Longitudinal ultrasound assessment of vagus nerve morphology in isolated REM sleep behavior disorder and Parkinson's disease.

INTRODUCTION

Ultrasonography has shown that the vagus nerve cross-sectional area (VN-CSA) is reduced in patients with Parkinson's disease (PD). However, the status of the VN in prodromal PD is unclear. The objectives of this study were to assess: 1) the VN-CSA in healthy control subjects versus patients with isolated rapid eye movement sleep behavior disorder (IRBD) or PD; 2) the laterality of VN size; 3) whether the VN-CSA changes over time; and 4) whether the VN-CSA can serve as an indicator of the progression of neurodegeneration in IRBD or PD.

METHODS

We performed ultrasonography to determine the right and left VN-CSA in 57 Japanese patients with IRBD, 41 patients with PD, and 27 controls. VN-CSA was followed up for 3 months or more after the baseline examination in 21 of the IRBD patients and 14 of the PD patients.

RESULTS

There were no significant differences in the mean right or left VN-CSA between the three groups. The mean left VN-CSA was significantly reduced in IRBD after a mean follow-up period of 2.3 ± 0.9 years (P = 0.0069). In the PD group, a negative correlation between motor function (assessed by the MDS-UPDRS part III) and the VN-CSA.

CONCLUSIONS

Repeatedly monitoring the left VN-CSA might serve as an indicator of IRBD progression. The VN-CSA may be further reduced in PD compared with IRBD. These data comparing changes in the VN-CSA over time in patients with IRBD and early PD provide a starting point for future research.