Neurological exam - LA (equine) Flashcards
Approaches - 2
- systematic approach e.g. tests of unconscious proprioception
- anatomic approach - most appropriate for horses/ large animals
Distinguish white/ grey matter
WHITE: myelinated axons
GREY: unmyelinated cells and bodies of the axons
- Opposite organisation in brain vs. spinal cord
Important aspects of hx to obtain
- did horse look/act clumsy before it was found down?
- any evidence of respiratory dz on property?
- any other horses?
- descriptions of behavioural abnormalities
- client video
What does excessive yawning indicate?
forebrain disease (unknown why)
What does abnormal behaviour indicate?
= forebrain disease
- e.g. circling, hyperaesthesia, head turn, odd postures
What does the cerebellum conrol?
- ascending proprioceptive pathways
- descending motor pathways
CS associated with cerebellar dysfunction - 4
- spastic or exaggerated movements
- absence/ diminished menace response
- intention tremor (worse when horse doing something)
- ataxia without weakness
Brainstem contents —
- pons and medulla
- reticular formation
- ascending proprioceptive pathways
- descending motor pathways (–> weakness)
- CN nuclei
- when you find dysfunction of these modalities together, think brainstem *
What does ataxia, paresis and CN deficits together suggest?
brainstem disease
What does a wonky muzzle indicate?
left sided facial nn paralysis
Outline PLR
= true reflex
- afferent limb is in optic nn (CN 2)
- efferent is parasumpathetic fibres that run in the oculomotor nn (3) to constrict the pupil
- direct and consensual/ contralateral response. The latter is difficult to assess in horses so as long as you get good direct PLRs in each eye, then don’t worry
What does the menace response test?
= requires perception of stimulus
- optic nerve
- optic chiasm
- thalamus
- opposite occipital cortex (but an unconscious event)
- facial nn and nucleus
- (cerebellum)
How is vision best tested?
- walk horse around / between obstacles
- fundic exam
- afferent limb of menace response
Control of eye position
- oculomotor nn (3)
- trochlear nn (4)
- abducens nn (6)
Frequency of strabismus as a CS
uncommon in UK, more common in USA.
Method - retractor oculi reflex
= press on cornea through the eyelid, feel for reflex retraction of the globe
- afferent: trigeminal (5) - sensory
- efferent: abducens (6) - motor
Lesions in the facial nn (7) are often accompanied by lesions where?
vestibular nn (CN 8) due to anatomical location
How do you determine central vs peripheral vestibular disease?
- difficult
- type of nystagmus?
- weakness?
- other CN involved?
- further testing
What type of nystagmus does central disease cause?
any type of nystagmus
What type of nystagmus does peripheral disease cause?
horizontal nystagmus
How does fast phase nystagmus help localise a lesion?
fast phase is away from the site of the lesion
What is physiological nystagmus?
changing what you are focusing on
How to assess pharyngeal and laryngeal function?
- swallowing
- vocalisation
- slap test (tests intrinsice laryngeal mm function)
- endoscopy *
What does eluphenazine toxicity cause? tx?
- causes extrapyrimidal system defects.
- Tx with diphenhydramine
- (n.b. eluphenazine is a drug used to calm horses)
Describe Horner’s syndrome
= interruption of sympathetic nn pathway between hypothalamus and eye
- Ptosis (examine eyelashes closely - normal horse they point out, with horner’s they point down)
- Miosis
- Enopthalmus
- Prominent TE
- conjunctival and nasal hyperemia
- sweating
Why do Horner syndrome horses sweat?
when SNS supply to skin is interrupted (this is normally autonomically controlled), horses BVs vasodilate and horses are prone to increased sweat production with vasodilation
Why might you get sweating over the mid and caudal neck?
controlled by vertebral nn (C2)
Define ataxia
a function deficit associated with defective proprioception
CS - ataxia
- hypermetria (exaggerated movements)
- hypometria (reduced movements)
- dysmetria
- truncal sway (back end doesn’t follow front end)
T/F: assymmetric spinal cord lesions can produce signs similar to certain lamenesses
True
What is ataxia generally associated with?
irregular irregularities (i.e. a neurological problem)
What is lameness usually associated with?
a regularly irregular problem is usually an orthopaedic problem
T/F: bilateral pelvic limb suspensory desmitis and sacroiliac pain are common causes of unusual ‘ataxia like’ deficint…but usually the deficit is regular
True (despite orthopaedic problems usually tending to be a regularly irregular problem)
What are clues that a horse is truly ataxic? 2
- pacing (worse when head lifts up)
- circumduction
Possible origins or weakness - 2
systemic or neurological
- granulomatous enteritis –> IBD and PLE –> mm wastage
- equine motor neuron disease is a neurological problem
What type of tail pull is useful to assess a LMN or UMN weakness problem?
- LMN: standing tail pull
- UMN - walking tail pull
Features of UMN weakness - 3
- inability to control mm
- normal or increased tone
- no mm atrophy
Features of LMN weakness - 3
- inability to contract the mm
- flaccidity
- mm atrophy if chronic
Examples of lameness caused by mm disease
- post-exercise lameness
- exertional rhabdomyolysis (tying up)
- polysaccharide storage myopathy - genetic
- ischaemic myopathy - uncommon, associated with parasite migration, (aorto-iliac thrombosis)
- measure CK and AST
Tips for locating spinal lesions
- limb weakness can indicate local SC damage
- in a standing horse you can assume that spinal reflexes are intact
- most spinal reflexes are hard to assess in adult horses
- withdrawal reflexes are useful
Sacral and perineal signs
- perineal reflex
- sensation
- tail flaccidity
- rectal exam
- urinary incontinence
Name some classic cauda equina signs
- impaction in the rectum
- no perineal reflex
