Physiology of hyperthyroidism

Question 1

FACTSHEET

Answer 1

Hyperthyroidism=

• Excessive production of T4
• Adenomatous hyperplasia of thyroid glands
• Mainly bilateral in cats
• Hyperthyroidism results in multi organ dysfunction

Question 2

Is feline hyperthyroidism usually unilateral or bilateral?

Answer 2

Bilateral

Question 3

Like risk factors for developing hyperthyroidism

Answer 3

• Canned products = may be high in iodine or other goitrogens
• Breeds (rare in Siamese)
• Age (10+)

Question 4

List some of the clinical signs associated with hyperthyroidism

Answer 4

• Weight loss
• Polyphagia
• PUPD
• Tachycardia
• Diarrhoea
• Vomiting
• Haircoat changes
• Goitre
• Hypersensitve to heat

Question 5

Why can hyperthyroidism cause vomiting?

Answer 5

• Activation of the emetic centre

- Due to overeating

Question 6

What behavioural changes are associated with hyperthyroidism?

Answer 6

• Hyperactivity
• Vocalisation
• Obsessive grooming

Question 7

Why does hyperthyroidism cause hypertrophic cardiomyopathy?

Answer 7

-Thyroid hormones have a direct effect on the myocytes

Indirect compensatory changes due to altered peripheral perfusion

Question 8

What tests can be used to diagnose hyperthyroidism?

Answer 8

• Baseline= Total T4 (normal a single test is enough to diagnose but may need repeating)
• T3 suppression test
• Thyroid scintigraphy

Question 9

What are the limitations of the total T4 test?

Answer 9

• Daily fluctuations

- May be normal in early stages of the disease

Question 10

Describe the T3 suppression test

Answer 10

• In normal cats an injection of exogenous T3 should cause a decrease in TSH and T4
• In hyperthyroid cats you have a very minimal decrease in T4

Question 11

Describe thyroid scintigraphy

Answer 11

• Use a radioactive marker to ID functional thyroid tissue
• Using IV injection of technetium or iodine
• Use a gamma camera to count

Question 12

Describe hyperthyroidism in dogs

Answer 12

• RARE-Only small amount of thyroid carcinomas are functional
• Highly metastatic
• Occurs in older dogs and particularly golden retrievers, boxers, beagles