Table 1

‚ÄÉTypical nerve conduction study abnormalities seen with axon loss or demyelination

Axon lossDemyelination
It is not necessary to have all the features of axon loss or demyelination to come to a conclusion. Some conditions only affect motor or sensory nerves, and some processes are length dependent and others universal. It can sometimes be quite difficult to decide whether a process is primarily demyelinating or demyelinating with secondary axonal changes as features of both may coexist.
Sensory responsesSmall or absentSmall or absent
Distal motor latencyNormal or slightly prolongedProlonged
CMAP amplitudeSmallNormal (reduced if conduction block or temporal dispersion)
Conduction block/temporal dispersionNot present (responses may disperse slightly)Present
Motor conduction velocityNormal or slightly reducedNotably reduced
F waves minimum latencyNormal or slightly prolongedSignificantly prolonged