denervation supersensitivity of alpha receptors after sympathectomy

There is, however, considerable risk of developing a post-sympathectomy pain syndrome that may be the result of a denervation supersensitivity of alpha receptors.

www.mc.vanderbilt.edu/.../Complex%20Regional%20Pain%20Syndrome-1...

Paradoxically it has been suggested that in some cases there may be abnormal vasoconstriction rather than the expected vasodilatation after sympathectomy. 
                  ats.ctsnetjournals.org/cgi/content/full/84/3/1025