Pituitary Endocrinopathies

Question 1

What clinical problems occur due to pituitary disorders?

Answer 1

Neuro signs - seizures, behavioural changes

Alterations in BW, size and growth

Altered cycling, libido and fertility

PU/PD

Question 2

If an animal is truly polydipsic and polyuric, what are the only two explanations?

Answer 2

1. Primary polydipsia
2. Renal dysfunction
   - Unable to concentrate urine volume normally

Question 3

What could renal dysfunction causing PUPD be due to?

Answer 3

Reduced nephron number
Enough nephrons, not functioning
Osmotic diuresis
ADH insensitivity/lack of ADH

Question 4

What are the intracranial effects seen with pituitary disorders?

Answer 4

Various non-specific neuro signs
Rarely seizures
Depression, under-response to external stimuli
Pituitary central so neuro changes usually bilateral

Question 5

What are the altered endocrine functions seen with pituitary disorders?

Answer 5

Hypersomatotrophism
Hyposomatotrophism
Diabeters insipidus
PD-hyperAC

Question 6

Outline the pathogenesis of hypersomatotrophism…

Answer 6

1. Autonomous GH production
2. Results in increased IGF1 (insulin-like growth factor 1)
3. Increased IGF1 produces:
   - Tissue proliferation
   - Insulin resistance

Question 7

Outline the pathogenesis of hypersomatotropism in dogs…

Answer 7

GH producing mammary tissue

Due to chronic inappropriate production/exposure to progesterone

Question 8

Outline the pathogenesis of hypersomatotrophism in cats…

Answer 8

GH producing pituitary tumour

Question 9

What is the history and clinical signs seen in dogs with hypersomatotrophism…

Answer 9

Intact females 
Males with history of progestin administration
Thick set facial features
Increased interdental space
Insulin resistance
\+/- PUPD
If DM, difficult to control

Question 10

Describe the link between GH and IGF1

Answer 10

GH acts on liver
Need insulin in system to work on liver
Liver produces IGF1

Question 11

Why is IGF1 more useful to measure than GH? What is necessary to produce IGF1?

Answer 11

GH pulsatile so peaks and troughs
IGF1 not so variable
Need insulin to produce IGF1

Question 12

Why may you have no IFG1 detectable in a newly diagnosed DM cat?

Answer 12

No insulin

Give insulin supplement and measure again

Question 13

What is fructosamine?

Answer 13

Compound that forms when glucose binds irreversible to albumin. Rate that occurs is dependant on glucose and albumin conc. So is a good biomarker for blood glucose for the last 3 weeks.

Question 14

Describe the clinical signs of feline hypersomatotropism…

Answer 14

PUPD
Increased appetite
Overshot mandible, increased body size, organomegaly
Insulin resistance
Clinically significant glucose intolerance
Poorly controlled DM

Question 15

Describe the management of acromegaly in cats…

Answer 15

Aggressive insulin treatment
Radiotherapy
Hypophysectomy
Pasireotide injections
(Multi-receptor somatotroph antagonist)

Question 16

Describe hypophysectomy for feline hypersomatotrophism…

Answer 16

Highly successful in certain circumstances
Almost instantaneous normalisation of IGF1
Given twice daily insulin
85% of cats off insulin within a month

Question 17

What should you do if you suspect hypersomatotrophism in a cat?

Answer 17

Index of suspicion based on serum IGF1
Confirmation based on MRI/CT
Sample all diabetics at early checkup

Question 18

Describe the control of body water with vassopressin (ADH)

Answer 18

1. V1, V2, V3 receptors
2. V2 activates cytoplasmic aquaporin-2
3. Aquaporin moves to tubular luminal membrane
4. Allows tubular water resporption
5. Water moves extracellulary down conc gradient
6. Endothelial cell V2 receptors

Question 19

What is central diabetes insipidus?

Answer 19

Absolute vasopressin deficiency

Primary pituitary problem

Question 20

What is nephrogenic or renal diabetes insipidus?

Answer 20

Vasopressin resistance

Primary renal problem or metabolic problem causing renal dysfunction

Question 21

What is the history and clinical signs of a central diabetes insipidus?

Answer 21

Marked PUPD usually >200ml/kg/day

Otherwise unremarkable

Question 22

How do you investigate central diabetes insipidus?

Answer 22

Hospitalise for 12-24 hours
Observe water consumption
If it stops drinking - primary polydipsic problem
If it keeps drinking - need to do more

Question 23

What diagnostic aids are there for central diabetes insipidus?

Answer 23

USG <1.008
Urine osmolality and SG fixed and unchanging
Water deprivation test
Followed by desmopressin response test if needed

Question 24

Describe the water deprivation test….

Answer 24

1. Patient must become dehydrated
2. Can take up to 72 hours
3. Administer desmopressin once inability demonstrated
4. Usually response within 2-12 hours
5. Usually USG >1.020 within 4 hours

Question 25

What is the treatment for central diabetes insipidus?

Answer 25

Conjunctivally administered desmopression
Given q12-24
Dose adjustments based on response

Question 26

What is the history and clinical signs for hyposomatotrophism?

Answer 26

Smaller animal with proportional stature
Non-chrondrodystrophic
Immature hair coat
Persistent oestrus 
Normal life expectancy

Question 27

What breed is predisposed to hyposomatotrophism?

Answer 27

GSD

Question 28

Explain the pathogenesis of hyposomatotrophism..

Answer 28

Adenohypophyseal malformation (abnormalities in enzymes that facilitate differentiation of pluripotent cells)

Deficiency in:
GH
FSH
LH
PRL
TSH

Question 29

What are the diagnostic aids for hyposomatotrophism?

Answer 29

Serum IGF1 estimation

Radiography - persisting epiphyseal plates

Question 30

What is the treatment for hyposomatotrophism?

Answer 30

Progestin administration

Manage expectations of owner