Peripheral Nervous System Pathology Overview

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()Map NERVOUS SYSTEM (Map)



Nerve Injury

Classification of Peripheral Nerve Disease

By Nerve Type By Anatomy By Pathology
  • Mixed
  • NMJ
Neuronopathy : The Whole nerve cell
  • Motor
  • Distal / Proximal
Axonopathy : The axon
  • Sensory
  • Root / Spinal Cord
Demyelination: Schwann cell


Types of Injury

Neuropraxia:
  • Temporary interruption of conduction - no histological change.
Axonotemesis:
  • Axon interupted but basal lamina intact (e.g. crush injury)
  • Regeneration occurs along original path - prospect for functional recovery good.
Neurotemesis:
  • Axon and basal lamina interupted (e.g. transection injury)
  • Success of regeneration depends on finding the correct distal stump


Clinical Signs with Peripheral Nerve Disease

Motor Neuropathy Signs (LMN signs)
Sensory Neuropathy
Autonomic Neuropathy
  • Flaccid paresis/paralysis of innervated structures
  • Decreased or abherrant 'pain' response or sensation
  • Aniscoria (dilated / constricted pupils)
  • Neurogenic muscle atrophy (very rapid)
  • Proprioceptive defects
  • Decreased tear production
  • Reduced / absent reflexes and muscle tone
  • Abnormal sensation (paraesthesia)/sensitivity (dysthesia)
  • Decreased salivation
  • Reduced / absent reflexes without muscle atrophy
  • Bradycardia


Peripheral Nerve Disease in Small Animals

Disease
Pathology
Clinical Signs
Diagnosis
Prognosis + Treatment
Distal Denervating Disease
  • Distal axonopathy, possibly of toxic origin
  • Tetraparesis
  • Dysphonia / Aphonia
  • Neck Weakness
  • Tetraparesis developing to tetraplegia in severe cases floppy dog
  • Sensory function preserved: Pain but no withdrawal
  • Biopsy / EMG unhelpful
  • Very good prognosis
  • Recovery in 3-6 weeks by axon regeneration
  • Good nursing to prevent pressure sores in the recumbant animal
Idiopathic Polyradiculoneuritis
  • Immune mediated demyelination often involving roots, directed against unknown epitopes in peripheral myelin.
  • May be post infection
  • May get axonal injury if severe
  • As for distal denervating (although more rapid onset)
  • May have sensory involvement.
  • By clinical signs
  • CSF changes if roots involved
  • Slower nerve conduction
  • H reflexes and F-waves may be lost
  • Very good prognosis
  • Recovery in 3-6 weeks by remyelination
  • Immunosuppresive levels of corticosteroids (although may delay remyelination)
Cauda Equina Traction
  • Tail pull injury
  • Esp. cats after RTA
  • Lesion via longitudinal traction
  • Sacrocaudal dislocation/fracture
  • Limp tail
  • Incontinence
  • Hindlimb Paresis
  • Diagnosis on Clinical signs and history
  • +/- Radiographs to show dislocation/fracture
  • Prognosis difficult to predict
  • Poor prognosis if tail limp & no anal tone
  • Supportive treatment
  • Persist for >3 months if possible
Peripheral Nerve Tumours
  • Nerve sheath tumours
  • Generally tumours of Schwann cells
  • Common in dog Brachial plexus
  • Chronic single forelimb lameness
  • Weakness
  • Muscle Atrophy
  • Pain in Axilla
  • LMN signs (may get UMN if grows into spinal cord
  • Clinical signs
  • Imaging
  • Prognosis dependant on location
  • Poor prognosis if in spinal cord
  • Amputation of limb?
Feline Dysautonomia
  • Common in 1980's - Sporadic now
  • Degeneration (toxic?) of autonomic ganglia
  • Mainly Parasympathetic
  • Vomiting
  • 3rd Eyelid protrusion
  • Dilated pupils + poor PLR
  • Reduced Lacrimation
  • Megaoesophagus
  • Bradycardia
  • Clinical signs
  • Poor Prognosis
  • Supportive therapy only
  • Similar sporadic disease seen in dogs

Peripheral Nerve Disease in Large Animals

Disease
Pathology
Clinical Signs
Diagnosis
Prognosis + Treatment
Idiopathic Laryngeal Hemiplagia (ILH)
  • Progressive loss of fibres (esp. large diameter) within left recurrent laryngeal nerve compared to right
  • Dying back axonopathy with myelin sheath involvement:
    • Degenerating fibres
    • Regenerating clusters
    • De/Re-myelination
  • Flattening of nerve between aorta & trachea
  • Inspiratory 'roaring' noise - flapping of vocal fold
  • 'Slap test' - adduction of contralateral arytenoid during expiration
  • Endoscopic examination - assymetric arytenoids, poor abduction of left vocal fold.
  • Palpable atrophy of laryngeal musculature
  • Laryngeal Ventriculectomy (Hobday procedure)
  • 'Tie Back'
  • Laryngeal muscle prosthesis
  • Prognosis usually good
Cauda Equina Neuritis
  • Equine version of Idiopathic polyradiculoneuritis
  • Extradural nerve roots of cauda equina thickened and discoloured
  • Inflammatory infiltrate (lymphocytes, plasma cells, macrophages)
  • Extensive axonal damage and demyelination
  • Cranial nerve involvement often occurs
  • Aetiology unknown:
    • Antecedent infection?
    • Antibodies to PNS myelin?
  • Paralysis & anaesthesia of tail
  • Urinary incontinence
  • Loss of anal reflex
  • Failure to defaecate
  • Pain/hypersensitivity in gluteal/tail-head area
  • Clinical signs
  • Recovery unlikely - most animals are destroyed.
Stringhalt
  • Causes poorly understood - similar signs caused by sweat pea plant ingestion (lathyrism)
  • Distal axonopathy (esp. large diameter fibres)
  • Abrupt onset continuous / intermittent hyperflexion of one or both hind limbs
  • May also have ataxia, urinary incontinence, perineal flaccidity
  • Differential diagnosis : Upward fixation of patella
  • May get spontaneous recovery
  • Move pasture
  • Tenectomy of lateral digital extensor may help
Equine Motor Neuron Disease
  • Weight Loss
  • Muscle atrophy
  • Generalised Weakness
  • Short strided gait + narrow based stance
  • Trembling
  • Sweating and fasiculations
  • Increased recumbency
  • Elevated CK
  • CSF protein
  • Denervation of EMG
  • May progress to constant recumbency (destroy), stabilise or improve
Suprascapular Nerve Injury
  • "Sweeny"
  • Commonly damaged by horse coliding into objects
  • Fibrous entrapment as nerve reflected around wing of scapula
  • Atrophy of supra- & infra- spinatous muscles
  • Lateral luxation of shoulder when weight bearing
  • Muscle wasting around shoulder
  • Clinical signs
  • History
  • No more than 30cm regrowth in 12 months expected due to irreversible muscle fibrosis.

Other Polyneuropathies

  • Tick Paralysis
  • Vincristine Toxicity
  • Endocrine polyneuropathy
    • Dogs - hypothyroidism, insulinoma, diabetes mellitus
    • Cats - diabetes mellitus
  • Genetic polyneuropathies
  • Protozoan polyradiculoneuritis
  • Idiopathic facial paralysis (e.g. Bell's Palsy)
  • Botulism

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