Always consider an anatomic crossover before labeling a study abnormal, because a normal variant can mimic conduction block or unexpected innervation. CMAP amplitude is the most useful quick marker of surviving axon count and recovery potential.

Martin-Gruber anastomosis is a common median-to-ulnar crossover in the forearm; The phrenic nerve arises from C3 to C5 roots; CMAP amplitude correlates with the number of intact axons; Lower CMAP amplitude generally indicates more severe axonal loss and poorer prognosis; Unexpected innervation patterns can be normal variants rather than disease