Cognitive predictors of cognitive change following bilateral subthalamic nucleus deep brain stimulation in Parkinson’s disease

The beneficial effects of deep brain stimulation (DBS) of the subthalamic nucleus (STN) for the motor symptoms in advanced Parkinson’s disease (PD) are well established. Early in PD, mild cognitive impairment is present in a proportion of patients. Hence, it can also be present in PD patients considered for DBS. The potential impact of even a modest decline post-surgically is a concern because it could result in impaired cognitive function. Therefore, attempts to determine which pre-operative cognitive measures predict post-operative cognitive change warrant further attention. We report our findings in a cohort of 30 routinely operated non-demented patients who underwent detailed neuropsychological assessments on average 7.1 months before and 9.4 months after STN DBS. We report the individual and group differences pre- and post-DBS. Stepwise regression analysis was used to analyse the best cognitive predictors of post-operative cognitive changes. We describe our data in relation to published normative data. Post-STN DBS, the immediate story recall component of verbal memory was the most affected cognitive function showing a significant decline in its group mean with a large effect size. The best predictors for this change were pre-surgical list learning and Full Scale Intelligence Quotient. These results suggest that non-demented patients, with even mild impairments in both general intellectual functions and list learning, may be at greater risk of decline in other aspects of verbal memory after STN DBS. Pre-existing mild executive dysfunction was not influenced post-operatively. These findings may help selection and consent for STN DBS.