Pallidal Stimulation in Parkinson's Disease Does Not Induce Apathy

Background: Whereas apathy is known as a common consequence of subthalamic nucleus deep brain stimulation in Parkinson's disease, few studies have investigated the psychiatric consequences of internal globus pallidus deep brain stimulation. Method: Twenty consecutive parkinsonian patients who underwent bilateral pallidal stimulation were assessed 3 months prior to surgery (M-3) and at both 3 (M3) and 6 months (M6) after surgery, using psychiatric, neuropsychological, and motor scales. Apathy, mood state, and anxiety state were scored using the Apathy Evaluation Scale, the Montgomery-Asberg Depression Rating Scale, and the anxiety scale from the Association for Methodology and Documentation in Psychiatry, respectively. Results: The mean apathy score remained stable between the preoperative M-3 assessment (37.2 +/- 6.2) and both the postoperative M3 (36.9 +/- 7.5) and M6 (37.2 +/- 5.0) assessments. The mean depression score did not differ between the M-3 assessment and M3 and M6 assessments. There was no difference between the preoperative mean anxiety score and both the postoperative M3 and M6 scores. The mean score for the Mattis Dementia Rating Scale remained stable at each study visit. Conclusions: The main result of this study is the absence of deterioration in psychiatric and cognitive scores 3 months and 6 months after pallidal stimulation.