Week 4- Approach to Equine Neurology Flashcards
What are the general principles of the neurological examination?
- Mentation/ Behaviour
- Cranial nerve assesment
- Spinal reflexes
- Gait Analysis
What might you notice when looking at the horses mentation?
Observe the horse loose from a distance
* Stable or pasture
» Altered consciousness
* QAR
* Dull/stupor
* (Comatose)
» Aberrant behaviour
* Wandering
* Circling
* Head Pressing
* Excessive yawning
» Seizure activity
What cranial nerves control the eye muscles?
3, 4 and 6
What is the cervicofacial reflex?
use a pen or forceps to test the region of C1–C3: expect nose/muzzle twitch in response
What is the cutaneous trunci reflex?
Continue testing over the shoulders and trunk region on both sides: expect skin to twitch in response
What is vestibular ataxia?
a type of ataxia (loss of coordination and balance) caused by dysfunction in the vestibular system, which includes the inner ear, vestibular nerve, and parts of the brain that control balance and spatial orientation
What is cerebellar ataxia?
a type of ataxia (loss of coordination and balance) caused by dysfunction in the cerebellum, the part of the brain responsible for coordinating movement, balance, and fine motor control.
What aetiologies may cause forebrain disease?
Head trauma »
Infectious encephalitis/meningitis* Bacterial, viral
» Electrolyte disturbances * Hyponatraemia, hypoglycaemia
» Hepatic encephalopathy & other causes of
hyperammonaemia
» Intra-carotid drug administration
» Poisoning/toxicity * Plants, drugs etc
» Neoplasia
» Epilepsy (rare)
What are the possible consequences of head-on trauma?
» Lacerations
» Fractures of frontal/maxillary bone
» Sinus trauma – epistaxis
» Ocular injury
» Fracture of calvarium
» Cerebral contusion
» Increased intracranial pressure
What are the possible consequences of poll trauma?
Fractures:
* Occiput
* Basilar skull
* Basisphenoid & Basioccipital bone
* Cranial C-spine
» Cerebral contusion
» Increased intracranial pressure
» Damage to brainstem
What does a basilar skull fracture cause?
Damage to brainstem:
* Cranial nerve deficits
* Ataxia/incoordination
What is the usual diagnostic for head trauma?
Often limited to neurological exam
* Detailed assessment of cranial nerves
* Check ocular reflexes closely
* Anisocoria, mydriasis and poor/absent PLR
associated with head trauma is an indicator of
increased ICP
What is the usual treatment for head trauma
Treatment is often conservative
NSAIDs: Phenylbutazone or flunixin meglumine
* Vitamin E (antioxidant)
* Hyperosmolar fluids to try and reduce ICP
* Hypertonic saline v mannitol
What controls seizure activity in horses?
Diazepam
What is the prognosis like for head trauma?
If condition stabilises quickly and improvement seen after early
treatment then prognosis = fair
» If severe CNS signs, uncontrollable seizures, or no significant
improvement after 24-48 hours then prognosis = very poor.
What is seizure activity usually secondary to?
Seizure activity usually secondary to primary cerebral lesion
* Inflammatory, traumatic, infectious, ischaemic lesions
What are the clinical signs of generalised seizures?
Loss of consciousness
* Tonic/clonic muscular spasms
* Jaw clamping, paddling legs
* Loss of body functions
How might you diagnose forebrain seizures?
Neurological exam
» Blood biochemistry
» CSF analysis
» Electroencephalography
» Advanced diagnostic imaging: CT, MRI
What is the emergency treatment for seizures?
Most seizures stop within a few minutes
» Keep horse and people safe
» If venous access established, anticonvulsant tx can be helpful:
* Diazepam (0.1-0.5mg/kg IV)
* Phenobarbital (5-10mg/kg IV, up to 20mg/kg IV per day)
» If anticonvulsants not available and veterinary intervention required:
* Sedation: Xylazine or detomidine +/ butorphanol
* Small vol pentobarbital (euthanasia solution) in saline
What is the longer term treatment for seizures?
Phenobarbital (5-10mg/kg PO BID)
* Potassium bromide (50-100mg/kg PO SID)
» Therapeutic drug monitoring
» Side effects: Sedation, ataxia, individual variation
» Safety concerns and cost often make long term treatment prohibitive
What causes central facial nerve paralysis
Damage to CN nucleus in brainstem or UMN * Often in conjunction with other signs of Cr N
dysfunction
* Less common
What causes peripheral nerve paralysis?
- Drooping of eye, ear, lip, deviation of nose,
reduced flaring of the nostril
Causes: * Trauma during anaesthesia/recumbency/restraint * Guttural pouch disease * Temporohyoid osteoarthropathy (THO)
How might you diagnose facial nerve paralysis?
History
* Guttural pouch endoscopy
* Radiography
* Head CT
How might you treat facial nerve paralysis?
Address initial problem
* Neuroprotective supplements: Vitamin E
* Electroacupuncture
* Supportive care: nutritional, ocular care
What is temporohyoid Osteoarthropathy?
Common cause of peripheral vestibular disease
(central VD = uncommon)
» Vestibular system functions to maintain
appropriate orientation of body & head & position
of eyes relative to head
What are the clinical signs of Temporohyoid Osteoarthropathy?
Facial nerve paralysis » Loss on one side > head tilt and body tilt towards
lesion
» ‘Room spinning’, wide based stance, short strides,
reluctance to move
» Compensate with vision
– head tilt & body tilt can
be exaggerated by applying a blindfold (care)
» Nystagmus if acute disease » Signs resembling spinal cord ataxia
What is Wobbler Syndrome?
The most common non-infectious cause of spinal cord ataxia in horses
» More common in young (2-3 yo) large growing horses
» Developmental abnormality of the cervical spine and/or displacement (CVSM Type 1)
» Results in stenosis of the intervertebral canal
» Stenosis of canal causes compression of spinal cord at one or more sites in the spine
What is the difference between static and dynamic CVSM?
Compression of spinal cord at neutral position versus when the neck is flexed/extended
What is cervical vertebral osetoarthritis?
» Similar clinical disease in older horses, due to osteoarthritic changes
» Arthritic overgrowths cause static compression of spinal cord
What are the main clinical signs of CVSM?
Reduced proprioception (ataxia; pelvic limbs > thoracic limbs)
» Progressing to paresis and/or spasticity as compression worsens
» Hindlimbs are more affected than the forelimbs
* Due to more peripherally placed spinocerebellar tracts
» Bilateral, but degree of change in each limb can vary depending on
area of compression
What is the CVSM treatment in young/ growing horses?
Dietary modification to slow growth rate and rest/controlled exercise
» Rest/exercise modification
» Anti-inflammatories used (but often little clinical response)
» Surgical correction of displacements (‘basket surgery’) – case dependent
* May improve 1-2 grades
» Young horses with high grade ataxia are euthanised due to poor prognosis
What is the CVSM treatment in older horses with a poorer prognosis?
osteoarthritis of the spine
Treatment options limited
» Intra-articular steroids, NSAIDs
» Prognosis for establishing athletic function or returning to previous function very guarded
