Identifying Poor Responders to STN DBS in Parkinson Disease: The Role of Rapid Disease Progression in the First Year in Optimal Responders to Levodopa

Background: The factors contributing to a poor response to subthalamic nucleus deep brain stimulation (STN-DBS) in Parkinson's disease (PD) are not yet fully understood. Accordingly, predicting the outcome might be challenging particularly in those who display an optimal response to the Levodopa challenge test. Objective: To determine which factors may contribute to poor outcome of STN-DBS in PD. Methods: We performed a retrospective analysis of consecutive PD patients treated with STN-DBS. Motor and non-motor variables were retrieved before surgery and at 1-year follow-up. Patients were divided into poor and good DBS responders by a cut-off value of less than 20% improvement of UPDRS-II in the OFF-medication ON-stimulation condition at 1 year. Results: Thirty-two (26.2%) of 122 patients were categorised as poor responders. Before surgery, poor responders had significantly less impairment in activity of daily living and less severe motor severity. Response to levodopa challenge test was similar between poor and good responders. Significant worsening of axial symptoms at 1-year follow-up in the off-medication off-stimulation condition was found in poor responders. On multivariable linear regression analysis, only the relative change of activity of daily living by dopaminergic medications before surgery predicted its improvement by neurostimulation at 1-year follow-up. Conclusions: Candidates for surgery with less impairment in activities of daily living may have less favourable outcomes after STN-DBS, despite an optimal response during the pre-operative Levodopa challenge. The worsening of axial symptoms due to disease progression might contribute to poorer outcomes, underscoring the need for better identification of these symptoms before surgery.