ABSTRACT
The main function of the sympathetic nervous system is to provide proper circulation to the end organs according to demand. If an extremity is inactive, it is going to need less arterial blood—hence, vasoconstriction. The reverse is true with activity. The commonest form of Reflex Sympathetic Dystrophy (RSD), RSD of disuse, is simply due to the vicious circle of inactivity perpetuating the sympathetic hyperactivity and pain of the original injury. Major causalgia is the best example of efferent dysfunction secondary to sensory nerve damage and RSD. The lack of proprioceptive input changes the pain to hyperpathia, and secondary sympathetic vasoconstriction develops. A common symptom of ephaptic RSD is aggravation of pain with simple touch with a bed sheet or a mild ambient temperature change or pressure change such as a mild breeze or the weight of a bed sheet. Ephaptic RSD is more commonly seen in watershed areas.
