Equine Neuro Flashcards
Give some viral causes of neurological disease
- EHV-1
- Borna disease
- Eastern, Western and Venezuelan encephalitis
- West Nile Virus
Give some bacterial causes of neurological disease
- Meningitis
- Encephalitis
Give a protozoal cause of neurological disease
EPM (equine protozoal myeloencephalitis; caused by Sarcosytsis)
Give some toxins that can cause neurological disease
- Botulism
- Tetanus
Give some neurodegenerative diseases of horses
- EDM (equine degenerative myeloencephalopathy)
- EMND (equine motor neurone disease)
- EGS (equine grass sickness)
- Cerebellar abiotrophy (kills off Purkinje cells in cerebellum)
Give some metabolic neurological diseases of horses
- HE (hepatic encephalopathy)
- Intestinal hyperammoniaemia
- HYPP (hyperkalaemic periodic paralysis disease)
- Electrolyte imbalances (eg Ca, Mg, Na)
What is CVSM?
Cervical vertebral stenotic myelopathy (‘Wobblers’)
Give some neurotoxins that can cause neurological disease in horses
-Avermectins
-Lead
-Amitraz (tick and mite tx)
-Bracken
-Rye grass (staggers)
Mouldy corn -> leukoencephalomalacia
Give a vascular cause of neurological disease in horses
Thromboembolic meningoencephalitis
What is stringhalt?
- Sudden, involuntary, exaggerated flexion of one or both hindlimbs during attempted movement
- Leg jerks in an unnatural, quick movement before dropping back down
- Seen mostly and walk and when walking backwards
- Cause unknown
- Digital extensor muscle contracts excessively
What is shivers?
-Reflex hypertonia of flexor muscles of pelvic limbs
-Initially horse snatches up the hindlimb when being picked up
-Accentuated when turning or backing horse and
if excited
-Pelvic limbs are flexed and held in a spastic space
for some time
-Draft breeds
-Always progressive.
-No effective tx
Give some neuromuscular diseases that can cause an abnormal gait
- Shivers
- Stringhalt
Which type of neuromuscular diseases cause localised weakness?
Peripheral nerve injuries
Give some neuromuscular diseases that cause diffuse weakness
- EMND (equine motor neurone disease)
- Botulism
- EGS (equine grass sickness)
- HYPP (hyperkalaemic periodic paralysis disease)
Give a neuromuscular disease that causes excessive activity
Tetanus
Give some clinical signs of forebrain disease
- Disorders of behaviour and personality: aggression, compulsive walking, loss of learnt behaviour, yawning
- Seizures (not common)
- Blindness
- Altered states of consciousness
- Head posture (head and neck turn, head pressing)
What is the cauda equina?
- Bundle of spinal nerves and spinal nerve roots: 2nd-5th lumbar nerves, 1st-5th sacral nerves, coccygeal nerve
- Located at base of spine
Give some causes of forebrain disease
- Trauma
- Abscess
- Cholesterol granuloma (can get cholesterol crystals in CSF with old age)
- Verminous
- Infectious meningoencephalomyelitis
- Neoplasia
- Toxins
- Intra-carotid injection
What kind of brain lesions cause narcolepsy and sleep deprivation?
Forebrain
Give some metabolic causes of forebrain disease
- HE (hepatic encephalitis; altered mentation, central blindness)
- Intestinal hyperammoniaemia
- Electrolyte imbalances
What are the most common causes of seizures and epilepsy in neonates?
- PAS/NMS/HIE
- (Perinatal Asphyxia Syndrome/Neonatal Maladjustment Syndrome/Hypoxic Ischaemic Encephalopathy)
- ‘Dummy foal’
Give some other causes of seizures and epilepsy in neonates
-Metabolic (hypoNa, hypoglycaemia), drug-associated, idiopathic (grows out of)
-Juvenile idiopathic Arab epilepsy: benign, up to 12
months of age
Give some clinical signs of brainstem disease
-Vestibular disease: peripheral or central (ataxia, head tilt, nystagmus, ventral strabismus)
-Facial nerve paralysis (VII and VIII frequently affected together)
-Pharyngeal/laryngeal deficits: dysphagia
-Other cranial nerve deficits
-Severe brainstem lesions: gait abnormalities,
coma
What is the best way to assess ataxia in the horse and why?
- Blindfolded, as horses can compensate with their eyesight
- Can also assess vestibular signs by walking horse up a ramp
What does the motor cortex control?
Fine movement (mainly done by mouth in horses)
Where do seizures tend to start in the horse?
- Around the mouth/lips/tongue
- Can see excessive chewing movements
Give some causes of vestibular disease
-Trauma: central or peripheral (petrous portion of
temporal bone)
-Idiopathic
-Otitis media/interna (temporohyoid osteoarthropathy) (peripheral vestibular disease)
What should be your first differential in cases of acute-onset vestibular dysfunction with facial nerve paralysis?
- Temporohyoid osteoarthropathy
- Chronic bony proliferation of the petrous temporal bone and stylohyoid bone -> ankylosis of the temporohyoid joint -> fracture of petrous temporal bone -> direct trauma to vestibulocochlear and facial nerves and hemorrhage into the middle and inner ear
Give some causes of facial nerve injury
- Commonly iatrogenic due to halters left on during field anaesthesia
- Trauma (± vestibular)
- THO (± vestibular)
Give some clinical signs of facial nerve injury
- Drooping of ear, eyelid (ptosis), lip
- Nostril deviation
Give some prolonged/permanent signs of facial nerve injury
- Poor performace (due to collapsed nostril)
- Exposure keratitis
- Dysphagia
What causes Horner’s syndrome?
Interruption of the sympathetic innervation to the head (and neck)
What is the most common cause of Horner’s syndrome in horses?
Iatrogenic due to extravascular injection of irritant substance (phenylbutazone, buscopan)
Give some clinical signs of Horner’s syndrome
- Miosis (constricted pupil), enophthalmos, ptosis, protruding nictitating membrane
- Hyperaemic membranes, sweating
Give the clinical signs of cauda equina syndrome
-Degrees of hypotonia, hyporeflexia and hypoalgesia
of the tail, anus (ie no anal tone) and perineal region, urinary bladder paralysis (incontinence), rectal dilation, penile prolapse
-May also see LMN weakness and paresis of HLs
Can a horse be ridden if it has ataxia?
No-too dangerous
Give some 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 (equine protozoal myeloencephalitis)
Give some effects of EHV-1
- Resp signs
- Abortion
- Occasionally myeloencephalopathy (sudden onset and early stabilisation of signs including ataxia, paresis, urinary incontinence, very rarely cranial nerve signs)
Why does EHV-1 myeloencephalopathy occur?
-Result of vasculitis and thrombosis of arterioles in spinal cord (and brain) -> viral endotheliotrophism
How can you diagnose EHV-1 myeloencephalopathy?
- CSF sample: xanthochromic (yellow colour that occurs several hours after bleeding) +/- antibodies to EHV-1
- Detection of virus in affected or in-contact horses (nasopharyngeal swabs or buffy coat)
- High antibody titre
How do you manage EHV-1 myeloencephalopathy?
- Isolate
- Recovery takes days to weeks
- Vasculitis -> anti-inflammatories: NSAIDs, corticosteroids, aspirin (anti-thrombotic)
- Antivirals: acyclovir, valacyclovir
Give some diseases that affect the spinal cord
- Cervical vertebral malformation (CVM)
- Cervical vertebral stenotic myelopathy (CVSM)
- Wobbler syndrome
How would a horse with spinal cord trauma present?
- History of sudden onset ataxia or recumbency, sometimes an observed incident
- No progression, frequently improvement, although later progression due to callus formation may occur
- May exacerbate CVM (cervical vertebral malformation)
In which sites are spinal cord trauma more likely to occur?
- Occipito-atlanto-axial region
- Caudal cervical
- Mid-back: usually unstable fracture, paraplegia and recumbency (dog sitting position)
Give some clinical signs of spinal cord trauma
Vary from ataxia and paresis to recumbency
What should you give to sedate horses when assessing spinal cord trauma?
Xylazine
How should you assess spinal cord trauma?
- Complete physical exam (check for unstable fractures)
- Neuro exam to localise lesion
- Plain radiographs to look for fractures (may see callus formation in follow-up cases)
- CSF analysis may rule out other causes
How would you treat a fracture of the spinal vertebrae?
- Neck brace
- Box rest
- Don’t ride again
How would you manage spinal cord trauma?
- Early aggressive anti-inflammatory therapy: corticosteroids (?), NSAIDs, DMSO (?)
- Surgical therapy?, Neck brace?
- Box rest if standing
- Nursing care if recumbent
Delayed callus formation on a spinal fracture may lead to what?
Compression of the spinal cord
What is CVM?
Cervical vertebrae malformation
What is the most common cause of ataxia in horses in the UK?
Cervical vertebrae malformation
What are the 2 types of cervical vertebrae malformation?
Type I:
- Young horses
- Compression as a result of developmental abnormalities
- Dynamic stenosis
- Any site
Type II:
- Older horses
- OA of articular processes
- Static stenosis
- C5-C6 and C6-C7 most common
Give the clinical signs of cervical vertebrae malformation
Ataxia in all 4 limbs, HLs worse than FLs
How do you diagnose cervical vertebrae malformation?
Radiography
Which changes occur with cervical vertebrae malformation?
-Stenosis of vertebral canal: dynamic or static
-Abnormal articular processes
-Subluxation of vertebrae on flexion or extension of
the neck
-Enlarged vertebral physeal growth regions
-Overriding of the vertebral arch and next caudal
vertebral body causing dynamic stenosis during
flexion or extension
-Proliferation of articular or periarticular soft tissues
-Is possible to not see any changes on radiography - could do myelography
Give some risks associated with myelography of the spine
- Anaesthetic risks (esp if ataxic)
- Iatrogenic damage to spine (need radiographic guidance)
- Risk of diffusion of contrast material into brain
How do you manage type 1 cervical vertebrae malformation?
-Early detection in young foals and dietary
restrictions have resulted in resolution of ataxia
and successful careers
-Poor prognosis once advanced
How do you manage type 2 cervical vertebrae malformation?
Intra-articular corticosteroids
Give some clinical signs of neuromuscular disease and the diseases that cause them
- Abnormal gait: shivering, stringhalt
- Localised weakness: peripheral nerve injuries
- Diffuse weakness: EMND, botulism, EGS, HYPP
- Excessive activity: Tetanus
What are the 2 types of stringhalt?
How would you treat each one?
-Australian or plant associated: dandelion, flat
weed? Treatment: remove from pasture
-Sporadic stringhalt: aetiology not fully understood. Treatment: myotenectomy of lateral digital extensor
Anecdotal improvements in Shivers has been noted with what kind of diet?
-Increased fat, decreased carbohydrates
How do radial nerve injuries typically occur?
- External blows
- Following lateral recumbency in anaesthesia
What are the clinical signs of radial nerve damage?
-Unable to flex shoulder, extend limb, flex elbow
What is Sweeny?
- ‘Shoulder slip’- shoulder is pushed laterally as leg is put down
- Due to suprascapular nerve damage
How does suprascapular nerve damage occur?
- External blows
- Poorly fitted collars in draft horses
Give some clinical signs of suprascapular nerve damage
- Atrophy of supra-and infraspinatus muscles
- Abduction of limb
- Unable to advance shoulder
How do you treat peripheral nerve injuries?
- Anti-inflammatories
- DMSO (anti-inflammatory)
- Physio
- Vitamin E (fresh pasture= good source)
What is equine motor neurone disease and what causes it?
- Degeneration of motor neurones in the spinal cord due to low vitamin E (and selenium?) concentrations
- Normally history of horse stabled with no access to pasture for a period of time
Give some clinical signs of equine motor neuron disease
- Weight loss (muscle wasting)
- Muscle fasiculations (eg triceps; diffuse muscle weakness)
- Walk better than they stand
- Elevated tail hair (muscle atrophy)
- Legs tucked under body when standing
- Ocular signs in 30-40% of cases (brown pigment accumulation in retina)
How do you diagnose equine motor neuron disease?
- Vitamin E (and selenium) levels
- Muscle biopsy (tail head)
How do you treat equine motor neuron disease?
Vitamin E supplementation
What causes Botulism?
Clostridium botulinum
Give some sources of botulism toxins
- Contaminated feed
- Water (eg with dead waterfowl in)
- Associated with poultry litter and carcasses
How does botulism cause weak muscles?
- Blocks Ach release at presynaptic membrane of neuromuscular junction -> no muscle contraction -> muscle weakness
- Abrupt progressive onset flaccid paralysis of skeletal muscle
Give some clinical signs of botulism
- Symmetrical weakness (muscle tremors)
- Stumble, ataxia
- Tongue weakness, dysphagia
- Hang head, nose on ground
- Eventually recumbent
- Dyspnoea (intercostal and diaphragm paralysis)
- GI stasis, urine dribbling
What causes shaker foal syndrome?
What age of foal is affected?
- Botulism
- 1-3 months old
- Initial episodes of trembling, die in 10 days due to respiratory muscle paralysis
How can you prevent shaker foal syndrome and botulism in adults?
Vaccinate mare twice in last month of gestation
How can you diagnose botulism?
- Identify toxin/spores (expensive)
- Stomach content (+/- faeces or feed)
How can you treat botulism?
- Antitoxin (USA, expensive)
- Penicillin (not procaine)
- Supportive care, fluids
The botulism vaccine is effective against which type of botulism?
Type B
What is the prognosis like for botulism?
Poor, esp if rapid onset tetraplegia
What causes tetanus?
Clostridium tetani
Where may a horse pick up tetanus?
Soil, GI flora
How would you describe clostridium tetani?
Gram +ve, anaerobic, sporulates in correct conditions eg wounds and releases toxins (2 types)
Which toxins does clostridium tetani release?
- Tetanospasmin: neurotoxin, migrates along motor neuron to spinal cord and brainstem
- Tetanolysin: increases tissue necrosis at site
Give some effects of tetanospasmin (clostridium tetani toxin)
- Inhibits release of glycine
- Inhibits presynaptic inhibitory neurons in spinal cord
- Muscles continuously contract
- Tetany elicited by sound, light, touch
Give some clinical signs of tetanus
- Elevated tail head
- Stiff gait
- Anxious: ears back, eyelids wide open, nostrils flared, head extended
- Lock jaw: drool, can’t swallow
- Prolapsed 3rd eyelid
- Recumbency, rigidity
- Secondary ulcers, trauma
How do you treat tetanus?
- Supportive: quiet, dark, low stimulation room. Hydration, deep bedding
- Eliminate source: open and flush wound. Treat with metronidazole (not penicillin as can make signs worse)
- If unvaccinated: antitoxin (15 units) plus toxoid. at separate sites
- If vaccinated: toxoid
- Muscle relaxation (ACP or diazepam)
When should you vaccinate against tetanus?
2, 3, 6 months, booster at 1 year
What is cervical vertebral malformation?
Narrowing of the cervical vertebral canal -> compression of the spinal cord, often with malalignment and malformation of the cervical vertebrae
