Afferent pathways of sympathetic skin response in spinal cord: a clinical and electrophysiological study

Sympathetic skin response (SSR) recording is an established test of sudomotor autonomic functions. However, knowledge of its pathways in spinal cord is putative.

This study involved subjects with isolated spinal cord lesions to evaluate the afferent pathways of SSR.

Clinical examination was done according to standard neurological classification of spinal cord injury. Electrophysiological evaluation included: (1) conventional nerve conduction studies to exclude peripheral nerve lesions, (2) scalp somato-sensory-evoked potentials (SEP) with posterior tibial nerve (PTN) stimulation and (3) SSR recording from palm by stimulating supra orbital nerve (SON) at forehead, and PTN at ankle. Subjects with absent SSR in palm to SON stimulation were excluded. In such patients, the afferent tracts were considered abnormal when SSR was absent in palm on stimulation of PTN.

Among 37 subjects (age-28.1+/-12.8 years), the afferent tracts of SSR were affected in 13. Sparing of afferent SSR tracts correlated with preservation of bladder sensations (P<0.01). There was no correlation between SSR and SEP.

Spinal cord lesions frequently involve afferent tracts of SSR. Spinal afferents of SSR are closely related with tracts of bladder sensations and are different from pathways for SEP.