Excitability recovery curve of the sympathetic skin response in healthy volunteers and patients with palmar hyperhidrosis

Objectives: Patients with primary palmar hyperhidrosis (PPH) might exhibit hyperexcitability of the reflex circuits involved in sweating. We hypothesi zed that this hyperexcitability could become evident in the study of the ex citability recovery curve of the sympathetic sudomotor skin response (SSR). Methods: In 10 patients with PPH and 10 healthy volunteers used as control subjects, we recorded the SSR in the palm of the right hand to pairs of med ian nerve electrical shocks separated by inter-stimuli intervals (ISIs) ran ging from 0.5 to 3.5 s. The amplitude of the SSR generated by the second st imulus (SSR2) was expressed as a percentage of that generated by the first (SSR1), and compared between control subjects and patients for each ISI. Results: None of the control subjects showed a recovery of the SSR for ISIs of 1.5 s or less. On the contrary, patients showed a statistically signifi cant enhancement of the SSR excitability recovery curve, with onset of reco very at 1.5 s in 5 patients. Two patients showed a double peak response to single electrical stimulation and were not considered in the calculation of the SSR recovery curve. Mean excitability recovery percentages were larger in patients than in control subjects at ISIs of 2, 2.5 and 3 s. Conclusions: The enhancement of the SSR recovery curve in patients with PPH suggests hyperexcitability of the somatosympathetic polisynaptic pathway i nvolved in sweating. This could partly underlie the pathophysiology of PPH. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.