Objectives: This study was designed to measure sympathetic skin responses (SSRs) following magnetic stimulation of the cervicothoracic spine and to evaluate its clinical usefulness.

Methods
Fifteen healthy volunteers who had no dysautonomic symptoms or signs and a patient with C6 spinal cord transection participated in this study. To evoke SSR, we stimulated the C7 spinous process (SP) and T2 SP with 90 mm circular coil (Magstim 200). We recorded the sensory nerve action potential (SNAP) from the right middle finger to ascertain whether the C7 dorsal root was depolarized by the C7 SP stimulation. The same stimulation intensity by which SNAP had been obtained was used to evoke the SSR by the C7 and T2 SP stimulation. The recording of SSR was done in both palms. SNAP was recorded by the magnetic stimulation on the C7 SP in all subjects.

Results
By the C7 SP stimulation, the latency of SSR was 1.35 sec in the right palm, 1.33 sec in the left palm and by the T2 SP stimulation, the latency was 1.24 sec, 1.23 sec in order. The right-left difference was not found by each SP stimulation, but the latency of SSR by the T2 SP stimulation was faster than that by the C7 SP stimulation (p＜0.01). The latency difference of C7 and T2 SP stimulation was 0.11 sec in the right palm, 0.10 sec in the left palm. In a case of C6 cord transection, SSR was evoked neither by the right median electric stimulation, nor by the C7 SP magnetic stimulation. However, SSR was successfully evoked by the T2 SP stimulation.

Conclusion
We believe that the latency difference of C7 and T2 spinous process stimulation reflects the central conduction time of SSR.