Compensatory hyperhidrosis following thoracic sympathectomy: a biophysical rationale

A side-effect of endoscopic thoracic sympathectomy (ETS) is compensatory hyperhidrosis (CH), characterized by excessive sweating from skin areas with intact sudomotor function. The physiological mechanism of CH is unknown, but may represent an augmented local sweat rate from skin areas with uninterrupted sympathetic innervation based on evaporative heat balance requirements. For a given combination of activity and climate, the same absolute amount of evaporation (if any) is needed to balance the rate of metabolic heat production both pre- and post-ETS. However, the rate of local sweating per unit of skin surface area with intact sudomotor activity must be greater post-ETS as evaporation must be derived from a smaller skin surface area. Under conditions with high evaporative requirements, greater degradations in sweating efficiency associated with an increased dripping of sweat should also occur post-ETS, further pronouncing the sweat rate required for heat balance. In conclusion, in addition to the potential role of psychological stimuli for increased sudomotor activity, the existence of CH post-ETS can be described by the interplay between fundamental thermoregulatory physiology and altered heat balance biophysics and does not require a postoperative alteration in physiological control.