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Peripheral Nervous System Pathology Overview (view source)

Revision as of 11:03, 18 August 2008

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==Nerve Injury==
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===Classification of Peripheral Nerve Disease===
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{| cellpadding="4" cellspacing="0" border="2"
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|-
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|style="background:#B0E0E6; color:black" width="200"|'''By Nerve Type
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|style="background:#B0E0E6; color:black" width="200"|'''By Anatomy'''
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|style="background:#B0E0E6; color:black" width="250"|'''By Pathology'''
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|-
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|
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*Mixed
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|
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*NMJ
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|'''Neuronopathy :'''    ''The Whole nerve cell''
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|-
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|
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*Motor
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|
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*Distal / Proximal
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|'''Axonopathy      :'''    ''The axon''
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|-
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|
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*Sensory
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|
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*Root / Spinal Cord
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|'''Demyelination:'''    ''Schwann cell''
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|-
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|}
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<br>
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===Types of Injury===
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{| cellpadding="4" cellspacing="0" border="2"
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|-
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|style="background:#B0E0E6; color:black"|'''Neuropraxia:'''||
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*Temporary interruption of conduction - no histological change.
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|-
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|style="background:#B0E0E6; color:black"|'''Axonotemesis:'''||
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*Axon interupted but basal lamina intact (e.g. crush injury)
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*Regeneration occurs along original path - prospect for functional recovery good.
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|-
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|style="background:#B0E0E6; color:black"|'''Neurotemesis:'''||
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*Axon '''and''' basal lamina interupted (e.g. transection injury)
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*Success of regeneration depends on finding the correct distal stump
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|}
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<br>
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===Clinical Signs with Peripheral Nerve Disease===
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{| align="center" cellpadding="4" cellspacing="0" border="0"
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|width="350"|
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:<u>'''Motor Neuropathy Signs (LMN signs)'''</u>
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|width="350"|
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:<u>'''Sensory Neuropathy'''</u>
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|width="350"|
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:<u>'''Autonomic Neuropathy'''</u>
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|-
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|
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*Flaccid paresis/paralysis of innervated structures
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|
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*Decreased or abherrant 'pain' response or sensation
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|
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*Aniscoria (dilated / constricted pupils)
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|-
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|
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*Neurogenic muscle atrophy (very rapid)
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|
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*Proprioceptive defects
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|
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*Decreased tear production
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|-
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|
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*Reduced / absent reflexes and muscle tone
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|
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*Abnormal sensation (paraesthesia)/sensitivity (dysthesia)
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|
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*Decreased salivation
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|-
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|
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|
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*Reduced / absent reflexes without muscle atrophy
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|
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*Bradycardia
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|}
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<br>
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==Peripheral Nerve Disease in Small Animals==
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{| cellpadding="4" cellspacing="0" border="2"
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|- style="background:#B0E0E6; color:black"
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|width="150"|<center><big>'''Disease'''</big></center>
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|width="200"|<center><big>'''Pathology'''</big></center>
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|width="250"|<center><big>'''Clinical Signs'''</big></center>
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|width="250"|<center><big>'''Diagnosis'''</big></center>
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|width="250"|<center><big>'''Prognosis + Treatment'''</big></center>
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|-
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|<center><big>'''Distal Denervating Disease'''</big></center>
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|
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*Distal axonopathy, possibly of toxic origin
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|
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*Tetraparesis
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*Dysphonia / Aphonia
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*Neck Weakness
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*Tetraparesis developing to tetraplegia in severe cases ''floppy dog''
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*Sensory function preserved: Pain but '''no''' withdrawal
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|
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*Biopsy / EMG unhelpful
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|
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*Very good prognosis
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*Recovery in 3-6 weeks by '''axon regeneration'''
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*Good nursing to prevent pressure sores in the recumbant animal
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|- style="background:#F0F8FF; color:black"
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|<center><big><span id="IPRN">'''Idiopathic Polyradiculoneuritis'''</span></big></center>
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|
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*Immune mediated demyelination often involving roots, directed against unknown epitopes in peripheral myelin.
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*May be post infection
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*May get axonal injury if severe
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|
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*As for distal denervating (although more rapid onset)
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*May have sensory involvement.
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|
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*By clinical signs
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*CSF changes if roots involved
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*Slower nerve conduction
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*H reflexes and F-waves may be lost
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|
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*Very good prognosis
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*Recovery in 3-6 weeks by '''remyelination'''
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*Immunosuppresive levels of corticosteroids (although may delay remyelination)
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|-
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|<center><big>'''Cauda Equina Traction'''</big></center>
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|
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*Tail pull injury
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*Esp. cats after RTA
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*Lesion via longitudinal traction
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*Sacrocaudal dislocation/fracture
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|
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*Limp tail
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*Incontinence
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*Hindlimb Paresis
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|
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*Diagnosis on Clinical signs and history
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*+/- Radiographs to show dislocation/fracture
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|
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*Prognosis difficult to predict
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*Poor prognosis if tail limp & no anal tone
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*Supportive treatment
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*'''Persist for >3 months if possible'''
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|- style="background:#F0F8FF; color:black"
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|<center><big>'''Peripheral Nerve Tumours'''</big></center>
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|
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*Nerve sheath tumours
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*Generally tumours of Schwann cells
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*Common in dog Brachial plexus
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|
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*Chronic single forelimb lameness
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*Weakness
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*Muscle Atrophy
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*Pain in Axilla
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*LMN signs (may get UMN if grows into spinal cord
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|
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*Clinical signs
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*Imaging
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|
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*Prognosis dependant on location
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*Poor prognosis if in spinal cord
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*Amputation of limb?
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|-
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|<center><big>'''Feline Dysautonomia'''</big></center>
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|
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*Common in 1980's - Sporadic now
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*Degeneration (toxic?) of autonomic ganglia
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|
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*Mainly Parasympathetic
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*Vomiting
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*3rd Eyelid protrusion
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*Dilated pupils + poor PLR
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*Reduced Lacrimation
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*Megaoesophagus
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*Bradycardia
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|
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*Clinical signs
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|
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*Poor Prognosis
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*Supportive therapy only
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*Similar sporadic disease seen in dogs
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|-
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|}
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==Peripheral Nerve Disease in Large Animals==
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{| cellpadding="4" cellspacing="0" border="2"
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|-- style="background:#B0E0E6; color:black"
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|width="150"|<center><big>'''Disease'''</big></center>
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|width="200"|<center><big>'''Pathology'''</big></center>
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|width="250"|<center><big>'''Clinical Signs'''</big></center>
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|width="250"|<center><big>'''Diagnosis'''</big></center>
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|width="250"|<center><big>'''Prognosis + Treatment'''</big></center>
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|-
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|<center><big>'''Idiopathic Laryngeal Hemiplagia (ILH)'''</big></center>
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|
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*Progressive loss of fibres (esp. large diameter) within left recurrent laryngeal nerve compared to right
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*[[PNS Repsonses to Injury#The 'Dying Back' Phenomenon|Dying back]] axonopathy with myelin sheath involvement:
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**Degenerating fibres
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**Regenerating clusters
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**De/Re-myelination
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*Flattening of nerve between aorta & trachea
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|
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*Inspiratory 'roaring' noise - flapping of vocal fold
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|
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*'Slap test' - adduction of contralateral arytenoid during expiration
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*Endoscopic examination - assymetric arytenoids, poor abduction of left vocal fold.
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*Palpable atrophy of laryngeal musculature
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|
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*Laryngeal Ventriculectomy (Hobday procedure)
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*'Tie Back'
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*Laryngeal muscle prosthesis
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*Prognosis usually good
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|-style="background:#F0F8FF; color:black"
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|<center><big>'''Cauda Equina Neuritis'''</big></center>
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|
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*Equine version of [[#IPRN|Idiopathic polyradiculoneuritis]]
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*Extradural nerve roots of cauda equina thickened and discoloured
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*Inflammatory infiltrate (lymphocytes, plasma cells, macrophages)
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*Extensive axonal damage and demyelination
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*Cranial nerve involvement often occurs
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*Aetiology unknown:
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**Antecedent infection?
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**Antibodies to PNS myelin?
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|
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*Paralysis & anaesthesia of tail
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*Urinary incontinence
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*Loss of anal reflex
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*Failure to defaecate
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*Pain/hypersensitivity in gluteal/tail-head area
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|
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*Clinical signs
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|
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*Recovery unlikely - most animals are destroyed.
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|-
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|<center><big>'''Stringhalt'''</big></center>
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|
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*Causes poorly understood - similar signs caused by sweat pea plant ingestion (lathyrism)
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*Distal axonopathy (esp. large diameter fibres)
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|
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*Abrupt onset continuous / intermittent hyperflexion of one or both hind limbs
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*May also have ataxia, urinary incontinence, perineal flaccidity
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|
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*Differential diagnosis : Upward fixation of patella
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|
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*May get spontaneous recovery
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*Move pasture
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*Tenectomy of lateral digital extensor may help
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|-
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|-style="background:#F0F8FF; color:black"
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|<center><big>'''Equine Motor Neuron Disease'''</big></center>
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|
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*Generalised LMN disorder
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*Degeneration of Ventral horn motor neuron
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*[[PNS Repsonses to Injury#Chromatolysis|Chromatolysis]]
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*Neurofilament accumulation
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*Gliosis
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*[[PNS Repsonses to Injury#Wallerian Degeneration|Wallerian degeneration]]
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*Denervation changes in muscle
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|
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*Weight Loss
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*Muscle atrophy
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*Generalised Weakness
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*Short strided gait + narrow based stance
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*Trembling
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*Sweating and fasiculations
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*Increased recumbency
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|
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*Elevated CK
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*CSF protein
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*Denervation of EMG
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|
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*May progress to constant recumbency (destroy), stabilise or improve
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|-
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|<center><big>'''Suprascapular Nerve Injury'''</big></center>
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|
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*'''"Sweeny"'''
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*Commonly damaged by horse coliding into objects
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*Fibrous entrapment as nerve reflected around wing of scapula
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*Atrophy of supra- & infra- spinatous muscles
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|
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*Lateral luxation of shoulder when weight bearing
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*Muscle wasting around shoulder
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|
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*Clinical signs
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*History
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|
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*No more than 30cm regrowth in 12 months expected due to irreversible muscle fibrosis.
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|-
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|}
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==Other Polyneuropathies==
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*Tick Paralysis
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*Vincristine Toxicity
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*Endocrine polyneuropathy
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**Dogs - hypothyroidism, insulinoma, diabetes mellitus
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**Cats - diabetes mellitus
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*Genetic polyneuropathies
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*Protozoan polyradiculoneuritis
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*Idiopathic facial paralysis (e.g. Bell's Palsy)
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*Botulism
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==Learning Tools==
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