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Electrophysiology
NCV: Demyelinating Neuropathy + Axonal loss
Conduction velocities
Uniformly slow in all nerves
Mean 17 to 20 M/s
Range 5 to 34 M/s
Time course of NCV slowing
Clearly present by 2 years
Onset before clinical signs appear
Slower in earlier onset patients
Stable after age 5 years
No conduction block
Compound motor action potential (CMAP): Small
Due to axonal loss
Degree of reduction: Correlates with
Disease severity
Slowing of NCV
Nerve length
May be progressively reduced over time
Distal latency: Prolonged, Even in 1st months of life
F-wave responses: Prolonged
Sensory potentials
Often absent
Slow velocity & Small amplitude when present
EMG: Denervation, Distal > Proxiomal
Brainstem auditory evoked potentials: Delayed wave I
CSF: High Protein, Less in duplication patients
Pathology: Early excess myelin production