Traumatic, Degenerative, and Toxic CNS Disease

Question 1

what are 3 common causes of traumatic CNS injury in horses?

Answer 1

1. flipping backward
2. falling
3. collision

Question 2

What is the pathophysiology that describes why there are multiple injuries involved in a traumatic brain injury?

Answer 2

There is a primary injury which is where the direct trauma occured. This is also called the coup. there is also a contrecoup where injury occurs on the opposite side of the trauma because the brain was displaced.

Then, there is the secondary injury which is increased ICP, hemorrhage, ischemia that results in edema, neuronal and axonal injury, and cellular death.

We cannot do anything about the primary injury, but we can intervene and prevent secondary injury from worsening.

Question 3

what 2 diagnostics are the MOST important in a traumatic CNS injury case?

Answer 3

1. neuro exam
2. hydration/blood pressure assessment

imaging is important too (need orthogonal xray views or CT)

Question 4

What are the MEDICAL treatment goals for a traumatic CNS injury?

Answer 4

1. decrease ICP and maintain CBF – hypertonic saline, fluids, and elevate the feed.
2. decrease inflammation and pain – banamine, gabapentin, acetaminophen
3. prevent sepsis if the fracture is open – broad spec antibiotics (oxytet)
4. maintain standing
5. treat seizures (gaba or phenytoin for prevention, diaz/midaz for immediate tx, and keppra or pheno for maintenance)

Question 5

what are 2 controversial treatment options in traumatic CNS injuries and why?

Answer 5

1. corticosteroids – assoc with increased mortality in humans and can lead to bacterial infection if there is an open fracture
2. DMSO – no benefit

Question 6

what is the ideal surgical treatment candidate in a traumatic CNS injury?

Answer 6

one that has NO or minimal neurological deficits

Question 7

what is the prognosis associated with traumatic CNS injuries?

Answer 7

the first 24-48 hr are crucial, but survival is likely
if there are basilar fractures or if the horse becomes recumbent, the prognosis is worsened.

Question 8

What is equine neuraxonal dystrophy (eNAD) and equine degenerative myeloencephalopathy (EDM)?

Answer 8

they are both inherited neurodegenerative disorders linked to vitamin E metabolism.
the difference between the two is:
eNAD has lesions that are confined to the caudal medulla oblongata
eDM has lesions that are more widespread and include demyelination within the ascending tracts of the spinal cord (worse)

Question 9

what are clinical signs associated with eNAD and EDM?

Answer 9

• symmetric ataxia and proprioceptive deficits in ALL limbs (develops over first 1-2 years of life)
• abnormal stance at rest
• thoracic and pelvic limbs weak and spastic
• excessive hypermetria when head is elevated.

+/- decreased menace and lack of fight or flight

Question 10

On histopathology, what do you see associated with eNAD and EDM?

Answer 10

spheroids (non-functional cells), axonal loss, and demyelination within the caudal brainstem and spinal cord.

Question 11

T/F: it is common for eNAD and EDM to be incidentally diagnosed prior to 1-2 years of life.

Answer 11

false – this is a common post-mortem diagnosis in horses with neuro disease.

Question 12

How are we able to potentially prevent foals from developing eNAD and EDM?

Answer 12

It is genetic
autosomal dominant incomplete penetrance, meaning that if a mare with eNAD or EMD gives birth to foal, they will be clinically affected UNLESS the environment is changed in a way to prevent the foal from expressing the trait (incomplete penetrance). We can do this by preventing oxidative damage from occurring (supplementing vitamin E which is an antioxidant).

Question 13

What causes expression of the neurologic phenotype in eNAD and EDM?

Answer 13

oxidative damage

vitamin E is a potent antioxidant and horses can get it from lush green grass.
So, risk factors include: low vitamin E environment, application of insecticide, exposure to wood preservative, housed in dirt lots.

Question 14

T/F: vitamin E supplementation in genetically-susceptible horses lowers the severity and incidence of eNAD and EDM.

Answer 14

true

Question 15

T/F: low vitamin E is not consistently present in all cases of eNAD and EDM

Answer 15

true
this is because some breeds such as QHs have increased rate of metabolism of vitamin E. So, they have a higher need for vitamin E compared to others.

Question 16

How can we distinguish eNAD and EDM from other neuro diseases that cause spinal ataxia (CVSM, EPM, viral encephalitis)?

Answer 16

we cannot clinically distinguish them and there is NO antemortem diagnostic test available.

Question 17

T/F: treatment of horses with clinical signs of eNAD or EDM with vitamin E has consistently shown to improve the neurological defects

Answer 17

false – once clinical signs are present, vit E supplementation will NOT improve neuro deficits. it can only halt the disease progression.

this is why prevention is key, we want to keep serum vitamin E levels above 3 ug/mL

Question 18

which TYPE of vitamin E is used to supplement horses with eNAD or EDM?

Answer 18

water soluble, natural, r-r-r alpha tocopherol

Question 19

what is EMND?

Answer 19

equine motor neuron disease
which is an ACQUIRED (non-genetic) neurodegenerative disorder of the motor neurons in the spinal cord and brainstem caused by vitamin E deficiency. It causes generalized neuromuscular weakness and muscle atrophy.

Question 20

how do the subacute and chronic forms of EMND look different?

Answer 20

subacute – symmetrical muscle atrophy, muscle fasciulations, weight shifting, toe dragging, and weakness

chronic – poor performance, failure to gain weight, muscle atrophy

+/- pigment retinopathy

Question 21

how do you definitively diagnose Equine motor neuron disease (EMND)?

Answer 21

sacrocaudalis dorsalis muscle biopsy – see denervation atrophy of type I muscle fibers

low vit E = supportive of diagnosis

Question 22

what is the treatment for EMND?

Answer 22

water soluble, natural, r-r-r alpha tocopherol vitamin E
no exercise until vitamin E is within normal ranges.

Question 23

What is equine dysautonomia (grass sickness)?

Answer 23

it is an ACQUIRED degenerative polyneuropathy that predominately affects neurons of the autonomic and enteric nervous system.
It is suspected that C. botulinum is the cause, but unknown for sure.

Question 24

How can you differentiate between acute, subacute, and chronic forms of equine dysautonomia (grass sickness)?

Answer 24

acute (0-48hr) – dysphagia*, bilateral ptosis, GI ileus, abdominal pain, hypovolemia, patchy sweating

subacute (3-7d) – dysphagia, bilateral ptosis, large colon impaction, intermittent colic and patchy sweating

chronic (wks-mon) – dysphagia, rapid/severe weight loss, sweating, muscle tremors, base-narrow stance, lean against walls, rhinitis sicca, piloerection

Question 25

Majority of equine dysautonomia cases are diagnosed based on clinical signs. What other diagnostics are available to support your diagnosis?

Answer 25

Phenylephrine eye challenge – apply to see if it reverse ptosis temporarily

Histopath – definitive diagnosis; shows degenerative changes in peripheral autonomic ganglia; Reduction of interstitial cells of Cajal** in the wall of the ileum.

Question 26

T/F: acute and subacute forms of equine dysautonomia require euthanasia

Answer 26

true

recovery from the chronic form is possible , but not likely. requires intensive nursing, supportive care, steroids, and short-term NG tube feedings.

Question 27

You are called to examine a 21 year old horse because the owners report he is have a hard time chewing his food. On exam, you see signs of facial nerve paralysis (ear droop, lip droop, and decreased lacrimation) and vestibular disease (head tilt, nystagmus, strabismus, and base-wide stance). What are your differentials?

Answer 27

1. temporohyoid osteoarthropathy
2. guttural pouch disease (lat comp)
3. traumatic injury to base of skull
4. otitis media/interna
5. EPM
6. brainstem or extracranial mass

Question 28

what is THO?

Answer 28

Temporohyoid osteoarthropathy
Characterized by osseous proliferation at the articulation of the stylohyoid and petrous temporal bone possibly caused by repetitive trauma/movement and extension of infection.
This osseous proliferation causes inflammation and compression of CN VII and/or CN VIII

Question 29

how do we diagnose THO?

Answer 29

1. radiographs (easiest but least sensitive)
2. guttural pouch endoscopy (more sensitive, but does not tell whole story)
3. CT (sensitive and provides detail about skull)

Question 30

what is the option for surgical management of THO?

Answer 30

certaohyoidectomy – remove the ceratohyoid bone to release pressure and eliminate movement at the temporohyoid joint where CN VII and VIII course.

this surgery provides immediate improvement. most return to previous use, some have persistent neuro deficits.

Question 31

what is the option for MEDICAL management of THO?

Answer 31

1. antibiotics
2. temp tarsorraphy or enucleate (bc facial paralysis inc risk for exposure keratitis)
3. antiinflammatories

Question 32

T/F: horses with THO that have more severe clinical signs and CT findings has a worse prognosis

Answer 32

false – neuro signs and CT/xray findings did not impact outcomes. treatment with surgery was what made patients have better outcomes.

Question 33

what are the 2 potential causes of hyperammonemia in horses?

Answer 33

1. liver fails to remove ammonia from the blood
2. overproduction of ammonia by intestinal bacteria

overall will lead to brain damage.

Question 34

how does hyperammonemia cause brain damage?

Answer 34

inhibits ATP production leading to increased glutamine which results in edema and increased ICP.

Question 35

what are clinical signs of hyperammonemia in horses?

Answer 35

bilateral forebrain dysfunction
(behavior changes, head pressing, central blindness, stertorous breathing, +/- seizures.

Question 36

how can we diagnose hyperammonemia in horses?

Answer 36

clinical signs
elevated plasma or CSF ammonia* (run this test immediately though bc ammonia is labile)

Question 37

what is the treatment for hyperammonemia in horses?

Answer 37

1. oral lactulose (converts NH3 –> NH4)
2. treat underlying hepatic disease or enterocolitis
3. antiinflammatories, hypertonic saline, fluids, supportive care
4. manage seizures
5. tracheostomy if necessary

Question 38

what is the prognosis for hyperammonemia in horses?

Answer 38

fair-poor
if its chronic, there will likely be permanent brain damage.

Question 39

what is the cause of equine leukoencephalomalacia (ELEM)?

Answer 39

ingestion of fungus Fusarium moniliforme (corn becomes contaminated during wet-harvesting season)

interferes with sphingolipid metabolism and disrupts endothelial cell walls and basement membranes which results in liquefactive necrosis and malacia of the white matter.

Question 40

When do clinical signs of ELEM appear after ingestion of Fusarium moniliforme and what are typical clinical signs?

Answer 40

3-4 weeks.

clinical signs are multifocal brain signs – circling, ataxia, blindness, seizures and hepatic disease – icterus, petechia, increased liver enzymes

Question 41

how can we diagnose ELEM?

Answer 41

• Diet history
• The fact that multiple horses will be affected
• Test feed for Fumonsin
• CSF: inc protein, hemorrhage

Question 42

what is the treatment and prognosis for Equine Leukoencephalomalacia (ELEM)?

Answer 42

supportive care, gastric lavage (to remove Fusarium moniliforme toxin), charcoal, antiinflammatories, mannitol

GRAVE prognosis (<10% survive)