Digital nerve sensory potentials in lesions of cervical roots and brachial plexus.

Normal values for the amplitudes of digital sensory nerve action potentials were obtained from 190 control subjects, using an orthodromic surface-recording technique. Lower limits were calculated, taking into account laterality, age and sex; the ratios of amplitudes between different digits were also estimated. The results in control subjects were compared with those of 20 cases of trauma involving root avulsion or extraspinal injury, 38 patients with intraspinal disease, 6 patients with extraspinal disorder and 9 cases of neuralgic amyotrophy. The variability of the dermatomes is discussed and it is concluded that digital sensory potential amplitudes offer a useful method of determining the site of a nerve lesion, provided certain limitations are recognized.