Short-term effect of dopaminergic medication on speech in early-stage Parkinson's disease

Abstract

The effect of dopaminergic medication on speech has rarely been examined in early-stage Parkinson's disease (PD) and the respective literature is inconclusive and limited by inappropriate design with lack of PD control group. The study aims to examine the short-term effect of dopaminergic medication on speech in PD using patients with good motor responsiveness to levodopa challenge compared to a control group of PD patients with poor motor responsiveness. A total of 60 early-stage PD patients were investigated before (OFF) and after (ON) acute levodopa challenge and compared to 30 age-matched healthy controls. PD patients were categorised into two clinical subgroups (PD responders vs. PD nonresponders) according to the comparison of their motor performance based on movement disorder society-unified Parkinson's disease rating scale, part III. Seven distinctive parameters of hypokinetic dysarthria were examined using quantitative acoustic analysis. We observed increased monopitch (p > 0.01), aggravated monoloudness (p > 0.05) and longer duration of stop consonants (p > 0.05) in PD compared to healthy controls, confirming the presence of hypokinetic dysarthria in early PD. No speech alterations from OFF to ON state were revealed in any of the two PD groups and speech dimensions investigated including monopitch, monoloudness, imprecise consonants, harsh voice, slow sequential motion rates, articulation rate, or inappropriate silences, although a subgroup of PD responders manifested obvious improvement in motor function after levodopa intake (p > 0.001). Since the short-term usage of levodopa does not easily affect voice and speech performance in PD, speech assessment may provide a medication state-independent motor biomarker of PD.

Fig. 1. Results of acoustic analyses across PD responders and PD nonresponders subgroups in both OFF and ON condition.

Symbols represent mean values and error bars represent SD values. The performances of healthy controls are depicted by a shaded area. Comparing subgroups of PD responders and PD nonresponders, no significant differences for effect of GROUP, MEDICATION or GROUP × MEDICATION were found. Statistically significant differences between PD subgroups and healthy controls: *p < 0.05; **p < 0.01; ***p < 0.001. PD Parkinson’s disease, HNR harmonics-to-noise ratio, VOT voice onset time, DDK rate diadochokinetic rate, NSR net speech rate, Int SD standard deviation of speech intensity, F0 SD standard deviation of the fundamental frequency, DPI duration of pause intervals.