Bowing Index in Individuals With Parkinson's Disease, Progressive Supranuclear Palsy, and Ataxia.

Abstract

Purpose: Variations in vocal fold bowing, as measured endoscopically with the bowing index (BI), across neurodegenerative diseases remain unexplored, which may inform interventions to minimize morbidity and mortality secondary to voice and airway protective dysfunction. The study's aim was to compare BI between people with Parkinson's disease, progressive supranuclear palsy, and cerebellar ataxia.

Methods: Thirty individuals with Parkinson's disease, 23 with progressive supranuclear palsy, and 24 with cerebellar ataxia were included and underwent flexible laryngoscopy. BI was measured using ImageJ software and a linear regression model was used to compare differences in total BI between groups, controlling for age.

Results: Average total BI was 14.60 (SD = 6.26, range 4.03-28.62) for people with progressive supranuclear palsy, 10.10 (SD = 6.64, range 0-34.13) for Parkinson's disease, and 8.35 (SD = 5.90, range 0-25.95) for cerebellar ataxia. Controlling for age, people with progressive supranuclear palsy demonstrated 4.74 greater BI compared to Parkinson's disease (95 CI: 1.19-8.28; p = 0.001), but there was no significant difference between people with Parkinson's disease and cerebellar ataxia (β = 0.37; 95% CI: -5.02, 5.77; p = 0.891) or people with progressive supranuclear palsy and cerebellar ataxia (β = 5.11; 95% CI: 0.01-10.21; p = 0.050).

Conclusions: The results suggest that BI is significantly greater in people with progressive supranuclear palsy compared to Parkinson's disease. It is important to recognize vocal fold atrophy and its potential impact on voice and airway protective measures in these patients.

Level of evidence: 3 Laryngoscope, 2025.