The distribution and severity of tremor in speech structures of persons with vocal tremor

Abby Leigh Hemmerich

doi:10.17077/etd.d8cjw4fi

<p>Background: Vocal tremor affects over half a million Americans. Tremor can affect structures within the respiratory, laryngeal, velopharyngeal, or oral regions (Critchley, 1949). No study has related the of tremor severity in structures in all four of these regions to the severity of vocal tremor. Purpose: The purpose of this study was (a) to describe the distribution and severity of tremor throughout the vocal tract and (b) to relate that to the severity of the voice tremor. We hypothesized that tremor would be widespread throughout the vocal tract, but most prevalent in the larynx, specifically in the true vocal folds. Additionally, we expected vocal tremor severity to be directly related to the distribution and severity of tremor in structures of the vocal tract. Method: Twenty adults with vocal tremor and two age-matched controls participated in the study. Two judges, experienced in assessment of laryngeal movement disorders, rated the tremor severity in each of 15 structures during sustained /i/, /s/, /h/, and rest breathing, and the severity of the voice tremor during sustained /i/, /s/, and /h/. Results: A novel finding of this study was the identification of distribution and severity of tremor in vocal tract structures associated with mild, moderate, and severe vocal tremor. Participants with mild voice tremor tended to show tremor limited to structures of the larynx, and in some cases, the velopharynx, and on average, had three structures affected (most commonly true vocal folds, supraglottic structures, and hypopharynx). Participants with moderate voice tremor tended to show tremor in the larynx and velopharynx, and on average, had five structures affected (most commonly true vocal folds, supraglottic structures, hypopharynx, vertical laryngeal movement, and some other velar, oral, or respiratory structure). Those with severe voice tremor showed tremor in the larynx, velopharynx, and beyond and on average, had eight structures affected (most commonly true vocal folds, supraglottic structures, hypopharynx, vertical laryngeal movement, anterior and lateral chest movement, velum, and jaw). A second novel finding, obtained through regression analyses, was that tremor severity of the supraglottic structures and vertical laryngeal movement contributed the most to the voice tremor severity during sustained phonation (r=0.77, F=16.17, p<0.0001). A strong positive correlation (r=0.72) was found between the Tremor Index, a composite value of the distribution and severity of structural tremor, and the severity of the voice tremor during sustained phonation. The correlation between the severity of tremor in the true vocal folds and the voice tremor was moderate (r=0.46). Mean voice tremor severity was greater in participants over age 75 (mean=2.25) than those between 66 and 75 years (mean=1.5) and under age 65 (mean=1.8). Mean Tremor Index, was greater in participants over age 65 (mean TI=68) than those under age 65 (mean=41). In this group of 20 participants, laryngeal/hypopharyngeal structures were most frequently (95%) and severely (rated 1.7 out of 3) affected, followed by velopharyngeal (40% occurrence, 1.3 severity), respiratory (40% occurrence, 1.1 severity), and oral (40% occurrence, 1.0 severity) regions during sustained phonation. Tremor was also identified more often and with greater severity in the larynx for sustained /s/ (70% occurrence, 1.7 severity), /h/ (40% occurrence, 1.7 severity), and rest breathing (45% occurrence, 1.6 severity) than other regions. During the voiceless and rest breathing tasks, the greatest tremor severity was noted in the true vocal folds. Conclusion: Evaluation of the distribution and severity of tremor may be useful in guiding behavioral and medical treatment of voice tremor and for providing prognostic information regarding response to laryngeal botulinum toxin injection.</p>

The distribution and severity of tremor in speech structures of persons with vocal tremor

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