Thyroid Flashcards
What is the primary function of the thyroid?
maintain/regulate metabolism in the body, helps children with growth and development, also temp regulation, wt, fat/CHO metabolism, HR, protein synthesis
3 glands involved in regulation of thyroid hormones?
hypothalamus, pituitary, thyroid
What is the normal TSH level
.4-4 mcg/mL
what is the normal T4free level?
.7-1.9 ng/mL
What is the key hormone when monitoring therapy?
TSH
What is the T1/2 of T4/T3?
T4- 7 days, T3- 1.5 days
What are the risk factors for thyroid disorders?
females 4x more likely, genetic predisposition
When to screen for thyroid disorders?
unexplained depression, cognitive dysfunction, hypercholesterolemia, sexual dysfunction, females>50
What is the hyperthyroidism prevalence?
1-2% of the population
What are the causes of hyperthyroidism
autoimmune (60-80%), thyroid ca, drug induced
What are sx of hyperthyroidism?
weakness, palpitations, increased sweating, tremor, nervousness, insomnia, distractibility, diarrhea, wt loss
What are physical findings of hyperthyroidism?
goiter, proptosis, blurred vision, thinning of hair, warm/moist skin, inc SBP, tachycardia, palmar erythema, high output heart failure
How is hyperthyroidism diagnosed?
increased free T4, TSH
What are treatment options of hyperthyroidism?
Thioamides, beta blocker, radioactive iodine, potassium iodine, thyroidectomy
Thioamides options
methimazole (Tapazole), propylthiouracil
MOA of thioamides
inhibit thyroid hormone synthesis by inhibiting peroxidase enzyme system of thyroid gland
How long do thioamides take for onset?
4-6 weeks, b/c does not impact the TH already available
What can thioamides be used for?
pregnancy, prior to surgery, graves’ disease
How does propylthiouracil work?
inhibits peripheral conversion of T4 to T3
What is the standard dosing for propylthiouracil?
50-150 mg TID until pt euthyroid then 50-200 mg TID for maintenance, has very short T1/2
How does methimazole work?
does not inhibit peripheral conversion, only works on the gland
Methimazole and propylthioruacil differences
M: preferred prior to surgery, PTU: preferred in pregnancy and lactation; M is 10x more potent than PTU, longer T1/2 QD
what is the standard dosing for methimazole
15-60 mg daily load, then 5-15 mg daily
How long is the treatment with thioamides?
1-2 years, then attemp tapering, 40-60% will fail off therapy, some require 5-10 therapy
What are the ADRs of thioamides?
agranulocytosis, aplastic anemia, leukopenia, thrombocytopenia, GI upset, (take with meals!), hepatitis, rash, urticaria, pruritus
How often should TSH and T4free be measured when on therapy?
4-8 weeks until at goal and then 3-4 months
When are Bblockers used for hyperthyroidism?
adjunct only because of tachycardia, short term (4-6 weeks) until controlled
What is the MOA of radioactive iodine?
ablates thyroid function without surgery, concentrates in thyroid gland and disrupt hormone synthesis, emits high energy B-particles that damages thyroid tissue
What is radioactive iodine the treatment of choice for?
Graves’ disease
How to give radioactive iodine?
dissolve in H2O of as a capsule, often successful after 1 dose, can repeat after 6 months
What usually happens to pts after radioactive iodine therapy?
usually become hypothyroid and require supplemental TH therapy
In what pts is radioactive therapy contraindicated?
pregnant pts
How are pts monitored after radioactive therapy?
TSH and thyroid scan
Potassium iodide MOA
block thyroid hormone synthesis and release, dec thyroxine synthesis, dec iodination of tyrosine and dec coupling of iodinated tyrosine residues, dec size and vascularity of thyroid gland
When is potassium iodide used?
as preop treatment in Graves to incrrease gland firmness, in pts experiencing thyrotoxic crisis
What are two forms of potassium iodide?
logol’s solution: 5% iodide, 10% KI, and SSKI
What is the dose of lugol’s solution?
3-5 drops TID for 10 days prior to surgery, 1 mL TID for thyrotoxic crisis
What is the dose of SSKI?
place drops in glass of water, juice or milk (1g/mL solution)
ADR for potassium iodide?
unpleasant/metallic taste, burning sensation in mouth and throat, soreness of teeth and gums, GI upset
When should thyroidectomy be performed?
in malignancy, large goiter, lack of remission w/ drug therapy, contraindication to drug therapy, usually use thionamides until euthyroid
What decreases the size of thyroid gland (before surgery)?
preoperative iodides
What is a thyroid storm?
life-threatening medical er with high mortality rate, tachy, hyperthermia, arrythmia, nausea, vomiting, diarrhea, delerium, coma
What precipitates severe hyperthyroidism?
infection, surgery, trauma, radioactive iodine, or withdrawal from anti-thyroid meds
How to treat thyroid storm?
treat precipitating cause, IV bblockers, iodide, PTU 300-400 mg PO TID and hydrocortisone 100 mg IV TID to combat hypoadrenalism
What is the prevalence of hypothyroidism?
3-5%, increases w/ age, and F>M
What are the causes of hypothyroidism?
presence of a goiter, autoimmune, Hashimoto’s disease, drugs (amiodarone, lithium, interferon-a), or absence of goiter- primary hypothyroidism, surgery/radiation, iodine deficiency, or secondary hypothyroidism
What are symptoms of hypothyroidism?
fatigue, depression, cold intolerance, wt gain, dry skin, constipation, muscle aches, loss of taste, bradycardia, thin nails, arthralgias, goiter, thnning/yellow skin, lethargy, hair loss, HF
How is hypothyroidism diagnosed?
elevated TSH>4.6, decreased free t4/T3
What are the treatment options for hypothyroidism?
Levothyroxine, liothyronine (cytomel), also thyroid USP, thyroglobulin, liotrix, desiccated thyroid
What is levothyroxine MOA?
synthetic T4, converted to T3
Dosage and forms of levothyroxine?
25-300 mcg once daily, IV too, start lower dose in elderly- 25-50 mcg
What is the education of levothyroxine?
take on empty stomach, 30-60 min before breakfast, take at same time each day, do not switch between brand
What is monitoring of levothyroxine?
obtain TSH every 6 weeks at initiation until stable, obtain TSH every 6 weeks after each dosage, no sooner, titrate dose based on TSH level, once stable can obtain TSH every 6 months or if symptomatic
What will increase TSH?
stress!!
ADRs of levothyroxine?
symptoms of hyperthyroidism if excessive dose
Drug interactions of levothyroxine?
cholestyramine, iron, fiber, antacid all decrease levels, CYP inducers increase the clearance
MOA of liothyronine (Cytomel)
synthetic T3, shorter T1/2 than levothyroxine- more peaks and troughs which present similarly to hyperthyroidism, can use in adjunct to levothyroxine
What is myxedema Coma?
advanced hypothyroidism with high mortality, acute decomposation of hypothyroidism, hypothermia, severe hypothyroid sx and coma
How is myxedema coma treated?
IV levothyroxine and corticosteroids, improvements in 24 hours
