4/4 Adrenal Glands - PPID in Horses COMPLETE ***

Question 1

Where is the Pituitary gland located in the brain? 3
- How is it separated from the brain?

Answer 1

on the ventral aspect of the brain
within the sella turcica
caudal to the optic chasm

by the diaphragm sella

Question 2

Pituitary gland: What 2 sections can it be divided into?
- What is the anterior one further divided into? 2

Answer 2

adenohypophysis
neurohypophysis

pars distalis
pars intermedia

Question 3

Pituitary gland: What hormones does the Adenohypophysis secrete (with examples) ? 5

Answer 3

gonadotrophin including FSH and lH
corticotrophs including POMC and ACTH
lactotrophs including prolactin
somatotrophs including growth hormones
thyrotrophs including thyroid stimulating hormone

Question 4

Pituitary gland: What does the Pars intermedia do?
- Hence, where is most POMC produced?
- What is different about the ACTH produced by the pars intermedia?
- What happens to most ACTH produced by the pars intermedia?

Answer 4

it secretes POMC which is cleaved to ACTH

in the pars distalis

it is not biologically active so will not affect cortisol concentrations

it is further cleaved into other hormones

Question 5

PPID: Why is PPID not thought of as the horse equivalent of Hyperadrenocorticism?

Answer 5

because you do not get elevated cortisol concentrations

Question 6

PPID: Describe how PPID occurs 2

Answer 6

hypertrophy of melanotropes in the pars intermedia
these cells are responsible for secreting POMC

Question 7

Pituitary gland: Why in PPID do you get this overgrowth of melanotropes? 2

Answer 7

neuro-degeneration of the periventricular neurones impairs hypothalamic dopamines ability to have negative feedback on the pituitary
this permits the development of adenomas

Question 8

PPID: What after causes the disease process of PPID?

Answer 8

a pars intermedia adenoma which is a benign tumour in the pars intermedia

Question 9

PPID: As PPID progresses, why do you get other neurological signs and symptom progression?

Answer 9

because the tumour is pushing on other parts of the pituitary gland causing dysfunction

Question 10

PPID: Give the signalment 2

Answer 10

older horses over 7
ponies are predisposed

Question 11

PPID: State the clinical signs from most common to least common 8

Answer 11

generalised hypertrichosis
weight loss
muscle wastage
polyuria and polydipsia
laminitis
recurrent infections
potbellied
neurological signs

Question 12

PPID: What causes the generalised hypertrichosis, even in warmer seasons?

Answer 12

the elevated MSH and pituitary compression of the hypothalamus thermoregulatory centre

Question 13

PPID: What causes Laminits?

Answer 13

due to persisten hyperinsulinaemia resulting from CLIP release

Question 14

PPID: What causes PU/PD?

Answer 14

due to pituitary compression causing reduced secretion of ADH

Question 15

PPID: What causes neurological signs?

Answer 15

blindness may be due to compression of the optic chiasm

Question 16

PPID: Describe the generic steps you would take to help diagnose 3
- State the names of 2 specialised tests that can be done

Answer 16

review history
review clinical examination
blood biochemistry

resting ACTH
TRH stimulation test

Question 17

PPID: What causes recurrent infections?

Answer 17

alpha MSH is an immunosuppressive hormone

Question 18

PPID: What could you expect to see on blood biochemistry? 4

Answer 18

hyperglycaemia
hyperinsulinaemia
neutrophilia
lymphopaenia

Question 19

PPID: Describe the process to carry out the resting ACTH test 3

Answer 19

collect blood in EDTA tubes
separate plasma within 4 hours of collection
chill in fridge and submit to lab

Question 20

PPID: Resting ACTH
- Describe the sensitivity and specificity of this test
- Why might you get false positives?
- Why might you get false negatives? 2

Answer 20

moderate sensitivity and high specificity

due to stress and pain from laminitis

if the sample was stored incorrectly
early PPID

Question 21

PPID: TRH Stimulation test
- What does TRH normally do?
- What is different in a PPID horse?
- Hence, what happens when injected with exogenous TRH?
- When would you perform this test?

Answer 21

it stimulates the pars intermedia to produce ACTH and MSH

the hyper plastic melotropes have a higher affinity for the TRH

the pars intermedia will secrete excessive ACTH in response

when you get a normal resting ACTH but have a high clinical suspicion

Question 22

What diagnostic imaging could be used to identify pituitary enlargement?

Answer 22

CT and MRI