Evolution of Voice Characteristics in People with Parkinson's Disease: A Five Year Follow-Up

Parkinson's disease (PD) is frequently associated with voice and speech impairments that negatively affect communication and quality of life. Although several studies have identified vocal variables with potential clinical value, long-term longitudinal studies that assess, within the same cohort and under standardized conditions, the joint evolution of acoustic parameters and self-perceived vocal impairment remain scarce.

To analyze the evolution of acoustic voice characteristics and vocal self-perception in individuals with PD over a 5-year follow-up period.

An observational longitudinal study with repeated within-subject measures was conducted. The initial cohort consisted of 35 participants with idiopathic PD; 15 completed the 5-year reevaluation. The Voice Handicap Index-30 (VHI-30) was administered, clinical progression was assessed using the Hoehn and Yahr scale, and acoustic voice recordings were analyzed using Praat. Fundamental frequency (F0) was defined a priori as the primary acoustic outcome and was analyzed separately by sex. Secondary or exploratory acoustic variables included formants F1, F2, F3, and F4, as well as alpha ratio, jitter, shimmer, and HNR. Longitudinal comparisons were performed primarily using the Wilcoxon signed-rank test, and Holm-Bonferroni correction was applied for secondary outcomes.

Significant clinical progression was observed over follow-up. Total VHI-30 score increased from 2.0 to 13.0 points and remained significant after adjustment for multiple comparisons (adjusted P = 0.0303). Its functional, physical, and emotional subscales also showed significant increases. In the acoustic analysis, F0 in men increased from 136.5 Hz to 151.0 Hz (P = 0.0020), whereas no significant changes were observed in women. Among the secondary acoustic variables, F2 and F3 showed unadjusted longitudinal changes; however, no secondary acoustic variable remained significant after Holm-Bonferroni correction.

These findings suggest longitudinal vocal deterioration in PD, reflected mainly in worsening vocal self-perception and in F0 changes observed in men. Secondary acoustic variables, including formant measures, should be interpreted as exploratory. The integration of subjective and objective measures may be useful for monitoring disease progression, although the results should be interpreted with caution, given the small sample size and the absence of a longitudinal control group.