Sonographic vagus nerve atrophy in Parkinson's disease: Myth or fact? A systematic review and meta-analysis of recent evidence answers

Background: Parkinson's disease (PD) is a major cause of disability. We aimed to assess the benefit of ultrasonography of the vagus nerve (VN) to compare between PD and healthy controls as well as to deliver reference values of nerve cross sectional area (CSA). Materials and methods: We performed a systematic search on Medline (PubMed), Scopus, Embase, and Web of Science, up till July 25, 2022. After article selection and screening, we performed a quality assessment using the Newcastle–Ottawa Scale. Furthermore, a statistical analysis and subgroup analysis was performed. Results: Eleven studies were included with a total of 809 participants (409 PD patients and 400 controls). A statistically significant difference in the CSA of the right and left VN between PD patients and healthy controls was observed, indicating the atrophy of VN in PD patients (p < 0.00001). The subgroup meta-analysis for average measurements of VN CSA showed insignificant heterogeneity for age (I2 = 48.67%, p = 0.058), level of measurements (I2 = 57.91%, p = 0.05), and disease duration (I2 = 27.1%, p = 0.241). Conclusion: Our meta-analysis showed a sonographically detectable degree of neuronal damage in PD, which correlates with VN atrophy with high confidence. Therefore, we believe this is a potential marker for vagus neuronal lesions. Future studies are required to assess the potential clinical correlation.