PATHOLOGY - Equine Endocrine Disease and Laminitis

Question 1

What is laminitis?

Answer 1

Laminitis is inflammation and/or fluid accumulation between the dermal and epidermal lamellae

Question 2

Describe the blood supply to the laminae

Answer 2

The laminae are supplied by the laminar arteries which branch from the circumflex arteries and are drained by the laminar veins which drain into the circumflex veins

Question 3

Why are the digital veins so sensitive to vasoactive mediators?

Answer 3

The digital veins are highly muscular are are thus very sensitive to vasoactive mediators

Question 4

What are the three classifications of laminitis?

Answer 4

Hyperinsulinaemia-associated laminitis (HAL)
Sepsis associated laminitis
Supporting limb laminitis

Question 5

What are the four possible triggers of laminitis?

Answer 5

Activation/infiltration of white blood cells
Increased pro-inflammatory mediators
Decreased anti-inflammatory mediators
Increased COX-2

Question 6

What are the two main theories of laminitis?

Answer 6

Vascular theory
Enzymatic theory

Question 7

What does the vascular theory propose as the triggering factors of laminitis?

Answer 7

Endothelial cell dysfunction
Release of vasoactive mediators

Question 8

List three possible causes of endothelial cell dysfunction resulting in laminitis?

Answer 8

Insulin resistance
Hyperglycaemia
Hyperinsulinaemia

Question 9

How does endothelial cell dysfunction and/or vasoactive mediator release trigger laminitis according to the vascular theory?

Answer 9

Endothelial cell dysfunction and vasoactive mediators cause a disruption in blood flow to the laminae resulting in vasoconstriction which results in an increase in fluid movement from the vessels into the interstitial space causing an increase in interstitial hydrostatic pressure and oedema between the laminae. This results in the formation of arteriovenous shunts between the circumflex vessels, causing blood to bypass the laminae resulting in ischaemia, inflammation and necrosis causing seperation of the dermal and epidermal laminae

Question 10

What does the enzymatic theory propose as the triggering factors of laminitis?

Answer 10

Increased matrix metalloproteinase (MMP) activity

Question 11

What is the normal function of matrix metalloproteinases (MMPs) in the hoof?

Answer 11

Normally, matrix metalloproteinases are involved in normal growth of the hoof through enabling the epidermal laminae to glide past the dermal laminae to allow for hoof growth

Question 12

How does increased matrix metalloproteinase (MMP) activity trigger laminitis according to the enzymatic theory?

Answer 12

Increase matrix metalloproteinase (MMP) activity can result in the break down of the extracellular matrix (ECM) and basement membranes which form the junction between the dermal and epidermal laminae, resulting in laminae seperation

Question 13

Describe how insulin resistance can contribute to laminitis

Answer 13

Insulin resistance reduces glucose uptake by the laminae which causes seperation of the dermal and epidermal laminae

Question 14

Describe how hyperglycaemia can contribite to laminitis

Answer 14

Hyperglycaemia causes increased insulin secretion and as insulin is a pro-inflammatory mediator this causes endothelial cell dysfunction and vasoconstriction

Question 15

What can occur following seperation of the dermal and epidermal lamellae?

Answer 15

Pedal bone rotation and possible pedal bone sinking

Question 16

Describe the phases of laminitis

Answer 16

1. Trigger factors +/- predisposing factors
2. Developmental phase which lasts several hours
3. Acute phase which lasts for several days and presents with pain and lameness
4. The acute phase can lead to either the subacute or chronic phase. The subacute phase is classified as there is no pedal bone collapse however the clinical signs have persisted beyond 72 hours. The chronic phase is classified as lamellar seperation and pedal bone collapse

Question 17

What are the three main clinical signs of laminitis?

Answer 17

Pain
Strong digital pulses
Abnormal hoof morphology

Question 18

How can you tell if a horse is in pain due to laminitis?

Answer 18

Rocking back and forth
Shortened strides
Reluctant to turn
Reluctant to move at all
Reluctant to have feed picked up
Pain with hoof testers on their toes

Question 19

Describe the abnormal hoof morphologies that can be indicative of laminitis?

Answer 19

Long toe
Short heel
Laminitic rings
Flattened or convex sole due to pedal bone collapse

Question 20

How would you describe a horse with a laminitis score of 1 using the Obel grading scale?

Answer 20

Horse is frequently lifting their feet (i.e. not putting as much weight on each foot)

Question 21

How would you describe a horse with a laminitis score of 2 using the Obel grading scale?

Answer 21

Horse is willing to walk and can lift forefeet without difficulty however does have a laminitic gait

Question 22

How would you describe a horse with a laminitis score of 3 using the Obel grading scale?

Answer 22

Horse resists lifting forefoot and moves reluctantly

Question 23

How would you describe a horse with a laminitis score of 4 using the Obel grading scale?

Answer 23

Horse is forced to move and may or may not be recumbent

Question 24

How should laminitis be treated?

Answer 24

It is important to treat the underlying cause of laminitis in combination with box rest, hoof support and analgesia

Question 25

What are the two main metabolic syndromes that can predispose horses to laminitis?

Answer 25

Equine metabolic syndrome (EMS) Pituitary pars intermedia dysfunction (PPID)

Question 26

What are the three primary criteria required to diagnose equine metabolic syndrome (EMS)?

Answer 26

Obesity Insulin dysregulation Predispostion to laminitis

Question 27

Which two diagnostic tests can be carried out for equine metabolic syndrome (EMS)?

Answer 27

Oral sugar test Combined glucose-insulin test (CGIT)

Question 28

Describe how to carry out an oral sugar test for equine metabolic syndrome (EMS)?

Answer 28

1. Fast the horse for 3 - 6 hours 2. Administer 0.45ml\kg of corn syrup 3. Measure insulin levels in the blood at 0 (basal), 60 and/or 90 minutes to look for excess insulin in the blood

Question 29

Describe how to carry out a combined glucose-insulin test (CGIT) for equine metabolic syndrome (EMS)?

Answer 29

1. Fast horse for 6 hours and place an I.V. catheter 2. Take basal blood insulin and glucose levels 3. Administer 150mg/kg 50% dextrose sugar I.V. and 0.1 U/kg of insulin I.V. 4. Measure blood glucose levels at regular intervals 5. Measure blood insulin levels at 45 minutes 6. There is insulin resistance if glucose levels remain above baseline for 45 minutes or more

Question 30

What should be done to treat equine metabolic syndrome (EMS)?

Answer 30

Weight loss

Question 31

What can be done to promote weight loss in horses?

Answer 31

Don't turn out onto pasture Feed hay only Increase exercise

Question 32

Why should hay be soaked for at least 60 minutes when promoting weight loss in a horse with equine metabolic syndrome (EMS)?

Answer 32

Soaking the hay removes any non-structural carbohydrates

Question 33

Which two diagnostic tests can you carry out for pituitary pars intermedia dysfunction (PPID) ?

Answer 33

Basal ACTH concentration TRH stimulation test

Question 34

When would you carry out a basal ACTH concentration test?

Answer 34

If you are presented with an older horse with obvious clinical signs of pituitary pars intermedia dysfunction (PPID)

Question 35

When would you carry out a TRH stimulation test?

Answer 35

If you are presented with a young horse with mild clinical signs or if you have ended up with an equivocal basal ACTH concentration test

Question 36

How should you treat pituitary pars intermedia dysfunction (PPID)?

Answer 36

Administration of a dopamine agonist