HypERthyroidism

Question 1

Hyperthyroidism

Answer 1

an endocrine Dz characterized by excessive circulating amounts of thyroid hormone

Question 2

Location of thyroid glands

Answer 2

mid-cervical region adjacent to the trachea

Question 3

What is the thyroid gland made up of?

Answer 3

follicles

Question 4

What is inside of the thyroid follicles?

Answer 4

colloid

Question 5

What is colloid made of?

Answer 5

thyroglobulin

Question 6

What is thyroglobulin?l

Answer 6

a large protein that contains each of the thyroid hormones

Question 7

Tyrosine molecules + ______________ = thyroid hormone

Answer 7

iodine

Question 8

What secretes colloid?

Answer 8

Epithelial cells that line the follicles

Question 9

What are thyroid hormones cleaved from? When are they cleaved?

Answer 9

cleaved from thyroglobulin prior to release of the hormone into circulatory system

Question 10

What pathological process in the thyroid gland leads to hyperthyroidism?

Answer 10

an overgrowth of thyroid tissue either due to benign or malignant tumor; in either case, the additional tissue is functional

Question 11

What species is most at risk for hyperthyroid?

Answer 11

cats

Question 12

Common clinical signs of hyperthyroid Dz

Answer 12

Increased cardiovascular func (HR, BP)
Hyperactivity
Muscle wasting 
Vomiting
Occasionally diarrhea
polyphagia

Question 13

What does increased perfusion to the kidneys result in? What about increased BP?

Answer 13

• increased perfusion to kidneys results in polyuria with compensatory polydipsia
• increased BP can lead to retinal hemorrhage or detachment resulting in blindness

Question 14

Why is hyperactivity seen in hyperthyroid cats?

Answer 14

secondary due to increased metabolism

Question 15

Why are muscle wasting and weight loss seen with hyperthyroid cats?

Answer 15

increased muscle activity and increased energy expenditure

Question 16

What causes vomiting in hyperthyroid cats?

Answer 16

increased metabolism of liver and GI tract

Question 17

Why are hyperthyroid cats polyphagic?

Answer 17

body is constantly burning energy and looking for more energy

Question 18

Abnormalities on PE with hyperthyroidism

Answer 18

• poor body condition due to muscle wasting and weight loss
• haircoat greasy and unkempt
• increased size of thyroid gland

Question 19

Abnormalities on bloodwork with hyperthyroidism

Answer 19

• Polycythemia (increased metabolism –> increased demand at tissue lvl for O2 –> RBC production amps up)
• Elevated liver enzymes (due to increased metabolic demand on liver)
• Azotemia
• Elevated T4

Question 20

What hormonal test is most beneficial in hyperthyroid confirmation?

Answer 20

Serum T4 concentration test

Question 21

4 Specialized tests that may be beneficial for hyperthyroidism confirmation

Answer 21

T3 suppression test
TSH rsponse test
TRH stimulation test
Radionuclid scan of thyroid gland

Question 22

3 Ways to treat hyperthyroidism

Answer 22

Methimazole
Thyroidectomy
Radioactive Iodine

Question 23

Methimazole

• type of Tx
• what it does
• pros
• cons

Answer 23

• tablet, orally SID
• reduces serum thyroid hormone concentration by blocking synthesis of thyroid hormones by thyroid gland; does not destroy thyroid tissue, so it is not a permanent cure
• Pro: easy to adjust dose and to give, inexpensive, no anesthesia/hospital stay/special equipment
• Con: vomiting, anorexia, development of bone marrow disorder

Question 24

Thyroidectomy

• type of Tx
• what it does
• pros
• cons

Answer 24

• surgery
• removes one or both glands; curative if not ectopic tissue
• Pro: can cure Dz
• Con: requires anesthesia which often isn’t ideal for older patients with increased metabolism of organs, expensive, hypocalcemia may result

Question 25

Radioactive Iodine - what it does - pros - cons

Answer 25

- overactive thyroid tissue takes up cytotoxic radioactive iodine thus destroying abnormal thyroid cells (unilateral or bilateral) and any ectopic tissue that might be present - Pro: potential to cure with 1 dose, no anesthesia, reactions are rare - Con: may require multiple doses, expensive, limited availability, prolonged hospital stay

Question 26

2 Complications seen with untreated hyperthyroidism

Answer 26

Heart -increased HR and increased pressure in circulatory system increases workload on the heart which leads to thickening of cardiac muscle (usually LV) resulting in secondary hypertrophic cardiomyopathy and heart failure Eyes -increased pressure in ocular circulation may lead to retinal hemorrhage and detachment resulting in sudden blindness

Question 27

Potential complication that may occur when starting therapy for hyperthyroidism

Answer 27

unmasking kidney failure - hyperthyroidisms can help sustain failing kidneys because it increases BP, and increased BP results in increased blood flow (perfusion) to kidneys - therapy normalizes BP, so blood flow to kidneys decreases and may reveal kidney failure

Question 28

How to treat if CRF and hyperthyroid?

Answer 28

balance methimazole to a level that drops thyroid hormone enough that it lessens risks of hyperthyroidism but also still allows for some increased BP for increased perfusion to kidneys