Sympathetic skin response and axon count in carpal tunnel syndrome

The aim of this study was to determine the sensitivity of sympathetic skin response (SSR) in evaluating autonomic involvement in carpal tunnel syndrome (CTS) while simultaneously showing the axonal loss by motor unit number estimation (MUNE). Bilateral SSR were recorded by suprasternal stimulus in 50 hands of 31 patients and compared with 50 hands of 25 healthy volunteers. The groups were examined for sympathetic symptoms and sympathetic symptom scores (SSS) were determined. Axon count was performed on the abductor pollicis brevis (APB) muscle by using the MUNE method (with incremental technique) in both groups. There was no SSR difference between groups, although a significant difference was found for SSS. No relationships were found between SSR parameters and SSS or the electrophysiologic stage. MUNE of the APB muscle was significantly lower in CTS group and there was a negative correlation between MUNE and the electrophysiologic stage. The comparison of the MUNE and the amplitude of median compound muscle action potential indicated that MUNE is a highly sensitive method of determining severity in patients with CTS. In evaluating autonomic involvement in CTS, SSR does not seem to be a sensitive method. MUNE is a good indicator of motor reserve and can be helpful when following the treatment and prognosis of CTS in clinical practice.