Essential tremor is among the most common movement disorders, affecting nearly 5% of people over the age of 65. Increased prevalence of this disorder is expected in the next 10 years due to the projected disproportionate growth of the older population. Essential tremor is characterized by rhythmic, involuntary movements that often affect the upper limbs but can also affect the head, trunk and voice-related structures. The origin of the tremor is thought to be within the cerebellum and related pathways of the central nervous system (CNS)1, 2. In essential voice tremor (EVT), repetitive movements of voice-related structures produce modulations of the speech signal. Perceptual voice effects include increased instability, hoarseness, and vocal effort3, 4, which negatively impact speech intelligibility and produce substantial psychosocial and physical burden3. Current treatment for EVT is inadequate, with variable effectiveness that may benefit a limited proportion of people4-6. Alcohol reduces tremor in many affected people, but its usefulness for treatment is limited by its intoxicating effects. Octanoic acid (OA) is a food additive that is related to alcohol, and produces a reduction in essential tremor of the limbs with minimal side effects7. Octanoic acid may directly affect the cerebellar pathways where tremor is thought to originate. The goal of the proposed project is to determine the effects of OA on the voice characteristics of people with EVT. This represents an innovative step toward advancing the evidence-based treatment of EVT by being the first study to address the voice-specific effects of OA. In a randomized, placebo controlled cross-over design, 22 participants will each receive the OA and placebo conditions, with both participants and experimenters blinded to condition during data collection and analysis. Outcomes will be determined by comparing changes in pre- to post-assessment measures of acoustic, perceptual and functional aspects of voice between the OA and placebo conditions. Specifically, Aims I and II will determine the effects of OA on the acoustic magnitude of tremor and perceived voice tremor severity.
Aim III will determine the functional impact of OA on quality of life and ability to communicate with family or friends. It is hypothesized that OA, which can affect multiple speech-related muscles, will produce a greater reduction in acoustic, perceptual and functional manifestations of voice tremor than the placebo condition.
Aim I V will determine the individual variability and characteristics of voice tremor, and how these relate to treatment response. The proposed project will significantly advance evidence-based decisions for the clinical treatment of EVT, providing a vital step toward reducing the debilitating effects f this disorder.
The public health relevance of this research is to improve the evidence-based, pharmacological treatment of voice disabilities in the estimated 5 to10 million Americans who have essential voice tremor. This research will use objective, perceptual and functional voice measures to determine the efficacy of octanoic acid for reducing the severity of voice tremor.