Low-frequency Subthalamic Stimulation in Parkinson's Disease: Long-term Outcome and Predictors

•Low frequency stimulation (LFS) can improve axial symptoms, but there are concerns that improvement may be transient.•We identified 85 STN DBS patients who received a trial of LFS and describe their characteristics and outcome predictors.•Most patients (64%) attained a subjective improvement of gait, speech or balance for 2 years.•Axial score before surgery and the y-axis coordinate of the active contact were independent predictors of LFS retention.•LFS may yield an enduring benefit in patients with axial motor symptoms during conventional stimulation.

BackgroundParkinson's disease patients undergoing subthalamic nucleus deep brain stimulation (STN DBS) at standard frequency (>100 Hz) often develop gait impairment, postural instability and speech difficulties. Low frequency stimulation (<100 Hz, LFS) can improve such axial symptoms, but there are concerns that improvement may be transient.ObjectiveTo identify long-term outcome and predictors of low-frequency subthalamic stimulation in Parkinson's disease.MethodsThrough a chart review we identified 85 out of 324 STN DBS patients who received a trial of LFS and describe their characteristics and outcome predictors.ResultsPatients were switched to LFS (<100 Hz) 3.8 ± 3.3 years after surgery. Most patients (64%) attained a subjective improvement of gait, speech or balance for 2.0 ± 1.9 years. Motor scores improved within the first year after the stimulation change and showed a slower progression over time when compared to patients switched back to high frequency stimulation. UPDRS III axial score on medication before surgery and the y-axis coordinate of the active contact were independent predictors of LFS retention.ConclusionsThis report provides evidence that the use of LFS yields an enduring benefit in a considerable percentage of patients who develop axial motor symptoms during conventional stimulation.