Thyroid and Parathyroid Flashcards
T4 is converted to T3 primarily where?
Liver
What is the best initial test to check thyroid function?
TSH levels
TSH levels are tightly regulated by levels of what?
Serum levels of T4 and T3
FT4 is more diagnostically relevant than TT4 and is used to evaluted what hormone?
TSH levels
Thyroid peroxidase antibodies (TPO Ab) is most often found in?
Hypothyroidism (Hashimoto’s)
Thyroglobin antibodies (TgAb) is most often found in?
Hypothyroidism (Hashimoto’s)
Thyrotropin receptor antibody (TRAb) is most often found in?
Hyperthyroidism (Grave’s)
What functional study is used to evaluted suppressed TSH?
Radioactive Iodine/thyroid uptake scan
What imaging study is used to assess structure of the thyroid gland tissue and nodules?
US
What is the single most accurate, reliable, cost effective test to DX thyroid CA?
Fine needle aspiration
Endogenous hyperthyroidsm is due to what?
Overproduction of thyroid hormone
What are the 4 most common causes of endogenous hyperthyroidism?
Graves’ disease, toxic multinodular goiter (MNG), toxic adenoma, thyroiditis
What are the most common causes of exogenous (iatrogenic) hyperthyroidism? (2)
Over-replacement in hypothyroidism, suppressive therapy (intentional for thyroid cancer)
What lab values would you expect to see with primary hyperthyroidism?
Low TSH, high FT4, high T3
What is the most common cause of primary hyperthyroidism?
Grave’s disease
What lab values would you expect to see with subclinical hyperthyroidism?
Low TSH, normal FT4, normal T3
What lab values would you expect to see with T3 toxicosis?
Low TSH, normal FT4, high T3
Opthalmopathy (exophthalmos, proptosis) is a common sign of what?
Graves’ disease
Radioactive iodine uptake and scan is used to evaluate what?
Hyperthyroidism
What uptake % is normal on radioactive iodine uptake and scan?
15% uptake after 6 hrs
Diffuse high/ elevated uptake on radioactive iodine uptake and scan indicates what?
De novo synthesis of hormone
Diffuse low/decreased uptake after a radioactive iodine and uptake sckin can indicate what? (2)
Inflammation/destruction of thyroid tissues (thyroiditis) or extrathyroidal source of thyroid hormone (factitious thyrotoxicosis)
What will Graves’ show on a radioactive iodine and uptake scan?
Diffuse uptake
What will a nodule or toxin MNG show on a radioactive iodine and uptake scan?
Irregular uptake
What is indicated by a hyperfunctioning “hot” nodule? (2)
Increased irregular uptake, rarely malignant
What is indicated by a hypofunctioning “cold” nodule? (2)
Decreased irregular uptake, more likely to be malignant
If you identify a cold nodule on radioactive iodine scan, what additional test should you consider?
FNA
What are the treatment options for Graves’? (4)
Beta blockers (sx control), antithyroid drugs (Methimazole, PTU), radioactive iodine ablation, surgery
What is the most common cause of primary hypothyroidism?
Hashimoto’s thyroiditis (autoimmune)
What are the 2 different types of central hypothyroidism?
Pituitary (secondary) or hypothalamic (tertiary)
What will TSH and FT4 levels show with central hypothyroidism?
Both low (T3 also low)
If TSH and FT4 levels are low and you suspect central hypothyroidism, what should the next step be?
Pituitary MRI
What is the treatment for iatrogenic hypothyroidism?
Radioactive Iodine
What medications can cause iatrogenic hypothyroidism? (4)
Lithium, amiodarone, other iodine-containing drugs, contrast agents
What labs would you expect to see w/ primary hypothyroidism?
High TSH, low FT4, normal or low T3
What labs would you expect to see w/ subclinical hypothyroidism?
High TSH, normal FT4, normal T3
In primary hypothyroidism, the serum TSH is increased in a reflex effort to stimulate what?
The failing gland (represented by low serum FT4)
What are the most important considerations when treating hypothyroidism with levothyroxine replacement? (4)
Weight based, take on empty stomach, mindful of meds that interfere w absorption, goal = acheive euthyroid state and alleviate sxs
Pt presents for a routine PE when you note a thyroid nodule. How do you proceed?
TSH and US first
What % of nodules are benign vs cancerous?
95% benign, 5% cancerous
Most cancerous thyroid nodules are what?
Papillary
When evaluating a thyroid nodule, if TSH is N or elevated, what should be ordered next?
Check for TPO antibodies
If low TSH and low FT4 what is the most likely cause of hypothyroidism?
Central (secondary or tertiary)
