The sympathetic skin response in carpal tunnel syndrome.

The sympathetic skin response (SSR) is an evoked change in electrical skin potential and is an index of the function of sympathetic pathways. We studied the SSR evoked by electrical stimulation of the median nerve and recording from the contralateral hands in 30 patients with carpal tunnel syndrome (CTS) without clinical autonomic signs and compared the results to the SSR in 30 normal controls. The SSR was absent in the affected hands in seven (23%) patients. In the other carpal tunnel syndrome patients (77%), a significant reduction in the SSR area was seen in the records from the affected hands. Subclinical sympathetic nerve fibre involvement occurs in the affected median nerves in CTS.