Thyroid

Question 1

What are the two major thyroid hormones?

Answer 1

Thyroxine (T4)

Tri-iodothyronine (T3)

Question 2

How much T3 is produced in the thyroid itself?

Answer 2

20%

Question 3

Where does the majority of T3 come from

Answer 3

80% comes from peripheral breakdown of T4

Question 4

How many half-lives do thyroid hormones have in steady state?

Answer 4

4-5

Question 5

What does the thyroid do?

Answer 5

Regulates hormone production

This is done via the hypothalamic pituitary thyroid axis

Question 6

How do we get thyroid hormone?

Answer 6

TSH secreted by anterior pituitary
Or..
T4 is converted to T3 outside the thyroid

Question 7

What kind of disorder is primary hypothyroidism

Answer 7

Disorders of the thyroid gland

Aka: Hashimoto’s thyroiditis

Question 8

What kind of disorder is secondary hypothyroidism

Answer 8

Pituitary or hypothalamic dosorders

Question 9

Sx of hypothyroidism

Answer 9

Weight gain
Depression*
When working a pt up for depression checking for hypothyroidism is ESSENTIAL

Question 10

Diagnosing hypothyroidism

Answer 10

Check TSH and a free T4 (or total but free is better)

Question 11

Levels of hormones in subclinical hypothyroidism

Answer 11

Increased TSH but normal T4

Question 12

Levels of hormones in hypothyroidism

Answer 12

Elevated TSH

Low T4

Question 13

Drug of choice for hypothyroidism

Answer 13

Levothyroxine

Question 14

Levothyroxine

Answer 14

Synthetic T4 
Long half life
Once daily dosing
IV dosing at 50% of oral dose
Dosing in mcg!

Question 15

Little used hypothyroidism tx

Answer 15

Desiccated beef/pork thyroid gland (Armour -> mg dosing)*
Obsolete and potential for allergy
T3 and T4 mixtures (Liotrix) -> expensive, no real theraputic rationale

Question 16

Levothyroxine dosing

Answer 16

Dosed one daily in AM on EMPTY STOMACH

Typical dose = 100-112 mcg/day

Question 17

Under what circumstances do we used alternative dosing of levothyroxine

Answer 17

Lower initial dosing for the elderly and pts w/ CV disease

Pregnancy usually requires higher dosing

Question 18

Hyperthyroidism sx

Answer 18

Nervousness
Anxiety
Palpitations
Heat intolerance
Finger tremor
Weight loss (cardinal sign)

Question 19

Main cause of hyperthyroidism

Answer 19

Grave’s disease

Question 20

Classic triad of Grave’s disease

Answer 20

Hyperthyroidism
Opthalmopathy (bugged out eyes)
Dermopathy (pretibial myxedema)

Question 21

Hormone levels in hyperthyroidism (dx)

Answer 21

Decreased TSH

Increased T4

Question 22

Hyperthyroidism tx

Answer 22

Antithyroid meds

Question 23

Anti-thyroid meds

Answer 23

Propylthiouracil (PTU)

Methimazole

Question 24

PTU

Answer 24

Inhibits conversion of T4 to T3
TID dosing
Evaluate pts 3 months after D/Cing to check for recurrence

Question 25

Methimazole

Answer 25

10xs more potent than PTU Blocks oxidation of iodine in thyroid No effect on T3 or T4

Question 26

Dosing of methimazole for mild, moderate, severe, and maintenance is how many times per day

Answer 26

3! | TID

Question 27

SE of anti-thyroid meds

Answer 27

Agranulocytosis Aplastic anemia Thrombocytopenia