Sensory nerve action potentials in patients with peripheral nerve lesions.

In 1949 Dawson and Scott described a method of examining sensory impulses in human peripheral nerves. By their technique, the median or ulnar nerve at the level of the wrist was stimulated electrically using single shocks, and the action potential of the afferent volley recorded through surface electrodes placed over the nerve trunk at a higher level in the arm. The afferent volley contained both sensory impulses and antidromic impulses in motor fibres and gave rise to a small diphasic or triphasic potential with an amplitude of less than 50 microvolts and a duration of 2 to 3 milliseconds. To eliminate the contribution of motor fibres, Dawson (1956) modified his original technique and stimulated the digital nerves through small ring electrodes wrapped round the fingers, the afferent volley being recorded as before through surface electrodes placed over the median or ulnar nerve trunk in the arm. The sensory potentials recorded were similar in form to the mixed nerve action potentials obtained previously, but, being derived from digital nerves, they were considerably smaller in amplitude. In view of Dawson's findings it seemed worthwhile to investigate the behaviour of sensory action potentials in patients with peripheral nerve lesions, and the present paper is based on some 50 cases examined in this way. In general the technique has proved to be of considerable value in the clinical assessment of patients, and in certain cases it has provided more information about sensory nerve function than could be obtained by formal sensory testing.