45. Thyroid Disorders Flashcards by Yerin M

2 thyroid hormones produced by the thyroid gland are ___ and ___

Triiodothyronine (T3)
Thyroxine (T4)

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The thyroid gland is the only organ that can absorb ___, which is required for the production of both thyroid hormones

Iodine

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T/F: T4 is primarily formed from the breakdown of T3

False - T3 is primarily formed from the breakdown of T4

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Compare T3 and T4 in terms of potency and half-life

T3 is more potent than T4 but has shorter half-life

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Thyroid hormone production is regulated by ___

Thyroid-stimulating hormone (TSH), aka thyrotropin

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TSH is secreted by the ___

Pituitary gland (located in brain and regulates growth and development)

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Drugs and Conditions that can cause hypothyroidism (hint: mneumonic)

Remember: I TALC
Interferons
Tyrosine kinase inhibitors (e.g. sunitinib)
Amiodarone
Lithium
Carbamazepine
Conditions: Hashimoto’s Disease

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Explain negative feedback loop in the setting of T4 and TSH

When the level of free T4 increases, it inhibits secretion of TSH. Less TSH = decrease in T4 production

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Hypothyroidism is a deficiency in ___ and elevation in ___

Deficiency in T4
Elevation in TSH

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What is the most common cause of hypothyroidism?

Hashimoto’s disease - autoimmune condition that attacks thyroid gland

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___ is an uncommon but potential fatal complication of hypothyroidism that can occur when hypothyroidism is left untreated for a long time or when hypothyroidism decompensates. It is a life-threatening emergency.

Myxedema coma

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Initial treatment for myxedema coma is ___

IV levothyroxine

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S/sx of hypothyroidism

Cold intolerance/sensitivity
Dry skin
fatigue
muscle cramps
voice changes
constipation
weight gain
goiter (possible; can be d/t low iodine intake)
Myalgias
weakness
depression
bradycardia
coarse hair or loss of hair
Menorrhagia (heavier than normal menstrual periods)
Memory and mental impairment

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Dx of hypothyroidism

Low free T4 (normal range 0.9-2.3)
High TSH (normal range 0.3-3)

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___ is the primary test to monitor thyroid function in those receive thyroid hormone replacement with drug treatment

TSH

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In hypothyroidism pts, TSH level and symptoms should be monitored every ___ until levels are normal, then ___ later, and then yearly

4-6 weeks
4-6 months

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What is the concern of thyroid hormone replacement use in elderly patients?

Too high of thyroid hormone replacement dose in elderly pts can cause Afib and fractures - monitor thyroid function as they age

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What is the drug of choice for hypothyroidism?

Levothyroxine (T4)

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T/F: When refilling levothyroxine, there is no difference between different manufacturers

Consistent preparation (i.e. same formulation and manufacturer) is preferred to minimize variability from refill to refill, not all generic formulations are A-rated (check Orange book)

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Levothyroxine Full replacement dose

1.6 mcg/kg/day (IBW)

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Levothyroxine starting dose if known CAD

12.5-25mcg

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Who is indicated for full replacement dose vs partial replacement dose?

Full replacement = otherwise healthy, young (<50yo) pts with markedly increase TSH
Partial = milder hypothyroidism and those with comorbidities
Elderly pts often need 20-25% less per kg; may require <1mcg/kg/day

Contraindications for hypothyroidism treatment

uncorrected adrenal insufficiency

Warnings for hypothyroidism treatment

Decrease dose in CV disease (chronic hypothyroidism predisposes in CAD)
Decreased BMD (osteoporosis risk)

Levothyroxine PO administration notes

Take with water at same time each day for consistent absorption at least 60 min before breakfast or at bed time (at least 3 hrs after last meal)

Levothyroxine IV to PO ratio

0.75:1

Which hypothyroidism treatment option may be a concern for patients avoiding porcine (pork) products?

Thyroid desiccated USP (T3 and T4) (Armour Thyroid) - natural porcine-derived thyroid that contains both T3 and T4

Levothyroxine tablet colors (hint: mneumonic)

Orangutans Will Vomit On You Right Before They Become Large, Proud Giants 25mcg - orange 50mcg - white (no dye) 75mcg - violet 88mcg - olive 100mcg - yellow 112mcg - rose 125mcg - brown 137mcg - turquoise 150mcg - blue 175mcg - lilac 200mcg - pink 300mcg - green

What drugs decrease levothyroxine absorption?

Antacids (iron, calcium, aluminum, mg, multivitamins, cholestyramine, sevelamer, sucralfate, orlistat) - separate by 4 hrs Others: Veltassa (separate by 3 hrs), lanthanum (separate by 2hrs)

What drugs decrease thyroid hormone levels?

Estrogen, SSRIs, hepatic inducers

What drugs decrease the effectiveness of levothyroxine by decreasing the conversion of T4 to T3?

Beta-blockers, amiodarone, PTU, and systemic steroids

T/F: thyroid hormone is highly protein bound >99%

True

Hyperthyroidism (also called overactive thyroid or ____) occurs when there is over-production of thyroid hormones

thyrotoxicosis

Dx hyperthyroidism

FT4 high TSH low

S/sx of hyperthyroidism

Heat intolerance or increased sweating weight loss agitation, nervousness, irritability, anxiety palpitations and tachycardia fatigue and muscle weakness frequent bowel movements and diarrhea insomnia tremor thinning hair goiter (possible) Exophthalmos (protrusion of eyeballs), diplopia Light or absent menstrual periods

The most common cause of hyperthyroidism is ____

Graves' disease (autoimmune disorder, antibodies stimulate thyroid to produce too much T4)

Drug-induced causes of hyperthyroidism include ____

iodine (from diet or exposure to radiographic contrast media), amiodarone, and interferons

Hyperthyroidism treatment

Medications, destroying part of the gland via radioactive iodine (RAI-131) or surgery

What is typically used as symptom control for hyperthyroidism?

Beta-blockers (to reduce palpitations, tremors, and tachycardia) PTU or methimazole can be used as temporary measure until surgery is complete

It takes ____ of treatment with antithyroid meds at high doses to control hyperthyroidism symptoms

1-3 months Note: dose should be reduced to prevent hypothyroidism once symptoms are controlled

MOA thionamides (PTU, methimazole)

Inhibit synthesis of thyroid hormones by blocking oxidation of iodine in the thyroid gland PTU also inhibits peripheral conversion of T4 to T3

Boxed warnings for PTU

Severe liver injury and acute liver failure Pregnancy - PTU is preferred in 1st trimester (d/t increase risk of fetal abnormalities with methimazole)

Warnings for thionamides

Hepatotoxicity, agranulocytosis, DILE, vasculitis

Side effects for thionamides

GI upset Other: HA, rash, fever, constipation, loss of taste, lymphadenopathy, bleeding

Of thionamides (PTU, methimazole (Tapazole)), which is drug of choice

Methimazole (d/t lower risk of liver damage) except PTU is preferred in thyroid storm and 1st trimester Methimazole is preferred in 2nd and 3rd trimesters

MOA iodides

Temporarily inhibit secretion of thyroid hormones; T4 and T3 levels will be reduced for several weeks but effect will not be maintained

Examples of iodides used in hyperthyroidism

potassium iodide and iodine solution (Lugol's solution) Saturated solution of potassium iodide (SSKI, ThyroSafe)

Why is potassium iodide used after exposure to radiation?

Blocks the accumulation of radioactive iodide, preventing thyroid cancer

What is a thyroid storm

Life-threatening medical emergency characterized by decompensated hyperthyroidism that can be precipitated by infection ,trauma, surgery, radioactive iodine treatment, and non-adherence to antithyroid meds

S/Sx of thyroid storm

Fever (>103ºF) Tachycardia Tachypenia Dehydration Profuse sweating Agitation Delirium Psychosis Coma

Thyroid storm treatment regimen

Antithyroid (PTU preferred) + iodide therapy (SSKI or Lugol's soution) + beta-blocker (propranolol) + systemic steroid (dexamethasone) + aggressive cooling with APAP and cooling blankets and other supportive treatments (e.g. antiarrhythmics, insulin, fluids, electrolytes)

Treatment options for hypothyroidism in pregnancy

Levothyroxine is safe and recommended - will require 30-50% increase in dose

Treatment options for hyperthyroidism in pregnancy

First trimester = PTU Rest of pregnancy = methimazole