The latest evidence on target selection in deep brain stimulation for Parkinson's disease

Deep brain stimulation (DBS) is one of the most promising neuromodulatory techniques to gain momentum over the last 20years, with significant evidence showing the benefit of DBS for Parkinson's disease (PD). However, many questions still exist pertaining to the optimal placement of stimulation contacts. This paper aims to review the latest and most relevant studies evaluating subthalamic nucleus (STN) and globus pallidus interna (GPi) stimulation. Additionally, it aims to shine a light on several of the lesser-known targets with mounting evidence of efficacy. Referenced literature for the main body of the article was gathered from Medline and PubMed databases. Results were limited to "full text", "English language" and publications from 1999 onwards. Case reports were excluded. The current evidence irrefutably demonstrates the benefits of both STN and GPi DBS on Unified Parkinson's Disease Rating Scale (UPDRS) III motor scores, with very similar outcomes seen after 1-2years. Currently, it appears the greatest differences lie in the associated adverse effects. STN DBS was associated with a greater reduction in dopamine replacement therapy, but also appeared to have more negative effects on speech and mood. Meanwhile, in regards to alternative targets, the pedunculopontine nucleus has shown promising improvement in axial symptoms, while the ventral intermediate nucleus has demonstrated significant efficacy at suppressing tremor, and the caudal zona incerta may be superior to the STN and GPi in improving UPDRS-III scores. Due to the complexity of Parkinson's disease, an individual disease profile must be determined in a patient-by-patient fashion such that appropriate targets can be selected accordingly.