Hypothyroidism Flashcards
thyroid hormone synthesis steps
trapping organification coupling storage secretion
what is trapping?
trapping of iodide, transported by NIS
organification
- of iodide into iodine and condensed into tyrosine residues
- forms MIT or DIT
- catalyzed by TPO
coupling
DIT + MIT = T3
DIT + DIT = T4
what is the Jod Basedow effect?
linear increase in organification / T4 formation with increasing iodide concentration
what is the wolff-chaikoff effect?
linear decrease in organification / T4 formation with increasing iodide concentration following the jod basedow effect
what is the escape phenomenon?
linear increase in organification / T4 formation with increasing iodide concentration following the wolff-chaikoff effect?
what is the primary binding protein?
thyroid binding globulin
what factors increase TBG?
estrogen (pregnancy, BCP)
congenital
what factors decrease TBG?
systemic illness
glucocorticoids
besides TSH what other hormone can be increased by TRH?
prolactin
which thyroid test is usually the best test of thyroid function? it is inversely proportional to what function?
TSH
inversely proportional to thyroid function
hypothryoidism: relationship of TSH and FT4 levels
TSH exceeds the reference range before FT4 gets too low
hyperthryoidism: relationship of TSH and FT4 levels
TSH drops below reference range before FT4 gets too high
which thyroid test predicts thyroiditis and hypothyroidism?
thyroperoxidase Ab
low T3/T4, low TSH
secondary / central hypothyroidism
low T3/T4, high TSH
primary hypothyroidism
normal T3/T4, low TSH
subclinical hypothyroidism
normal T3/T4, high TSH
subclinical hypothyroidism
high T3/T4, low TSH
primary hyperthyroidism
high T3/T4, high TSH
central hyperthyroidism / resistance
secondary / central hypothyroidism
low T3/T4, low TSH
primary hypothyroidism
low T3/T4, high TSH
subclinical hypothyroidism
normal T3/T4, low TSH
or
normal T3/T4, high TSH
primary hyperthyroidism
high T3/T4, low TSH
central hyperthyroidism / resistance
high T3/T4, high TSH
what is the most common cause of hypothyroidism in iodine-sufficient areas?
hashimoto thyroiditis
hashimoto thyroiditis: pathogenesis
autoimmune mediated destruction of thyroid - lymphocytic infiltration
what are the clinical features of hashimoto’s thyroiditis?
goiter
surface may have a ‘bossillated’ feel
what are the labs associated with hashimoto thyroiditis?
- elevated TSH +/- low T4
- usually TPO antibodies are elevated
- classical heterogeneous appearance on US
what is the treatment for hypothyroidism?
levothyroxine (T4)
what are the contributing factors to hypothyroidism during pregnancy?
- weight gain
- increasing TBG levels
- increased 5 deiodination
what are the clinical features of myxedema coma?
medical emergency consisting of
- mental status changes
- hypothermia
- hypoglycemia
- respiratory failure, hypotension, bradycardia
during what condition(s) is TSH no longer reliable? what should be used to guide adjustments?
pituitary or hypothalamic insult
free T4
