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