To Establish Severity of the Lesion

Electrodiagnostic testing can see if the injury is just the myelin sheath, or if there is axonal involvement, and to what degree. 

On nerve conduction testing:

• The amplitude of compound muscle action potentials can be compared against reference values,
• Potentials can also be compared internally against the patient’s unaffected side, to estimate a percentage of axon loss. Nerve conduction velocities and distal onset latencies can be used in a similar way.

On needle EMG:

• The detection of muscle membrane irritability, the ability of muscle to recruit motor units, analysis of motor units for different parameters, and their stability, gives rise to an estimation of the severity of axonal involvement