Morphological and functional assessment of the vagus nerve in multiple sclerosis

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).

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.

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.

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.