Thyroid Flashcards
What are the two major thyroid hormones?
Thyroxine (T4)
Tri-iodothyronine (T3)
How much T3 is produced in the thyroid itself?
20%
Where does the majority of T3 come from
80% comes from peripheral breakdown of T4
How many half-lives do thyroid hormones have in steady state?
4-5
What does the thyroid do?
Regulates hormone production
This is done via the hypothalamic pituitary thyroid axis
How do we get thyroid hormone?
TSH secreted by anterior pituitary
Or..
T4 is converted to T3 outside the thyroid
What kind of disorder is primary hypothyroidism
Disorders of the thyroid gland
Aka: Hashimoto’s thyroiditis
What kind of disorder is secondary hypothyroidism
Pituitary or hypothalamic dosorders
Sx of hypothyroidism
Weight gain
Depression*
When working a pt up for depression checking for hypothyroidism is ESSENTIAL
Diagnosing hypothyroidism
Check TSH and a free T4 (or total but free is better)
Levels of hormones in subclinical hypothyroidism
Increased TSH but normal T4
Levels of hormones in hypothyroidism
Elevated TSH
Low T4
Drug of choice for hypothyroidism
Levothyroxine
Levothyroxine
Synthetic T4 Long half life Once daily dosing IV dosing at 50% of oral dose Dosing in mcg!
Little used hypothyroidism tx
Desiccated beef/pork thyroid gland (Armour -> mg dosing)*
Obsolete and potential for allergy
T3 and T4 mixtures (Liotrix) -> expensive, no real theraputic rationale
Levothyroxine dosing
Dosed one daily in AM on EMPTY STOMACH
Typical dose = 100-112 mcg/day
Under what circumstances do we used alternative dosing of levothyroxine
Lower initial dosing for the elderly and pts w/ CV disease
Pregnancy usually requires higher dosing
Hyperthyroidism sx
Nervousness Anxiety Palpitations Heat intolerance Finger tremor Weight loss (cardinal sign)
Main cause of hyperthyroidism
Grave’s disease
Classic triad of Grave’s disease
Hyperthyroidism
Opthalmopathy (bugged out eyes)
Dermopathy (pretibial myxedema)
Hormone levels in hyperthyroidism (dx)
Decreased TSH
Increased T4
Hyperthyroidism tx
Antithyroid meds
Anti-thyroid meds
Propylthiouracil (PTU)
Methimazole
PTU
Inhibits conversion of T4 to T3
TID dosing
Evaluate pts 3 months after D/Cing to check for recurrence
Methimazole
10xs more potent than PTU
Blocks oxidation of iodine in thyroid
No effect on T3 or T4
Dosing of methimazole for mild, moderate, severe, and maintenance is how many times per day
3!
TID
SE of anti-thyroid meds
Agranulocytosis
Aplastic anemia
Thrombocytopenia
