Sympathetic skin response: a decade later.

Sympathetic skin response (SSR) is a simple, reproducible test of function of a polysynaptic reflex having diverse afferents, a common efferent pathway through the spinal cord, pre and post-ganglionic sympathetic fibers and with sweat glands as effectors. The reflex is co-ordinated in the posterior hypothalamus or upper brainstem reticular formation. It has been used in a variety of disorders of peripheral and central nervous system. Methodology, possible anatomic substrates, changes in SSR in various diseases and their correlation with clinical features of dysautonomia, bed side tests for dysautonomia and other electrophysiological parameters are critically evaluated. Almost a decade after the start of its widespread clinical utilization, several aspects of SSR remain inconclusive. A consensus as to what change in SSR to consider abnormal is yet to be reached. Though its ease of application supersedes a variety of other autonomic function tests, relying only on SSR changes for prognostication or therapeutic decisions appears impracticable. A battery of tests is thus a necessity.