Subthalamic nucleus (STN) deep brain stimulation (DBS) has become an effective method for treating motor symptoms in advanced Parkinson's disease (PD), but data on its neuropsychological effects are conflicting.OBJECTIVE
To assess in a controlled fashion the cognitive and behavioral effects of bilateral STN DBS in patients with PD.DESIGN AND INTERVENTION
This prospective study in patients with idiopathic PD was conducted across several Dutch hospitals, and comprised a surgery group (n = 99; mean age 57.9 ± 8.1 years; mean disease duration 13.7 ± 6.1 years) and a control group (n = 36; mean age 63.0 ± 9.1 years; mean disease duration 10.4 ± 4.6 years). Bilateral stereotactic surgery for the implantation of DBS electrodes into the STN was performed within 3 months after baseline. Follow-up assessments were conducted 6 months after surgery for the STN DBS group and 6 months after baseline for the control group, and included neuropsychological tests of language, memory, visuospatial function, mental speed and executive function. Depression and quality of life were also evaluated. Effect sizes were estimated using Cohen's d, with a negative value indicating a worsening for the STN DBS group.OUTCOME MEASURES
The outcomes were the changes from baseline in neuropsychological measures.RESULTS
Cognitive testing at 6 months revealed a significant decline from baseline in all verbal fluency tasks in the STN DBS group (d = −0.3 to −0.6; P≤0.01). This group also showed declines in the speed of naming colors in the Stroop Color Word Test (d = −0.6; P<0.001), in selective attention (data not provided), and in delayed verbal recall in the Rey Auditory-Verbal Learning Test (AVLT; d = −0.5, P = 0.02). Patients in the STN DBS group showed a decrease in tension as assessed using the Profile of Mood States questionnaire (d = 0.4; P = 0.02), but they also reported a decrease in positive affect on the Positive and Negative Affect Scale (d = −0.6; P = 0.01). Nevertheless, as measured using the PD Quality of Life questionnaire, quality of life in the STN DBS group was significantly improved (d = 0.7; P<0.001). Family members reported that operated patients had increased irritability or lability on the Neuropsychiatric Inventory (d = −0.7; P = 0.01). After adjustment for pre surgery anticholinergic drug use (899.3 vs 629.6 levodopa-equivalent units for the STN DBS group vs the control group) and for surgical complications that were followed by global cognitive decline (observed in four patients), all the observed differences between the groups remained statistically significant except the change score on the AVLT delayed recall. Psychiatric events in the STN DBS group comprised depression (n = 3), transient psychosis (n = 2, with one suicide attempt), voyeurism (n = 1), pathological gambling (n = 1), aggressive behavior (n = 1) and mania (n = 1); in the control group, one patient developed depression.CONCLUSION
STN DBS in patients with PD had a negative effect on executive functioning and was associated with psychiatric complications; however, the overall quality of life improved.