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Year 3 - Clinical (Winter) > 5 - Thyroid > Flashcards

Flashcards in 5 - Thyroid Deck (29)
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1
Q

Causes of primary hypothyroidism

A
  • Autoimmune thyroiditis (Hashimoto’s)
  • Congenital
  • Iodine deficiency
  • Infiltrative disease (viral, bacterial)
  • Drugs (lithium, amiodarone, interferons, tyrosine kinase inhibitors)
2
Q

Describe hormone trends

A
  • Primary hyperthyroidism = high T3 and T4, low TSH; primary = target organ (thyroid gland) is damaged
  • Primary hypothyroidism = low T3 and T4, high TSH
  • Secondary hyperthyroidism = high T3, T4, and TSH (dysfunction is at pituitary gland)
  • Secondary hypothyroidism = low T3, T4, and TSH
3
Q

Describe the function of thyroid hormones

A
  • Affect the function of virtually every organ system
  • Important for normal growth & dev’t in children
  • Maintain metabolic stability in adults
4
Q

Clinical manifestation (signs and sx) of thyroid disorders

A
  • Hypothyroidism = weakness, fatigue, poor concentration/ memory, bradycardia, constipation, weight gain w/ poor appetite
  • Hyperthyroidism = hyperactivity, irritability, dysphoria, tremor, tachycardia, diarrhea, goiter (enlarged thyroid gland -> swelling of neck)
5
Q

Describe the role of TSH, T4, and T3

A
  • TSH releases T4 & T3 (T4»_space;> T3)
  • Majority protein bound = inactive
  • Biologically most active = free T3
  • T4 converted to T3 in periphery by 5’-deiodinase
6
Q

Why isn’t T3 used as a drug? (levothyroxine = T4)

A

T4 is converted to T3 & we don’t want to lose the body’s ability to perform this conversion & T4 has longer t1/2 (almost like a pro-drug)

7
Q

How do autoimmune thyroid diseases occur? What is the tx?

A
  • Infiltration of thyroid w/ sensitized T lymphocytes (WBC)
  • Acute inflammation of thyroid -> damage to gland -> release of T3 & T4
  • Initially pt is hyperthyroid (high T3 & T4) but may become hypothyroid (in weeks to months)
  • Chronic autoimmune thyroiditis (Hashimoto’s thyroiditis)
  • Most common initial presentation = enlargement of thyroid gland (goiter)
  • Tx = exogenous T4
8
Q

Describe a goiter

A
  • Generalized (diffuse) enlargement
  • Caused by continuous stimulation by TSH
  • Hashimoto’s – goiter eventually disappears due to progressive destruction of thyroid
9
Q

Describe thyroid nodules

A
  • Enlargement in 1 part of the gland (asymmetrical)
  • Caused by benign/ malignant nodule
  • Rarely associated w/ destruction of gland & hypothyroidism
10
Q

Describe Graves’ disease

A
  • Common cause of primary hyperthyroidism in adults & children
  • Autoimmune, familial disposition
  • Thyroid stimulating antibodies (TSAb) or thyroid stimulating immunoglobulins (TSI) mimic TSH -> autoimmune stimulation
  • Continuous stimulation => high T3/T4; increase thyroid size
  • Specific to Graves’ disease = opthalmopathy (pathogenesis unclear) & dermopathy (deposition of mucopolysaccharide; shin most common)
11
Q

How are thyroid disorders classified?

A
  • Hypothyroidism diagnosed when TSH is high & FT4 is less than population reference range
  • Subclinical hypothyroidism
    • Mild to moderate increased TSH, but total & FT4 normal
    • If TSH very high (> 10) tx may be offered as these px may be at higher risk of CV complications
  • TSH is the most reliable therapeutic endpoint for tx of hypothyroidism b/c most sensitive marker for monitoring
12
Q

Lab monitoring for L-thyroxine tx

A
  • FT4 is measured instead of FT3 b/c FT3 can be affected by other sources, so FT4 is more reliable
  • After initiating or changing dose, re-measure FT4 & TSH 1 month later; want to measure levels in the morning
13
Q

Factors that alter thyroxine & triiodothyronine binding in serum

A
  • Increased TBG (T4-binding globulin) – estrogens, methadone, perphenazine, SERMs
  • Decreased TBG – androgens, anabolic steroids, glucocorticoids
  • Binding inhibitors – salicylates, furosemide, phenytoin, carbamazepine, NSAIDs, heparin
14
Q

Consequences of untreated hypothyroidism

A
  • Increased CV mortality
  • Impaired intellectual function, depression, slowed speech, memory loss in elderly
  • Anovulation, impaired fertility, increased rate of spontaneous abortion
  • Myxedema coma (hypothermia, hypotension, hypoventilation, hyponatremia, bradycardia) – medical emergency
15
Q

Dosing levothyroxine

A
  • Healthy, young adults (< 50 y/o), children, older adults recently diagnosed w/ hypothyroidism, older adults recently treated for hyperthyroidism – initial 100-150 mcg/day titrated by 25 mcg q4-6weeks
  • Adults > 50 y/o w/o cardiac disease, adults < 50 y/o w/ cardiac disease – 25-50 mcg/day titrated by 12.5-25 mcg q4-6weeks
  • Adults > 50 y/o w/ cardiac disease – 12.5-25 mcg/day titrated by 12.5-25 mcg q4-6weeks
  • Sx improvement in 2-3 weeks; maximal sx improvement in 4-6 weeks
16
Q

Drug interactions w/ levothyroxine

A
  • TUMS, ranitidine, multivitamin – reduce absorption
  • Metformin – decrease TSH secretion, increase levothyroxine requirements, & hypo/hyperthyroidism has effect on insulin sensitivity (hyper = increased sensitivity & vice versa)
  • Carbamazepine – increases levothyroxine clearance
17
Q

Monitoring for hypothyroidism

A
  • TSH (primary hypo) or FT4/FT3 (central hypo) – 6-8 weeks until TSH normal, then q1year
  • Signs & sx of hypo – weekly by pt (improve in 2-3 weeks; skin change 3-6 months)
  • If clinical manifestations not resolved or re-appear –> check TSH level; consider drug/meal interactions or malabsorption
18
Q

Hypothyroidism tx during pregnancy

A
  • T4 requirements increase to maintain euthyroid state (onset 4-6 weeks gestation; increases until week 16-30 then remains constant until delivery)
  • Newly pregnant & receiving LT4 -> increase dose by 25-30% in first trimester (if once daily, increase to 9 doses/week)
  • TSH is most accurate indication of thyroid status
    • Measure q4weeks in 1st half of pregnancy, then q1week in week 26-32
  • Following delivery –> reduce LT4 dose, then check TSH 6 weeks postpartum
19
Q

Pt counseling tips for thyroid replacement therapy

A
  • Levothyroxine should be taken in the AM on empty stomach; important to take same time each day
  • Do not take antacids, iron preparations, calcium supplements w/in 4 h of thyroid medication (decreased absorption)
  • Try not to change brands (less fluctuation in TFT if using the same brand – “interchangeability” province-dependent)
  • Signs & sx to report = chest pain, rapid HR, palpitations, heat intolerance, excessive sweating, increased nervousness, agitation, lethargy
20
Q

Describe liothyronine/ cytomel (T3)

A
  • Used in some px monotherapy or in combo w/ levothyroxine (T4) to control hypothyroidism
  • Long-term benefit of combo therapy remains unknown
21
Q

Consequences of untreated hyperthyroidism

A
  • CV –> A fib, angina, HTN, peripheral edema, heart failure
  • Ocular –> double vision, corneal damage, vision loss
  • Skeletal –> hypercalciuria, mild hypercalcemia, slight increased fracture risk
  • Thyroid storm – medical emergency
22
Q

Hyperthyroidism tx. Describe SE, duration, and monitoring

A
  • Antithyroid medications (propylthiouracil, methimazole)
    • PTU & MMI inhibit thyroid peroxidase (TPO) –> block iodination of tyrosine
    • PTU inhibits 5’ deiodinase –> block peripheral conversion of T4 to T3
  • Radioactive iodine to destroy gland
    • Used in Graves’ disease, not used in thyroiditis
  • Surgery to remove gland
  • Sx relief w/ beta blockers
  • SE –> maculopapular rash (responds to antihistamines), arthralgia, transient fever, GI intolerance
    • Low risk of permanent hypothyroidism in the long-term
    • Risk of cross-sensitivity between PTU & MMI is 50%
  • Response in 4-8 weeks; max response in 4-6 months
  • Duration = ~1-2 years
  • Monitor q4weeks until euthyroid (CBC, PT, TFT, INR); after remission monitor q6-12months
23
Q

Pt counseling tips for radioactive iodine

A
  • Concentrates in gland & destroys thyroid tissue
  • SE  mild thyroidal tenderness/ dysphagia; permanent hypothyroidism
  • Differ pregnancy 6-12 months post RAI; no breastfeeding (okay for future pregnancies)
  • Most cost effective
  • Have the potential to contaminate close contacts via saliva, urine, or radiation emitting from their neck => don’t kiss, exchange saliva, or share food/eating utensils for 5 days; wash dishes in dishwasher if available
  • Avoid close contact w/ infants, young children (< 8 y) & pregnant women for 5 days (can be in the same room, stay 2 m away)
  • Flush toilet twice after urinating & wash hands thoroughly
24
Q

Radioactive iodine & SSKI

A
  • SSKI = saturated solutions of potassium iodide
  • Don’t use SSKI pre-RAI b/c RAI needs to concentrate in thyroid
  • MOA = saturates iodide transport system, decreases size & vascularity of gland
  • Efficacy – reduced sx x 2-7 days (quick onset), reduce T3 & T4 in weeks
25
Q

Beta blockers for thyroid disorders

A
  • Propranolol & nadolol partially block T4 -> T3 conversion (but this is a small effect on tx)
  • Role = adjunctive therapy w/ ATD (anti-thyroid drugs), RAI, iodides, surgery, thyroid storm, Graves or toxic nodules for sx management
  • SE = N/V, anxiety, insomnia, bradycardia
  • Verapamil, diltiazem may be considered if BB’s aren’t tolerated or CI
26
Q

Euthyroid sick syndrome

A
  • Abnormal thyroid function in px w/ nonthyroidal illness
  • Natural human response to getting sick
  • Common in ICU px w/ no thyroid problem
  • Reduced conversion of T4 -> T3 by T4-5’-deiodinase
  • Thyroid function shouldn’t be assessed in seriously ill px unless there is a strong suspicion of thyroid dysfunction
  • Tx not recommended – studies showed tx doesn’t improve survival
27
Q

Thyroid function in non-thyroidal illness

A
  1. Sick – T3 drops first (ex: hospital inpatient)
  2. TSH drops but not to zero (transient central hypothyroidism, low TBGs)
  3. Sickest – T4 drops (low T4 = poor prognosis)
28
Q

Hypothyroidism in the elderly

A
  • Elderly px may have fewer sx than younger adults
    • Memory loss, confusion, weight gain, dry skin, sleepiness
  • Specific signs in elderly = ataxia, non-joint pain/ muscle ache, falling
29
Q

When to treat thyroid disorders

A
  • Overt hypothyroidism
  • Subclinical hypothyroidism if symptomatic, presence of anti-thyroid antibodies, or CV disease
  • TSH target range = 0.45 – 4.12 mIU/L
  • Dose according to pt response (sx improvement) & TSH tests
  • Few px require doses > 200 mcg/day