Vagus somatosensory-evoked potentials are prolonged in patients with multiple sclerosis with brainstem involvement

Vagus somatosensory-evoked potentials (VSEP) were proposed as a neurophysiological indicator of brainstem dysfunction based on prolonged latencies found in Alzheimer's dementia and Parkinson's disease. We now aimed at a further confirmation of this view independent from neurodegenerative diseases and hypothesized that VSEP in multiple sclerosis with brainstem affection show prolonged latencies, too. In 15 patients with multiple sclerosis according to McDonald and 15 healthy controls after stimulation of the auricular branch of the vagus nerve at the tragus (electrical square impulses, impulse width 0.1 ms, interstimulus interval 2 s, intensity 8 mA), evoked potentials were recorded from electrode positions C3-F3, C4-F4, Fz-F3 and Fz-F4. Analysis of variance showed a significant main effect of the factor diagnosis on latency P1 (F(1,24)=7.067, P=0.001), no significant effect for latencies N1 and P2 nor for the amplitudes. A subgroup of patients with signs of brainstem affection showed a trend for longer P1 latencies (F(1,11)=5916, P=0.033) as compared with the group without. We take this result as further hint for VSEP to be generated at brainstem level which needs confirmation in larger-scale studies and other brainstem-affecting diseases. The method could be suitable for the demonstration of the involvement of differential brainstem nuclei in various neurodegenerative diseases.