Impact of levodopa treatment in the voice pattern of Parkinson's disease patients: a systematic review and meta-analysis

Purpose: Investigate the association between levodopa therapy and vocal characteristics in Parkinson's disease patients. Search strategy: Studies published at MEDLINE, LILACS, and SciELO, from 1960 to December 2016. A systematic review and meta-analysis was performed using the following keywords: Parkinson's disease; levodopa; L-dopa; voice; speech disorders; dysphonia; dysarthria. After analyzing titles and abstracts, two independent reviewers selected all clinical trials that met the eligibility criteria and selected the articles and the data recorded in a previously standardized table. Selection criteria: Trials published in English between 1960 and December 2016 individuals with clinical diagnosis of Parkinson's disease; use of levodopa therapy in stable doses; acoustic analysis combined or not with auditory-perceptual analysis to evaluate the vocal parameters under investigation. Data analysis: The following vocal parameters were analyzed: fundamental frequency (F0), jitter, and vocal intensity. Standardized mean differences (SMD) were calculated using the Comprehensive Meta-analysis V2 software. Results: Nine articles met the eligibility criteria and were selected, with a total of 119 individuals. From these, six articles with 83 individuals were included in the meta-analysis. During the levodopa therapy "on" state, modifications in F0 (SMD=0.39; 95% CI - 0.21-0.57) and jitter (SMD=0.23; 95% CI - 0.02-0.45) were observed. Vocal intensity was not affected (SMD=0.09; 95% CI - 0.22-0.39) by levodopa ingestion. Data of the included studies were controversial in the auditory-perceptual analysis of voice. Conclusion: Levodopa therapy modifies F0 and jitter. No changes in vocal intensity were observed in either the "on" or "off" states of levodopa therapy.