Equine Endocrine (PPID & EMS) Flashcards
What is equine cushings disease?
TRICK QUESTION! don’t call it cushings, call it PPID
What are the three divisions of the Anterior pituitary?
Pars intermedia Pars distalis Pars tuberalis
What part of the anterior pituitary is affected in PPID?
Pars intermedia
What is produced by the posterior pituitary gland (aka pars nervosa)?
Oxytocin and ADH
What are the cells in the pars intermedia called?
Melanotropes
What’s POMC?
pro-opiomelanocortin
What is made from POMC?
B-endorphin
a-MSH (melanocyte stimulating hormone)
CLIP (cortisol like intermediate peptide)
<2% ACTH
Is the pars intermedia affected by glucocorticoids in the circulation?
Nope, no negative feedback from circulting gluco corts
What is the pars intermedia regulated by?
Dopamine inhibits
Serotonin (5HT3) stimulates
What happens when you get loss of dopaminergic inhibition?
PPID! & therefore over production of the hormones made by the pars intermedia
What causes the loss of dopaminergic inhibition?
We don’t know, does seem to have oxidative damage on post mortem but don’t know why.
What happens to the melanotropes in PPID?
Initially they just hypertrophy and produce more hormone, eventually adenomatous change
Slowly progressive
Why do we see such a rise in ACTH signs?
The ACTH produced is up to 6x more potent
Actual number of cortisol doesn’t increase very dramatically but is more active
What other parts of the pituitary might be compressed and thererfore malfunctional?
Posterior pituitary - less ADH prodcued
Why might you see blindness/seizures in PPID horses?
Compression of the brain due to massive pituitary adenoma (rare)
What age group does PPID affect?
Older horses. Average 19, very rare under 10
mares or geldings more common? (PPID)
no sex predilection
Ponies or horses more likely? (PPID)
Ponies!
What percentage or horses are affected by hypertrichosis?
55-80%
Why do you get hypertrichosis?
Reason unclear, pressure on thermoregulatory centre in brain?
We don’t actually know why..
What proportion of PPID horses get laminitis? (roughly)
About 20%
Often ends up in demise of animal as recurrent/chronic
Why do you get laminits with PPID?
Due to cortisol/insulin
What proportion of PPID horses get weight loss?
88%
Why do we get increased sweating in PPID?
Possibly due to increased catecholamines circulating and stimulating B-adrenergic controlled sweat glands
Or maybe just due to long hair coat?
With PU/PD horses with PPID, can they concentrate their urine if water deprived?
Yes
What are the theories for PUPD in PPID?
Cortisol antagonising actions of ADH on collecting ducts
Cortisol causing hyperglycaemia and osmotic diuresis
Destruction of other areas of pituitary gland with reduced ADH
Combination of the above?
No evidence as yet
Where do you get a typical fat pad?
Supraorbital fat pad as opposed to normal dipped in fossa in older horses
What two infections do they most often seem to get with PPID?
Sinusitis
Skin infections
Why are PPID animals more susceptible to infections?
Impaired Neutrophil function (due to altered hormone concentrations)
What test should you do if you have subtle signs of early PPID?
TRH stim test or resting ACTH test
What test should you do if you have more advanced signs of PPID?
Resting ACTH sufficient, don’t need TRH stim
Why might you do an oral sugar test in a possibly PPID horse?
Insulin status assesment
When is the seasonal rise in hormone production in horses?
Autumn. Animals with PPID do an even greater seasonal rise so best time to test
When is the best time to do a basal ACTH assay in a suspect PPID horse?
Autumn (as long as lab has seasonally adjusted ref range)
Why do you give TRH?
TRH (for some reason) is a physiologic release factor for the pituitary
What do you measure in a TRH stim test?
ACTH (not cortisol) at 0 and 30 minutes
What result do you need on a TRH stim to call it positive at a) 10 minutes or b) 30 minutes
a) ACTH >100pg/ml
b) >36pg/ml
High sens and spes but does have effect by feeding and by season
Why do you have insulin dysregulation in some PPID animals?
Answer not known, ideas are:
Cortisol antagonises insulin, body responds by producing more insulin
CLIP may stimulate insulin secretion
Why does insulin dysregulation have a worse prognosis in PPID?
More likely to get laminitis
Which treatment must you start with if you shoose to medically manage PPID?
Pergolide (trade name prescend)
What does pergolide do?
It is a dopamine agonist and so replaces inhibition of the pituitary
What are the possible side effects of pergolide?
Diarrhoea, Depression, Anorexia, Colic
What is the dose rate of pergolide?
2mg/kg SID
What is cyproheptadine?
It is a serotonin antagonist, so inhibits the stimulation of the gland.
Less effective than pergolide
Why don’t we use Trilostane in horses?
Doens’t work at the level of the pituitary, works at the level of the adrenal so only really useful in signs related to the adrenal (cortisol and ACTH)
How long does it take to imrpove on PPID medication?
Up to one year!
What should you do if the horse tests negative for PPID on your treatment
Stay on same dose and repeat test in 6 months
What should you do if you test for cushings when the horse is being managed and the clinical signs have improved but the test is still positive?
Stay on same dose or increase
What should you do if the test is still positive after management and no clinical response?
Incresae dose by 1-2mg/kg/day
can add in cyproheptadine
