03a: Thyroid

Question 1

Thyroid hormones contain (X)% (iodide/iodine).

Answer 1

X = 60-65

Iodine

Question 2

(X) enzyme (oxidizes/reduces) (iodide/iodine) and organifies the product by attaching (Y).

Answer 2

X = thyroid peroxidase (TPO)
Oxidizes Iodide (into iodine)
Y = thyroglobulin

Question 3

Thyroid: (X) enzyme couples MIT and DIT to form (Y).

Answer 3

X = thyroid peroxidase (TPO)
Y = T3 (DIT+MIT) or T4 (2DIT)

Question 4

T/F: A small portion, about 10%, of T3 is made by peripheral conversion of T4 to T3.

Answer 4

False - 80% is made in this manner

Question 5

(X) enzyme converts T4 to T3

Answer 5

X = D1 deiodinase (kidney and liver)

Question 6

T/F: T3 is 20-100x more bioactive than T4.

Answer 6

True

Question 7

T/F: rT3 is biologically inactive

Answer 7

True

Question 8

T/F: MIT and DIT are biologically inactive.

Answer 8

True

Question 9

(X)% of T4 is free; the rest is bound to (Y).

Answer 9

X = 0.04
Y = TBG, transthyreitin, or albumin

Question 10

Thyroid hormone acts at the
(hypothalamus/pituitary) to inhibit
secretion (X).

Answer 10

Both

X = TRH and TSH

Question 11

Pregnancy may change thyroid hormone requirements due to (increase/decrease) in thyroid binding proteins

Answer 11

Increase

Question 12

Cirrhosis and nephrotic syndrome may change thyroid hormone requirements due to (increase/decrease) in thyroid binding proteins

Answer 12

Decrease

Question 13

OCP may change thyroid hormone requirements due to (increase/decrease) in thyroid binding proteins

Answer 13

Increase

Question 14

T/F: T3 acts via RTK similar to IGF1.

Answer 14

False - intranuclear receptor

Question 15

(X) is the BEST test to determine thyroid function because for every 2-fold change in (Y), there is a 100-fold change in (X).

Answer 15

X = TSH
Y = free T4

Question 16

Autoimmune Hypothyroidism is associated with Ab against (X)

Answer 16

X = TPO

Question 17

Most common cause of mental retardation worldwide

Answer 17

Hypothyroidism (due to iodine deficiency)

Question 18

90% of neonatal hypothyroidism is due to which cause?

Answer 18

Dysgenesis/Agenesis of thyroid (missing or severely underdeveloped)

Question 19

About 10% of neonatal hypothyroidism is due to (X). What would you see on imaging?

Answer 19

X = Dyshormonogenesis (defects in thyroid hormone production; abnormal TPO activity)

Normally placed thyroid gland that’s normal size or enlarged (goiter)

Question 20

Sarcoidosis can cause hypothyroidism, most commonly (primary/secondary/tertiary). What are other etiologies?

Answer 20

Tertiary (level of hypothalamus)

Histiocytosis, tumors, radiation

Question 21

Most common cause of goiter worldwide is:

Answer 21

Iodine deficiency (hypothyroid)

Question 22

(X) receptor mutation is a rare cause of hypothyroidism due to thyroid hormone resistance

Answer 22

X = T3

Question 23

Pt Sx include mental retardation, hearing loss, and short stature. TSH levels are high, T4 levels are high. What is the likely cause of the (hypo/hyper)-thyroidism?

Answer 23

Hypothyroidism

Resistance to thyroid hormone (T3-R defect; v rare)

Question 24

T/F: HT is symptom of hypothyroidism

Answer 24

True

Question 25

T/F: Total and LDL cholesterol levels are decreased in hypothyroidism.

Answer 25

False - elevated

Question 26

List some GI issues associated with hypothyroidism

Answer 26

1. Abd distension, constipation | 2. Autoimmune atrophic gastritis (achlorhydria, pernicious anemia)

Question 27

What's cretinism?

Answer 27

severely stunted physical and mental growth owing to untreated congenital hypothyroidism

Question 28

Standard Rx for hypothyroidism is:

Answer 28

Oral L-thyroxine (T4)

Question 29

Hypothyroidism: once patient is on Rx and reaches steady state, how often should (X) levels be checked?

Answer 29

X = TSH 6-12 months (unless symptoms occur)

Question 30

Hypothyroidism: the rate of T4 replacement depends on which factor(s)?

Answer 30

Age and risk of CAD (titrate slowly in elderly to prevent CV issues)

Question 31

Hypothyroidism: T4 dose is determined once which list of factors has been considered?

Answer 31

1. Age/wt of pt 2. Previous I-131 Rx 3. Meds/pregnancy (increase thyroid hormone proteins) 4. Diet/GI status that may interfere with T4 absorption

Question 32

Decompensated state of severe hypothyroidism can result in (X), with as high as 50% mortality.

Answer 32

X = Myxedema coma

Question 33

T/F: Pt presenting with Myxedema Coma has very low core temp so should be treated with heat blanket asap.

Answer 33

False!!! Avoid external warmth (sudden vasodilation and vascular collapse)

Question 34

Myxedema Coma: key first steps in treatment

Answer 34

1. IV L-thyroxine 2. IV fluids (w glucose) 3. Assisted ventilation (warm, moist air)

Question 35

(X) Ab are the most specific | marker for Hashimoto's.

Answer 35

X = Antimicrosomal antibodies against TPO | Antithyroglobulin Ab less specific