Music-Supported Vocal Rehabilitation in Parkinson's Disease: Effects on Voice Intensity and Speech Performance

Hypokinetic dysarthria is a highly prevalent and functionally disabling communication disorder in Parkinson's disease (PD), encompassing hypophonia, imprecise articulation, and festinating speech. Music-supported vocal rehabilitation-operationalized through the Accent Method (AM), a rhythm- and breathing-based voice therapy approach grounded in hierarchical respiratory-phonatory-prosodic coordination-offers a theoretically grounded mechanism for addressing PD dysarthria by exploiting the well-documented facilitatory effect of external rhythmic auditory cueing on motor control in PD. Despite widespread clinical use of the AM in Scandinavian centers, rigorous controlled evidence for its effects on voice intensity and speech performance in PD remains limited. Prospective, parallel-group, randomized controlled trial comparing a structured, four-phase PD-adapted AM protocol with an active nonspecific control program (vocal hygiene and general breathing exercises) over 20 weeks. Ninety-two adults with idiopathic PD (Hoehn and Yahr stages 2-3) were randomized to music-supported AM rehabilitation (n = 46) or active control (n = 46). Blinded assessors evaluated outcomes at baseline and at 6, 12, and 20 weeks. Primary outcome: Voice Handicap Index-30 (VHI-30). Secondary outcomes: GRBAS perceptual dysphonia scale, sound pressure level (SPL), maximum phonation time (MPT), acoustic parameters (jitter, shimmer, fundamental frequency [F0]), speech intelligibility rated by blinded naive listeners, UPDRS speech sub-item, and PDQ-39 communication subscale. All between-group comparisons at 20 weeks favored music-supported AM rehabilitation (all P < 0.001, Bonferroni corrected; adjusted α = 0.005). VHI-30 improvement: -36.8 points (AM) vs. -9.4 points (Control); between-group difference 26.8 points (95% CI: 22.2-31.4; Cohen's d = 2.47). Voice intensity (SPL) improved by +14.8 dB in the AM group versus +4.3 dB in the control group-a nearly threefold greater improvement. Speech intelligibility improved from 67.4% to 84.6% in the AM group versus 68.1% to 73.4% in the control group (+17.2%-point between-group difference), representing a movement from clinically impaired intelligibility to near-functional communicative levels. Jitter normalized from 4.12 ± 0.98% to 1.04 ± 0.31% (AM) versus 4.08 ± 0.94% to 2.96 ± 0.77% (Control), and shimmer from 10.41 ± 2.37% to 3.18 ± 0.84% versus 10.28 ± 2.29% to 6.74 ± 1.61%. Effect sizes were large to very large across all domains (Cohen's d range: 1.41-2.47). Music-supported vocal rehabilitation using the PD-adapted Accent Method yields large, consistent, and clinically meaningful improvements in voice intensity, acoustic stability, speech intelligibility, and communication-related quality of life compared with an active nonspecific control program. These findings establish the AM as an evidence-based behavioral management option for PD-associated hypokinetic dysarthria. Head-to-head comparative trials against LSVT LOUD and SPEAK OUT! are the essential next step.