The sympathetic skin response: neurophysiological basis, normal values, clinical applications

The sympathetic skin response (SSR) represents the momentary change in skin potential reflexively evoked by a variety of arousal stimuli. Although sudomotor unmyelinated fibres are the final efferent pathway of SSR, little is known about the afferent and central components. SSR was recorded using different classes of stimuli in 20 controls, 15 peripheral neuropathy and 13 stroke patients. In controls SSR latencies changed significantly with different recording sites but not with different stimulation sites. Additionally, ischemic conduction block of the arm abolished SSR recorded at the hand after median nerve stimulation. In 1 patient with subacute ganglionitis and in 3 with demyelinating neuropathies the SSR could be elicited with deep inspiration but not by electric stimulation. These results suggest that myelinated fibres serve as afferents for SSR. In stroke patients SSR was absent bilaterally after stimulation of the paralyzed side but present after stimulation of the normal one. Therefore in humans the cortex seems to have a suprasegmental excitatory influence on SSR. The above findings imply that an unobtainable SSR by electric stimulation may be due not only to dysfunction of the autonomic efferent nerve fibers, but also to involvement of sensory afferents or suprasegmental structures.