A Critical Analysis of the Treatment Effect in Deep Brain Stimulation Surgery for Parkinson's Disease: A Systematic Review and Focus on Patient-centered Outcomes

Introduction: Studies concerned with outcome measures for both ablative and deep brain stimulation (DBS) procedures for individuals with intractable or poorly controlled Parkinson’s disease (PD) often present data comparing average Unified Parkinson’s Disease Rating Scale (UPDRS) scores of an experimental group before and after intervention. Few investigations identify individual outcomes and response rates of treatment for these unique procedures.

Methods: We analyzed the English language peer-reviewed literature concerning treatment outcomes and improvement in individual patient motor/non-motor symptoms following unilateral or bilateral subthalamic nucleus (STN) or globus pallidus interna (GPi) DBS surgery in PD. A standardized, pre-piloted form was used to extract data for the assessment of study quality and evidence synthesis.

Results: A comparison between average pre- and post-surgical UPDRS III scores (unilateral/bilateral, STN, GPi) demonstrates an improvement between 7 and 78%, with an average group rate improvement of approximately 50%. Similar analysis of UPDRS Part IV Dyskinesia score demonstrates a group improvement average ranging from 10 to 93%. The percentage of patients with DBS for PD targeting bilateral STN showed a favorable treatment response that ranges from 83% to 92%. Over twice the number of individual patients demonstrate improvement in 6-month motor function scores following all-target DBS for PD versus best medical therapy, and nearly 89% of all individual patients undergoing DBS for PD reported at least a 5-point improvement in their UPDRS III score. Similar responses for individual and group rates of improvement in non-motor symptoms were found.

Conclusion : Individual response rates for DBS surgery for PD are greatly under-reported. The definition of “good outcome” in DBS for PD has not been reported in the published literature; consequently, it is difficult to identify a “gold standard’ to measure individual treatment responses in DBS surgery using available evaluation tools. Patient-centered outcomes are meaningful and assist in determining the effectiveness of a treatment.