Thyroid Disorders and Cancers Flashcards
The pituitary monitors circulating concentrations of what?
free T4 and T3
(over 99% of circulating T4 and T3 is bound to TBG and other binding proteins)
What type of hormone is T3 and T4? Why is this important?
Steroid hormone, don’t dissolve well in water which is why they have binding proteins.
Effect of changes in binding protein concentration
Changes in binding protein concentrations change serum concentration of total T4 and T3. However, _FREE T4 and T3 concentrations remain unchanged. _
People who don’t have TBG have perfectly normal thyroid physiology
What causes increased concentrations of thyroid binding globulin? (5) What is the effect then on total T4 and free T4?
- Oral contraceptives / hormon replacement therapy
- pregnancy
- raloxifene (treats and prevents osteoporosis)
- tamoxifen
- chronic hepatitis
increase circulating concentrations of TBG AND total T4, but they DO NOT alter free T4
What causes decreased TBG? (3)
- x-linked genetic (TBG gene is on x-choromsome)
- chronic illness, cirrhosis (once the liver is dead, you can’t make anymore)
- androgens
Atrial fibrillation association
Cumulative incidence of A fib over time when TSH is less than 0.1 when over 60 yo
What happens during acute illness
You get less of Deiodinase 2 (converts T4–>T4), get build up of T4, TSH falls
Also get build up of inactive rT3 (D3 will then convert the excess T4 –>rT3
How do you distinguish between subclinical hyperthyroidism vs hyperthyroxinemia of acute illness?
The latter causes a build up of T4 due to decreased Deiodinase 3 levels. The half life of T4 is a week, so repeat the TSH and T4 in 1-2 weeks.
A healthy 72 yo woman is screened:
TSH = 14.2 (0.4-5)
Free T4 = 1.1 (0.9-1.8)
Should she be treated?
While her free T4 is in normal range, her high TSH tells us that the free T4 is low for HER. Therefore, we usually treat.
Hypothyroidism is due to Hashimoto’s and is progressive. Treatment is likely safe.
How to treat hypothyroidism in patients with angina and why
Start with LOW DOSES of levothyroxina
In hypothyroidism: increased alpha receptors (cause vasocontriction), decreased beta receptors (so you get less vasodilation)
- if you have more alpha, when you release catecholalmines, you will get a TON of constriction –> afterload –> bad for CAD because heart has to work harder and use more oxygen
- hence why we give levlo starting out low and slow to elderly
Thyroid uptake of 123-iodine in Graves vs exogenous thyroid hormone injections. Explain importance of this
In Graves: Increased iodine uptake, thyroid m aking more hormones so needs the iodine
Exogenous source of throid hormones: this shuts off her TSH and will shrink thyroid gland. So there will be low uptake of iodine since your gland doesn’t need it.
If a women has low TSH and high FT4, you want to do a thyroid uptake of 123-iodine to differentiate the problem, but it is important to give a PREGNANCY TEST FIRST because 123-iodine is harmful for baby.
2 disorders where 131-iodine uptake is high
3 disorders where 131-iodine uptake is low
high uptake:
- Graves
- Multinodular goiter
low uptake:
- silent thyroiditis
- painful thyroiditis
- factitious hyperthyroidism
Silent Thyroiditis (subacute granulomatous thyroiditis)
Hashimoto’s variant:
in measuring T4:
-increased at delivery, hyperthyroidism, then loops down to hypothyroid over a few months
Options for Graves’ therapy (3)
- thyroidectomy
- iodine-131
- anti-thyroid drugs (temporaizing): PTU vs. Methimazole
Side effects of PTU (3)
rash, agranulocytosis, hepatic failure
agranulocytosis is rare but severe: white count drops to zero suddenly and unpredictably. Patient prone to infection and death
