Reduced Sympathetic Skin Response in the Isolated Spinal Cord of Subjects With Spinal Cord Injury

Pan S-L, Wang Y-H, Hou W-H, Wang C-M, Huang T-S. Reduced sympathetic skin response in the isolated spinal cord of subjects with spinal cord injury. Objective: To compare the excitability of the sympathetic skin response (SSR) between subjects with spinal cord injury (SCI) and healthy controls with intact supraspinal connection. Design: Cross-sectional survey. Setting: Referral center. Participants: A total of 37 men with traumatic neurologically complete SCI (26 with tetraplegia, 11 with paraplegia) and history of autonomic dysreflexia were included. Twenty age-matched healthy male controls were recruited as the control group. Subjects with SCI were at the mean age ± standard deviation of 36.5±11.0 years (range, 20.1-61.3y) and the mean injury duration was 11.3±9.3 years (range, 1.0-38.1y). Interventions: Not applicable. Main Outcome Measures: The SSR tests were grouped into 3 test sets according the stimulation and recording sites: (1) right supraorbital nerve stimulation with left hand recording (SH set); (2) right supraorbital nerve stimulation and left foot recording (SF set); and (3) right posterior tibial nerve stimulation and left foot recording (TF set). Results: In patients with tetraplegia (n=26), none showed positive SSR in the SH or the SF set, and only 5 (19.2%) showed a positive SSR in the TF set. In subjects with paraplegia (n=11), the positive response rates of SSR were 72.7% for the SH set, 0% for the SF set, and 9.1% for the TF set. Electric stimulation at high intensity (100mA for 1ms) was required to elicit SSR for the TF set in the patients with SCI. The SSR amplitudes in the SH and TF sets were smaller in subjects with SCI than those in controls (SH set, P=.004; TF set, P<.001). The SSR latency in the SH set was longer in patients with SCI (P=.04), whereas the SSR latency in the TF set tended to be shorter in subjects with SCI (P=.09). Conclusions: The excitability of SSR was reduced in an isolated spinal cord. This suggests that excitability of sympathetic sudomotor response in subjects with an isolated spinal cord is lower than in healthy controls.