Thyroid And Anti-thyroid Flashcards
Name the anti-thyroid medications
Propylthiouracil
Methimazole
Propranolol
Iodide (lugol solution)
Radioactive iodine
How does propylthiouracil work?
Inhibits TPO: less thyroid hormones produced by gland
Inhibits 5’-deiodinase: less T4 to T3 conversion peripherally
How does methimazole work?
Inhibits TPO: less thyroid hormones made by gland
How does propranolol work?
Blocks catecholamine action
Mildly inhibits 5’-deiodinase: less T4 to T3 conversion peripherally
Sise effect of amiodarone?
Can cause hypothyroidism via excess iodine (wolff-chaikoff effect)
How does amiodarone affect TSH?
Mimics T4 therefore inhibits 5’-deiodinase
Therefore less T3
Therefore TSH rises
Later it normalises
Effect of radioactive iodine?
In low doses it can be used for imaging but in high doses it destroys thyroid tissue
What happens if thyroid binding globulin is low?
Thyroid hormones are not very soluble so without thyroid binding globulin there will not be much T4 in circulation available to tissues
What can effect TBG levels?
Pregnancy raises it
Liver failure reduces it
How does the body respond when TBG increases?
More TBG
More bound T4
Less free T4
More TSH
More total T4
More free T4 (back to normal)
TSH back to normal
What are the ratios of thyroid hormones in the blood?
T4>T3
Total T4»_space; Free T4
Drugs used in hypothyroidism?
Levothyroxine (T4)
Liothyronine (T3)
What causes myxedema?
Hypothyroidism
Effect of iodine deficiency?
Hypothyroidism
Goiter
Effect of excess iodine?
Hypothyroidism
Wolff-Chaikoff
Effect of iodine load?
Hyperthyroidism
What is the Wolff-Chaikoff effect?
A protective mechanism for the gland
Excess iodine inhibits organification and therefore hormone production
Chronic excess iodine can cause goiter
What is reverse T3?
Isomer of T3 also derived from T4
Importance of reverse T3?
In euthyroid sick syndrome
In critically I’ll patients there is low TSH, T4 and T3
This resembles central hypothyroidism
However in this case rT3 is also high due to impaired clearance
This excludes central hypothyroidism
Why is methimazole preferred over propylthiouracil to decrease thyroid hormones synthesis?
Longer half life
Less side effects
How do we treat exophthalmos in hyperthyroidism?
Steroids
Radiation
Surgery
What does it mean if the thyroid does not take up radioactive iodine much?
Chance of cancer
How does oral lugol’s solution block thyroid hormones release?
Mechanism not yet understood
