Background: Essential tremor (ET) occurs in approximately 4% of the population, and 25% of patients with ET have vocal tract involvement referred to as essential tremor of voice (ETV). Treatment of vocal tremor has a variable success rate most likely as a result of inaccurate identification of the affected area(s). A vocal tremor assessment system was developed to standardize the evaluation and scaling of vocal tremor. Applying this system clinically can help determine who will benefit most from botulinum toxin injection treatment. The Vocal Tremor Scoring System (VTSS) can also be used as a tool to determine treatment efficiency for all treatment modalities of ETV, including surgery, medications, and implantable devices.
Study design: The authors studied instrument development and validation.
Methods: A clinical consensus conference was conducted to develop an assessment tool for standardized rating of vocal tremor location and severity. The assessment tool was then tested for reliability using video-perceptual analysis. Once validated, the assessment tool was applied to 10 examinations of patients with vocal tremor who had been treated with botulinum toxin A (BtxA) injections of the thyroarytenoid muscle(s) to determine the ability of the scoring instrument to predict treatment outcome.
Results: : The VTSS is based on severity scores for different anatomic sites within the vocal tract. The assessment areas of the VTSS are the palate, base of tongue, pharyngeal walls, larynx, supraglottis, and true vocal cords. Statistical analysis of the video-perceptual analysis results showed that the anatomic sites with the best interrater agreement were the true vocal folds, palate, base of tongue, and supraglottis. Overall, the VTSS demonstrated a level of interrater reliability of at least 0.914 at all sites. Intrarater reliability was excellent. The consensus group also analyzed 10 standardized examinations and the scores from both reviewer groups were then compared and found to have a reliability of at least 0.6 at each site. Pretreatment VTSS scores of 10 patients with ETV who underwent BtxA therapy were then compared with treatment response. The VTSS predicted the favorable treatment outcome 100% of the time when the score given to the true vocal folds was equal or greater to the mean of the scores given to the other sites.
Conclusion: The VTSS represents the first standardized system for rating anatomic site(s) and severity of vocal tremor. This tool will allow improved communication between otolaryngologists, facilitate research in vocal tremor treatments, and establish a descriptive system for assessing vocal tremor. Using this assessment tool for patients with vocal tremor increases optimal patient selection and success rate for intralaryngeal botulinum toxin treatment.