Reduced spontaneous sympathetic nerve activity in multiple sclerosis patients

• First direct measures of muscle sympathetic nerve activity (MSNA) in MS patients
• Resting MSNA was reduced in MS patients compared to healthy individuals.
• Plasma norepinephrine concentrations mirrored the findings of reduced MSNA in MS.
• Reduced MSNA may signify impaired autonomic control of cardiovascular function in MS.

For the first time, we obtained direct intra-neural measurements of muscle sympathetic nerve activity (MSNA) in relapsing–remitting multiple sclerosis (MS) patients to test the hypothesis that spontaneous resting MSNA is reduced in MS patients compared to age, sex-matched healthy controls. Spontaneous MSNA (microneurography; peroneal nerve), plasma norepinephrine, arterial blood pressure (finger photoplethysmography), and heart rate were measured at rest in three groups: 1) relapsing–remitting MS patients on disease modifying therapy only (MS-DT; n = 6); 2) relapsing–remitting MS patients on disease modifying therapy and medications for MS-related symptoms that are known to effect the central nervous system (MS-DT/ST; n = 5), and 3) healthy age and sex-matched controls (CON; n = 6). Compared to the CON group, MSNA burst frequency (bursts/min) was significantly lower in both MS-DT (P = 0.027) and MS-DT/ST groups (P = 0.003). Similarly, MSNA burst incidence (bursts/100 heartbeats) was significantly reduced in both MS-DT (P = 0.049) and MS-DT/ST groups (P = 0.004) compared to the CON group. Burst frequency and burst incidence were not different between MS-DT and MS-DT/ST groups. Resting plasma norepinephrine was also significantly lower in both MS-DT (P = 0.039) and MS-DT/ST groups (P = 0.021) compared to the CON group. Reduced MSNA may signify an important dysfunction in autonomic control of cardiovascular function in patients with MS.