Estimation of Median Nerve Axonal Degeneration without Needle Electromyography

Abstract

Background and Aim: The present study aimed to use the median nerve Compound Muscle Action Potential (CMAP) amplitude by stimulation at the palm instead of Abductor Pollicis Brevis (APB) needle Electromyography (EMG) for determining axonal loss in patients with Carpal Tunnel Syndrome (CTS). Methods and Materials/Patients: This study was performed on 180 patients with CTS referred to the Electrodiagnostic (EDX) Center, Poursina Hospital, Guilan Province, Iran, in 2018-19. In this study, the APB needle EMG diagnostic test was used as the gold standard, and median nerve CMAP amplitude with stimulation at the palm and wrist were used to compare the two nerve stimulation tests. Results: All of the cases with abnormal amplitude loss detected by median nerve stimulation at the palm also had an axonal loss in the needle EMG of APB. So this test could be a good indicator of axonal loss if there is an abnormality (sensitivity: 73%, specificity: 100%). The results with wrist stimulation were not as accurate as of the palm stimulation, and some cases with decreased CMAP amplitude of median nerve had normal needle EMG of APB muscle (sensitivity: 86.6%, specificity: 94.9%). Conclusion: In cases with CTS, the abnormally decreased amplitude of the median nerve detected by stimulation at the palm could be a good indicator of axonal loss.

Keywords

• median nerve
• electromyography
• carpal tunnel syndrome