Thyroid Flashcards
which type of hypothyroidism is most common?
primary
why is TSH normal-range w/ secondary hypothyroidism?
- inappropriately low TSH given low T4
- glycosylation machinery is dependent on TRH
w/out TRH –> make TSH still, but it is inactive –> low T4
causes of primary hypothyroidism
iodine deficiency
hashimoto’s
resistance to thyroid hormone - uncommon
cretinism
thyroid hormone is needed for CNS development of infant. dx w/in 4-6 wks –> catch up with normal development
target genes for thyroid hormone
developmental: CNS, long bone growth
metabolism: mito # and function, metabolic clearance of endogenous (LDL, CPK, cortisol, hyaluronic acid) and exogenous molecules (digoxin, anesthetics)
expression of beta-adrenergic receptors: skeletal and cardiac striated muscle
galactorrhea may occur in primary hypothyroidism. why?
high TRH –> causes production of prolactin
ddx primary hypothyroidism
iodine deficiency hashimoto's congenital subacute thyroiditis surgical or radioiodine ablation drugs - amiodarone, PTU, methimazole, lithium
ddx secondary hypothyroidism
hypothalamic disease
pituitary disease
genetic (TSH deficiency, pit-1/prop-1 mutations)
draw pit-1, prop-1 lineage diagram
see notes
resistance to thyroid hormone
rare
dominant negative mutation
high T4 and TSH, but hypothyroid appearing organs
how to tx hypothyroidism w/ coexisting hypoadrenalism
DON’T prescribe thyroid hormone. may precipitate adrenal crisis from increased turnover of cortisol.
treating hypothyroidism in pregnancy
increase dosage b/c increased T4 degradation by the placenta
how might initiation of thyroxine worsen underlying myocardial ischemia?
increases HR –> increase oxygen demand
- replace gradually
effect of thyroid hormone on heart
- increase HR
- decrease BP and peripheral resistance
- increase myocardial efficiency
causes of thyrotoxicosis in order of prevalence
Graves
TMG
toxic adenoma
thyroiditis
how does thyrotoxicosis cause sympathetic sx?
increases beta adrenergic receptors –> enhanced cAMP response
graves sx
enlarged gland goiter, sometimes w/ hums/bruits graves triad: 1. diffuse thyroid hyperplasia 2. infiltrative opthalmopathy 3. infiltrative dermopathy = pretibial myxedema
thyrotoxicosis factitia - labs
high thyroid hormone, low TSH
low thyroglobulin
0% iodine uptake nuclear scan due to suppression
how much of thyroid hormone is bound to binding protein
> 99% = bound and inactive
conditions that increase thyroid hormone binding to TBG
- -> HIGH total T4/T3
- pregnancy
- estrogen
- acute hepatitis
- congenital > TBG
- mutant albumin molecule
conditions that reduce thyroid binding to TBG
--> LOW total T4/T3 androgens corticosteroids salicylates barbituates major illness/trauma nephrotic syndrome congenital low TBG
euthyroid sick syndrome
low free T3 and T4 w/ low or normal TSH in severe illness
diagnostic features of papillary carcinoma
- papillary architecture
- psamomma bodies
- unique nuclear features: nuclear pseudo inclusions, nuclear grooves
diagnostic features of follicular adenoma
- capsule surrounding a solitary nodule
- no evidence of invasion
- commonly micro follicular pattern
