Levodopa-induced alterations in speech rate in advanced Parkinson's disease.

The effect of speech rate on overall intelligibility in Parkinson's Disease (PD) is still a matter of debate. A comparison of the results of previous studies on speech rate in PD is hampered by methodological differences. In this study, we evaluated the effects of levodopa on speech rate and on its variability in a standardized reading task. Twenty-five patients were studied before and after levodopa administration while reading a standardized text. In accordance with previous studies, no significant improvement of speech rate was found. Rather an increased variability of speech rate in the on-medication state could be demonstrated. It is possible that this increased variability may be the consequence of respiratory deficits due to levodopa-induced dyskinesia or an increase of dysfluencies. However, the effects of defective auditory feedback and disturbed executive function cannot be ruled out.