Influence of chronic bilateral stimulation of the subthalamic nucleus on cognitive function in Parkinson's disease

Background: The clinical efficacy of chronic deep brain stimulation in the treatment of parkinsonian patients with severe levodopa-related motor adver se effects has been repeatedly shown. Bilateral subthalamic nucleus (STN) s timulation has been shown to present an advantage over pallidal stimulation as it induces a higher antiakinetic effect and has positive effects on all parkinsonian symptoms. The morbidity of such surgery is usually considered to be very low. However, few studies have extensively examined the effects of chronic STN stimulation on cognitive function. Objective: The aim of th e present study was to assess the effects of chronic bilateral STN stimulat ion on performance in an extensive battery of neuropsychological tests, thr ee months and one year after surgery. Methods: Nine patients with Parkinson 's disease were selected for STN electrodes implantation. They underwent a neuropsychological evaluation at one month before and at three months after surgery. Six of them were examined again at one year after surgery. Result s: Before surgery, no patient showed cognitive decline. At three months aft er surgery, no modification was observed for most tasks. The information pr ocessing speed tended to improve. There was a significant reduction of the performance in a delayed free recall test and a trend toward a significant reduction of categorial word fluency. At one year after surgery, most task measures did not change. Slight impairment was observed for tasks evaluatin g executive function. Examination of individual results showed that some pa tients (30% at 3 months after surgery) showed an overall cognitive decline. Behavioural changes were also observed in 4 patients with overall cognitiv e decline in one of them. Conclusion: In general, STN deep brain stimulatio n can be considered as a significant contribution to the treatment of sever e Parkinson's disease However, in some patients it can induce overall cogni tive decline or behavioural changes.