Thyroid Flashcards
What are the two types of thyroid disorders?
Hypothyroidism and hyperthyroidism
Does thyroid disease affect women or men more frequently?
Women
What are causes for hypothyroidism?
- Autoimmune thyroid disease
- Hashimoto thyroiditis (most common in NA) - Iatrogenic
- surgical removal of thyroid
- radioactive iodine therapy
- amiodarone
- lithium
- sulfonylureas
- immunotherapy - Iodine deficiency (rare in NA)
- Resistance to thyroid hormone
What is a very sensitive indicator of hypothyroidism?
Elevated thyroid-stimulating hormone (TSH)
*Note: may be low or normal in pituitary or hypothalamic disease
What is subclinical hypothyroidism?
Elevated TSH but normal thyroid hormone levels
What are normal TSH levels?
0.3-0.4 mU/L
Should we treat subclinical hypothyroidism?
Can consider in following:
- TSH>10
- Abnormal lipid profile
- Symptoms of hypothyroidism
- Planning pregnancy
What are some common or serious signs and symptoms of hypothyroidism?
Fatigue
Impaired memory
Constipation
Cold intolerance
Changes in skin or hair (coarse/dry)
Hypertension
Bradycardia
If TSH is abnormal or unclear, what else can we test?
fT4 (free thyroxine)
fT3 (free triiodothyronine)
What supplement can interfere with thyroid tests?
Biotin (discontinue for at least 48 hours prior to testing)
When are anti-TPO antibodies tested?
Helps indicate whether the disease is autoimmune in nature
Only tested if it helps with patient-management decisions (Ex: recurrent spontaneous abortion or miscarriages)
What is secondary hypothyroidism?
Pituitary hypothyroidism
- TSH low or normal (fT4 usually low)
What is tertiary hypothyroidism?
Hypothalamic disorder
- TSH low or normal (fT4 usually low)
What’s a common cause of transiently elevated TSH? (typically not a cause for concern)
Recovering phase of nonthyroidal illness (cold)
What are TSH, fT3, and fT4 levels like when patients are resistant to thyroid hormone?
High TSH, fT3, and fT4
What’s the treatment of choice for hypothyroidism?
Levothyroxine (L-T4)
What the typical dosing for levothyroxine?
Adults= 1.6mcg/kg/day
Newborn= 10-15 mcg/kg/day
How often do we dose adjust?
Why do we pick this interval?
Every 6 weeks as needed
Time to new steady state after dose adjustment
How often do we dose adjust for pregnancy?
Every 4 weeks
What’s the special dosing regimen for older patients?
Why?
Start with low dose of 12.5mcg/day
Titrate every 4 weeks
High doses and low TSH is associated with increased risk of fracture.
Why is replacing T4 preferred over replacing T3?
Not as stable as T4 (which has longer half-life).
Even long-acting T3 formulations resulted in fluctuations (too high)
Why is elevated T3 levels dangerous?
Increases risk of side effects like atrial fibrillation
Using T3 therapy in hypothyroidism is rare, but what is one situation where it can be helpful?
Short-term management for patient with thyroid cancer undergoing withdrawal of L-T4 when recombinant TSH is not an option for radioactive iodine therapy
It’s short half life makes it ideal for this use
Is a combo of L-T4 and T3 used often?
No. Little or no benefit shown
Rare scenario: if symptoms not relieved with L-T4 despite normal TSH
What is desiccated thyroid? Is is used often?
Thyroid replacement therapy from animal thyroid.
No. Unreliable dosing. No clear therapeutic advantage.
What are the risks of hypothyroidism and pregnancy?
Infertility and miscarriage
What happens to TSH levels in the first trimester? Why?
Usually low due to high beta hCG levels.
If not on the lower side or not suppressed, may indicate diagnosis of hypothyroidism.
Repeat TSH and begin treatment if TSH >4mU/L
Is levothyroxine (L-T4) safe in pregnancy?
Yes. Vital for healthy fetal development
Is T3 appropriate during pregnancy?
Not as sole therapy, as it does not cross the placenta
What dose adjustment is needed for pregnant patients who are already on L-T4?
Increase dose by 2 extra tablets per week immediately following a positive pregnancy test
Further adjust based on TSH levels (maintain between 03-2.5 mU/L)
Why is this dose adjustment needed during pregnancy?
Thyroid binding globulins increase during pregnancy so L-T4 requirements may increase up to 50%
How often should you test TSH levels when pregnant?
Every 6 weeks or 4 weeks after dosage adjustment.
If pregnant patient is not on L-T4 therapy, what’s the ranging values?
TSH should be <4 mU/L
Initiate therapy if TSH>10 mU/L or if patient confirmed TSH>4 mU/L
What’s a common drug interaction for pregnant patients?
Iron can decrease absorption of L-T4. Separate administration time by at least 6 hours.
Is levothyroxine safe during breastfeeding?
Yes
What medical emergency can be caused by severe hypothyroidism?
Myxedema coma
- hypotension
- decreased level of consciousness
How do you treat myxedema coma?
Levothyroxine 300-500mcg IV initially, followed by 100mcg IV daily
Concomitant hydrocortisone 100mg q8h IV
What is thyrotoxicosis?
Excessive thyroid hormone
What is subclinical hyperthyroidism? Is it common?
TSH levels are suppressed (lower than normal), but thyroid levels are normal
Yes, can be a risk factor for a.fib
What is hyperthyroidism a risk factor for?
Atrial fibrillation
When is treatment indicated for subclinical hyperthyroidism?
If patient is:
- older or frail.
- has risk factors for a.fib
- osteoporosis
- symptoms of thyroid hormone excess
What are some causes of thyroid storm?
- Radioactive iodine
- Infection
- Trauma
- Surgery
- Withdrawal from antithyroid drugs
What are symptoms of hyperthyroidism?
Weight loss
Palpitations
Diarrhea
Heat intolerance
Anxiety
Eyelid lag/stare
Goitre/nodules
How is hyperthyroidism diagnosed?
- TSH, fT3, fT4
- Thyroid scan
- Radioactive iodine uptake (RAIU)
Which of the above test is contraindicated in pregnancy and breastfeeding?
Thyroid scan
Radioactive iodine uptake
When is RAIU high or low in hyperthyroidism?
If the cause of hyperthyoidism is due to overactive thyroid, then the RAIU will be high.
Ex: Grave’s disease, goitre
If it’s due to external causes, then RAIU will be low.
Ex: thyroiditis, iatrogenic (due to meds)
Which common drug or comorbid condition can suppress TSH?
Corticosteroids and depression
When is thyroid surgery considered in hyperthyroidism?
Thyroid nodules
Large goitre
Grave’s disease (if likely to be pregnant)
If patient is going the surgery route, how do medications come into play?
Antithyroid drugs to bring patient to euthyroid
What is a common side effect to surgery?
Hypothyroidism
Monitor patient post-op to see when thyroid replacement is needed.
Which condition do we need to be extra careful about hypothyroidism post-op? Why?
Graves orbitopathy
Fluctuating levels of thyroid can worsen the eye disease
What are the pharmacological choices for hyperthyroidism?
- Radioactive iodine
- Methimazole and propylthiouracil
- Beta-blockers
- Iodine
- Corticosteroids
- Selenium
How does radioactive iodine work? What’s the main side effect?
Ablate thyroid tissue
Hypothyroidism
When is radioactive iodine contraindicated?
Pregnancy
Patient with significant orbitopathy (if used, use with corticosteroid under guidance of ophthalmologist)
What are two anti-thyroid agents?
Methimazole and propylthiouracil
How does methimazole and propylthiouracil work?
Decrease the production of thyroid hormone
At high doses, propylthiouracil can also block conversion of L-T4 to T3
When should PTU and methimazole be stopped?
Prior to thyroid scan (5 days prior)
How do you choose between methimazole and propylthiouracil?
Methimazole is preferred due to lower incidence of serious hepatotoxicity.
PTU should be avoided in children.
PTU can make thyroid more resistant to 131I.
Long term treatment of methimazole is more acceptable.
What are side effects of antithyroid agents?
Allergy, rash, agranulocytosis, hepatotoxicity, nephrotoxicity
Where does beta blockers come into hyperthyroidism therapy?
Adjunct in Grave’s disease and toxic nodules
How does beta blockers help with hyperthyroidism?
Blocks the conversion of L-T4 to T3.
When should we use beta blockers with caution?
Asthma, heart failure, obstructive respiratory disorders, Raynaud phenomenon
Where does iodine come into hyperthyroidism?
It blocks thyroid hormone production and is given 1 hour after administration of antithyroid drug
Where does corticosteroid therapy come into play?
In treatment-resistant cases to lower the level of fT3.
When does selenium come into play?
Prevent worsening of mild Graves orbitopathy
What is the typical dosing for selenium?
Selenium 100 mcg BID
What is thyroid storm?
Life-threatening medical emergency due to severe thyrotoxicosis.
How do you manage thyroid storm?
Aggressive treatment with antithyroid medication + beta blockers + corticosteroid
Which beta blocker is preferred in thyroid storm?
Propranolol
For patients with hyperthermia during thyroid storm, which agent should be used?
Tylenol.
Avoid ASA and NSAIDs, as they can displace protein bound thyroid hormone and increase circulating
What’s the most common type of hyperthyroidism in pregnancy?
Grave’s disease
What’s the projection of hyperthyroidism in pregnancy?
In most patients, it gets better in second and third trimester (so treatment may not be required).
May flare up again postpartum however.
How do you manage hyperthyroidism in pregnancy?
Why is it important to treat
Treat to upper limits of normal for fT3 and fT4.
Should achieve good control prior to conception if possible (if unable, use lowest effective dose with antithyroid drugs)
If patient received radioactive iodine, wait at least 6 months before conceiving
If only low doses of antithyroid drugs are needed, a trial without treatment is ok.
Can try beta blocker for mild symptoms.
Hyperthyroidism can increase risk of fetal loss.
If an anti-thyroid agent is needed during pregnancy, which agent is preferred?
Propylthiouracil preferred in first trimester due to lower risk of congenital abnormalities. Switch patient to PTU if ok.
Switch back to methimazole after first trimester to minimize risk of hepatoxicity
For patient who are on existing hyperthyroidism treatment, how do you manage for pregnancy?
Aim for upper limit of normal to avoid overtreatment.
May need to decrease dose, as patient often go into remission.
While pregnant patient are on antithyroid medications, what should they monitor?
Pre-treatment CBC and hepatic function tests that include ALT and bilirubin are recommended.
Neutropenia (most common in first 90 days)
Hepatic effects (within first 120 days)
Stop drug if they notice fever, rash, or jaundice
How often should levels be checked in pregnancy?
Every 6-8 weeks
How do you manage hyperthyroidism in breastfeeding?
Treat to upper limits of normal for fT3 and fT4 to avoid overtreating.
Avoid use of radioactive scans or iodine treatment.
Can use beta blocker short-term until control is achieved with antithyroid drugs.
Which antithyroid drugs is preferred in breastfeeding?
Methimazole
While pregnant patient are on antithyroid medications, what should they monitor?
Pre-treatment CBC, ALT, and bilirubin should be tested if possible.
Stop meds if patient has fever, rash, or jaundice.
Routine screening for s/e of drugs is not recommended.
If patient presents with goitres, what are the two treatment options?
If euthyroid and growing to cause compressive symptoms= surgery
If higher TSH= levothyroxine
What are risks associated with surgery?
Hypothyroidism, vocal cord paralysis
What is the difference between thyroid nodule and goitre?
A goiter is an enlarged thyroid gland, while a nodule is a lump or enlarged area within the thyroid gland.
Nodules are common, but should be investigated to exclude malignancy.
How do you determine if nodule is at risk of malignancy? If suspected, what’s the next step?
Thyroid imaging reporting and data system (TI-RADS) is a points-based system to determine risk.
If suspected, fine needle biopsy is performed
What are risk factors that increase risk for malignacy?
<20 or >60 years of age
Family history
Lymphadenopathy (swollen lymph nodes)
Male
Nodule >4cm or rapidly growing
Nodule fixed to soft tissue
Previous malignancy
Prior radiation exposure
Vocal cord paralysis
How do you treat toxic multinodular goitre or a hot nodule?
Radioactive iodine
