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 hypothesized that this hyperexcitability could become evident in the study of the excitability 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 median nerve electrical shocks separated by inter-stimuli intervals (ISIs) ranging from 0.5 to 3.5 s. The amplitude of the SSR generated by the second stimulus (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 significant enhancement of the SSR excitability recovery curve, with onset of recovery 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 involved in sweating. This could partly underlie the pathophysiology of PPH.