Interplay between speech and gait variables in Parkinson's disease patients treated with subthalamic nucleus deep brain stimulation: A long-term instrumental assessment

Objective To evaluate correlations between speech and gait parameters in the long-term and under different medication and subthalamic nucleus deep brain stimulation (STN-DBS) conditions in a cohort of advanced Parkinson’s Disease (PD) patients. Methods This observational study included consecutive PD patients treated with bilateral STN-DBS. Axial symptoms were evaluated using a standardized clinical-instrumental approach. Speech and gait were assessed by perceptual and acoustic analyses and by the instrumented timed up and go test (iTUG) respectively. Disease motor severity was evaluated with the total score and subscores of the UPDRS part III. Different stimulation and drug treatment conditions were assessed: on-stimulation/off-medication, off-stimulation/off-medication, and on-stimulation/on-medication. Results Twenty-five PD patients with a five-year median follow-up after surgery (range 3-7) were included (18 M; disease duration at surgery:10.44 [sd:4.62] years; age at surgery:58.40 [sd:5.73] years). In the offstimulation/ off-medication and on-stimulation/on-medication conditions, patients who spoke louder had also the greater acceleration of the trunk during gait whereas, in the on-stimulation/on-medication condition only, patients with the poorer voice quality were also the worse to perform sit to stand and gait phases of the iTUG. On the contrary, patients with the higher speech rate performed well the turning and walking phases of the iTUG. Conclusions This study underlines the presence of different correlations between treatment effects of speech and gait parameters in PD patients treated with bilateral STN-DBS. This may allow us to better understand the common pathophysiological basis of these alterations and to develop a more specific and tailored rehabilitation approach for axial signs after surgery.