Compensatory hyperhidrosis

# Overview
Compensatory hyperhidrosis is a form of neuropathy. It is encountered in patients with spinal cord disease, thoracic disease, cerebrovascular disease, nerve trauma or surgeries. The exact mechanism of the phenomena is poorly understood. It is attributed to the brain, hypothalamus perceiving the body temperature as being too high. The sweating is induced to reduce body heat. Excessive sweating due to nervousness, anger, previous trauma or fear is called hyperhidrosis.
Compensatory Hyperhidrosis is the most common side-effect of Endoscopic thoracic sympathectomy - a surgery to treat Hyperhidrosis. It is an abnormal sweating (below the level of the sympathetic chain disruption). Some of the literature refers to it as 'rebound' or  'reflex hyperhidrosis'.
According to Dr Hooshmand, Sympathectomy permanently damages the temperature regulatory system. The permanent destruction of thermoregulatory function of SNS causes latent complications, e.g., RSD in contralateral extremity.
The term 'compensatory' is largely misleading, as it indicates that there is a 'compensatory mechanism' that takes effect after sympathectomy,in which the body 'redirects' the sweating from the palms or face to other area of the body. However there is no evidence to support this claim. Compensatory Hyperhidrois is an aberrant SNS function. The only study evaluating the total body sweat prior and post sympathectomy concluded that patients sweat more and not less after the surgery,  thus undermining the 'compensatory' theory. Lin and Telaranta presented their findings at the 4th Symposium on Sympathetic Surgery in Vienna. According to their paper, sweating after sympathetic surgery is a reflex cycle between the sympathetic system and the anterior portion of the hypothalamus. Reflex sweating will not happen if hand sweating can be stopped without interrupting sympathetic tone to the human brain. (Chien-Chih Lin, M.D., Timo Telaranta, M. D.)
This "Reflex" sweating can be tolerable for some patients, but there are many who end up with incapacitating sweating that requires them to change their clothes several times during the day and renders many activities impossible. It is impossible to predict who will end up with a more sever version of this disorder, as it appears gender, age, weight independent.
Following surgery for axillary (armpit), palmar (palm) hyperhidrosis and blushing, the body sweats excessively at untreated areas, most commonly the lower back and trunk, but can be spread over the total body surface below the level of the cut. The upper part of the body, above the sympathetic chain transection, the body becomes anhidriotic, where the patient is unable to sweat or cool down, which further compromises the body's thermoregulation and exacerbates the Compensatory Hyperhidrosis.
Gustatory sweating or Frey's syndrome is another expression of autonomic neuropathy, and side effect of this surgery.  Gustatory Sweating is brought on while eating, thinking or talking about food that produce a strong salivary stimulus. It is thought that autonomous fibres to salivary glands have become connected in error with the sweat glands when they become reconnected after nerve regeneration. Apart from sweating in the anhidriotic area of the body, it can produce flushing, goosebumps, drop of body temperature (vasoconstriction) and paresthesia.
Aberrant gustatory sweating follows up to 73% of surgical sympathectomies ] and is particularly common after bilateral procedures. Facial sweating during salivation has also been described in diabetes mellitus, cluster headache, following chorda tympani injury, and following facial herpes zoster.
Phantom sweating is another form of autonomic neuropathy. It can also be observed in patients with nerve damage (accidents), diabetes mellitus and following Sympathectomy. 
Phantom sweating is a sensation that one is sweating, while the skin remains dry. Sufferers can not distinguish if it is real sweating or just a sensation. It is only experienced in the anihidriotic, denervated area of the body, pointing to abnormal sympathetic nervous system function.