Objective: Parkinson’s disease (PD) is a neurodegenerative disorder characterized by the loss of dopaminergic neurons within the basal ganglia and related neural pathways. Reduction in dopamine level leads to several motor and nonmotor symptoms. Levodopa is widely considered to be the gold-standard for treatment of PD motor symptoms, and its efficacy in improving gross motor function is well established. However, previous studies have reported inconsistent findings regarding its effect on voice and motor speech. The present study aimed to determine the short-term effect of levodopa on vocal function in individuals with PD.
Methods: Fifteen individuals diagnosed with PD and 15 age- and sex-matched healthy controls were recruited. All the PD participants were evaluated in the morning under a practically defined OFF-medication state (following 12 hours of levodopa withdrawal) and retested in the defined ON-medication state (60- 90 minutes after intake of their usual morning dose of levodopa). All other medications were continued as normal. Vocal function was assessed using acoustic measures of F0, intensity, standard deviation of F0 and intensity, percent jitter, percent shimmer, harmonics-to-noise ratio, cepstral peak prominence, and maximum phonation time, and auditory-perceptual rating (GRBAS).
Results: Preliminary findings revealed that individuals with PD exhibited poorer voice quality compared with healthy controls. No significant differences were found between the ON and OFF medication states across acoustic and perceptual measures.
Conclusion: The short-term usage of levodopa does not easily affect vocal function in PD, voice assessment may provide a medication state-independent motor biomarker of PD.