Thyroid Flashcards

1
Q

Functions of the thyroid

A
  • produces hormones
  • regulates metabolism
    body temperature
    cardiac and nervous systems
    skin dryness
    menstrual cycles
    cholesterol levels

it is the only gland that absorbs iodine

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2
Q

Describe the pathophysiology of the thyroid hormones from hypothalamus to periphery

A

Hypothalamus -> Thyroid releasing hormone (TRH) –> pituitary (TSH- aka thyrotropin regulates growth and development)–> Thyroid–> T4 (thyroxine) and T3 (triiodothyronine, 3 iodines) to the periphery - most of the T4 gets converted to T3, only small amount of T3 is made by thyroid

there is a negative feedback loop to regulate this

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3
Q

hypothyroidism vs hyperthyroidism

A

decreased free T4, increase TSH - hypothyroidism

increased free T4, decreased TSH - hyperthyroidism

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4
Q

Hypothyroidism symptoms and causes and emergency

A
  • slowed down everything
    hard ones to remember:
    depression
    voice changes
    menorrhagia
    dry skin
    feeling cold / cold intolerance
    muscle cramps, myalgias
    weakness
    bradycardia
    coarse hair/loss of hair
    memory loss/impairment
    weight gain
    Goiter (lump felt on throat due to enlarged thyroid)

causes: hashimotos disease (autoimmune - antibodies attack), drugs, iodine deficiency

emergency : myxedema coma - full slowing of all their systems, life threatening - tx with IV levothyroxine

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5
Q

Drugs that cause hypothyroidism

A

I TALC

Interferons** (can also cause hyperthyroidism)
Tyrosine kinase inhibitors
Amiodarone ** (can also cause hyperthyroidism)
Lithium
Carbamezapine

Conditions: hashimotos disease ; others include anything that affects iodine, pituitary, or thyroid gland

Other drugs:
- oxcarbazepine
- eslicarbazepine
-phenytoin

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6
Q

when should we screen patients for hypothyroidism

A

60

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7
Q

normal T4 and TSH levels

A

0.9-2.3ng/dl = T4
0.3-3 mIU/L = TSH

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8
Q

how often should we monitor TSH and symptoms

A

every 4-6 weeks until levels are normal. as patients get older a reduction in their thyroid dose may be required.

once euthyroid, we can check every 4-6 months

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9
Q

Why do we need to caution for too high thyroid replacement dose in elderly

A

can cause afib and fractures

excessive doses of thyroid in any age patient can cause hyperthyroidism

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10
Q

what is FT4

A

it is part of the thyroid function test (TSH, T4, and FT4 (free T4)) and its monitored when tx hypothyroidism in pregnancy

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11
Q

true or false. while patient is on thyroid treatment in the U.S. they should also receive iodine supplementation

A

false. In the U.S. we supplement table salt with iodine, so goiter has been virtually eliminated.

If people are on a salt restricted diet they can supplement with iodine or eat iodine rich foods like meat, seafood, dairy, and some breads

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12
Q

Counseling points with levothyroxine

A

take the dose consistently!

it binds to everything, so take 60 min before breakfast with water OR take at bed time at least 3 hrs after the last meal and no snacks can be eaten after.

(avoid Ca2+, antacids, multivitamins, etc. – also avoid hepatic inducers bc they decrease the levels (amiodarone, beta blockers, protein bound drugs)

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13
Q

true or false: we can switch patients on different levothyroxine formulations because they are very interchangable.

A

false. avoid this. there are therapeutic equivalence issues with variable amounts and we don’t want to mess with the patients thyroid. If we need to interchange with levothyroxine, we can use the orange book.

Cytomel (liothyronine, T3), and desiccated thyroid (ex: Armour thyroid) aren’t recommended because they have variable amounts of T3 and T4.

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14
Q

Levothyroxine IV:PO conversion

A

0.75 IV: PO 1

75 % of oral dose

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15
Q

List the levothyroxine colors and strengths

A

Orangutans - orange = 25 mcg
Will - white = 50 mcg
Vomit - violet = 75 mcg
On - olive = 88 mcg
You - yellow = 100 mcg
Right - rose = 112 mcg
Before - brown = 125 mcg
They - turquoise = 137 mcg
Become - blue = 150 mcg
Large - lilac = 175 mcg
Proud - pink = 200 mcg
Giants - green = 300 mcg

these are standardized. great for safety checks so that the patient recognizes when they have wrong dose

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16
Q

Hyperthyroidism symptoms and causes

A

everything is sped up/heated up

heat intolerance/sweating
agitation
palpitations
tachycardia
light/absent menstrual periods
diarrhea
weight loss
tremor
thinning hair
exophthalamos - bulging eyes

cause: graves disease (autimmune- antibodies stimulate thyroid to increase T4), thyroid nodule, certain drugs (amiodarone, iodine, thyroid replacement drugs, interferons), excess hormone replacement.

17
Q

Levothyroxine (T4) brand names

A

synthroid, levoxyl, unithroid, euthrix, tirosint, tirosint-SOL

available as capsule, tablet, and injection, and oral solution

separate this from other ion/chelating drugs by at least two hours (the longer the better)

18
Q

full replacement dose for levothyroxine and who should get it. who should get partial replacement

A

full: 1.6 mcg/kg/day using IBW

healthy, young (<50 yrs) pts with high TSH

partial : elderly, or milder hypothyroidism and those with comorbidities. Elderly pts may need < 1mcg /kg/day, or 20-25% less per kg

19
Q

What dose of levothyroxine should pts get if they have CAD

A

12.5-25 mcg daily

20
Q

Desiccated thyroid (T3 & T4)

A

Armour thyroid tablets
15-30 mg daily and titrate up. usual dose is 60-120 mg /day

not recommended usually

21
Q

Liothyronine (T3)

A

Cytomel tablet
Triostat injection

25 mcg daily , titrate. usually dosed 25-75 mcg daily

this drug has a shorter half life, which causes more fluctuations in T3 levels.

22
Q

boxed warning for thyroid replacement hormone

A

never use for weight loss. high doses can cause fatal effects.

23
Q

Contraindication for thyroid replacement hormone

A

uncorrected adrenal insufficiency

24
Q

in what condition do we need to decrease the dose of thyroid hormone replacement therapy

A

patients with CVD (hypothyroidism increases risk of coronary artery disease)

25
Q

T or F: thyroid hormone replacement therapy can cause osteoporosis

A

true. decreases BMD

26
Q

SE of thyroid hormone replacement therapy

A

hyperthyroid symptoms if you give too much

(palpitations, tachycardia, arrythmias, irritability, sweating, weight loss)

27
Q

levothyroxine doses likely need to be increased or decreased during pregnancy or breastfeeding ?

A

increased

28
Q

thyroid hormone is highly protein bound so we need to be aware of other drugs that might compete with the protein and affect drug levels

A

ex: phenytoin

29
Q

Thyroid hormones can impact the concentration/effect of warfarin and theophylline how?

A

increases warfarin effectiveness, increases INR

decreases theophylline

30
Q

drugs that can cause both hypo and hyperthyroidism

A

amiodarone
interferons

31
Q

Describe treatments for hyperthyroidism

A

radioactive iodine (RAI-131) or surgery - preferred in graves disease

Thionamides:
Propylthiouracil (PTU)- 50 - 150 mg Q8H until euthiroid, and eventually reduce - preferred in thyroid storm or in first trimester of preg.
OR Methimazole (topazole)** preferred in all pts d/t low risk of liver damage and in 2nd and 3rd trimester of pregnancy after PTU in first. mild hyperthyroidism: 5 mg Q8H, titrate to 5-15 mg daily
^both of these inhibit synthesis of thyroid hormones and conversion of T4 to T3. always monitor for liver tox. SE: GI upset, rash ,fever, constipation, bleeds
BOXED WARNING for severe liver injury and acute renal failure for both thionamides . both are teratogenic, but PTU is more, so preferred in first trimester.

Potassium Iodide (lugols solution) - temporarily inhibits secretion of T3 and T4 for several weeks but eventually diminishes. diluted and taken with water
Contraindicated if hypersensitive to iondide or iodidne or. has heart disease. SE: rash, sore throat/gum, GI upset. hyperthyroidism with prolonged use. off label for preparation for thyroidectomy or for after the radioactive iodine to prevent thyroid cancer

Beta blockers are used to help with symptoms (arrhythmia, tremors, palpitations, etc) Ex: propranolol

32
Q

thyroid storm definition and symptoms and treatment

A

life threatening emergency, hyperthyroidism that caused by trauma, infection, surgery, radioactive iodine treatment or non adherence to antithyroid meds.

Sx: heightened version of hyperthyroidism, coma, psychosis, delirium

treatment:
PTU (propylthiouracil) AND potassium iodide solution, beta blocker (propranolol) systemic steroid (dexamethasone), aggressive cooling with APAP and other supportive tx.

33
Q

true or false: levothyroxine can’t be used in pregnancy

A

false. it can. 30-50 % increase in the dose throughout the course of their pregnancy and several months after giving birth. we should aggressively control the hypothyroidism in pregnancy and ideally start treatment before pregnancy.

For hyperthyroidism, also should try and postpone pregnancy and treat hyper before. because there are risks to baby and mom. if hyper and becomes pregnant, see if tx can be stopped safely in mild disease otherwise (PTU first trimester, and methimazole 2nd and third