Sympathetic skin response before and after surgical release of carpal tunnel syndrome.

Sympathetic skin response (SSR) was performed before and 1 year after surgical release of the median nerve in 20 subjects (mean age 52.8 years) with unilateral idiopathic carpal tunnel syndrome (CTS). SSR was evoked by stimulation of the ulnar nerve at the wrist contralateral to the side with CTS, recording from the palm, third (M3) and fifth fingers, and from the third finger contralateral to the side of CTS (M3c). Before surgery, anomalies of M3 SSR were found in 8 hands (40%): M3 SSR was absent in 1 hand; and the M3c/M3 SSR largest area ratio was abnormal in 7 hands, 3 of which also had abnormal mean differences between M3 and M3c SSR latencies. M3 SSRs were not significantly modified after surgery. The absence of postsurgical improvement may be due to the poor reinnervation capacity of sympathetic fibers.