Sympathetic skin response asymmetry in early stage idiopathic Parkinson's disease

Simultaneous bilateral plantar sympathetic skin response (SSR) was studied in 25 patients with early stage idiopathic Parkinson's disease (IPD), characterized by monolateral motor involvement (Hoehn and Yahr, stage <2) and without clinical evidence of autonomic dysfunctions. Thirteen (mean age: 68.69 +/- 7.70, range 55-76) had extrapyramidal clinical signs only at the left body side, 12 (mean age 66.60 +/- 7.43, range 51-73) at the right body side. A group of 25 healthy, age-matched, subjects were also evaluated. To evoke the responses, trains of 10 electrical pulses were applied at different intensities and frequencies. Only intensities of stimulation > or = 5 times the sensory electrical threshold always assured bilateral plantar responses in all the examined subjects. Amplitude asymmetry between left and right responses was found only in the IPD patients (P < 0.05). The amplitude reduction corresponded to the motor affected side. No analogue latency variation was observed in any group. Independently from the peripheral or central origins of such phenomena, these findings suggest that simultaneous bilateral SSR amplitude evaluation could be useful, in early IPD patients, to demonstrate and to monitor the sympathetic cholinergic dysfunction, despite the lack of autonomic symptoms.