Evaluating the Efficacy of Voice Therapy for Neurogenic Voice Disorders

Neurogenic voice disorders negatively impact communication-related quality of life for millions of patients. Yet current options for medical treatment including pharmacological and surgical interventions do not consistently improve voice and can have adverse effects. Although some patients with neurogenic voice disorders receive behavioral treatment like voice therapy, systematic treatment research evaluating the efficacy of behavioral treatment is limited. For example, in speakers with voice disorders related to essential tremor, the most common movement disorder in the world, only five studies have evaluated the effects of behavioral interventions. Of these studies, two were case studies (N=1, N=2), two were single-case experiments (N=1, N=3), and one was a prospective group study comparing control and experimental conditions (N=10). These studies evaluated a variety of treatment ingredients using various functional, perceptual, and acoustical treatment outcomes. However, some treatment ingredients and outcome measures were not specific to the underlying voice impairments in essential tremor. In neurogenic voice disorders with other etiologies like dystonia, more studies with larger sample sizes have been conducted. However, only eight studies have been published: two were case studies (N=1, N=1), one was a single-case experiment (N=1), one was a prospective group study comparing pre- and post-treatment phases (N=36), one was a retrospective group study comparing control and experimental conditions (N=37), one was a randomized cross-over study (N=9), one was a non-randomized controlled trial (N=17), and one was a randomized controlled trial (N=31). These studies also evaluated various treatment ingredients using functional, perceptual, and acoustical outcomes, as well as aerodynamic and acoustic outcomes. But again, some treatment ingredients and outcome measures were not specific to the underlying voice impairments related to dystonia. Finally, although a considerably higher number of treatment studies with greater sample sizes have been conducted with speakers who have voice disorders related to Parkinson's disease, the most widely studied treatment ingredients have limitations. For example, Lee Silverman Voice Therapy requires high-intensity, high-frequency treatment provided by speech-language pathologists with specialized training, and expiratory muscle strength training is also high-frequency, high-intensity treatment that requires specific equipment and physiologic capabilities. Thus, there is an important need for systematic treatment research in speakers with neurogenic voice disorders using treatment ingredients and outcome measures that are specific to patients' neurophysiologic impairments and functional limitations.