Seddon Classification of nerve injury

1. What is neuropraxia and how does it affect the EMG?
2. What is axonotmesis and how does it affect the EMG?
3. What is neurotmesis and how does it affect the EMG?

Answers:
1. Neuropraxia occurs when there is a nerve compression injury and the axon is intact underneath. Due to the myelin injury, there is a conduction block. NCS is normal distal to the lesion but abnormal across it. EMG may show decreased recruitment.
2. Axonotmesis results from a nerve crush injury in which there is axonal interruption, but the CT and Schwann cell are intact. The NCS is similar to in neuropraxia until Wallerian degen occurs (4-5 days). EMG is abnormal.
3. Neurotmesis is a nerve transection in which there is complete axonal interruption, CT disruption (endoneurium, perineurium, and epineurium), and conduction failure. Unlike axonotmesis, there is no recovery. EMG is abnormal.