Chronological changes of sympathetic outflow to muscles in amyotrophic lateral sclerosis

To confirm correlations between muscle sympathetic nerve activity (MSNA) and patients' chronological data, we selected 40 consecutive patients with sporadic amyotrophic lateral sclerosis (ALS) recorded by similar methods. MSNA at rest was quantified as the number of sympathetic bursts per 100 heartbeats and as the value expressed as a percentage of the predicted value based on control data. Twelve patients who underwent recordings of MSNA twice at intervals of 6 months or more showed marked decreases in MSNA amplitudes and frequencies between examinations. There was a slightly positive correlation between the frequency of MSNA and age, though younger patients exhibited higher values of MSNA than older patients. The standardized value of MSNA correlated negatively with disease duration and disability levels (p<0.01, 0.05, respectively), but several patients with duration shorter than 12 months showed low values of MSNA. Twelve patients who underwent repeated recordings of MSNA showed a significant decrease in the mean standardized value of MSNA (102.6+/-24.9%) at the second examination, compared to the value (114.3+/-18.9%) at the first one. In ALS, sympathetic outflow to muscles tends to increase initially and then decrease with increasing age and duration. This pattern may be similar to chronological changes at motor neurons.