Sympathetic skin response and cardiovascular autonomic function tests in Parkinson's disease and multiple system atrophy with autonomic failure

The relationship between sympathetic skin response (SSR) and cardiovascular autonomic function tests (CVTs) was investigated in 15 patients with idiop athic Parkinson's disease (PD), 15 patients with clinical evidence of multi ple system atrophy (MSA) with autonomic failure, and in 15 healthy control subjects. SSR was elicited by electrical stimulation of the right and left median nerves and simultaneously recorded on the palms of both hands. CVTs included the following sympathetic and parasympathetic tests: orthostatism, head-up tilt, cold presser test, deep breathing, Valsalva maneuver, and hy perventilation. The SSR was normal in all patients with PD and control subj ects but was abnormal or absent in all patients with MSA. For patients with MSA, SSR latency was significantly longer and amplitude was significantly smaller than that of patients with PD and control subjects. For patients wi th PD, SSR did not differ from that of control subjects. In these patients, SSR latency was significantly longer and SSR amplitude was smaller when th e side with more marked motor symptoms was stimulated, both ipsilaterally a nd contralaterally to the side of stimulation. A statistically significant difference in SSR latencies and amplitudes was found between patients with PD and control subjects only when motor asymmetries were considered. CVTs s howed severe sympathetic and parasympathetic hypofunction in patients with MSA, but not in patients with PD or control subjects. No correlation was fo und between SSR and CVTs that assess sympathetic function in patients and c ontrol subjects. SSR is indicated as an additional test for the evaluation of sympathetic degeneration in patients with MSA.