A group of nursing home residents

The gold standard drug used to treat symptoms of Parkinson’s disease, levodopa, does not appear to have an effect on speech early in the disease course, a new study finds.

Distinctive symptoms called hypokinetic dysarthria occur in up to 90% of Parkinson’s patients. They cause what is sometimes described as monotone or emotionless speech patterns. Previous research has been inconclusive about whether levodopa is linked to changes in these patterns, according to the researchers.

In the current study, investigators tested the speech of 60 participants with early-stage disease using an acoustic analysis that is sensitive to subtle changes. The study group included patients whose motor symptoms were alleviated by levodopa and a control peer group of patients whose symptoms did not significantly respond to the drug. Results were also compared to those of participants without Parkinson’s. 

No effect of levodopa was found on seven parameters of voice and speech performance in either of the Parkinson’s groups, reported Jan Rusz, Ph.D., of the Czech Technical University in Prague. This was true during “on” periods, when more of the drug was in their system and “off” periods, when it was not.

The results show that Parkinson’s speech impairment is not easily altered by dopaminergic medication used to treat the disease, Rusz and colleagues wrote.  This suggests that the level of speech impairment, which is known to become more pronounced with time, could be used to help clinicians judge Parkinson’s disease severity without a patient’s medication dose interfering with the diagnosis, they concluded.

The study was published in the online journal npj Parkinson’s Disease.