Thyroid Disease

Question 1

Hashimoto’s Thyroiditis

Answer 1

• also known as chronic autoimmune thyroiditis
• it is the most common cause of hypothyroidism in adults
• caused by antibodies to thyroid peroxidase (anti-microsomal/TPO antibodies) and thyroglobulin
• TSH is appropriately elevated in response to low T3/T4

Question 2

How does hypothyroidism present?

Answer 2

insidious onset of…

• weight gain despite lowered appetite
• cold intolerance
• hyperactivity, lethargy, fatigue, weakness
• constipation
• diminished reflexes with slowed relaxation
• hypothyroid myopathy (proximal muscle weakness with increased creatine kinase)
• facial and periorbital myxedema
• dry, cool skin with coarse, brittle hair
• bradycardia and dyspnea upon exertion
• hypercholesterolemia due to diminished expression of LDL receptors

Question 3

What is subclinical hypothyroidism?

Answer 3

the absence of symptoms, normal free T4, and elevated TSH

Question 4

Levothyroxine

Answer 4

• an oral formulation of T4
• must be taken on an empty stomach at least one hour away from food
• initial therapy begins with 1.6 mcg/kg
• half life is seven days
• must beware when prescribing to those with advanced age or heart disease; start at a lower dose and gradually titrate
• binds to calcium and iron, reducing absorption
• re-evaluate dose at 8 week intervals until stable and then every 6-12 months there after

Question 5

Triiodothyronine

Answer 5

• an oral formulation of T3
• given at substantially lower doses than levothyroxine
• less commonly used than levothyroxine because it only has a half life of one day

Question 6

How does estrogen impact thyroid hormone?

Answer 6

• it increases levels of thyroid binding globulin, reducing the amount of bioavailable hormone
• a healthy thyroid will compensate by increasing production and the net result will be an increase in total T3/T4 but no change in the amount of bioavailable hormone
• someone with hypothyroidism, however, will need larger doses of levothyroxine

Question 7

How do androgens impact thyroid hormone?

Answer 7

it decreases levels of thyroid binding globulin, increasing the amount of bioavailable hormone

Question 8

How do glucocorticoids impact thyroid hormone?

Answer 8

it decreases levels of thyroid binding globulin, increasing the amount of bioavailable hormone

Question 9

How do salicylate and furosemide impact thyroid hormone?

Answer 9

they displace thyroid hormone from thyroid binding globulin, increasing the amount of bioavailable hormone

Question 10

Which substances are known to decrease the absorption of thyroid hormone or T4?

Answer 10

• cholestyramine
• colestipol
• PPIs
• raloxifene
• iron and calcium
• bran, soy, coffee

Question 11

What are the symptoms of hyperthyroidism?

Answer 11

• enlarged, homogenous (no nodules) thyroid with a bruit during auscultation
• weight loss despite increased appetite
• heat intolerance
• hyperactivity, anxiety, insomnia, hand tremor
• diarrhea
• brisk reflexes
• thyrotoxic myopathy (proximal muscle weakness with normal creatine kinase)
• pre-tibial myxedema and periorbital edema
• exophthalmos, lid lag ophthalmoplegia, conjunctivitis, altered visual acuity, and corneal ulceration
• warm, moist skin with fine hair
• chest pain, palpitations, arrhythmias due to an increase in number and sensitivity of beta-adrenergic receptors
• hypocholesterolemia due to elevated LDL receptor expression

Question 12

Graves Disease

Answer 12

• the most common cause of hyperthyroidism
• an autoimmune disorder characterized by IgG that activate TSH receptors on thyroid cells
• labs include decreased TSH, increased T3/T4, increased radioactive iodine uptake (RAIU), and positive tests for thyroid stimulating antibodies
• beta blockers and calcium channel blockers are used to treat symptoms
• radioactive iodine can be used to ablate the thyroid but thioamides, which inhibit thyroid hormone synthesis are more common today

Question 13

Thioamides

Answer 13

• a group of drugs that inhibit thyroid hormone synthesis by blocking iodination of the tyrosyl groups and coupling of iodotyrosines
• first line therapy for Grave’s disease
• propylthiouracil has a short half life; methimazole has a longer one and is use more often
• rash is the most common side effect but is tolerable
• may cause significant bone marrow depression, especially in patients over 40 or with doses of more than 40 mg/day, so monitor their CBC

Question 14

How is iodide used in the treatment of hyperthyroidism?

Answer 14

• once used to inhibit organification and hormone release
• but it has the potential to precipitate hyperthyroidism in those with existing thyroid disease
• no longer used therapeutically except in cases of thyroid storm refractory to thioamide
• it’s primary role is in nuclear emergencies to block the effects of radioactive iodine isotopes from damaging the thyroid

Question 15

Toxic Nodular Goiter

Answer 15

• hyperthyroidism caused by hyper functioning of a thyroid nodule
• may develop from a long-standing simple goiter
• more common in the elderly than Graves disease
• PE typically reveals an enlarged, nodular thyroid
• unlike Grave’s disease, ophthalmopathy and dermopathy are usually absent
• labs show decreased TSH, increased T3/T4, an absence of thyroid stimulating immunglobulins, and the RAIU shows a focal area of increased uptake
• treatment involves radioactive iodine ablation, thioamides, or surgery

Question 16

Thyroiditis

Answer 16

• inflammation of the thyroid
• there is a risk for thyrotoxicosis if inflammation leads to excessive release of thyroid hormone
• however, there is no actual increase in production, in fact there is a decrease in RAIU
• therefore, treatment is symptomatic relief and does not utilize any anti-thyroid medications (or you can induce a hypothyroidism)
• TSH is decreased, T3/T4 are increased, ESR is elevated > 50, and RAIU is decreased
• treatment involves beta blockers, aspirin, NSAIDS, and corticosteroids

Question 17

Which beta-blocker, in addition to providing symptomatic relief of hyperthyroidism, is capable of inhibiting the peripheral conversion of T4 to T3?

Answer 17

propranolol

Question 18

What drugs block the peripheral conversion of T4 to T3?

Answer 18

• radiocontrast media
• propranolol
• corticosteroids
• amiodarone

Question 19

How do iodides inhibit thyroid hormone synthesis?

Answer 19

they inhibit proteolysis and coupling