hyperthyroidism and hypothyroidism

Question 1

Thyrotropin-releasing hormone (TRH)

Answer 1

• Secreted by hypothalamus occurs in response to cold, stress, and decreased levels of thyroxine (T4)
• Secretion stimulates the synthesis of thyroid-stimulating hormone (TSH) by the anterior pituitary

Question 2

thyroid stimulating hormone (TSH)

Answer 2

Stimulates the thyroid gland to produce thyroid hormones

Question 3

thyroid hormones

Answer 3

T4 and triiodothyronine (T3)
- Synthesized from iodine and tyrosine molecules by follicular cells in the thyroid gland

The thyroid gland synthesizes and releases about 20% of T3 with the remainder of T4 converted to T3 peripherally when additional thyroid hormone is needed
- Such as during stress and cold temperatures

Question 4

T4 and T3 are only clinically active when they are free

Answer 4

The amount of active thyroid hormone in the plasma produces a feedback loop that inhibits or further stimulates TRH and TSH secretion to decrease or increase thyroid hormone production

Question 5

thyroid function tests

Answer 5

The provider should consider ordering a TSH and free T4 in the primary care office to assess thyroid function
- Serum TSH results are most sensitive for diagnosing common forms of hypothyroidism and hyperthyroidism

Question 6

goiter

Answer 6

Excess growth could be from an autoimmune process or abnormal cellular function

Size does not correlate with function!!
May be:
- Euthyroid (normal functioning)
- Collections of subfunctioning tissue
- Focal cellular growths (nodules) that might produce excess amounts of thyroid hormones

Question 7

hyperthyroidism

Answer 7

Also called thyrotoxicosis
- Occurs when the feedback loop fails, and excessive levels of thyroid hormone are circulating

Question 8

causes of hyperthyroidism

Answer 8

o Hyperfunctioning thyroid nodule
o Toxic diffuse goiter (Graves disease)
o Thyroiditis
o Anterior pituitary disorders
o Toxic multinodular goiter
o Excess thyroid supplementation
o Iodine-induced disease, including amiodarone therapy

Question 9

graves disease

Answer 9

An autoimmune disorder characterized by generation of abnormal immunoglobulin G (IgG) autoantibodies to thyroid peroxidase and thyroglobulin
- These antibodies bind to the TSH receptors -> activate excessive glandular growth and hormone production
- Alters the feedback system such that the hyperfunction of the thyroid gland does not trigger suppression of TSH and TRH as it normally would

Question 10

what does graves disease cause?

Answer 10

Causes hyperfunction of the thyroid gland with increased iodine uptake and subsequent systemic metabolism
- Causes the thyroid gland to become more vascular, enlarged, and form a goiter
- A disproportionate increase in T3 production is a result of long-term overstimulation of the gland
- Leads to decreased concentration of thyroxine-binding globulin and increased circulating levels of free hormone

Question 11

s/s graves disease

Answer 11

 palpitations
 tremor
 anxiety
 possible weight loss
 heat intolerance
 heightened sensitivity to sympathetic nervous system stimulation

Question 12

hyperthyroidism - medications

Answer 12

antithyroid drugs (ATDs) that inhibit the synthesis of new thyroid hormone by thyroid gland, but do not treat the underlying pathophysiology of hyperthyroidism

1. propylthiouracil
   - also inhibits the peripheral conversion of T4 to T3
2. methimazole
   - typically preferred d/t longer half life -> allows for once daily dosing

Question 13

low-dose beta blockers for hyperthyroidism

Answer 13

may be prescribed as adjunct therapy to control symptomatic tachycardia from hyperthyroidism
1. propranolol
2. atenolol
- allows for once daily dosing
- better choice for patients with hx of reactive airway disease or DM b/c atenolol is cardioselective

Question 14

preoperative preparation for hyperthyroidism

Answer 14

1. ATDs to prevent postoperative thyroid storm
2. Potassium iodide
   - Should be prescribed TID for 10 days before surgery
3. Beta blocker
   - to improve preoperative control of tachycardia

Question 15

potassium iodide for hyperthyroidism

Answer 15

might be considered before preoperative preparation for thyroid surgery
- blocks peripheral conversion of T4 to T3
- inhibits hormone release
- decreases the vascularity of the tissue

Question 16

initial drug of choice for hyperthyroidism

Answer 16

methimazole
 Once daily dosing
 Reduced interference with RAI
 Decreased risk of hepatic side effects

Question 17

methimazole dosing severe disease or large goiter

Answer 17

20-40mg/day

Question 18

methimazole dosing mild disease or small goiter

Answer 18

10-15mg/day

Question 19

methimazole pediatric dosing

Answer 19

0.25-1mg/kg/day

Question 20

propylthiouracil dosing

Answer 20

 Initial dose: 50-100 mg TID
 Typical maintenance dose: 100-150mg/day
 If severe disease or large goiter: up to 400mg/day

Question 21

patients should consider radioactive iodine therapy if they

Answer 21

 Are unable to achieve symptom control
 Relapse after completion of treatment
 Are unable to take ATDs

Question 22

surgery for hyperthyroidism

Answer 22

recommended for goiters larger than 80 grams
 Considered the fastest intervention for treatment
 Total removal of the gland decreases the risk for relapse seen with a partial gland removal

Question 23

adverse reactions with ATDs

Answer 23

o Agranulocytosis (rare but potentially fatal complication)

o The hepatic concerns with propylthiouracil makes methimazole a safer alternative for all age groups

Question 24

monitoring for ATDs

Answer 24

Monitor changes in TSH and free T4 levels
- Monitor every 3-4 weeks until a euthyroid state is achieved
- TSH might remain decreased for several weeks even after there is an euthyroid state
- Once TSH level is WNL -> monitoring is decreased to every 3-6 months, then annually based on symptom relief

Question 25

primary hypothyroidism disorders

Answer 25

* autoimmune thyroiditis * endemic iodine deficiency * ATDs used to treat hyperthyroidism

Question 26

secondary causes of hypothyroidism

Answer 26

Conditions that cause either pituitary or hypothalamic failure - TSH response is inadequate so that the gland is normal or reduced in size, with both T3 and T4 synthesis equally reduced

Question 27

primary hypothyroidism is based on the hypothalamic-pituitary-thyroid gland feedback system

Answer 27

Occurs when the hypothalamus response to a decreased thyroid hormone level with an increase in TRH -> resulting in increased TSH secretion -- This stimulates thyroid gland enlargement, goiter formation, and preferential synthesis of T3 and T4

Question 28

Hashimoto thyroiditis

Answer 28

an immune-mediated disorder in which all components of the thyroid gland are injured, especially the TSH receptors Antibodies generated to attack glandular antigens impair: - TSH response - Hormone synthesis - Hormone release

Question 29

subacute thyroiditis

Answer 29

an inflammation of the thyroid often preceded by a viral infection - Elevated levels of thyroid hormones are d/t the release of stored thyroglobulin related to the inflammatory process - NSAIDs: used to address inflammation - Beta blockers: used to reduce tachycardia Usually spontaneous remission of this disorder - Can become chronic

Question 30

congenital hypothyroidism

Answer 30

occurs in infants because of absent thyroid tissue and hereditary defects in thyroid hormone synthesis An infant with no T4 during fetal life will be mentally impaired - Can be modulated with administration of T4 immediately after birth

Question 31

secondary hypothyroidism can result from

Answer 31

1. Administration of drugs that reduce thyroid hormone production and treat hyperthyroidism 2. Pituitary disorders  Cushing syndrome  Acromegaly  Pituitary adenomas

Question 32

net result of secondary hypothyroidism

Answer 32

inadequate TSH production that results in poor production of both T3 and T4

Question 33

the clinical features of hypothyroidism are attributed to the metabolic effects of decreased circulating levels of thyroid hormone

Answer 33

Pt develops a low basal metabolic rate  Cold intolerance  Lethargy  Slightly lower body temp

Question 34

severe hypothyrodism

Answer 34

can cause a medical emergency of myxedema coma s/s  hypoventilation  hypotension  hypoglycemia  lactic acidosis

Question 35

treatment of hypothyroidism

Answer 35

patients should be prescribed a replacement therapy with the administration of synthetic thyroid hormones o levothyroxine (T4) o liothyronine (T3) o liotrix (4:1 or 3:1 mixture of T4 and T3)

Question 36

levothyroxine dosing

Answer 36

patients with a TSH > 10mlU/L o initial dose: levothyroxine 50-75 mcg daily patients with a TSH > 20 mlU/L o weight based approach o 0.6mcg/kg daily

Question 37

if there is a need to rapidly correct a hypothyroid state

Answer 37

liothyronine is preferable because of its rapid onset and dissipation of action - advantages must be weight against the wide swings in T3 levels and possible cardiotoxicity

Question 38

monitoring for hypothyroid tx

Answer 38

TSH level to be evaluated at the initiation of therapy and every 4-8 weeks until the patient achieves a stable euthyroid state - Prescribed TSH levels to be repeated 6-8 weeks after any dose adjustment - Normalized and stable TSH levels often take 6-12 months to achieve Once euthyroid -> stable TSH monitoring occurs every 12 months depending on symptoms and stability