Common equine neurological disease Flashcards
What are different causes of neurological diseases in horses? (viral / Bacterial / parasitic / clostridial toxins / neurodegenerative / metabolic / neurotoxins / vascular)
- Viral = EHV1; rabies; Borna disease; Eastern, Western and Venezuelan encephalitis; West Nile Virus
- Bacterial = meningitis, encephalitis
- Protozoal = EPM
- Parasitic = aberrant migration
- Clostridial toxins = tetanus, botulism
- Neurodegenerative disorders = EDM; EMND; EGS; cerebellar abiotrophy
- Metabolic = HE; intestinal hyperammoniaemia; HYPP, Electrolyte imbalances (Ca, MG, Na…)
- CVSM
- Trauma
- Peripheral nerve pathology = facial paralysis, radial nerve paralysis, sweeney, polyneuritis equi
- Neurotoxins = Avermectins; Lead, Amitraz, Bracken fern; Leukoencephalomalacia (mouldy corn); raygrass staggers
- Vascular = Thromboembolic meningoencephalitis
- Neoplasia
What are syndromes of equine neurological problems?
- Forebrain disease: including seizures and alterations in consciousness
- Brainstem abnormalities: Cranial nerve abnormalities (facial, vestibular)
- Horner’s syndrome
- Urinary incontinence and Cauda Equina Syndrome
- Spinal cord disease
- Neuromuscular disease:
–Abnormal gait: shivering, stringhalt
–Localised weakness: peripheral nerve injuries
–Diffuse weakness: EMND, botulism, EGS, HYPP
–Excessive activity: Tetatus
What is seen with forebrain disease?
- Disorders of behaviour and personality = aggression, compulsive walking, loss of learnt behaviour, yawning…
- Seizures
- Blindness
- Altered states of consciousness:
-Alert → Quiet → Depressed → Obtunded → Comatose - Head posture
What can cause forebrain disease in adults?
– Trauma = ↑↑
– Metabolic = HE, intestinal hyperammoniaemia,
– Intracarotid injection
– Cholesterol granuloma
– Infectious meningoencephalomyelitis
– Neoplasia
How would you treat forebrain disease due to trauma in horses?
- Oxygen supplementation
- Fluid therapy
- NSAIDs
- Elevate head
- Steroids?
What are forebrain diseases due to metabolic disease?
- Hepatic encephalopathy - check liver parameters
- Intestinal hyperammoniaemia
-enteritis / /colitis
-increased permeability
What are forebrain disease due to sleep disorders?
- True narcolepsia = rare
- Sleep deprivation =
-inability to lie down
-muscoskeletal pain
-fear
What are forebrain disease due to seizures?
- Rare in adults - high seizure threshold
-trauma, encephalitis, metabolic, neoplasia - Neonatal seizures + epilepsy =
-low seizure threshold
-most common = PAS, sepsis, trauma
-also = metabolic juvenile idiopathic arab epilespy (<12m/o)
What are signs of brainstem + cranial nerve disease?
- Vestibular disease = peripheral or central
- Facial nerve paralysis (VII and VIII frequently affected together)
- Pharyngeal/laryngeal deficits: dysphagia
- Other cranial nerve deficits
- Severe brainstem lesions: gait abnormalities, coma (RAS
What are signs of vestibular disease? What are causes?
- CS =
-Head tilt
-Nystagmus
-Ventral strabismus
-Ataxia - Causes =
-trauma = central / peripheral
-idiopathic
-otitis media / interna
What can cause facial nerve injury? What are CS?
- Causes =
-Iatrogenic = halters left on during field anaesthesia
-trauma (+/-vestibular)
-THO (+/-vestibular) - CS =
-dropped ear
-ptosis
-nostril deviation
What can prolonged facial nerve injury lead to?
- Prolonged / permanent deficits =
-exposure keratitis
-dysphagia - feed pouching
-poor performance = nostril collapse
What is horners syndrome? Causes? Signs?
- Interruption of the sympathetic innervation to head + neck
- Causes = iatrogenic due to extravascular injection of irritant substance (PBZ / buscopan)
- CS =
-miosis, enophthalmos, ptosis, protruding nictitating membrane
-hyperaemic membranes, sweating
What is cauda equina syndrome?
- Sacrococcygeal spinal cord segments, cauda equina, sacral plexus + peripheral nerves to the bladder, rectum, anus, tail + perineum
-leads to gait abnormalities
What are signs of cauda equina syndrome?
- Degrees of hypotonia, hyporeflexia ad hypalgesia of the tail, anus and perineal region, urinary bladder paralysis, rectal dilation, penile prolapse
- May also see LMN weakness and paresis of pelvic limbs
- Can be difficult to distinguish UMN disease with urinary retention and 2ary contusion of tail and anus from recumbency
What are causes of cauda equina syndrome?
- Trauma = sacrococcygeal fracture and luxation, avulsion of the cauda equina
- Infectious, inflammatory, immune =
-Inflammatory = polyneuritis equi (± cranial nerve signs)
-Viral / immune = EHV-1 (± ataxia, ± cranial nerve signs)
-Verminous = EPM
How is EHV-1 myeloencephalopathy diagnosed?
- Lesion location
- Rule out other causes
- History of respiratory disease +/or abortion
- CSF sample = xanthochromic +/-Abs to EHV-1
- Detection of virus in affected or in-contacts
- High antibody titres
How would you manage EHV-1 myeloencephalopathy?
- Isolate
- Good prognosis w good nursing
- Vasculitis = NSAIDS, steroids, aspirin
- Antivirals = acyclovir, valacyclovir
What are causes of spinal cord disease?
- Spinal cord trauma
- Cervical vertebral malformation (CVM) / Cervical vertebral stenotic myelopathy (CVSM) / Wobbler syndrome
What are signs of spinal cord trauma? What is management?
- CS = Vary from ataxia + paresis to recumbency
- Management =
-aggressive NSAIDs / steroids
-surgical tx
-box rest if standing
-nursing care if recumbent
-TIME
What is the most common cause of ataxia in horses in the UK? What are the 2 cateogories?
- Cervical vertebral malformation
- Type I =
-young horses, dynamic stenosis, at any site
-compression as result of developmental abnormalities - Type II =
-Older horses, Static stenosis, OA of articular process
-C5-C6 and C6-C7 most common
How can you diagnose CVM?
- Clinical signs
- Radiography = doesn’t always show abnormalities
- Myelography - extra information
What are risks of myelography?
- Doesn’t always provide extra info
- Has risks of anaesthesia - induction + recovery of ataxic animal
- Has risk associated with technique - iatrogenic damage to spine, diffusion of contrast into brain
- Not performed very often
What is management of cervical vertebral malformation?
- Surgery can be performed but it is costly and may only improve the horse on average one grade
- An ataxic horse should not be ridden
- Type I = Early detection in young foals and dietary restrictions have resulted in resolution of ataxia and successful careers.
-Once disease is advanced prognosis is poor - Type II = intraarticular corticosteroids (US guided)
What are other spinal cord disease?
- Occipitoatlantoaxial malformation
- Neoplasia
- Vertebral body osteomyelitis
What is seen with neuromuscular disease?
- Abnormal gait = shivering, stringhalt
- Localised weakness = peripheral nerve injuries
- Diffuse weakness = EMND, botulism, EGS, HYPP
- Excess activity = tetanus
What is stringhalt?
- Sudden, involuntary, exaggerated flexion of one / both hindlimbs during attempted movement
- 2 types =
-australian / plant associated = dandelion, flat weed = Tx = remove from pasture
-sporadic stringhalt = unknown = Tx = myotenectomy of lateral digital extensor
What nerves are commonly affected by peripheral nerve injuries? What is treatment?
- Radial nerve / suprascapular nerve
-often external blows - Tx = antiinflammatories, DMSO, physiotherapy
What is equine motor neuron disease?
- Degeneration of motor neurons in spinal cord due to low vit E (and Se?) concentration.
- Normally history of horse stabled with no access to pasture for a period of time
- Signs: weight loss (muscle wasting), muscle fasciculations, prolonged recumbency
- Ocular signs in 30-40% cases: brown pigment accumulation in retina
How is equine motor neuron disease diagnosed? Treatment?
- Vit E (+selenium) levels
- Muscle biopsy
- Tx = Vit E supplementation
What causes botulism? What does it do?
- Clostridium botulinum
-from contaminated feed (big bales), grass / corn silage
-water (dead waterfowl)
-poultry litter + carcasses - Blocks ACh release at presynaptic membrane of N-M junction = failure of muscle contraction = weak
-Flaccid paralysis
What are signs of botulism?
- Symmetrical weakness (muscle tremors)
- Stumble, ataxia
- Tongue weakness, dysphagia
- Hang head, nose on ground
- Dyspnoea - intercostal + diaphragm paralysis
- GI stasis, urine dribbling
- SHAKER FOAL SYNDROME
- Eventually recumbent
How is botulism diagnosed / treated? Prognosis?
- Dx = identify toxin / spores
-stomach content (+/-faces / feed) - Tx = antitoxin
-penicillin
-supportive, fluids - Poor prognosis - if tetraplegia
What causes tetanus? What does it do?
- Clostridium tetani
-gram + anaerobic
-tetanospasmin =
neurotoxin = migrates retrograde along motor neurone to spinal cord + brainstem
-tetanolysin = increase tissue necrosis at site
What does tetanospasmin do?
- Inhibits release of glycine
- Inhibits presynaptic inhibitory neurons in spinal cord
- Muscles continuously contract
- Tetany elicited by sound, light, touch
What are signs of tetanus?
– Elevated tail head
– Stiff gait
– Anxious: ears back, eyelids wide open, nostrils flared, head extended
– Lock jaw: drool, can’t swallow
– Prolapse 3rd eyelid
– Recumbency, rigidity
– Secondary ulcers, trauma
How is tetanus treated?
- Support = quiet, dark, low stimulation room. Hydration, deep bedding
- Eliminate source = open, flush wound. Treat with metronidazole
- Neutralise unbound toxin = antitoxin
- Muscle relaxation = acepromazine, diazepam
- Toxoid = treatment + prevention
