Vagus nerve (VN) has been suggested as one of the major routes of Parkinson’s disease (PD) progression from enteric nervous system to brain. Therefore, the recent studies have investigated the VN structurally, with a focus on the changes in its size in PD patients using high-frequency ultrasonography. This systematic review and meta-analysis aims to evaluate VN size via ultrasound in PD compared to controls.
Totally, five studies were included with a total of 238 participants (128 PD patients and 111 controls).
The estimate mean difference in four studies showed that the VN CSA was smaller in PD patients with 0.29 mm (95% CI, -0.52 to -0.06) and 0.23 mm (95% CI, -0.42 to -0.05) for right and left VNs respectively. The test for overall effect was significant for both measurements (p = 0.01).
This review reveals that there is a degree of vagus nerve atrophy in PD which could be detected sonographically with high confidence, thus can be used as a marker for vagus neuronal lesion or neuropathy. Further studies are needed to examine its clinical correlation thoroughly.

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