45. Thyroid Disorders Flashcards
2 thyroid hormones produced by the thyroid gland are ___ and ___
Triiodothyronine (T3)
Thyroxine (T4)
The thyroid gland is the only organ that can absorb ___, which is required for the production of both thyroid hormones
Iodine
T/F: T4 is primarily formed from the breakdown of T3
False - T3 is primarily formed from the breakdown of T4
Compare T3 and T4 in terms of potency and half-life
T3 is more potent than T4 but has shorter half-life
Thyroid hormone production is regulated by ___
Thyroid-stimulating hormone (TSH), aka thyrotropin
TSH is secreted by the ___
Pituitary gland (located in brain and regulates growth and development)
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
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
Hypothyroidism is a deficiency in ___ and elevation in ___
Deficiency in T4
Elevation in TSH
What is the most common cause of hypothyroidism?
Hashimoto’s disease - autoimmune condition that attacks thyroid gland
___ 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
Initial treatment for myxedema coma is ___
IV levothyroxine
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
Dx of hypothyroidism
Low free T4 (normal range 0.9-2.3)
High TSH (normal range 0.3-3)
___ is the primary test to monitor thyroid function in those receive thyroid hormone replacement with drug treatment
TSH
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
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
What is the drug of choice for hypothyroidism?
Levothyroxine (T4)
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)
Levothyroxine Full replacement dose
1.6 mcg/kg/day (IBW)
Levothyroxine starting dose if known CAD
12.5-25mcg
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
