Re‐Emergent Vocal Tremor in a Patient with Parkinson's Disease

Tremor is a cardinal symptom of Parkinson's disease (PD) that occurs throughout the disease course in approximately 80% of patients. Re-emergent tremor is characterized as a resting tremor that recurs after a variable delay during postural maintenance.1 It is usually observed in the extremities and rarely in speech-related organs, such as the tongue and jaw.2, 3 To our knowledge, no studies have reported on re-emergent tremors involving voice. A 71-year-old woman developed tremors in her extremities and was diagnosed with tremor-predominant PD. Levodopa was effective for rigidity and akinesia, but had no effect on tremor. On examination, 9 years post diagnosis, rigidity and mild bradykinesia in the arms and legs were observed, but she could walk unassisted. Metaiodobenzylguanidine myocardial scintigraphy revealed a decreased heart-to-mediastinum ratio (early phase/delayed phase, 1.25/1.08). We also observed left dominant resting and re-emergent tremors in the arms of the patient (Video 1). For auditory-perceptual analysis of voice, the grade of dysphonia was used (roughness, breathiness, asthenia, and strain [GRBAS]), which was assessed using four rankings. GRBAS-scale was G1 R1 B0 A0 S1 (median of three speech pathologists). Maximum phonation time was 17.7 seconds. She showed normal speech function with preserved voice volume, and vocal tremor was not observed during conversation or reading. Interestingly, the patient was unaware of any voice problems and could speak for approximately 2 hours without any concern. However, when the patient was asked to vocalize sustained vowels, her voice gradually became tremulous on auditory-perceptual examination. The acoustic analysis (Multi Speech, PNTAX Medical, NJ) showed that the amplitude remained low for approximately 2 seconds after the onset of vocalization (minimum range: ~2 dB), but gradually increased, thereafter, reaching a maximum range of approximately 7 dB (Fig. 1). Evaluation of the pharynx and larynx using a flexible video endoscopy system (VISERA-ELITE OTV-S190 ENF typeV2; OLYMPUS, Tokyo, Japan) revealed that during sustained vowels /i:/, the tremor originated at the root of the tongue. Although the tremor spread was nonuniform, it extended throughout the larynx, from the lateral wall of the hypopharynx to the arytenoid region and further to the false and vocal cords. The tremor frequency detected using the flexible video endoscopy system was approximately 4 Hz, consistent with the frequency observed via acoustic analysis. The recording was conducted only in the medication-on state, and no comparison was made between the medication-on and -off states. This case highlights the importance of assessing sustained phonation in differentiating vocal tremor disorders as vocal tremors may disappear during normal conversation, which was observed in our patient. This phenomenon makes conditions, such as essential vocal tremors and spasmodic dysphonia, less likely.4 This case is particularly valuable as it highlights a specific symptom of PD because it first reported a re-emergent tremor, which affected the voice, captured both acoustically and laryngoscopically. We propose naming this tremor a “re-emergent vocal tremor” (Video 2). The pathophysiology of this condition remains unclear, but it appears to involve the basal ganglia and cerebello-thalamo-cortical circuit, similar to resting tremors.5 This case report lacked electromyographic evaluation, which limits our ability to precisely identify whether the tremor originates from the tongue or the laryngeal muscles. Incorporating electromyography alongside flexible video endoscopy in future studies will be crucial to delineating the specific muscles involved. Such investigations may provide deeper insights into the pathophysiology of re-emergent vocal tremors and their relationship with other PD-associated tremors. (1) Research project: A. Conception, B. Organization, C. Execution; (2) Statistical analysis: A. Design, B. Execution, C. Review and critique; (3) Manuscript preparation: A. Writing of the First Draft, B. Review and critique. T.T.: 1A, 1B, 1C, 2B, 3A, 3B Y.T.: 1A, 1B, 2A, 2B, 2C, 3B K.K.: 1A, 1B, 1C; R.H.: 1A, 1B, 1C, 2C, 3B Y.I.: 1A, 1B, 1C, 2C N.N.: 1A, 2C T.T.: 1A, 2C, 3B M.S.: 1A, 2C M.K.: 1A, 2C, 3B I.A.: 1A, 1B, 1C, 2C, 3B Ethical Compliance Statement: The authors obtained approval from the NHO Higashinagoya National Hospital ethics committee. Written consent was obtained from the patient to publish the case report and video. We confirm that we have read the journal's position on issues related to ethical publication and affirm that the conduct of this work is consistent with those guidelines. Funding Sources and Conflicts of Interest: This work was supported by Ministry of Health, Labour and Welfare, Health, Labour, and Welfare Science Research Grants with grant number JPMH23FC1008. The authors declare that there are no conflicts of interest relevant to this work. Financial Disclosures for the Previous 12 Months: The authors declare that there are no additional disclosures to report. The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.