Flashcards in Thyroid Deck (33):
How is thyroid hormone produced in the body?
The hypothalamus releases thyrotropin releasing hormone so the pituitary gland releases thyroid stimulating hormone which causes the thyroid gland to make thyroid hormones which has negative feedback on the pituitary gland for thyroid stimulating hormone
How does T4 (levothyroxine) work?
It gets converted to T3 and rT3 (when body is ill) at the site of action
How does T4 circulate throughout the body?
On the protein thyroglobulin. If there is not enough of the protein, more will be free to do work.
What are the half lives of the thyroid hormones? How long will it take to reach steady state?
T4 has a half life of 7 days. T3 has a half life of 1 day. It takes about 5 half lives to get to steady state.
Must wait 1 month (5 half lives) to see if drug treatment is working/dosage is correct
What are the serum levels in hypothyroidism?
Low T4, low or normal T3, high TSH and low thyroglobulin
What are the serum levels in hyperthyroidism?
High T4, high T3, low TSH and high thyroglobulin
How does hypothyroidism present?
Slowing of body functions, heart, mental acuity, strength, response to catecholamines (SNS), cold and scaly skin, sparse hair, tiredness, fatigue, weight gain, saddle nose, thickened lips (due to build up of fluid)
Often misdiagnosed as dementia
What causes hashimoto's thyroiditis?
Antibodies work against and shut down thyroid production and thyroglobulin
What are some symptoms of Hashimoto's thyroiditis?
Slower metabolism, reduced CNS activity-weight gain, fatigue, depression, bradycardia, constipation
But can also have short term reactive hyperthyroidism causing mania, tachycarida, panic attacks
Gets misdiagnosed as bipolar disorder, anxiety, depression
How is Hasimoto's thyroiditis detected?
Presence of specific antibodies
Will also see increased TSH ad thyroglobulin and lymphocyte invasion of the thyroid gland
Ultrasound will show an enlarged thyroid gland
Radioactive iodine uptake scan will show diffuse uptake in thyroid gland
What are some precautions when treating hypothyroidism?
Thyroid hormone increase adrenergic sensitivity to catecholamines (hyper SNS response)
Thyroid hormones doesn't cross the placenta
How can thyroid problems affect a pregnancy?
Hypothyroid will make you have difficulty getting pregnant
Hyperthyroid can cause an abortion
Monitor dose regimen carefully during pregnancy
How is hypothyroidism treated?
If due to iodine deficiency, add iodine to the diet
In gland failure, give levothyroxine (T4) because long half-life, given at birth, lag before effects are observed and body converts it to T3 as required
What should be done if you are giving levothyroxine in cardiovascular disease?
Give T4 slowly so it doesn't worsen the heart
What is Graves Disease?
The most common form of hyperthyroidism in which antibodies are activating to the TSH receptor causing more T3 and T4 to be made.
How does the diagnosis of hyperthyroidism change with age?
Less than 40 years old has mainly nervous system effects
More than 40 years old has mainly cardiovascular effects (catecholamine response)
Have to get up and eat at night, always hungry, 10-15 lb weight loss
What is 1st line treatment for Grave's disease?
Radioiodine (3 choices-131 I used most commonly due to 8 day half life)
Surgery can also be done (risky)
How does radioiodine work?
Ionizing radiation destroys the gland. Goes right to the thyroid gland, stays there for a month or so and then leaves with the thyroid gland partially or fully destroyed.
What are precautions in treatment with radioiodine?
There is a delay in therapeutic response (2-6 months which may need other pharm intervention in meantime), radiation induced thyroiditis, hypothyroidism, thyroid cancer, contraindicated in pregnancy and children
What is the 1st line treatment in mild Grave's disease or pregnancy?
The thioamide drugs: PTU (1st line-feel better faster)
Methimazole (Carbimazole precursor) is a 2nd line
How do the thioamide drugs work?
Competitive inhibitor of peroxidase which interferes with organification of iodine, blocks MIT conversion to DIT, inhibits coupling of iodinated tyrosines, inhibit conversion from T4 to T3 (PTU)
What does onset of thioamide drugs require?
Depletion of thyroid hormone stores
How does the dosing between the thioamide drugs differ?
Methimazole is give once daily while PTU is given every 8 hours or 3 times daily
How is thioamide drug dosing adjusted?
Adjusted and/or reduced every 4-6 weeks
What are the side effects of thioamide drugs?
Fever, rash, arthritis-like symptoms
Leukopenia (wait until patient gets sick to do something)
Agranulocytosis (rare and usually reversible)
What occurs during a thyroid storm?
Greatly increased blood temperature, shortness of breath, anxiety, sweating, tachycardia, chest pain, MI
What is given during a thyroid storm?
Propranolol to decrease the cardiovascular symptoms/toxicity and some suppression of T4 to T3 conversion
How does dexamethasone affect thyroid hormone?
Inhibits the conversion of T4 to T3
How does lithium affect thyroid hormone?
Inhibits the secretion and degradation in peripheral tissue
How do sulfonamides affect thyroid hormone?
Interfere with organification of iodine
How does long term sodium nitroprusside affect thyroid hormone?
Thiocyanate accumulation inhibits iodine uptake of the thyroid
How does amiodarone affect thyroid hormone?
Contains lots of iodide
Large doses of iodide decreases degranulation of thyroglobulin and gland vascularity. Useful prior to surgery.