Evoked potentials in the investigation of traumatic lesions of the peripheral nerve and the brachial plexus.

Nerve conduction studies using nerve action potential (NAP), sensory nerve action potential (SNAP), evoked muscle action potential (M-response), retrograde conduction in the motor axon (F-response), and cortical and subcortical somatosensory evoked potential (SEP) are useful tools for evaluation of the peripheral nervous system. SEP recording has the advantages of being applicable to severely damaged nerves because of its amplification mechanism and of disclosing proximal root lesions that would not be disclosed by other methods. When SEP recording is used in an operating theater, the amplification mechanism is suppressed by the effect of the anesthetic. Nevertheless, it is valuable for evaluating proximal root lesions in conjunction with NAP recording and M-response. Strong M-response of the serratus anterior and paraspinal muscles is a most encouraging finding if nerve repair is performed more than seven days after brachial plexus injury. SEP recording can clarify the functional continuity of the spinal root to the spinal cord. Thus the presence of SEPs becomes an important positive finding and implies the potential of nerve repair even when an M-response is not provoked by a situation such as prolonged conduction block.