Dysautonomia

Question 1

what age horses are affeted by dysautonomia?

Answer 1

• Occurs in all ages from 4 months to over 20 years but the greatest number of cases occurs in 2 to 7 year olds

Question 2

what are the risk factors of dysautonomia?

Answer 2

• Causal agent unknown - Likely associated with toxin
• Horses on pasture
• Mechanical droppings removal
• Presence of domesticated birds on field
• Stress
• Animals in good-fat body condition
• Cool, dry weather with a temperature between 7 and 11°C
• Frequent worming
• History of grass sickness cases on premises

Question 3

give a summary of dysautonomia (equine grass sickness)?

Answer 3

• A generalized dysautonomia affecting primarily the enteric nervous system
• Non-GI signs aid in its diagnosis
• Mainly parasympathetic NS
  three types:
• Acute – die rapidly
• Sub Acute – survive >2days
• Chronic – survive >7 days
• A clinical diagnosis
  ◦ Decrease in GI motility from mouth to anus with a decrease in GI secretions

Question 4

what are the slinicla signs of acute grass sickness?

Answer 4

• Severe gut paralysis leads to signs of acute colic
• Difficulty swallowing - dysphagia
• Drooling Saliva
• Nasogastric reflux
• Mucous coated, hard droppings
• Muscle tremors and patchy sweating
• Tachycardia
• Usually die or areeuthanisedwithin 2 days of clinical signs

Question 5

what are the clinicla signs of sub-acute grass sickness?

Answer 5

• Similar toacute but less severe
• Difficulty swallowing
• Mild-moderate colic
• Sweating, muscle tremors
• Rapid weight loss - tucked up apperance
• May eat small amounts of food
• May die or be euthanised within 1 week of clinical signs

Question 6

what are the clinical signs of chronic grass sickness?

Answer 6

• More insidious (gradual, subtle)
• Mild or intermittent colic
• Reduced appetite
• May have some difficulty eating, but salivation, gastric reflux and ileus are not a major feature
• Rapid and severe weight loss/emaciation
• Some may recover.

Question 7

what are the diagnositic tests for grass sickness?

Answer 7

• ileal biopsy - best
• rectal biopsy
• phenylephrine test - not diagnostic on it’s own as false +ves seen, but supportive
• oesophageal endoscopy

Question 8

give a summary of ileal biopsy for grass sickness diagnosis?

how is it done, what is looked for,?

Answer 8

• Best diagnostic test
• Requires laparotomy (midline or flank)
  ◦ Laparotomy decreases survival
  ◦ Neuronal degeneration within ganglia
  ◦ Depletion of ganglia
  ◦ Vacuolation

Question 9

what has been suggested for why chronic grass sickness has milder sings?

Answer 9

Pathology localized to ileum in chronic EGS
◦ might explain why milder signs and are more likely to recover, larger portion of GIT that is still functional
* Generalised intestinal pathology in acute disease

Question 10

what is the benefit of rectal biopsy for diagnosis of equine grass sickness, what is the sensitivity and specificity?

Answer 10

• is able to be carried out in the standing horse
  71% sensitivity, 100% specificity
• reduced sensitivity so some false negatives and can’t be used to rule out disease

Question 11

what is seen on histologoical examination of biopsies in equine grass sickness?

Answer 11

• Chromatolysis,vacuolation of cellswithin autonomicganglia​

Question 12

what is the phenylephrine test for the diagnosis of equine grass sickness?

what is done, positive result

Answer 12

• Topicalapplicationof 0.5% phenylephrine to oneeye​
• examination30 minuteslater​
• Positivetest = reversal of the ptosis in that eye, increase in angle between the cornealsurface and theeyelash.​
• testuseful in supporting evidence of defective smooth muscle activity as an underlying cause oftheptosis​
• BUT False positives seen - normalhorses can show some responseto thistest
  (Ptosis is when the upper eyelid droops over the eye.)

Question 13

what is oesophageal endoscopy used for in the diagnosis of equine grass sickness? what are the issues with this?

Answer 13

• to look for Linearoesophagealulcers​
• indicative of gastro-oesophagealreflux​
• In absence of severeileus and extensivegastric distension​- suggestiveof loweroesophagealspincterdysfunction​
• ManyEGS horses do nothaveoesophagealulcers​

Question 14

what is the treatment for equine grass sickness?

Answer 14

Treatment
Nursing care is paramount for a successful outcome

• Symptomatic therapy for each individual problem

Analgesia
◦ Promotes voluntary feeding – reduces pain associated with swallowing and abdominal pain
◦ Oesophageal/gastric ulceration – Acid suppression and sucralfate

Question 15

what supportive care is used in cases of equine grass sickness?

Answer 15

• Feeding
  ◦ Small feeds every 30-60minutes
  ◦ Hand feeding (don’t leave horse to eat)
  ◦ Hand grazing
  ◦ Varied diets
• Appetite stimulation
  ◦ Diazepam 0.02mg/kg IV BID-TID
• Nursing
  ◦ Grooming
  ◦ Access to other horses
  ◦ Rhinitis – steam, mucolytics
• Prokinetics
  ◦ Cisapride has most data – no longer available
  ◦ Neostigmine

Question 16

what is the prognosis of equine grass sickness?

Answer 16

acute or sub-acute form - euthanasia
chronic -large varriations in:
- time to return to normal BW
- ime to return to work

Question 17

how is equine grass sickness confirmed?

Answer 17

done at post mortem
* Cranial cervical ganglion​

Question 18

what is the preventic methods for grass sickness?

Answer 18

• In areas where the disease is prevalent, stabling the animals during the spring and early summer will reduce the likelihood of disease.
• Association with weather, some owners living in affected areas now stable their horses when dry weather with a temperature of 7-11°C has persisted for 10 consecutive days.
• Stabling new horses that move onto premises where the disease is known to occur.
• If certain fields are ‘bad’ for the disease, they can be grazed by other stock, especially in spring and summer.
• If a case occurs amongst a group of horses, it is probably best to move the others out of that field provided this does not involve too much stress associated with transportation or mixing with strange horses.