Diagnosis of brachial plexus traction lesions by sensory nerve action potentials and somatosensory evoked potentials.

Forty-two patients with unilateral brachial plexus traction lesions were investigated by recording sensory nerve action potentials (SNAPs) from the lower arm and somatosensory evoked potentials (SEPs) from the clavicle, the cervical spine and the scalp overlying the contralateral somatosensory cortex, in response to electrical stimulation of peripheral nerves. The median and radial nerves were assumed to derive principally from the C6 and C7 roots, and the ulnar nerve from the C8 and T1 roots. Combination of SEP and SNAP findings suggested a location for the lesion (preganglionic, postganglionic or combining pre-and postganglionic elements) which was found to be accurate in 10 out of 16 operated cases, and substantially accurate in another 3. There was a poor correlation, however, between the presence of absence of SNAPs in the musculocutaneous nerve and the location of the lesion to the C5 root.