Equine Endocrine (PPID & EMS)

Question 1

What is equine cushings disease?

Answer 1

TRICK QUESTION! don’t call it cushings, call it PPID

Question 2

What are the three divisions of the Anterior pituitary?

Answer 2

Pars intermedia Pars distalis Pars tuberalis

Question 3

What part of the anterior pituitary is affected in PPID?

Answer 3

Pars intermedia

Question 4

What is produced by the posterior pituitary gland (aka pars nervosa)?

Answer 4

Oxytocin and ADH

Question 5

What are the cells in the pars intermedia called?

Answer 5

Melanotropes

Question 6

What’s POMC?

Answer 6

pro-opiomelanocortin

Question 7

What is made from POMC?

Answer 7

B-endorphin

a-MSH (melanocyte stimulating hormone)

CLIP (cortisol like intermediate peptide)

<2% ACTH

Question 8

Is the pars intermedia affected by glucocorticoids in the circulation?

Answer 8

Nope, no negative feedback from circulting gluco corts

Question 9

What is the pars intermedia regulated by?

Answer 9

Dopamine inhibits

Serotonin (5HT3) stimulates

Question 10

What happens when you get loss of dopaminergic inhibition?

Answer 10

PPID! & therefore over production of the hormones made by the pars intermedia

Question 11

What causes the loss of dopaminergic inhibition?

Answer 11

We don’t know, does seem to have oxidative damage on post mortem but don’t know why.

Question 12

What happens to the melanotropes in PPID?

Answer 12

Initially they just hypertrophy and produce more hormone, eventually adenomatous change

Slowly progressive

Question 13

Why do we see such a rise in ACTH signs?

Answer 13

The ACTH produced is up to 6x more potent

Actual number of cortisol doesn’t increase very dramatically but is more active

Question 14

What other parts of the pituitary might be compressed and thererfore malfunctional?

Answer 14

Posterior pituitary - less ADH prodcued

Question 15

Why might you see blindness/seizures in PPID horses?

Answer 15

Compression of the brain due to massive pituitary adenoma (rare)

Question 16

What age group does PPID affect?

Answer 16

Older horses. Average 19, very rare under 10

Question 17

mares or geldings more common? (PPID)

Answer 17

no sex predilection

Question 18

Ponies or horses more likely? (PPID)

Answer 18

Ponies!

Question 19

What percentage or horses are affected by hypertrichosis?

Answer 19

55-80%

Question 20

Why do you get hypertrichosis?

Answer 20

Reason unclear, pressure on thermoregulatory centre in brain?

We don’t actually know why..

Question 21

What proportion of PPID horses get laminitis? (roughly)

Answer 21

About 20%

Often ends up in demise of animal as recurrent/chronic

Question 22

Why do you get laminits with PPID?

Answer 22

Due to cortisol/insulin

Question 23

What proportion of PPID horses get weight loss?

Answer 23

88%

Question 24

Why do we get increased sweating in PPID?

Answer 24

Possibly due to increased catecholamines circulating and stimulating B-adrenergic controlled sweat glands

Or maybe just due to long hair coat?

Question 25

With PU/PD horses with PPID, can they concentrate their urine if water deprived?

Answer 25

Yes

Question 26

What are the theories for PUPD in PPID?

Answer 26

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

Question 27

Where do you get a typical fat pad?

Answer 27

Supraorbital fat pad as opposed to normal dipped in fossa in older horses

Question 28

What two infections do they most often seem to get with PPID?

Answer 28

Sinusitis Skin infections

Question 29

Why are PPID animals more susceptible to infections?

Answer 29

Impaired Neutrophil function (due to altered hormone concentrations)

Question 30

What test should you do if you have subtle signs of early PPID?

Answer 30

TRH stim test or resting ACTH test

Question 31

What test should you do if you have more advanced signs of PPID?

Answer 31

Resting ACTH sufficient, don't need TRH stim

Question 32

Why might you do an oral sugar test in a possibly PPID horse?

Answer 32

Insulin status assesment

Question 33

When is the seasonal rise in hormone production in horses?

Answer 33

Autumn. Animals with PPID do an even greater seasonal rise so best time to test

Question 34

When is the best time to do a basal ACTH assay in a suspect PPID horse?

Answer 34

Autumn (as long as lab has seasonally adjusted ref range)

Question 35

Why do you give TRH?

Answer 35

TRH (for some reason) is a physiologic release factor for the pituitary

Question 36

What do you measure in a TRH stim test?

Answer 36

ACTH (not cortisol) at 0 and 30 minutes

Question 37

What result do you need on a TRH stim to call it positive at a) 10 minutes or b) 30 minutes

Answer 37

a) ACTH \>100pg/ml b) \>36pg/ml High sens and spes but does have effect by feeding and by season

Question 38

Why do you have insulin dysregulation in some PPID animals?

Answer 38

Answer not known, ideas are: Cortisol antagonises insulin, body responds by producing more insulin CLIP may stimulate insulin secretion

Question 39

Why does insulin dysregulation have a worse prognosis in PPID?

Answer 39

More likely to get laminitis

Question 40

Which treatment must you start with if you shoose to medically manage PPID?

Answer 40

Pergolide (trade name prescend)

Question 41

What does pergolide do?

Answer 41

It is a dopamine agonist and so replaces inhibition of the pituitary

Question 42

What are the possible side effects of pergolide?

Answer 42

Diarrhoea, Depression, Anorexia, Colic

Question 43

What is the dose rate of pergolide?

Answer 43

2mg/kg SID

Question 44

What is cyproheptadine?

Answer 44

It is a serotonin antagonist, so inhibits the stimulation of the gland. Less effective than pergolide

Question 45

Why don't we use Trilostane in horses?

Answer 45

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)

Question 46

How long does it take to imrpove on PPID medication?

Answer 46

Up to one year!

Question 47

What should you do if the horse tests negative for PPID on your treatment

Answer 47

Stay on same dose and repeat test in 6 months

Question 48

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?

Answer 48

Stay on same dose or increase

Question 49

What should you do if the test is still positive after management and no clinical response?

Answer 49

Incresae dose by 1-2mg/kg/day can add in cyproheptadine