Objective: To find out the incidence of reduced median conduction velocity of forearm (MNCV-F) in carpal tunnel syndrome (CTS) and to compare clinical and electrophysiologic characteristics of CTS with reduced MNCV-F and to observe the changes of reduced MNCV-F after carpal tunnel release.

Method: One hundred and fifty nine hands with CTS are divided into two groups; MNCV-F of 50 m/sec and above as group I and that of below 50 m/sec as group II. For the electrophysiologic comparison, median sensorimotor distal latency, peak-to-peak amplitudes and abnormal spontaneous activity of abductor pollicis brevis were observed and for clinical comparison, sensorimotor symptoms, Phalen and Tinel sign were observed. Twenty four hands which had successful carpal tunnel release were examined for the changes of MNCV-F.

Results: The hands with reduced MNCV-F were 29 among 159 hands. Sensorimotor distal latency were significantly prolonged and sensorimotor amplitudes also significantly reduced in group II. Sensory change and Phalen signs were more frequently observed in group II. MNCV-F in group I had not changed after carpal tunnel release, but MNCV-F in group II was improved significantly. The changes MNCV-F in group II were much delayed than the improvement of parameters of distal conduction studies.

Conclusion: The incidence of reduced MNCV-F in CTS was 18.24%. Patients with reduced MNCV-F had more severe CTS both electrophysiologically and clinically. Reduced MNCV-F had improved significantly, but there was significant time gap between the electrophysiologic improvements of distal and proximal portions of nerve. This findings may suggest that retrograde degeneration may play a partial role in reduced forearm motor nerve conduction velocity of the median nerve in CTS.

Objective: We investigated the useful electrodiagnostic indicators and the extent of retrograde degeneration (RD) in carpal tunnel syndrome (CTS).

Method: We measured median mixed nerve action potentials (MMNAP) in 26 CTS and 37 normal hands by recording at the elbow and stimulating 0, 3, 6 and 9 cm proximal to the distal wrist crease. The 3 MMNAP parameters such as amplitude, latency and conduction velocity were compared between CTS and control group. The most useful indicator was compared between subgroups of CTS (mild and severe) and control group.

Results: The amplitudes of all MMNAPs in CTS group, except stimulating 9 cm proximal to the wrist (MA9), were significantly smaller than those in control group (p＜0.05). MA9 in severe CTS subgroup, not mild subgroup, was significantly smaller than that in control group (p＜0.05). CTS and control group were not significantly different in the MMNAP latencies, except stimulating 9 cm proximal to the wrist (p＜0.05), and in the MMNAP conduction velocity, except stimulating in 0 cm to 3 cm segment proximal to the wrist.

Conclusion: The amplitude of MMNAP in forearm can be the most useful indicator of RD in CTS, and the conduction velocity, a less useful indicator. We believe that RD progresses as the severity of CTS increases, and dose beyond 9 cm proximal to the distal wrist crease.

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 approach 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.