Vagus Nerve Ultrasonography Helps Distinguish Multiple System Atrophy from Other Parkinsonian Syndromes.

Background: Distinguishing multiple system atrophy from other parkinsonian syndromes is challenging. Objectives: To evaluate vagus nerve ultrasonography for differentiating parkinsonian syndromes. Methods: A single-center, cross-sectional, observational study assessed 85 consecutive adult patients with de novo parkinsonism between June 2020 and December 2022, using 12 MHz ultrasonography of the vagus nerve cross-sectional area. Results: Bilateral vagus nerves were smaller in multiple system atrophy than in other parkinsonian syndromes. The area under the receiver operating characteristic curve for differentiating multiple system atrophy was 0.79 on the right side and 0.74 on the left. The cut-off values to diagnose multiple system atrophy were 0.71 and 0.86 mm2 on the right and left sides, respectively, with sensitivities of 82.6% and 87.0%, specificities of 74.2% and 64.5%, positive predictive values of 54% and 47.6%, and negative predictive values of 92.0% and 93.0%. Conclusions: Vagus nerve ultrasonography may differentiate multiple system atrophy from other parkinsonian syndromes.