Neuropsychological outcome after deep brain stimulation for Parkinson disease.

OBJECTIVE: To assess the neuropsychological outcome 12 months after bilateral deep brain stimulation (DBS) of the globus pallidus pars interna (GPi) or subthalamic nucleus (STN) for advanced Parkinson disease. METHODS: We randomly assigned patients to receive either GPi DBS or STN DBS. Standardized neuropsychological tests were performed at baseline and after 12 months. Patients and study assessors were masked to treatment allocation. RESULTS: Univariate analysis of change scores indicated group differences on Stroop word reading and Stroop color naming (confidence interval [CI] 1.9-10.0 and 2.1-8.8), on Trail Making Test B (CI 0.5-10.3), and on Wechsler Adult Intelligence Scale similarities (CI -0.01 to 1.5), with STN DBS showing greater negative change than GPi DBS. No differences were found between GPi DBS and STN DBS on the other neuropsychological tests. Older age and better semantic fluency at baseline predicted cognitive decline after DBS. CONCLUSIONS: We found no clinically significant differences in neuropsychological outcome between GPi DBS and STN DBS. No satisfactory explanation is available for the predictive value of baseline semantic fluency for cognitive decline. CLASSIFICATION OF EVIDENCE: This study provides Class I evidence that there is no large difference in neuropsychological outcome between GPi DBS and STN DBS after 12 months. The study lacks the precision to exclude a moderate difference in outcomes.