Peripheral Nervous System Pathology Overview

From WikiVet English
Jump to navigation Jump to search
WikiPathWikiPath Banner.png
()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

Learning Tools