Thyroid Disorders Flashcards by Charmain Ng

Explain how negative feedback helps to regulate thyroid hormone levels

Hypothalamus release TRH to pituitary. Pituitary in turn then releases TSH to the thyroid gland.
Negative feedback works when free T4 hormones act on both hypothalamus and pituitary to stop it from releasing TRH and TSH.

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What are the physiological functions of the thyroid hormones?

Thyroid hormones increases oxygen consumption and thus, increase basal metabolic rate. This then affects body temperature, CNS, sleep, cardiac function, GI function, muscle strengthening, breathing and menses.

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Determine the changes in TSH seen for the two main types of thyroid disorders

Hypothyroidism: TSH elevated
- increase due to attempt to unsuccessfully try and stimulate thyroid hormone

Hyperthyroidism: TSH decreased
- due to high TH whereby hypothalamus attempts to decrease high secretion of TH

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What is essential for the production of thyroid hormones?

Iodine consumption. Iodine must be obtained exogenously

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Define what is thyroxine binding globulin and explain its physiology.

Assuming patient has no thyroid issue, pregnant women and those on estrogen tend to have a higher TBG. As a result, FT4 and FT3 decreases since more T3 and T4 binds to extra TBG. TSH is then released to instruct thyroglobulin to release higher levels of thyroid hormones to return thyroid hormones to equilibrium.

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What are the compelling indications for screening thyroid function test?

Symptoms of hyperthyroid/hypothyroid
History of head/ neck radiation for malignancies
Presence of autoimmune disorders
Taking amiodarone/lithium
Psychiatric disorders
First degree relative with autoimmune thyroid disorders

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Which subgroup population requires routine screening of thyroid function test?

Pregnant
Pediatric

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Define hypothyroidism

Decrease in activity of thyroid gland

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What are the primary and secondary causes of hypothyroidism?

Primary causes: Iodine deficiency, Early hashimoto disease (ATgA Antibodies; TPO Autoantibodies); Iatrogenic (due to thyroid resection or RAI)

Secondary causes: Central hypothyroidism (due to hypothalamus or pituitary); drug induced

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What are the signs and symptoms associated with hypothyroidism?

Cold intolerance
Dry skin
Fatigue, lethargy, weakness
Weight gain
Bradycardia
Slow reflexes
Coarse skin and hair
Periorbital swelling
Menstrual disturbances: more frequent and more blood
Goiter: thyroid gland enlargement

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What are the potential complications listed with those of hypothyroidism?

Increase in LDL and TG, Increase atherosclerosis, Increase CPK, Increased miscarriage risk and impaired fetal development

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How do I diagnose one with hypothyroidism?

Check for signs and symptoms
Do a thyroid function test.
Primary hypothyroidism: Low T4 and high TSH
Central hypothyroidism: low T4 and TSH

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What drug should I consider initiating for those with hypothyroidism and what is the agent’s mode of action?

Levothyroxine
Provide and replaces synthetic T4

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How should I dose patients initiated on levothyroxine? What do I consider for their dosing?

Young healthy adults: 1.6 mcg/kg/day
50-60 years: 50mcg daily
CVD risk: 12.5 -25 mcg . day

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How do I titrate patient/s levothyroxine dose?

Increase dose by 12.5 - 25 mcg / day
Increase by 10-15%

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What should I advice patients who are taking levothyroxine for their hypothyroidism?

Take 30-60 mins before breakfast OR 4 hours after dinner. Best taken on an empty stomach

Avoid taking with calcium/ iron supplements and antacids

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Cite monitoring parameters and frequency of monitoring for those on levothyroxine upon initiation and maintenance dosing.

Monitor 4-8 weeks upon initiation to assess response of TSH.
Upon reaching euthyroid state, thyroid functions test can be done every 6 month-1 year

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For patients on central hypothyroidism, what monitoring parameters should I look out for?

FT4
TSH will be inaccurate as it will remain suppressed long term.

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What are the adverse drug reactions of levothyroxine?

Increased cardiac abnormalities
Hyperthyroidism
Increases risk of fractures

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What is the mode of action of liothyroxine and why is it not recommended ?

Act as synthetic T3 and is not recommended due to short t1/2 and higher susceptibility to ADR

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What is the place in therapy for liothyroxine though not widely used?

Normalized TSH with complains of hypothyroidism symptoms

Myxedema coma

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For patients who are pregnant and have hypothyroidism, what are some potential risks associated if untreated?

Increased risk of miscarriage and spontaneous abortion

Increased congenital defects

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Why should hypothyroidism be treated ASAP for those who are pregnant?

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Maternal thyroid hormones provide fetus thyroid hormones for up to 6 weeks

Takes time for fetus to form their own thyroid gland

How should levothyroxine be dosed for those who are pregnant and have hypothyroidism?

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Increase thyroid medication by 30-50%

What are the monitoring parameters for those with hypothyroidism and are pregnant? List them according to the 3 trimesters and the value of each target.

Target TSH 1st trimester < 2.5 mIU/l 2nd trimester < 3.0 mIU/l 3rd trimester < 3.5 mIU/l

Define subclinical hypothyroidism

Elevated TSH with normal T4

What are the risks associated with subclinical hypothyroidism

TSH > 7.0 mIU/L : Increased risk of HF TSH > 10 mIU/L: Increased risk of CHD

When should subclinical hypothyroidism be treated?

TSH > 10 mIU/L TSH 4.5 - 10 mIU/L with: 1. Symptoms of hypothyroidism 2. TPO antibodies present 3. History of CVD, heart failure and other risk factors

What is the starting dose for levothyroxine for subclinical hypothyroidism?

25 - 75 mcg

Define hyperthyroidism

Overabundance of circulating thyroid hormone that mimic effects of an activates sympathetic nervous system

What are the primary and secondary causes of hyperthyroidism?

Primary causes: Toxic diffuse goiter (TRAb mimicking TSH); Pituitary adenoma; Toxic adenoma; Toxic multinodular goiter Secondary causes: Drug induced; subacute thyroiditis due to infections or early Hashimoto's disease

What are the signs and symptoms associated with hyperthyroidism?

Weight loss and increased appetite Heat intolerance Goiter Fine hair Tachycardia Nervous, anxiety, insomnia Menstrual disturbances (lighter and less frequent) Sweating Exophthalamus: bulging eyes

How should I diagnose hyperthyroidism?

Check for signs and symptoms Do thyroid function test: High free T4 and low TSH Consider radioactive iodine uptake to check for amount of iodine uptaked by thyroid gland

What are the pharmacological therapies to consider for hyperthyroidism?

Surgical resection Radioactive iodine ablative therapy (DO NOT use in pregnancy) Thyroidectomy Antithyroid pharmacotherapy

List the three agents for antithyroid pharmacotherapy

Thioamides Iodides Nonselective beta blockers

What is the indication for use of oral antithyroid pharmacotherapy?

Those awaiting for ablative therapy and surgical resection Not ablative / surgical candidates that failed to normalize thyroid hormones Mild disease Small goiter Low or negative antibody titer Women - too young/ old; pregnant; cannot go through radiotherapy due to disability to isolate themselves

What is the mode of action of thinoamides? What is the special mode of action associated with PTU?

Inhibits iodination and synthesis of thyroid hormones PTU can block T4 to T3 conversion at periphery at high doses

What are the adverse effects of thionamides?

Hepatotoxicity Rashes linked to SJS Agranulocytosis early in therapy Fever

Cite the monitoring parameters for those on thoionamides and justify the monitoring parameter

FT4 should be monitored every 6-8 weeks TSH remains suppressed for months even after therapy begins

Can thioamides be 100% effective?

No. Not solving root cause of issue

What are some signs and symptoms associated with those having hyperthyroidism and pregnancy?

Failure to gain weight despite good appetite Tachycardia

What agent is considered for 1st trimester hyperthyroidism and pregnancy? Why is the other agent not preferred?

PTU Carbimazole can cause increase risk of congenital malfunctions

What agent is considered for 2nd and 3rd trimester hyperthyroidism and pregnancy? Why is the other agent not preferred?

Carbimazole PTU can increase risk of hepatotoxicity

What is the mechanism of action for non-selective beta blockers (e.g. propanolol)?

Block many hyperthyroidism manifestations by beta-adrenergic receptors Block T4 to T3 conversion at high doses

What are some indications for use of nonselective beta blocker?

High risk patients such as elderly with CVD Treat thyroiditis Symptomatic relief Bridging therapy for thionamides effect to kick in / before ablation / surgery

What is the mode of action of iodides?

Inhibit release of stored TH Decrease vascularity and size of thyroid gland Decrease effect of hormone synthesis

Define the place in therapy for iodides and why is this so

Before surgery (7-10 days) : shrink thyroid gland After surgery (3-7 days): Inhibit thyroiditis-mediated release of stored hormones Thyroid storm

What are some special considerations associated with the use of iodides?

Limit its use to 7-14 days as it thyroid hormone secretion continues after that

Define subclinical hyperthyroidism

Low/undetectable TSH with normal T4

What are some risks associated for subclinical hyperthyroidism? Who are more likely to get these risk?

Age > 60 years more likely to get Afib Postmenopausal women more likely to get bone fracture

What are some compelling indications for one to initiate therapy for subclinical hyperthyroidism

Young age TSH < 0.10 mIU/L

What is the agent for subclinical hypothyroidism with AFib?

Beta blockers - propanolol

List the drugs responsible for inducing thyroid disease

Lithium and Amiodarone

How does lithium induce thyroid disorders?

Hypothyroidism: inhibition of thyroid hormone secretion and release cause increased TSH and goiter Hyperthyroidism: Thyroiditis

How does amiodarone induce thyroid disorders?

Contains iodine structure that can affect how iodine is uptake, secreted and produced Thyroiditis also can cause hyper/ hypothyroidism

Thyroid Disorders Flashcards

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