Peripheral autonomic involvement in the carpal tunnel syndrome.

The sympathetic skin response (SSR), evoked from the middle finger of both hands by electrical stimuli to the median nerve (MN) at the wrist, was studied in 21 patients with bilateral carpal tunnel syndrome (CTS) and in 16 patients with monolateral CTS (14 at the right and 2 at the left side) without clinical signs of autonomic involvement. In monolateral and bilateral CTS there was a decrease in the SSR areas of both sides. In monolateral CTS the decrease was greater contralaterally to the lesion. A decrease in the SSR in CTS generally indicates a local blockade of sympathetic nerve excitability due to MN entrapment. Contralateral reduction of the sympathetic response suggests an involvement of the efferent pathway of the autonomic reflex far from the lesion at the wrist. However, dispersion of the excitement over a long distance and throughout numerous synaptic connections may affect contralateral more than homolateral SSR excitability. Finally, sympathetic damage in CTS is in accord with the anatomo-functional correlation (in the peripheral nerve and ganglia) between somatic sensory, which were most markedly involved in our patients, and sympathetic afferent nerve fibers.