Unit 10: Thyroid Flashcards by Michelle Herman

What is the function of the thyroid hormones?

metabolic pacemaking

influence/regulate:  
growth
body temperature
energy metabolism
heart rate
cholesterol metabolism
mood

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What is the difference between total T3 and T4 versus bound T3 and T4?

most T3 and T4 are bound to protein and are metabolically inactive
Free T3 and Free T4 are active/not bound

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What is the name for T3?

triiodothyronine

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What is the name for T4?

tetraiodothyronine = thyroxine

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Which is more potent, T3 or T4?

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Which is present in higher amounts, T3 or T4?

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Describe the HPA for the thyroid

hypothalamus secretes TRH
TRH stimulates the pituitary to secrete TSH
TSH stimulates the thyroid to secrete T3 and T4

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What is TRH?

thyroid-releasing hormone

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What is TSH?

thyroid-stimulating hormone

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What is the best test for screening for hypo/hyperthyroidism?

TSH

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What is the best test for medication adjustment for the thyroid?

TSH

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How long does it take the TSH to adjust to a new medication level via the body’s negative feedback loop?

4-6 weeks

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TSH is ______ proportional to the amount of active thyroid hormone in the serum

INVERSELY

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If TSH is high, then what?

there is not enough circulating thyroid –> hypothyroid

GREAT EXAM QUESTION

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If TSH is low, then what?

there is too much circulating thyroid –> hyperthyroid

GREAT EXAM QUESTION

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Why don’t we check Total T3 and Total T4?

Not very important measurements, as we want to know how much T3 and T4 are available

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Why check anti-thyroid antibodies?

to determine if hyperthyroidism or hypothyroidism are autoimmune

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Antibody to thyroid peroxidase is what? In what disease is it seen?

TPO

Hashimoto’s Thyroiditis

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What antibody stimulates the TSH receptor? In what disease is it seen?

TRAb

Grave’s Disease

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What is the FNA test?

completed on a solitary thyroid nodule to rule out malignancy

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True or False: It is common for the thyroid to have nodules

True

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What is the Radioactive Uptake Scan, and for what is it used?

completed in hyperthyroid patients to identify cause of it

to identify non-active nodule which is likely to be malignant

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Why is the FNA test important?

identifying thyroid malignancy EARLY is important, as it often metastasizes

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What does iodine have to do with the thyroid?

required to make thyroid hormones

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How do we make sure we get enough iodine?

salt is iodized

For what is radioactive iodine used?

I-131-- destroy the tissue | 1.123 -- to identify metabolically active nodules

What heart condition does hyperthyroidism commonly cause?

A-Fib

How is hyperthyroidism treated?

medically radiation surgery

What foods commonly have iodine?

cod | milk

What medications are used to treat hyperthyroidism?

THIODAMIDES: methimazole (Tapazole) propylthiouracil (Propyl-Thyracil)

What is the drug of choice for hyperthyroidism?

methimazole (Tapazole)

What is the drug of choice for hyperthyroidism and pregnancy?

propylthiouracil (Propyl-Thyracil) | increased protein binding --> less crosses the placenta

What can methimazole (Tapazole) cause?

elevated liver enzymes

What do the thiodamides do?

prevent T3/T4 synthesis via 3 mechanisms

How long does it take for thiodamide medications to have their effects?

3-4 weeks

What is a thyrotoxic crisis?

extreme hyperthyroidism

Methimazole can be hepatotoxic; when should it be discontinued?

if transaminases (AST/ALT) are 3x normal

AE of methimazole

``` low prothrombin levels --> bleeding bone marrow suppression hepatotoxic lupus-like syndrome vasculitis hypothyroidism ```

Important thing to remember about older thyroid suppression meds: potassium iodide (SSKI) potassium iodide-iodine solution (Lugol's)

keep thyroid hormones from being released, so the sudden discontinuation of the meds can cause excessive levels of hormones

When are SSKI or Lugol's solution used?

short term pre-operatively before thyroidectomy | thyroid protection during radiation of thyroid

What is I-131?

Radioactive iodine used for hyperthyroidism and after surgery for some thyroid cancers to get rid of any remaining cancer

What normally happens after administration of I-131?

thyroid becomes enlarged briefly, but not painful | effect evident 1-2 weeks after administration

With what drugs does I-131 interact?

other thyroid meds, especially suppressants | amiodarone

Why is a low iodine diet recommended with I-131?

The thyroid pulls in iodine indiscriminately; we ant it to pull in the radioactive iodine

Why should people who receive I-131 be encouraged to drink and void frequently?

to release radiation via urine

What is I-123?

Radioactive sodium iodide used in thyroid scintigraphy

What is thyroid scintigraphy?

"thyroid uptake scan" OR "radionuclide thyroid scan" where metabolically active nodules take up radioactive iodide; hypo functioning nodules are suggested of malignancy **if nodules are not making hormones, they will not take up iodine

Name other meds used in hyperthyroidism

BETA BLOCKERS -- for sx control of tachycardia; prevent A-Fib or A-Fib + RVR (propranolol preferred) CCBs -- verapamil (for HR rhythm/rate control) Cholestyramine (bile acid sequestrant) to bind to T3/T4 in the gut

Signs and symptoms of hypothyroidism

``` weight gain fatigue dry skin cold intolerance depression constipation **slows most things down ```

What is subacute thyroiditis?

due to intermittent presence of antibodies, brief periods of hyperthyroidism in early Hashimoto's

Symptomatic treatment of Subacute Thyroiditis

Beta blockers steroids NSAIDs

What is transient thyrotoxicosis?

spontaneously resolving hyperthyroidism

How is hypothyroidism treated?

synthetic replacement: - -levothyroxine - -levothyronine - -liotrix animal replacement: --dessicated thyroid

What is myxedema?

severe hypothyroidism

What can result from myxedema?

stupor lethargy coma

What is levothyroxine?

T4 that converts to T3

Why do we treat hypothyroidism with T4 and not T3?

because the half life of T3 is so short | and it is easier to keep a steady level of hormones if we replace T4 (levothyroxine) than T3

What is the cause of secondary hypothyroidism?

hypopituitary causes

What is the cause of tertiary hypothyroidism?

hypothalamic causes

For treating hypothyroidism, how often should TSH levels be checked?

4-8 weeks after starting tx or changing dose 6 months after stable dosing then every 12 months anytime there are hypothyroid/hyperthyroid symptoms during treatment

What is Tirosint?

a soft gel version of levothyroxine that absorbs more quickly and is less affected by coffee and gastric pH

What organ is very sensitive to thyroid replacement?

the heart

What other endocrine dysfunction should be corrected first, before treating hypothyroidism?

adrenal insufficiency

What can happen for patients with CAD who are also hypothyroid and treated with levothyroxine?

arrhythmias | angina

What is thyroxine toxicity?

too much circulating thyroid hormone

Symptoms of thyroid toxicity in children

restlessness insomnia accelerated bone maturation and growth

Symptoms of thyroid toxicity in adults

``` nervousness heat intolerance palpitations tachycardia unexplained weight loss ```

Symptoms of long term thyroid toxicity in adults

A-fib | increased rate of bone loss in osteoporosis

Drugs that increase hepatic microsomal enzymes increase metabolism of what hormones?

T3 and T4

What needs to happen with thyroid meds if the patient is also on meds that increase hepatic microsomal enzymes?

increase dose of thyroid meds

What happens with estrogen (dosed and in pregnancy) and thyroid hormones?

increases binding of thyroxine and liothyroxine --> so less is available

What is desiccated thyroid?

thyroxine from an animal source

What are the risks of desiccated thyroid?

antibody formation

What is liothyronine?

Why don't we use liothyronine to treat hypothyroidism?

harder to make amount of available T3 level/even when using this drug

When is thyroid replacement contraindicated?

for weight loss when TSH, T3, T4 are normal abnormal vaginal bleeding depression urticaria

Risks of thyroid replacement being given when it is not truly needed

osteopenia/osteoporosis A-Fib CAD/CHF