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.
Highlights
Hypokinetic dysarthria is a common symptom of Parkinson’s disease (PD), manifesting in up to 90% of patients during the disease course[1]
We revealed increased VOT in all PD subgroups (p > 0.05) except for PD responders in ON state (p = 0.49), decreased Int SD in all PD subgroups (p > 0.05), and decreased F0 SD in all PD subgroups (p > 0.01)
No effect of levodopa was found on voice and speech performances in any PD subgroup, despite the PD responders subgroup manifested obvious improvement in motor function after levodopa intake
Summary
Hypokinetic dysarthria is a common symptom of Parkinson’s disease (PD), manifesting in up to 90% of patients during the disease course[1]. Improvements in voice quality[13,15,17], loudness[11,19], speaking rate[14], speech dysfluency[12], respiration[5,8] and overall speech intelligibility[8] have been reported, while other studies found no significant changes in voice quality[5,6,9], loudness[5,10,18], speaking rate[7,9,18], vowel articulation[11,18], consonant articulation[20], monopitch[5,9,18] or respiration[9,16]. This inconsistency may be caused, at least partially, by different disease duration and motor severity of investigated PD patients. Evidence about the acute effect of levodopa on speech in early PD patients is pivotal to provide more insights into the pathophysiology of dysarthria in PD. One might hardly expect that PD patients with minimal change in motor function will manifest significant improvement in their speech performance
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