How reliable are sympathetic skin responses in subjects with spinal cord injury?

To determine the test–retest reliability of sympathetic skin responses (SSR) in individuals with spinal cord injury (SCI).

Fourteen men and four women with traumatic SCI (age: 44 ± 18 years; C2–T11; AIS A-D; 1–383 months post-injury) participated in two electrophysiological testing sessions separated by an average of 1 day. During each session, sudomotor function was tested supine by recordings of SSRs in both hands and feet. Two stimulation approaches were chosen: median nerve stimulation and a deep breath maneuver. SSR recordings were analyzed as SSR scores representing the presence or absence of responses. In addition, SSR amplitude and latencies were calculated. Test–retest reliability for the SSR score was calculated by the intraclass correlation coefficient (ICC) and its confidence interval. Coefficient of variation (CV) was calculated for SSR amplitudes and latencies.

SSR score to median nerve stimulation demonstrated ‘almost perfect’ reliability with ICCs of 0.97 and 0.96, for both hands and feet, respectively. The SSR score to deep breath maneuver was slightly lower, such as 0.89 and 0.74 for hands and feet. The CV of SSR amplitudes to median nerve stimulation was 48 and 18 % for hands and feet, respectively, and 7 and 12 % for the latency.

The qualitative interpretation of SSR by its presence or absence is a reliable way to assess sudomotor function in individuals with SCI. Although methodical procedures try to standardize SSR testings, quantitative SSR outcomes (amplitude, latency) are still highly variable.