Retrograde Degeneration of Median Nerve in Carpal Tunnel Syndrome -Comparison of Orthodromic and Antidromic Forearm Median Nerve Action Potential-

J Korean Assoc EMG Electrodiagn Med 1999;1(2):165-169.
Published online May 9, 1999.

Abstract

Objectives : To clarify the retrograde degeneration and its extent in the median nerve of carpal tunnel syndrome by measuring forearm nerve action potential orthodromically and antidromically. Methods : Thirty one hands of carpal tunnel syndrome(CTS) and 23 hands of normal controls were studied. Orthodromic forearm median nerve action potential(Orth) was recorded at antecubital fossa by stimulating the median nerve at wrist, and antidromic forearm median nerve action potential(Anti) was recorded vice versa. Baseline to peak amplitude and onset latency of Orth and Anti were measured, and the ratio of Anti to Orth was evaluated. Correlation between ampitude of Orth and Anti and forearm conduction velocity was also evaluated. Results : There was no difference at the latency of Anti and Orth both in CTS(Orth 2.84±0.23msec vs Anti 2.96±0.32msec) and control(Orth 2.92±0.32sec vs Anti 3.17±0.49msec). The amplitude of Anti was low in CTS(32.19±19.16μV) compared to that of control(59.72±35.38μV), and the amplitude of Orth was also low in CTS(31.76±15.21μV) compared to that of control(Orth 45.30±24.54μV) significantly. The ratio of Anti to Orth amplitude was significantly low in CTS(1.04±0.50) compared to that in control(1.57±0.59). Forearm median nerve conduction velocity well correlated with both Anti and Orth amplitude in CTS. Conclusion : Retrograde degeneration of median nerve do occur and may be extended to elbow level,so that it could play a role in reduced forearm nerve conduction velocity in CTS.

Key Words: Carpal tunnel syndrome, Forearm median nerve action potential, Retrograde degeneration, Forearm nerve conduction velocity