Sympathetic Skin Response and Cardiovascular Autonomic Function Tests in Parkinson's Disease

Autonomic dysfunction commonly occurs in Parkinson's disease, but the pathogenesis of autonomic dysregulation remains uncertain. Autonomic functions regulating the cardiovascular system have been investigated in Parkinson's disease, but those involving the extremities has not been well demonstrated. To compare autonomic dysfunctions of the cardiovascular system with those of the extremities, we performed sympathetic skin response (SSR) and cardiovascular autonomic function tests (CAFT) - 30:15 ratio, E:I ratio, Valsalva ratio, isometric exercise test (IET) - in 37 patients with Parkinson's disease and 33 age- and sex-matched healthy controls. The patients were asked to stop antiparkinsonian medications for at least 12 hours prior to the tests. SSR was measured at the right hand and foot after electrical stimulation of the right median and posterior tibial nerves. Absent SSR at either one or both extremities and CAFT beyond normal ranges were regarded as abnormal. Abnormal SSR was observed in 59% of patients, while abnormal CAFT were found in the range of 32%∼81%. Patients with abnormal SSR showed more frequent and severe CAFT abnormalities than did patients with normal SSR. Among the CAFT, IET was well correlated with the SSR. The results suggest that parkinsonian sympathetic dysfunction involving either the cardiovascular system or the extremities may have the same pathophysiology.