Determining neurapraxia in carpal tunnel syndrome.

In the evaluation of carpal tunnel syndrome by nerve conduction testing it is desirable to produce prognostic as well as diagnostic information. The finding of conduction block, or neurapraxia, is regarded as evidence that treatment can result in prompt recovery of nerve function. A technique is presented for stimulating the motor branch of the median nerve in the palm in order to detect the degree of neurapraxia due to entrapment in the carpus. In 23 normal subjects the response after palmar stimulation compared to a wrist stimulation site had a mean increase in amplitude of 0.56 mV. Persons affected with carpal tunnel syndrome had a mean amplitude increase of 2.2 mV demonstrating partial conduction block. The difference between these two values is statistically significant (P = 0.001). The routine use of this method is recommended both for more accurate diagnosis and for evaluation of the degree of neurapraxia.