Mild injury causes "neuropraxia". The nerve is still there, it just is slowed down. There is decreased impulse conduction, and prognosis is good. Moderate injury may cause interruption of axoplasmic flow and axonotmesis. Wallerian degeneration occurs over 2-3 weeks. Full recovery generally occurs within 2 months. Severe injury is called "neurotmesis". Wallerian degeneration occurs over 3-5 days, misdirected axon regeneration occurs and patients experience prolonged recovery and end up with synkinesis.

Fragmentation, swelling and degeneration is often seen in axon cylinders. There may be lymphocytic infiltration of nerve bundles. Viruses may be found - HSV, Epstein Barr, mumps, CMV and influenza.