Ultrasonography of the Vagus Nerve in Parkinson's Disease: Links to Clinical Profile and Autonomic Dysfunction.

Parkinson's disease (PD) is a progressive neurodegenerative disorder characterized by both motor and non-motor symptoms, including autonomic dysfunction. Structural alterations in the vagus nerve (VN) may contribute to PD pathophysiology, though existing data remain inconsistent. This study aimed to evaluate morphological changes in the VN using high-resolution ultrasound (USVN) and to investigate associations with autonomic symptoms, heart rate variability (HRV), and clinical characteristics in PD patients. A cross-sectional study was conducted involving 60 PD patients and 60 age- and sex-matched healthy controls. USVN was performed to assess VN cross-sectional area (CSA), echogenicity, and homogeneity bilaterally. Autonomic symptoms were measured using the Composite Autonomic Symptom Scale 31 (COMPASS-31). HRV parameters-SDNN, RMSSD, and pNN50-were obtained via 24 h Holter monitoring. Additional clinical data included Unified Parkinson's Disease Rating Scale (UPDRS) scores, transcranial sonography findings, and third ventricle width. PD patients showed significantly reduced VN CSA compared to controls (right: 1.90 ± 0.19 mm vs. 2.07 ± 0.18 mm; left: 1.74 ± 0.21 mm vs. 1.87 ± 0.22 mm; < 0.001 and < 0.02). Altered echogenicity and decreased homogeneity were also observed. Right VN CSA correlated with body weight, third ventricle size, and COMPASS-31 scores. Left VN CSA was associated with body size parameters and negatively correlated with RMSSD ( = 0.025, r = -0.21), indicating reduced vagal tone. USVN detects structural VN changes in PD, correlating with autonomic dysfunction. These findings support its potential as a non-invasive biomarker for early autonomic involvement in PD.