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 a sign of axonal loss in patients with carpal tunnel syndrome (CTS).

Methods and Materials/Patients:

 This study was performed on 180 patients with CTS referred to Poursina Hospital at the Electrodiagnosis (EDX) Center in 2018-19. In this study, the APB needle EMG diagnostic test was used as the gold standard, and median nerve CMAP AMP with stimulation at the palm and wrist were used to compare the two nerve stimulation tests. 

All of the cases with abnormal amplitude loss detected by median nerve stimulation at the palm had also axonal loss in the needle EMG of APB, and this test could be a good indicator of AL if there is an abnormality (sensitivity: 73%, specificity: 100%). The results with wrist stimulation were not as accurate as the palm stimulation, and some cases with decreased CMAP amplitude of median nerve, had normal limits needle EMG of APB muscle (sensitivity: 86.6%, specificity: 94.9%). 

It was found that in cases with CTS, abnormally decreased amplitude of median nerve detected by stimulation at the palm could be a good indicator of axonal loss.