Morphological and functional assessment of the vagus nerve in multiple sclerosis.

Purpose: The aim of this work is to determine the relationship between the cross-sectional area (CSA) of the vagus nerve and cardiovagal function in people with multiple sclerosis (pwMS) and healthy controls (HC).

Methods: We enrolled 50 pwMS and 50 HC. All participants underwent an ultrasound of the vagus nerve and autonomic nervous system testing. The Croatian version of the COMPASS-31 questionnaire was used as a measure of autonomic symptom burden. Cardiovagal function was evaluated with the respiratory sinus arrhythmia (RSA), Valsalva ratio (VR), and heart rate variability.

Results: The mean vagus CSA in pwMS was 2.03 ± 0.49 mm² on the right side and 1.72 ± 0.38 mm² on the left side. The mean vagus CSA in HC was 2.08 ± 0.50 mm² on the right side and 1.74 ± 0.37 mm² on the left side. There was no statistically significant difference between the two groups in right (p = 0.615) or left (p = 0.866) vagus CSA. In the HC, there was a statistically significant positive correlation between the mean right CSA and both RSA (r_p = 0.331, p = 0.019) and VR (r_p = 0.327, p = 0.020). On univariable linear regression analysis in the HC group, the mean right CSA was a predictor of both RSA (B = 5.599, 95% CI 0.974-10.224, p = 0.019) and VR (B = 0.253, 95% CI 0.041-0.466, p = 0.020). These findings were not present in pwMS.

Conclusions: The loss of correlation between vagus nerve CSA and parameters of parasympathetic nervous system function in pwMS corroborates the presence of cardiovagal dysfunction in multiple sclerosis.