Thyroid Flashcards by Kathryn Cannaday

What is the difference between T3 and T4 hormones?

-T4 is solely secreted from the thyroid
-T3 is mostly produced by conversion of T4 (80%)

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What lab values indicate hyperthyroidism?

increased T3, increased T4, decreased TSH

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Define: Thyrotoxicosis

clinical state resulting from inappropriately high levels of thyroid hormone (T3 and T4) that could be caused by many factors

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Define: Hyperthyroidism

inappropriately high synthesis and secretion of thyroid hormone

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What are the signs and symptoms of hyperthyroidism?

-cardiac (palpitations, tachycardia, atrial fibrillation, heart failure)
-dermatologic (hair loss/fine hair, warm/moist skin, heat intolerance)
-anxiety/irritable/fatigue
-gastrointestinal (increased appetite, weight loss, diarrhea, dysphagia)
ophthalmologic (decreased tears, exophthalmos, diplopia)
-menstruation changes

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What does radioactive iodine uptake (RAIU) indicate?

-elevated= thyroid gland is over producing hormone, hyperthyroidism
-suppressed= thyrotoxicosis due to thyroid inflammation

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Hyperthyroidism + normal or increased RAIU indicates…

-GRAVES DISEASE
-toxic adenoma
-toxic multinodular
-TSH-producing pituitary adenoma

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Hyperthyroidism + decreased RAIU indicates…

-painless thyroiditis
-amiodarone-induced thyroiditis
-latrogenic thyrotoxicosis
-ingestion of thyroid hormone
-thyroid cancer

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What are the goals of therapy when treating hyperthyroidism?

-eliminate excess thyroid hormone (normalize TSH and T4)
-minimize symptoms
-reduce long-term consequences

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What are the long-term consequences of untreated hyperthyroidism?

atrial fibrillation, heart failure, vision loss, osteoporosis, thyroid storm

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What are the treatment options for hyperthyroidism?

-symptom management
-anti-thyroid medication
-radioactive iodine (RAI)
-surgery

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What drugs can be used for symptom management of hyperthyroidism?

-beta blockers (propranolol, metoprolol) or non-DHP calcium channel blockers (verapamil, diltiazem)

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What is the indication for using symptom management treatment?

-overt clinical symptoms
-heart rate > 90 or cardiovascular symptoms

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What are characteristics for favorable outcomes using anti-thyroid medication?

-female sex
-patients > 40 yo
-low T4:T3 ratio
-small goiter
-short duration of disease (<6 months)
-no previous history of relapse
-low TSAb titers at baseline or reduced with treatment

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What drugs are anti-thyroid?

methimazole, propylthiouracil

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MOA: anti-thyroid medication

inhibits oxidation of iodine in the thyroid gland, blocks synthesis of T4 and T3

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What anti-thyroid medication cannot be used in the first trimester pregnancy?

methimazole

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What medication may be used in the case of a thyroid storm?

propylthiouracil

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Adverse Effects: Anti-thyroid medication

-RASH, FEVER, MYALGIA
-HEPATOTOXICITY (higher with PTU)
-congenital defects (MMI)
-leukopenia
-agranulocytosis
-aplastic anemia
-arthralgia (lupus-like syndrome)
-GI disturbances

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What types of hyperthyroidism is radioactive iodine indicated for?

-GRAVES DISEASE
-toxic autonomous nodules
-toxic multinodular goiters

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MOA: Radioactive Iodine

rapid concentrates in the thyroid, initially disrupts thyroid hormone synthesis, overtime leads to necrosis/destruction of thyroid gland

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How often should TSH/T4 be monitored after radioactive iodine therapy?

4-6 weeks, then every 6 months

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Adverse effects: radioactive iodine

-thyroid tenderness
-dysphagia
-cancer risk

What are the instructions to minimize radioactive exposure?

-sleep in separate beds
delay return to work
-maximize distance from children
-limit time in public spaces (2-3 days)
-do not travel via public transport or with others for prolonged periods of time (2-3 days)
-drink plenty of fluids
-flush the toilet 2-3 times after urination
-sleep in separate bed or at least 6 feet away from pregnant partners or children ( for up to 20 days)
-avoid conception both men and women (4-6 months)

When would patients be considered for surgery?

-large thyroid gland -low RAIU results -malignancy -severe ophthalmopathy -planning pregnancy in less than 4-6 months -lack of remission on anti-thyroid drug treatment

What are contraindications to surgery to treat hyperthyroidism?

substantial comorbid condition, 1st and 2nd trimester pregnancy

What is the pre-treatment for surgery for hyperthyroidism?

-anti-thyroidism: achieve euthyroid state prior -beta blocker: maintain HR < 90 beats/min -potassium iodine solution: decreases thyroid flow, vascularity, and intraoperative blood loss

How often should thyroid hormone (T4) be monitored after surgery for hyperthyroidism?

monthly

How often should TSH be monitored after surgery for hyperthyroidism?

6-8 weeks

What are the signs and symptoms of thyroid storm?

-decompensated thyrotoxicosis -high fever -tachycardia, tachypnea -dehydration -delirium, coma -N/V, diarrhea

What may cause thyroid storm?

-infection -trauma -surgery -radioactive iodine therapy -withdrawal from anti-thyroid medications

What is the treatment plan for thyroid storm?

-suppression of thyroid hormone: methimazole and propylthiouracil -beta blocker therapy -inorganic iodine -corticosteroids -treat complications or precipitating factors

What drugs may cause hyperthyroidism?

amiodarone, lithium, interferon alpha, interleukin 2

Indication: teprotumumab

treats thyroid eye disease to reduce bulging eyes, improve double vision, relief of eye pain, redness, and swelling

What are the signs and symptoms of hypothyroidism?

-bradycardia -constipation -depression -infertility -dermatologic (thickening of the skin, cool rough dry skin, loss of hair, decreased sweating) -cold intolerance -edema -weight gain -fatigue

What lab values indicate hypothyroidism?

decreased T3, decreased T4, increased TSH

What are the diseases that cause PRIMARY hypothyroidism?

-*autoimmune disease (HASIMOTOS DISEASE)* -*iatrogenic (radioactive iodine therapy or surgery)* -congenital -iodine deficiency -enzyme defects

What are the diseases that cause SECONDARY hypothyroidism?

-pituitary tumors -hypothalamic diseases

What are the goals of therapy for hypothyroidism?

-restore normal thyroid hormone concentration (initiate treatment when TSH > 10mIU/L) -systematic relief -prevent neurologic deficits in newborns and children -reverse the biochemical abnormalities -avoid overtreatment

What is levothyroxine?

synthetic T4

What is liothyronine?

synthetic T3

What is liotrix?

synthetic T4:T3 in 4:1 ratio

What is thyroid USP?

desiccated pork thyroid gland

What are the advantages of levothyroxine?

-minimal adverse effects -adequate absorption -long half-life -inexpensive

What is the dosing of levothyroxine?

start at 1.6 mcg/kg daily, check TSH in 6 weeks, may increase or decrease dose 12.5-25 mcg at this time *note: elderly or pt with cardiovascular disease start at 12.5-25mcg daily*

What are important counseling points for levothyroxine?

-take on an empty stomach (30 mins before breakfast or 4 hours after last meal) -side effects of excessive dosing include heart failure, angina, MI -do not switch between levothyroxine brands

What are the monitoring parameters while taking levothyroxine?

TSH and T4 every 6 weeks until euthyroid then yearly

What can decrease the absorption of levothyroxine?

-vitamins and minerals: iron, calcium, aluminum -GI medications: fiber, bile acid sequesters, sucralfate, PPIs -oral bisphosphonates

What can increase the absorption of levothyroxine?

-antiepileptic medications: phenobarbital, phenytoin, carbamazepine -sertraline -estrogens

When would liothyronine be used in therapy over levothyroxine?

if pt is unable to convert T4 -> T3

What medication may suppress TSH?

-glucocorticoids -dopamine -bromocriptine -somatostatin -rexinoids

What medications may inhibit T4/T3 synthesis or secretion?

-propylthiouracil -methimazole -lithium -iodide -amiodarone -thalidomide

What is myxedema coma?

decompensated hypothyroidism

What are the signs and symptoms of myxedema coma?

hypothermia, advance stages of hypothyroid symptoms, altered mental status (delirium coma)

What is the treatment for myxedema coma?

200-400 mcg IV levothyroxine, then 1.6mcg/kg daily reduced 20% for IV dosing, then may transition to oral therapy *note: mortality is %60-70*