Reduced spontaneous sympathetic nerve activity in multiple sclerosis patients

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.