Effects of Central Dopaminergic Stimulation by Apomorphine on Vocal Parameters in Parkinson's Disease

In Parkinsonian patients, abnormal vocal qualities are frequently observed. Previous research has suggested that laryngeal muscle rigidity may be responsible for the vocal symptoms. While rigidity is one of the most responsive symptoms to dopaminergic therapy, studies investigating speech changes following dopaminergic therapy are very limited. In this study, phonatory responses to dopaminergic stimulation were examined using a double-blind, placebo-controlled design. Ten Parkinsonian patients with speech impairment served as subjects. They were given placebo or apomorphine during two consecutive visits. Data were collected at baseline and 30 minutes post-injection during each visit. Subjects produced maximally sustained, and comfortably phonated vowels. Instrumental analysis was used to assess changes in phonatory function. Nonspeech motor functions were assessed using the Unified Parkinson's Disease Rating Scale. While nonspeech motor functions improved significantly following the dopaminergic stimulation, the vocal parameters showed no changes. This suggests that dopaminedepletion may not be responsible for the laryngeal dysfunction.