The effect of levodopa on vocal function in Parkinson's disease.

Phonatory and articulatory dysfunctions are frequent observations in Parkinson's disease. We have investigated, using acoustic measures, the effects of levodopa treatment on vocal function in 20 patients with Parkinson's disease before and after levodopa. These patients were also compared with a matched control group. The mean age was 63.5 +/- 9.66 years, Hoehn-Yahr stage was 2.38 +/- 0.45, and onset mean age was 56.5 +/- 10.36 years. Paired Wilcoxon tests were performed to compare measurements before and after levodopa. The acoustic analysis using Computerized Speech Lab and MultiDimensional Voice Program software programs (Kay Elemetrics, Lincoln Park, NJ, USA) showed that measurements of fundamental frequency (p < 0.017) were significantly increased after medication, whereas short-term frequency perturbation jitter (p < 0.033), soft phonation index (noise parameter) (p < 0.015 ), and frequency tremor intensity index (p < 0.018) were significantly decreased after medication. The objective measurements of acoustic analysis are useful in evaluating the dopaminergic pharmacologic response in Parkinson's disease. The improvement in fundamental frequency and other vocal parameters may be a result of decrease in laryngeal hypokinesia and rigidity.