Equine Endocrinopathies Flashcards
What is PPID? What are other names for it?
Pituitary pars intermedia dysfunction
Cushing’s
Adenoma
Equine hyperadrenocorticism
What are the most important hormones produced by the pars intermedia in horse? What regulated the pars intermedia?
ACTH
a-MSH
CLIP
B-endorphin
Dopamine and serotonin from hypothalamus
Outline the pathophysiology of PPID
1) Loss of dopamine inhibition in pars intermedia
2) Melanotropes hypertrophy
3) Melantropes undergo adenomatous change
4) Overproduction of pars intermedia hormones and compression of adjacent structures
What pathology does compression by hypertrophied pars intermedia cause in PPID?
Reduced ADH secretion
Blindness, seizures
Outline the typical signalment of PPID
- 19yo
- F=M
- Ponies > horses
What are the early clinical signs of PPID?
Poor performance, lethargy
Reduced shedding of coat
Regional adiposity
Laminitis
What are the late clinical signs of PPID?
Lethargy Hypertrichosis Muscle atrophy Rounded abdo Sweating PUPD Recurrent infections Adiposity Infertility Laminitis Hyperglycaemia Neuro deficits, blindness
What causes hypertrichosis in PPID?
Pressure on hypothalamic thermoregulation centre
What causes laminitis in PPID?
Excessive cortisol +/- insulin
What causes weight loss in a PPID horse?
Metabolic effects of cortisol
Susceptibility to infection and parasites
Dental care
What causes profound sweating in PPID horses?
Long hair coat
Elevated catecholamines action on B-adrenergic controlled sweat glands
What causes PU/PD in the PPID horse?
Cortisol antagonising ADH in collecting ducts
Cortisol –> hyperglycaemia –> osmotic diuresis
Compression on pituitary –> reduced ADH
How is PPID diagnosed?
Hx, signalment Clinical signs Basal ACTH TRH stim Insulin dysregulation Histology
What hormone assay is used to diagnose PPID? What are problems with this test?
Basal ACTH
- ACTH varies with season
- Only 75% spec and sens –> chance of false +ve and -ve results
What dynamic test is used to diagnose PPID? Outline the test and what can affect the results…
TRH stim
Inject 1mg TRH IV - measure ACTH at 0 and 10 minutes
Season
Feeding
What can cause insulin dysregulation in PPID? Why does this worsen prognosis?
Cortisol antagonises insulin
CLIP stimulate insulin secretion
Inflammation and oxidative stress from EMS –> PPID
Increased risk of laminitis
What is the most life-limiting clinical sign of PPID? How can clinical signs be managed?
Laminitis
- prevent/treat lami
- prevent/treat 2’ infections
- clip coat
- alter diet
How can PPID be managed medically?
Pergolide - dopamine agonist that inhibits pituitary gland
How is PPID treated/managed?
Manage clinical signs
Medication
Diet and exercise
Monitor wt and BCS
How should PPID be monitored?
Improvement of CS
Repeat ACTH/TRH stim
What is the prognosis for PPID?
Good, although life long
Euthanasia is usually due to laminitis
What is EMS?
Equine Metabolic Syndrome A combination of: - Insulin dysfunction - Increased fast tri levels - Altered adipokines - +/- obesity - Increased risk of laminitis
Outline the current theory for EMS pathogenesis…
Horses on pasture high in WSC:
Prolonged insulinaemia –> endothelial dysfunction –> laminitis
Hindgut carb overload –> inflammatory injury to laminae
What is the theory for pathogenesis of endocrinopathic laminitis?
Insulin binds to receptors in lamellar tissue –> increase cell growth, adhesion and survival –> lamellar epidermal cell proliferation and weakening
