Hypothyroidism

Question 1

___ is released from the _____ pituitary, which acts on the thyroid and stimulates thyroid hormone release

Answer 1

TSH, anterior pituitary

Question 2

Which hormone released from the hypothalamus stimulates TSH release from the anterior pituitary?
A) T4
B) TRH
C) T3
D) thyroxine

Answer 2

B - thyroid releasing hormone

Question 3

Which element is vital for thyroid hormone production?
A) iron
B) zinc
C) iodine
D) molybdenum

Answer 3

C - iodine

Question 4

T/F: there is more T3 in the body than T4

Answer 4

False, T4 80%, T33 20%

Question 5

A primary thyroid disease involves disease in the:
A) blood
B) pituitary
C) thyroid
D) hypothalamus

Answer 5

thyroid

Question 6

Disease of the pituitary is _______ and of the hypothalamus is ______.

Answer 6

secondary and tertiary

Question 7

Most common type of hypothyroidism (95% of cases)

Answer 7

primary hypothyroidism

Question 8

Breakdown of hypothyroidism

Answer 8

95% primary - most due to lymphocytic thyroiditis, rest idiopathic
other 5% - secondary congenital/acquired or primary congenital

Question 9

3 other major causes of low T4

Answer 9

iatrogenic (I131, antithyroid drugs, thyroidectomy)
Euthyroid sick syndrome (decreased protein binding, fT4 –> rT3)
Drug therapy (glucocorticoids, carprofen, furosemide, phenobarbital/sulfas)

Question 10

Factors affecting T4 levels

Answer 10

age, breed, pregnancy, exercise, fasting, anesthesia

Question 11

Signalment of hypothyroid dogs

Answer 11

middle aged
medium to large breed dogs
can be inherited

Question 12

Clinical signs of hypothyroidism

Answer 12

lethargy, alopecia, hyper pigmentation, rat tail, seborrhoea, myexdema

Question 13

What causes myxedema?

Answer 13

deposition of mucopolysaccharides in the dermis

Question 14

reproductive signs of hypothyroidism

Answer 14

failure to cycle, weak pups

Question 15

ocular signs of hypothyroidism

Answer 15

lipid in cornea, anterior chamber

Question 16

T/F: normal T4 rules out hypothyroidism

Answer 16

True

Question 17

T/F: it is easy to diagnose hypothyroidism in a sick dog

Answer 17

False, it is difficult because low levels may indicate hypothyroidism or euthyroid sick syndrome

Question 18

Serum T4 levels reflect:

Answer 18

bound and free T4

Question 19

You have a patient with low T4 and you suspect hypothyroidism. You submit  for TSH and it comes back high. What is your next step?
A) Measure T3 levels
B) euthanize, it doesnt stand a chance 
C) Leave it, it will resolve on its own
D) Treat with levothyroxine

Answer 19

D - treat with levothyroxine

Question 20

Is it possible to have low T4 with normal TSH levels?

Answer 20

Yes, you can either treat, retest later, or perform further testing

Question 21

A patient comes in with seborrhoea, myxoedema, alopecia and is lethargic. You decide to take a blood sample to assess the T4 status. The T4 value is within the normal range but is at the low end of normal. You suspect hypothyroidism. What can you do?

Answer 21

fT4 by equilibrium dialysis

Question 22

You conduct a TSH stimulation test and collect T4 levels 8 hours after TSH administration. You notice there is a significant increase in T4 levels compared to before the TSH was given. What is your conclusion?

Answer 22

This dog is normal! A hypothyroid dog would have no increase in post-T4 (due to gland atrophy/destruction)

Question 23

Treatment for hypothyroidism

Answer 23

Synthetic T4

Soloxine 0.02mg/kg/BID or Leventa 0.02mg/kg/SID

Question 24

Time line of therapy monitoring for hypothyroidism?

Answer 24

1-2w - improvement in attitude
4-6w - improvement in term signs
2-3m - hair regrowth

Question 25

An owner is concerned about the appearance of her hypothyroid dog. She is getting married in 4 months and wants her dog to be in all of her wedding photos. You have just started the dog’s treatment. Will her dog’s hair be grown in by her wedding?

Answer 25

Yes, hair regrowth at 2-3m

Question 26

T/F: treatment of hypothyroidism can be stopped once T4 levels are normal

Answer 26

false, treatment is lifelong

Question 27

You want to assess the treatment plan you have been using for a hypothyroid dog, Sparky. Sparky has been receiving 0.02mg/kg Soloxine BID for the past month. When should you take a blood sample?
A) It doesn’t matter when as long as it’s one month after tx plan began
B) As soon as you finish giving the first dose of the day
C) 4-6h after the first does was given
D) Right before bed

Answer 27

C - if you are giving the doses BID, you want to make sure you are not taking a sample during a peak or trough time. 4-6h is roughly halfway between doses

if SID, would test ~8h after dose

Question 28

Signs of drug treatment overdose in hypothyroid dogs

Answer 28

PU/PD/PP, nervousness, aggression, panting, excess weight loss, fever