Transient effects of 80 Hz stimulation on gait in STN DBS treated PD patients: a 15 months follow-up study.

Background: Subthalamic nucleus deep brain stimulation (STN DBS) is an effective therapeutic option for advanced Parkinson's disease (PD). Nevertheless, some patients develop gait disturbances despite a persistent improvement of PD segmental symptoms. Recent studies reported that stimulation of STN with low frequencies produced a positive effect on gait disorders and freezing episodes. Objective: To evaluate the effects of 80 Hz stimulation frequency on gait in PD patients undergoing STN DBS and to determine whether such effects are maintained over time. Methods: We evaluated 11 STN DBS treated PD patients who had developed gait impairment several years after surgery. Gait was assessed by means of the Stand-Walk-Sit (SWS) test. Motor symptoms and activities of daily living were evaluated through the Unified PD Rating Scale (UPDRS). The stimulation frequency was switched from 130 Hz to 80 Hz, adapting the voltage to maintain the same total delivered energy. Patients were assessed at baseline and 3 hours after switching the stimulation frequency to 80 Hz. Follow-up evaluations were carried out after 1, 5, and 15 months. The clinical global improvement scale was rated at every follow-up visit. Results: A significant improvement of gait (SWS test) was evident immediately after switching the stimulation frequency to 80 Hz, with no deterioration of PD segmental symptoms. However, gait improvement was no longer detectable by the SWS test at follow-up evaluations 1, 5, and 15 months later. Three patients were switched back to 130 Hz because of unsatisfactory control of motor symptoms. Of the eight patients maintained at 80 Hz up to 15 months, five showed a global improvement and three showed no change. Conclusions: Stimulation frequency at 80 Hz has an immediate positive effect on gait in STN DBS treated patients; however, the objective gait improvement is not maintained over time, limiting the use of this frequency modulation strategy in the clinical setting.