Deep brain stimulation and cognitive functions in Parkinson's disease: A three-year controlled study.

There is debate over the cognitive and behavioral effects of deep brain stimulation (DBS) of the subthalamic nucleus (STN) in advanced Parkinson's disease (PD). To evaluate these effects, we performed a prospective, naturalistic controlled, 3-year follow-up study. A total of 65 PD patients were enrolled, of whom 32 underwent STN-DBS (PD-DBS) and 33, even though eligible for this treatment, declined surgery and chose other therapeutic procedures (PD-control). Motor and neuropsychological functions were assessed in all the subjects at baseline (T0) and 36 months (T36). The PD-DBS patients were also evaluated at 1, 6, 12, and 24 months after surgery (T1, T6, T12, and T24). At T1, compared with T0, the PD-DBS patients recorded worse logical executive function task and verbal fluency (FAS) scores, whereas their performance of memory tasks remained stable. At T12, their cognitive profile had returned within the pre-DBS range, thereafter remaining stable until T36. FAS scores at T36 were significantly worse in the PD-DBS compared with the PD-control patients. This is the first long-term naturalistic controlled study of cognitive functions in PD patients submitted to STN-DBS. Our results confirm previous reports of a worsening of verbal fluency after DBS, but show that STN-DBS seems to be relatively safe from a cognitive standpoint, as the short-term worsening of frontal-executive functions was found to be transient.