Pathogenesis of peripheral nerve diseases

Two pathological processes predominate in diseases of peripheral nerves:

• axonal degeneration:
  • severely damaged axons degenerate distally
  • within a week the nerve becomes electrically inert
  • muscle fibres supplied by damaged motor nerves atrophy
  • EMG records show fibrillation potentials
  • axons may regrow at about 1 mm/day
  • undamaged motor fibres sprout to supply more muscle fibres
    
    
• demyelination:
  • demyelination of peripheral nerve fibres initially leaves the axon intact
  • the result is blockage or slowing of conduction
  • pressure or entrapment neuropathies are primarily caused by demyelination
  • inflammatory processes e.g. Guillan-Barre are caused by demyelination