Cognitive effects of subthalamic nucleus stimulation in Parkinson's disease: a controlled study.

BACKGROUND Subthalamic nucleus deep brain stimulation (STN-DBS) improves motor function in selected patients with Parkinson's disease (PD) but can be associated with variable changes in cognitive functions. METHODS We studied 21 patients selected for STN-DBS and compared 6-month clinical and neuropsychological outcomes between those who underwent surgery (n = 9) and those who voluntarily refused it (n = 12). RESULTS Motor and quality of life outcomes were markedly superior in the STN-DBS group versus controls. A wide neuropsychological battery was administered, and the whole sample showed a statistically significant worsening in phonemic verbal fluency, time to perform the Trail Making Test part B, Digit Symbol score of WAIS-III and color-naming score of the Stroop Test. In comparison to controls, a trend to a slightly worse deterioration in phonemic verbal fluency was observed in the STN-DBS patients and was significantly correlated with reductions in the L-dopa-equivalent daily dose (r = 0.850, p = 0.007). CONCLUSION Our study confirms the safety of STN-DBS from a cognitive standpoint; a reduction in verbal fluency at 6 months after surgery can also be related to PD progression and medication reduction.