Unit 10: Thyroid Flashcards
What is the function of the thyroid hormones?
metabolic pacemaking
influence/regulate: growth body temperature energy metabolism heart rate cholesterol metabolism mood
What is the difference between total T3 and T4 versus bound T3 and T4?
most T3 and T4 are bound to protein and are metabolically inactive
Free T3 and Free T4 are active/not bound
What is the name for T3?
triiodothyronine
What is the name for T4?
tetraiodothyronine = thyroxine
Which is more potent, T3 or T4?
T3
Which is present in higher amounts, T3 or T4?
T4
Describe the HPA for the thyroid
hypothalamus secretes TRH
TRH stimulates the pituitary to secrete TSH
TSH stimulates the thyroid to secrete T3 and T4
What is TRH?
thyroid-releasing hormone
What is TSH?
thyroid-stimulating hormone
What is the best test for screening for hypo/hyperthyroidism?
TSH
What is the best test for medication adjustment for the thyroid?
TSH
How long does it take the TSH to adjust to a new medication level via the body’s negative feedback loop?
4-6 weeks
TSH is ______ proportional to the amount of active thyroid hormone in the serum
INVERSELY
If TSH is high, then what?
there is not enough circulating thyroid –> hypothyroid
GREAT EXAM QUESTION
If TSH is low, then what?
there is too much circulating thyroid –> hyperthyroid
GREAT EXAM QUESTION
Why don’t we check Total T3 and Total T4?
Not very important measurements, as we want to know how much T3 and T4 are available
Why check anti-thyroid antibodies?
to determine if hyperthyroidism or hypothyroidism are autoimmune
Antibody to thyroid peroxidase is what? In what disease is it seen?
TPO
Hashimoto’s Thyroiditis
What antibody stimulates the TSH receptor? In what disease is it seen?
TRAb
Grave’s Disease
What is the FNA test?
completed on a solitary thyroid nodule to rule out malignancy
True or False: It is common for the thyroid to have nodules
True
What is the Radioactive Uptake Scan, and for what is it used?
completed in hyperthyroid patients to identify cause of it
to identify non-active nodule which is likely to be malignant
Why is the FNA test important?
identifying thyroid malignancy EARLY is important, as it often metastasizes
What does iodine have to do with the thyroid?
required to make thyroid hormones
How do we make sure we get enough iodine?
salt is iodized
For what is radioactive iodine used?
I-131– destroy the tissue
1.123 – to identify metabolically active nodules
What heart condition does hyperthyroidism commonly cause?
A-Fib
How is hyperthyroidism treated?
medically
radiation
surgery
What foods commonly have iodine?
cod
milk
What medications are used to treat hyperthyroidism?
THIODAMIDES:
methimazole (Tapazole)
propylthiouracil (Propyl-Thyracil)
What is the drug of choice for hyperthyroidism?
methimazole (Tapazole)
What is the drug of choice for hyperthyroidism and pregnancy?
propylthiouracil (Propyl-Thyracil)
increased protein binding –> less crosses the placenta
What can methimazole (Tapazole) cause?
elevated liver enzymes
What do the thiodamides do?
prevent T3/T4 synthesis via 3 mechanisms
How long does it take for thiodamide medications to have their effects?
3-4 weeks
What is a thyrotoxic crisis?
extreme hyperthyroidism
Methimazole can be hepatotoxic; when should it be discontinued?
if transaminases (AST/ALT) are 3x normal
AE of methimazole
low prothrombin levels --> bleeding bone marrow suppression hepatotoxic lupus-like syndrome vasculitis hypothyroidism
Important thing to remember about older thyroid suppression meds:
potassium iodide (SSKI)
potassium iodide-iodine solution (Lugol’s)
keep thyroid hormones from being released, so the sudden discontinuation of the meds can cause excessive levels of hormones
When are SSKI or Lugol’s solution used?
short term pre-operatively before thyroidectomy
thyroid protection during radiation of thyroid
What is I-131?
Radioactive iodine used for hyperthyroidism and after surgery for some thyroid cancers to get rid of any remaining cancer
What normally happens after administration of I-131?
thyroid becomes enlarged briefly, but not painful
effect evident 1-2 weeks after administration
With what drugs does I-131 interact?
other thyroid meds, especially suppressants
amiodarone
Why is a low iodine diet recommended with I-131?
The thyroid pulls in iodine indiscriminately; we ant it to pull in the radioactive iodine
Why should people who receive I-131 be encouraged to drink and void frequently?
to release radiation via urine
What is I-123?
Radioactive sodium iodide used in thyroid scintigraphy
What is thyroid scintigraphy?
“thyroid uptake scan”
OR
“radionuclide thyroid scan”
where metabolically active nodules take up radioactive iodide; hypo functioning nodules are suggested of malignancy
**if nodules are not making hormones, they will not take up iodine
Name other meds used in hyperthyroidism
BETA BLOCKERS – for sx control of tachycardia; prevent A-Fib or A-Fib + RVR (propranolol preferred)
CCBs – verapamil (for HR rhythm/rate control)
Cholestyramine (bile acid sequestrant) to bind to T3/T4 in the gut
Signs and symptoms of hypothyroidism
weight gain fatigue dry skin cold intolerance depression constipation **slows most things down
What is subacute thyroiditis?
due to intermittent presence of antibodies, brief periods of hyperthyroidism in early Hashimoto’s
Symptomatic treatment of Subacute Thyroiditis
Beta blockers
steroids
NSAIDs
What is transient thyrotoxicosis?
spontaneously resolving hyperthyroidism
How is hypothyroidism treated?
synthetic replacement:
- -levothyroxine
- -levothyronine
- -liotrix
animal replacement:
–dessicated thyroid
What is myxedema?
severe hypothyroidism
What can result from myxedema?
stupor
lethargy
coma
What is levothyroxine?
T4 that converts to T3
Why do we treat hypothyroidism with T4 and not T3?
because the half life of T3 is so short
and it is easier to keep a steady level of hormones if we replace T4 (levothyroxine) than T3
What is the cause of secondary hypothyroidism?
hypopituitary causes
What is the cause of tertiary hypothyroidism?
hypothalamic causes
For treating hypothyroidism, how often should TSH levels be checked?
4-8 weeks after starting tx or changing dose
6 months after stable dosing
then every 12 months
anytime there are hypothyroid/hyperthyroid symptoms during treatment
What is Tirosint?
a soft gel version of levothyroxine that absorbs more quickly and is less affected by coffee and gastric pH
What organ is very sensitive to thyroid replacement?
the heart
What other endocrine dysfunction should be corrected first, before treating hypothyroidism?
adrenal insufficiency
What can happen for patients with CAD who are also hypothyroid and treated with levothyroxine?
arrhythmias
angina
What is thyroxine toxicity?
too much circulating thyroid hormone
Symptoms of thyroid toxicity in children
restlessness
insomnia
accelerated bone maturation and growth
Symptoms of thyroid toxicity in adults
nervousness heat intolerance palpitations tachycardia unexplained weight loss
Symptoms of long term thyroid toxicity in adults
A-fib
increased rate of bone loss in osteoporosis
Drugs that increase hepatic microsomal enzymes increase metabolism of what hormones?
T3 and T4
What needs to happen with thyroid meds if the patient is also on meds that increase hepatic microsomal enzymes?
increase dose of thyroid meds
What happens with estrogen (dosed and in pregnancy) and thyroid hormones?
increases binding of thyroxine and liothyroxine –> so less is available
What is desiccated thyroid?
thyroxine from an animal source
What are the risks of desiccated thyroid?
antibody formation
What is liothyronine?
T3
Why don’t we use liothyronine to treat hypothyroidism?
harder to make amount of available T3 level/even when using this drug
When is thyroid replacement contraindicated?
for weight loss when TSH, T3, T4 are normal
abnormal vaginal bleeding
depression
urticaria
Risks of thyroid replacement being given when it is not truly needed
osteopenia/osteoporosis
A-Fib
CAD/CHF
