Ethics approval statementAll human and animal studies have been approved by the appropriate ethics committee and have therefore been performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments.

Background: Hypokinetic dysarthria -with hypophonia as its main symptom-is a common feature of Parkinson's disease, affecting approximately 90% of patients. Hypophonia, characterized by reduced speech volume, leads to difficulties in communication with others due to decreased speech intelligibility. Current treatments involve intensive and cognitively demanding behavioral therapies such as the Lee Silverman Voice Treatment (LSVT). The SpeechVive is a wearable device that produces noise to elicit increased vocal intensity utilizing a natural reflex through the Lombard effect. Methods: We propose a multicenter, phase III, two-armed, parallel, open-label, randomized controlled trial comparing the effectiveness of LSVT with SpeechVive. We seek to assign 238 patients to either LSVT or SpeechVive device in a 1:1 ratio through a stratified permuted block randomization. Patients ages 50 to 80 years, diagnosed with idiopathic Parkinson's Disease based on MDS-Unified Parkinson's Disease Rating Scale (MDS-UPDRS) criteria, a Hoehn and Yahr stage 2 and 3, on stable dopaminergic doses for the past 3 months, with perceived communication difficulties will be included in the trial. Patients will be excluded if they present additional neurodegenerative diseases, prior stroke, laryngeal pathologies, hearing or a severe visual impairment, or who underwent speech therapy or have a deep brain stimulation electrode implanted. The primary outcome is speech intelligibility measured through the Speech Intelligibility Test (SIT) for windows. Secondary outcomes include adherence, the vocal intensity measured with Sound Pressure Level (SPL), Vocal Handicap Index (VIH), and Parkinson's Disease Questionary-39. We will measure each outcome at baseline and after eight weeks of treatment. Our principal statistical analysis is multiple linear regression analysis, with age, gender, site, and PD severity as covariates. Discussion: We present a protocol for a randomized controlled trial addressing an important issue that hampers the ability of Parkinson's Disease patients to communicate effectively. We aim at exploring SpeechVive as an alternative, more accessible treatment for hypophonia in patients with Parkinson's Disease.