Forearm median nerve conduction velocity in carpal tunnel syndrome.

Reduced velocity of median nerve conduction in the forearm of patients with carpal tunnel syndrome (CTS) has been attributed to an artifact of the electrodiagnostic method rather than pathophysiologic changes in the forearm segment. Standard nerve conduction velocity (NCV) tests measure the forearm segment in combination with the distal latency and this may not represent an accurate assessment of conduction in the proximal portion of the nerve. A new technique of direct evaluation of the forearm median nerve was developed by the stimulation and recording of the forearm nerve action potential (FNAP) proximal to the wrist. The FNAP measurement was compared to the usual NCV in persons with CTS and control subjects. Forearm median nerve conduction velocities in the CTS group were significantly slower (p less than 0.05) than normal subjects using both FNAP and standard NCV techniques. The finding of decreased conduction speeds by the direct measurement of the forearm segment confirms that the reduced speeds derived from NCV are valid and suggests that retrograde degeneration of the nerve axons may result from entrapment in the carpal tunnel.