Figure.

Muscle action potentials after distal and proximal stimulation of a nerve to a muscle such as abductor pollicis brevis. The upper trace of each pair is the record after distal stimulation. In the normal nerve the distal motor latency is short and nerve conduction velocity rapid (>50m/sec). In demyelinating neuropathy the distal motor latency is prolonged and nerve conduction velocity slowed to less than 80% of normal. In axonal neuropathy the action potential is reduced, but the distal motor latency and nerve conduction velocity are unaffected. Multifocal abnormalities with normal conduction velocity suggest multiple mononeuropathy