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 ultraso-nography 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.