychosocial outcomes indicated no clinically significant differences between GPi and STN DBS. Both groups showed subtle cognitive decline after surgery for most tests. Preoperative mild cognitive impairment (PD-MCI) proved not to be a contraindication for DBS per se. These results indicate that the STN is, in general, the preferred target. Future studies should investigate whether rare individual cases with significant cognitive decline after DBS can be predicted before surgery. The International Parkinson and Movement Disorder Society has proposed PD-MCI criteria to aid in uniform assessment. In this thesis, we evaluated the prognostic validity of level I (based on an abbreviated neuropsychological assessment) PD-MCI criteria for development of PD dementia (PDD). We found that level I PD-MCI is related to the hazard of PDD with lower performance on neuropsychological assessment increasing this hazard. More insight into the course of PD-MCI is needed for information sharing with patients and caregivers and for investigating potential treatment interventions