Canis ISSN: 2398-2942

Brachial plexus: root avulsion

Synonym(s): Brachial plexopathy, brachial plexus neuritis, radial neuritis

Contributor(s): Rodney Bagley, Harry Scott

Introduction

  • Cause: trauma - usually RTA (HBC).
  • Most common cause of thoracic limb paralysis.
  • Signs: sudden onset neurological deficits in thoracic limb following trauma.
  • Diagnosis: thoracic limb paralysis.
  • Treatment: local wound treatment, physiotherapy/amputation.
  • Prognosis: guarded, very poor to fair.

Pathogenesis

Etiology

  • Trauma, eg road traffic accident → traumatic traction of nerve roots at their origin inside dura mata.

Predisposing factors

General
  • Entire male.
  • (Pro) estrus female.
  • Dog lives on busy road or in city.
  • Dog allowed to exercise unsupervised.
  • Old or faulty extending lead.
  • Dog exercised off the lead.

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.
  • A neuropraxia (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.
  • Axonotmesis suggests 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.
  • Brachial plexus avulsion occurs as a result of a trauma.
  • Clinical signs include LMN paresis/plegia in the affected thoracic limb.
  • Ipsilateral loss of the cutaneous trunci reflex (due to damage to the lateral thoracic nerve that exits the spinal cord at C8-T1 area) and/or Horner's syndrome (sympathetic nerves exit the spinal cord at T1-3) may be associated signs.
  • It is the nerve roots that are actually avulsed off of the spinal cord.
  • The innervation of regional nerves from the plexus varies in animals.
  • When regional nerves are formed by more cranial spinal rootlets than is usually seen, the plexus is said to be prefixed.
  • When the nerves originate from more caudal spinal cord segments than normal, the plexus is said to be post-fixed.
  • The relationship between prefixed, median, and post-fixed plexus types in the dog is 1:3:1.
  • Allam (1952) studied the nerves that form the brachial plexus in dogs and found the following percentages of dogs had the brachial plexus derived from the associated spinal segments:
    • 58.6 % were formed by C 6, 7, 8, and T1.
    • 20.7 % were formed by C 5, 6, 7, 8, and T1.
    • 17.24% were formed by C 6, 7, 8, T1, and T2.
    • 3.4% were formed by C 5, 6, 7, 8, T1, and T2.
  • Brachial plexus avulsion most commonly occurs in a single thoracic limb following automobile trauma.
  • (a) Pathologically, the nerve roots are contused or separated from the spinal cord.
  • (b) Diagnosis is based upon history and appropriate clinical signs.
  • (c) There is no currently available treatment.
  • (d) Prognosis depends upon the severity of nerve injury. Loss of pain sensation in the limb is a worse prognostic sign.
  • Limb forcibly abducted or rotated at its attachment to the body → traumatic traction on the spinal nerve roots at their origin inside the dura mater → disruption of the neural elements → interruption of spinal reflexes.
  • Skin desensitization and decreased muscle tone → neurogenic muscle atrophy → decreasing area of skin desensitization when nerves grow in from surrounding innervated areas.
  • Initial assessments should attempt to determine the extent of injury to the nerve:
    • Neuropraxia: a functional rather than anatomical interruption in peripheral nerve function.
    • Axonotmesis: more severe than neuropraxia. Actual axons within the nerve are separated, however, the nerve itself remains intact.
    • Neurotmesis: a complete severance of the nerve with anatomical separation of all axons.

Timecourse

  • Neurological deficits apparent immediately after injury.
  • Neurogenic muscle atrophy from 7-10 days after injury.

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.
  • Braund K G (1991) Nerve and muscle biopsy techniques. Prog 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.
  • Allam M W, Lee D G, Nulsen F E & Fortune EA (1952) The anatomy of the brachial plexus of the dog. Anat Rec 114 (2), 173-180 PubMed.

Other sources of information

  • Rodkey W G (1993)Peripheral Nerve Surgery.In:Textbook of Small Animal Surgery. 2nd edn. Slatter D(ed). Philadelphia: W B Saunders. pp 1135-1141.


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