Background The authors examined the effects of thermal stimulation on electrodermal activity (EDA) in patients with primary palmar hyperhidrosis (PPH). The authors hypothesised that temperature changes may induce abnormal sudomotor reactions because of simultaneous activation of sudomotor centres through thermal and emotional pathways, and compared patients before and after thoracoscopic sympathectomy.

Methods The authors studied 18 PPH patients and 20 controls. Patients reported subjective evaluation of their symptoms using a visual analogue scale for palmar sweating and for body sweating (bs-VAS). The authors applied focal thermal stimulation to quantify sensory perception and measure ongoing changes in EDA recorded from the palm of the hands.

Results Before sympathectomy, patients had lower sensory perception thresholds and higher EDA levels than controls. Increased EDA occurred along the whole test, with no significant modulation by changes in thermal stimulation. Sensory perception normalised after sympathectomy, but thermal modulation of EDA remained abnormal whenever sudomotor activity was present after surgery. There was a significant positive correlation between EDA levels before treatment and the bs-VAS (from r=0.45 to r=0.57).

Conclusions Patients with PPH show perceptual abnormalities and exaggerated sudomotor reactions to thermoalgesic stimulation, consistent with central sensitisation of sympathetic circuits. The reduced sympathetic outflow after thoracoscopic sympathectomy induced normalisation of sensory perception, but it did not modify the abnormal control of efferent sudomotor activity.