Predictors of dementia-free survival after bilateral subthalamic deep brain stimulation for Parkinson's disease

Objective: Bilateral subthalamic nucleus deep brain stimulation (STN DBS) improves motor complications and quality of life (QOL) in patients with Parkinson's disease (PD). However, it does not delay or prevent the occurrence of dementia. The deleterious effects of dementia on QOL and activities of daily living (ADL) underscore the importance of identifying predictors of dementia-free survival in PD patients considered for STN DBS. Aims and Methods: The baseline clinical and neuropsychological data and the occurrence of dementia recorded during the longitudinal follow-up of a cohort of patients with PD with at least 2 years follow-up after bilateral STN DBS, were reviewed. Results: One hundred and sixteen patients operated between 1999 to 2014 satisfied the inclusion criteria. Their mean age was 56.5 (±10) years and the mean duration of PD at surgery was 11.2 (±4.2) years. During the 542 person-years of follow-up, 30 patients developed dementia. The mean dementia-free survival after surgery was 8.7 [95% confidence interval (CI): 7.8-9.6] years. In univariate analysis, the baseline factors of older age, longer disease duration, past history of depression or psychosis, freezing of gait in OFF phase, worse ADL scores in ON phase, lower levodopa response of the Unified Parkinson's Disease Rating Scale (UPDRS) III axial sub-scores, and poor performances in the Addenbrooke's Cognitive Examination and Wisconsin Card Sorting Test (WCST) were associated with a shorter dementia-free survival. Among these, only freezing of gait and poor performance in WCST were independent predictors. Conclusion: Presence of freezing of gait in the drug OFF state and executive dysfunction predict the occurrence of earlier dementia in PD patients who otherwise qualify for bilateral STN DBS.