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Nerve trauma neuropathy

icanis
Contributor(s):

Rodney Bagley

Synonym(s): Traumatic neuropathy


Introduction

  • Most common cause of neuropathies.
  • Cause:
    • Accident - mechanical blow, road traffic accidents (RTAs), gunshot wounds, fractures, pressure and stretching.
    • Iatrogenic - crushing, cutting or spiking the nerve during surgery (especially orthopedic procedures) compression by casts, splints or other dressings, injection into or adjacent to nerve.
  • Signs: depend on severity of injury: range from temporary loss of function to complete loss of function and muscle atrophy.
  • Diagnosis: loss of nerve function.
  • Treatment: surgical anastomosis, neurolysis, electromyography.
  • Prognosis: depends on severity of lesion. Good to poor.

Pathogenesis

Etiology

  • Accident: trauma, eg gunshot, RTA, mechanical blow, fracture, pressure, ischemia.
  • Iatrogenic, eg cutting, crushing, spiking, compression by dressings, casts or splints, injections into or adjacent to nerve.
  • Brachial plexus avulsion most common after automobile trauma.
  • Peripheral limb nerves may be iatrogenically damaged during orthopedic surgery.

Predisposing factors

General
  • Access to traffic.
  • Use, eg gun dog, cattle dog.
  • Orthopedic procedure.
  • Intramuscular injections.
  • Boisterous, clumsy, temperament.

Pathophysiology

  • Trauma can occur to a single nerve (misplaced injection into the sciatic nerve) or multiple nerves (brachial plexus avulsion).
  • The severity of involvement clinically will determine prognosis.
  • Aneuropraxia(least severe injury) is an interruption in function and conduction in the nerve, usually associated with a lesion of the myelin without severe axonal involvement.
  • Axonotmesissuggests separation and damage of axons, where neurotmesis (most severe injury) is complete severance of all structures of the nerve.
  • The likelihood of regeneration is less with neurotmesis as compared to neuropraxia.
  • Mild trauma → temporary conduction block → physiological disruption of axonal function → no structural damage to axon.
  • More severe trauma → transection of axon (axotomy) → degeneration of distal axon divorced from cell body → impulses travelling down proximal stump no longer innervate muscle (motor) or receptor (sensory):
    • Motor disruption → loss of muscle function (paresis/paralysis), hypotonia, flaccidity.
    • Sensory disruption → anesthesia or dysthesia.

    First degree injury
  • No structural damage, loss of function - neuropraxia.
    Second degree injury
  • Axotomy, but basal lamina intact - axonotemesis.
  • Loss of function to sensory dermatomes and muscle supplied by affected nerve.
    Third degree injury
  • Axotomy with disruption of basal lamina; perimeurium, epineurium intact - neurotemesis I.
  • Epineurial and perineurial scarring at site of injury may impede regeneration.
  • Loss of function → endoneurial scarring reduces chances of reinnervation.
    Fourth degree injury
  • Axotomy with basal lamina, perineurial and epineurial disruption, ie transection - neurotemesis II.
  • Epineurial and perineurial scarring at site of injury most likely in this form of injury - may impede regeneration.
  • Loss of function → endoneurial scarring reduces chances of successful reinnervation.
    Fifth degree injury
  • Nerve completely severed.

Timecourse

  • Neurological deficits immediately after injury.
  • Onset of muscle atrophy after 7-10 days.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Jeffery N D & Blakemore W F (1999) Spinal cord injury in small animals. 1.​ Mechanisms of spontaneous recovery. Vet Rec 144 (15), 407-413 PubMed.
  • Braund K G (1991) Nerve and muscle biopsy techniques. Progress Vet Neurol 2 (1), 35-56 VetMedResource.
  • Kline D G (1990) Surgical repair of peripheral nerve injury. Muscle and Nerve 13 (9), 843-852 PubMed.
  • Gibson K L & Daniloff J K (1989) Peripheral nerve repair. Comp Cont Educ Pract Vet 11 (8), 938-944 VetMedResource.
  • Steinberg H S (1988) Brachial plexus injuries and dysfunctions. Vet Clin North Am Small Anim Pract 18 (3), 565-580 PubMed.
  • Thomas P K (1988) Clinical aspects of PNS regeneration. Advances Neurol 47, 9-29 PubMed.
  • Fanton et al (1983) Sciatic nerve injury as a complication of intramedullary pin fixation of femoral fractures. JAAHA 19 (5), 687-94 VetMedResource.
  • Allam M W, Lee D G, Nulsen F E & Fortune E A (1952) The anatomy of the brachial plexus of the dog. Anat Rec 114 (2), 173-9 PubMed.

Other sources of information

  • Rodkey W G (1993)Peripheral Nerve Surgery.In:Textbook of Small Animal Surgery.2nd edn. Ed: Slatter D. Philadelphia: W B Saunders. pp 1135-1141.
  • Swain S F (1987)Peripheral nerve surgery.In:Veterinary Neurology.Eds: Oliver, Horlein & Mayhew. W B Saunders.

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