Retrograde Changes of Median-Nerve Fibers in Carpal Tunnel Syndrome

ABSTRACT

Slowing in forearm median nerve conduction in patients with carpal tunnel syndrome(CTS) has been described. But the cause of slowing is still unclear whether it is related to a technical artifact on electrodiagnostic appr oach or pathophysiologic changes in the proximal segment of median nerve. To investigate the possible retrograde degeneration of median nerve in the forearm segment(wrist to elbow) in patients with known carpal tunnel syndrome, the median nerve conduction studies were performed in 23 normal persons as control and 25 patients with carpal tunnel syndrome. To evaluate the median nerve conductions in the forearm, the recording bar-electrode were placed at the volar aspect of the wrist and stimulating electrodes were applied at the elbow area. The mixed nerve action potentials and conduction velocities were measured. The median mixed nerve action potential(FNAP) amplitudes recorded at the wrist and motor nerve conduction velocity(MMCV) in patients with carpal tunnel syndrome patients were significantly reduced compared to those of control group(p<0.05). However, the median mixed nerve conduction velocity(FNCV) was not reduced significantly. The median mixed nerve action potential amplitudes demonstrated positive correlation with the decrease of motor and sensory action potential amplitudes and velocities. This result suggests that the retrograde degeneration progresses as the carpal tunnel syndrome progresses and the retrograde degeneration may play a major role in reduced motor nerve conduction velocity of the median nerve in the forearm. We propose that FNAP amplitude and MMCV might be used to evaluate the severity of retrograde degeneration in patients with carpal tunnel syndrome.