Hypothyroidism

Question 1

thyroid hormone synthesis steps

Answer 1

trapping 
organification 
coupling 
storage 
secretion

Question 2

what is trapping?

Answer 2

trapping of iodide, transported by NIS

Question 3

organification

Answer 3

• of iodide into iodine and condensed into tyrosine residues
• forms MIT or DIT
• catalyzed by TPO

Question 4

coupling

Answer 4

DIT + MIT = T3

DIT + DIT = T4

Question 5

what is the Jod Basedow effect?

Answer 5

linear increase in organification / T4 formation with increasing iodide concentration

Question 6

what is the wolff-chaikoff effect?

Answer 6

linear decrease in organification / T4 formation with increasing iodide concentration following the jod basedow effect

Question 7

what is the escape phenomenon?

Answer 7

linear increase in organification / T4 formation with increasing iodide concentration following the wolff-chaikoff effect?

Question 8

what is the primary binding protein?

Answer 8

thyroid binding globulin

Question 9

what factors increase TBG?

Answer 9

estrogen (pregnancy, BCP)

congenital

Question 10

what factors decrease TBG?

Answer 10

systemic illness

glucocorticoids

Question 11

besides TSH what other hormone can be increased by TRH?

Answer 11

prolactin

Question 12

which thyroid test is usually the best test of thyroid function? it is inversely proportional to what function?

Answer 12

TSH

inversely proportional to thyroid function

Question 13

hypothryoidism: relationship of TSH and FT4 levels

Answer 13

TSH exceeds the reference range before FT4 gets too low

Question 14

hyperthryoidism: relationship of TSH and FT4 levels

Answer 14

TSH drops below reference range before FT4 gets too high

Question 15

which thyroid test predicts thyroiditis and hypothyroidism?

Answer 15

thyroperoxidase Ab

Question 16

low T3/T4, low TSH

Answer 16

secondary / central hypothyroidism

Question 17

low T3/T4, high TSH

Answer 17

primary hypothyroidism

Question 18

normal T3/T4, low TSH

Answer 18

subclinical hypothyroidism

Question 19

normal T3/T4, high TSH

Answer 19

subclinical hypothyroidism

Question 20

high T3/T4, low TSH

Answer 20

primary hyperthyroidism

Question 21

high T3/T4, high TSH

Answer 21

central hyperthyroidism / resistance

Question 22

secondary / central hypothyroidism

Answer 22

low T3/T4, low TSH

Question 23

primary hypothyroidism

Answer 23

low T3/T4, high TSH

Question 24

subclinical hypothyroidism

Answer 24

normal T3/T4, low TSH

or

normal T3/T4, high TSH

Question 25

primary hyperthyroidism

Answer 25

high T3/T4, low TSH

Question 26

central hyperthyroidism / resistance

Answer 26

high T3/T4, high TSH

Question 27

what is the most common cause of hypothyroidism in iodine-sufficient areas?

Answer 27

hashimoto thyroiditis

Question 28

hashimoto thyroiditis: pathogenesis

Answer 28

autoimmune mediated destruction of thyroid - lymphocytic infiltration

Question 29

what are the clinical features of hashimoto’s thyroiditis?

Answer 29

goiter

surface may have a ‘bossillated’ feel

Question 30

what are the labs associated with hashimoto thyroiditis?

Answer 30

• elevated TSH +/- low T4
• usually TPO antibodies are elevated
• classical heterogeneous appearance on US

Question 31

what is the treatment for hypothyroidism?

Answer 31

levothyroxine (T4)

Question 32

what are the contributing factors to hypothyroidism during pregnancy?

Answer 32

• weight gain
• increasing TBG levels
• increased 5 deiodination

Question 33

what are the clinical features of myxedema coma?

Answer 33

medical emergency consisting of

• mental status changes
• hypothermia
• hypoglycemia
• respiratory failure, hypotension, bradycardia

Question 34

during what condition(s) is TSH no longer reliable? what should be used to guide adjustments?

Answer 34

pituitary or hypothalamic insult

free T4