Association between ventral subthalamic deep brain stimulation and apathy in Parkinson’s disease

Abstract

Introduction: Apathy, i.e. loss of motivation and energy, is relatively prevalent in patients with Parkinson's disorder (PD) treated with subthalamic deep brain stimulation (STN DBS). Longitudinal studies show no consistent correlation between postoperative apathy and reduction of dopaminergic medication. There are strong indications that DBS-related apathy may develop by stimulating non-motor limbic circuits that have a role in motivation. Patients and methods: We investigated apathy scores in 15 PD patients before and after 6 months of STN DBS and correlated these scores with the neuroanatomical location and white matter connections of the active DBS contact, using pre-operative structural and diffusion-weighted (DWI) MRI scans, and post-operative CT-scans. We also tested in three patients whether apathy after STN DBS may be reversed by switching the activated contact on the DBS-electrode from a ventral to a more dorsal region. Apathy was defined as a minimum score of 14 on the Starkstein Apathy Scale (SAS). Results: Of the 15 included patients, 6 patients scored above the cut-off score for apathy after STN DBS. In these patients, we failed to detect a specific association between apathy and more ventrally located stimulation or stimulation in proximity to the medial forebrain bundle. However, in the three apathetic patients that underwent a switch from ventral to dorsal stimulation, apathy resolved immediately. Conclusion: These results confirm that apathy is a prevalent side-effect of STN DBS in PD that might be reversed by dorsal instead of ventral stimulation. However, future studies should investigate DBS-related apathy in larger PD samples using neuro-imaging to determine which pathways are involved. Keywords: Deep brain stimulation, subthalamic, apathy, Parkinson's disease