Physiology of Hyperthyroidism

Question 1

• Which is very rare, canine or feline hyperthyroidism?

Answer 1

Canine hyperthyroidism

Question 2

• Are most feline hyperthyroidism cases bilateral or unilateral?

Answer 2

70% are bilateral

Question 3

• What does a hyperthyroid gland resemble histopathologically?

Answer 3

A toxic goitre

Question 4

• What are the main thyroid hormone functions?

Answer 4

Thermoregulation, carbohydrate, protein & lipid metabolism and interaction with the CNS (increases sympathetic drive)

Question 5

• What are the most common clinical signs?

Answer 5

Weight loss, polyphagia, PU/PD, tachycardia, diarrhoea, respiratory abnormalities, vomiting, hair coat changes

Question 6

• What cardiac abnormalities can occur?

Answer 6

Hypertrophic cardiomyopathy, tachycardia, systolic murmur, dysrhythmias – atrial and ventricular premature contractions

Question 7

• Why can vomiting occur?

Answer 7

Thyrotoxic effect on emetic centre

Question 8

• What can be palpated in cats suffering from hyperthyroidism?

Answer 8

Thyroid nodule

Question 9

• What dynamic hormone tests can be performed to diagnose hyperthyroidism?

Answer 9

T3 suppression test & TRH stimulation test

Question 10

• What are the limitations of a total T4?

Answer 10

Daily/hourly fluctuations, may be normal in early or mild hyperthyroidism, depressed by non-thyroidal illnesses

Question 11

• How does the T3 suppression test work?

Answer 11

In hyperthyroid cats there is a minimal decrease in T4 as a response

Question 12

• Wheat is thyroid scintigraphy?

Answer 12

Radioactive marker identifies functional thyroid tissue, confirms diagnosis and determines whether benign or malignant