2/3 Thyroid Hormones - Hyperthyroidism COMPLETE ***

Question 1

Hyperthyroidism: Which species is this common in?
- Why species is this less common in?

Answer 1

cats

dogs

Question 2

Hyperthyroidism: What is hyperthyroidism?
- What causes it?

Answer 2

excessive production of thyroxine

adenomatous hyperplasia of the thyroid gland

Question 3

Hyperthyroidism: What is the consequence of having excess T4 on basal metabolic rate? 2

Answer 3

increased metabolic rate
so increased catabolism of stores

Question 4

Hyperthyroidism: Aside from basal metabolic rate, what does increased T4 effect? 3

Answer 4

thermoregulation
emetics centre
increases sympathetic drive

Question 5

Hyperthyroidism: What are some potential risk factors for developing the disease? 3

Answer 5

flea products
cat litter
food containing high iodine

Question 6

Hyperthyroidism: Signalment 2

Answer 6

cats older than 10
rare in siamese cats

Question 7

Hyperthyroidism: List the clinical signs from most common to least common 7

Answer 7

weight loss
polyphagia
polyuria and polydipsia
tachycardia
vomiting
diarrhoea
hair coat changes

Question 8

Hyperthyroidism: Why do we get weight loss and polyphagia?

Answer 8

because T4 increases metabolic rate and catabolism

Question 9

Hyperthyroidism: Why do we get PU/PD?

Answer 9

increased cardiac output increasing glomerular filtration rate

Question 10

Hyperthyroidism: Why do we get tachycardia?

Answer 10

increased sympathetic drive

Question 11

Hyperthyroidism: Why do we get vomiting? 2

Answer 11

due to overeating
due to activation of the emetics centre

Question 12

Hyperthyroidism: why do we get diarrhoea?

Answer 12

due to hyper mobility of the gastrointestinal tract and malabsorption

Question 13

Hyperthyroidism: Why might we get hair coat changes?

Answer 13

the cat may forget to groom or overgroom

Question 14

Hyperthyroidism: What might you pick up on clinical examination? 4

Answer 14

poor body condition
cervical nodule
tachycardia
other cardiac abnormalities

Question 15

Hyperthyroidism: Aside from Tachycardia, what other cardiac abnormalities could be present? 2

Answer 15

hypertrophic cardiomyopathy
systolic murmur

Question 16

Hyperthyroidism: What happens in scintigraphy?

Answer 16

radioactive 123 idoine isotope is administered to identify functional thyroid tissue

Question 16

Hyperthyroidism: Diagnosis
- Which test is sufficient for diagnosis of Hyperthyroidism?
- Why do we sometimes only need to do this one?
- What are the only problems? 3
- Hence, which test would be better the perform if possible and why?

Answer 16

total t4

because there is no other reason for T4 to be elevated

there are daily fluctuations
it may be within normal parameters in early-mid hyperthyroidism
could be depressed by non-thyroidal illnesses

free T4 as it is less affected by non-thyroidal illnesses

Question 17

Hyperthyroidism: State 3 other diagnostic tests that could be done, although often dont need to be done outside of Total/Free T4?

Answer 17

T3 suppression test
TRH stimulation test
scintigraphy

Question 18

Hyperthyroidism: Describe the procedure for carrying out a T3 suppression test 2
- Why do we test for both T4 and T3?
- In a normal cat, what would be the result and why?
- what would you see in a Hyperthyroid cat?

Answer 18

administer a tablet containing T3
measure blood T4 and T3

to check owner compliance

T4 concentration would be significantly reduced due to negative feedback from exogenous T3

minimal decrease in T4 concentration

Question 19

Hyperthyroidism: Treatment
- State 4 ways of treating Hyperthyroidism

Answer 19

inhibitors of thyroid hormone synthesis
surgical removal of enlarge thyroid gland
radiotherapy to destroy local thyroid tissue
dietary control

Question 20

Hyperthyroidism: Treatment
- What does ‘dietary control’ involve?

Answer 20

exclusively feeding a diet that is deficient in iodine and selenium