Evaluating the efficacy of voice therapy for functional, organic and neurological voice disorders

Evaluating the evidence of treatment efficacy allows clinicians to select the delivery of the intervention that is most likely to improve the patient outcomes for a given clinical condition. Collation and critical appraisal of this evidence highlights areas of strength but also areas of research weakness. This paper provides a collation and summary appraisal of the evidence of treatment efficacy for voice therapy for a number of voice disorders that are routinely treated by speech pathologists/therapists. Table 1 lists a hierarchy that is commonly used and is highly applicable to behavioural interventions (www.joannabriggs. edu.au). It is interesting to note that this hierarchy also includes level IV evidence which acknowledges opinion of respected authorities, clinical experience and reports of expert committees. Strictly speaking, this is not evidence at all. The summary of evidence in the following sections of this paper will refer to the hierarchical level detailed in Table 1. However, Robey1 argues that evaluation of treatment effectiveness must also be considered within a broader organising structure for conducting clinical-outcome research activities. His five-phase model (Table 2) describes a logically ordered sequence from initial ‘proof of concept’ via various stages of ‘treatment efficacy’ and then ‘treatment effectiveness’ through to complete adaptation into clinical practice. Treatment efficacy research (Phase 1–3) examines clinical outcomes in an environment that ‘minimizes all sources of extraneous or confounding variation’ and ‘indexes the maximum potential of a treatment protocol for bringing about change’ (pg 402). In contrast, treatment effectiveness research examines the benefit of an intervention ‘provided in a typical fashion by typical practitioners to typical patients in typical clinical settings’ (pg 402). Therefore, the ultimate goal is evidence of treatment effectiveness but effectiveness can only be tested when efficacy has been firmly established. However, as Pring2 highlights, these essential phases of building an evidence base can often be overlooked in the ‘rush’ to publish large group trials and make claims about clinical effectiveness. The five levels are summarised in Table 2. This paper addresses the literature and evidence base for speech/voice therapy intervention for five types of voice disorders which commonly utilise voice therapy intervention as a primary strategy. These are functional voice disorders, vocal nodules, organic voice disorders, unilateral vocal fold paralysis (UVFP) and Parkinson’s disease voice disorder. This evidence will be categorised according to Robey’s five-phase model. The study descriptions and levels consistent with the Joanna Briggs terminology listed in Table 1 will also be documented. Each section also includes a summary table of all recent relevant voice treatment efficacy published studies.