In contrast, it is of particular interest to find that patients with cerebroischemic syndrome who received thoracic sympathectomy rarely developed substantial postsympathectomy compensatory hyperhidrosis (PCH). The etiology of PCH is still unclear. Obviously, it is not simply a compensatory hyperhidrosis transposition from postoperative reduction of palmar sweating. Based on our observations, we postulated two possible mechanisms. The first of these mechanisms is denervation hypersensitivity of the surgically injured distal sympathetic stump. This could explain why CH may appear soon after sympathectomy, but is not found in patients who undergo local excision of axillary sweat glands or undergo local treatment. Another mechanism is regeneration of preganglionic fibers or collateral sprouting of sympathetic fibers from the proximal stump of the sympathetic trunk. This could explain the long-term existence of PCH.
Ann Thorac Surg 2001;72:667-668
Receptor hypersensitivity is a common problem after significant sympathetic injury, including clammy hands, erythema, and allodynia. When sympathetic nerves regenerate, they may establish aberrant connections to sensory receptors, muscles, or other sympathetics receptors; this may lead to an over-response or abnormal response.
http://wiki.cns.org/wiki/index.php/Injury,_Sympathetic_Nerve