Hypothyroid Flashcards
What is the function of the thyroid gland
Secrete thyroid hormones (T3/T4) to regulate metabolism
Secrete calcitonin to regulate calcium (decrease)
What is thyroglobulin
Protein that synthesizes and stores T3 and T4
What is the HPA axis overview
Hypothalamus releases TRH to the ant pituitary
Ant pit releases TSH to the thyroid
TSH tells the thyroid to make T3 and T4
Unused T3/T4 in the blood go to the hypothalamus and anterior pituitary with negative feedback
Hypothalamus and Ant pit stop stimulating T3/T4 release
What are the two overall manifestations of hypothyroidism
Generalized slowing of metabolism
Accumulation of polysaccharides in the matrix
What are general slow metabolic Sx of hypothyroidism
Fatigue cold intolerance weight gain (mild) cognitive dysfunction constipation slow movement/speech delayed relaxation of DTR Bradycardia
What are Sx of polysaccharide accumulation in hypothyroidism
Dry skin hoarseness edema coarse skin puffy face loss of eyebrows periorbital edema tongue enlargement
Other (not as frequent) Sx of hypothyroidism are
decreased hearing myalgias depression menstrual changes pubertal delay diastolic HTN pleural/pericardial effusions ascites galactorrhea
Some PE findings for hypothyroidism include
carpal tunnel (2/2 edema causing nerve compression)
Hypoactive bowel sounds
Dyspnea
Hypertension Sx of vitiligo or alopecia
Classic hypothyroidism labs show
High TSH
Low free T4
May want to get BMP (Na and Cr), Lipids (HLD), and drug levels (hard to metabolize drugs)
How can you tell the difference between primary and subclinical hypothyroidism
Primary: high TSH, low T4
Subclinical: high TSH, normal T4
What are the anti-thyroid antibodies
Anti-TPO: high in graves and hashimotos
Anti Tg: high in graves and hashimotos
TSH recetor (TSI): high in GRAVES (specific)
MCC of hypothyroidism in U.S. is
Hashimotos (autoimmune thyroiditis)
In the world: iodine deficiency
Also: iatrogenic, meds, transient (pregnancy), infiltrative, congenital
Do you screen everyone for hypothyroidism?
USPSTF says no (no EBM on effectiveness)
But in real practice, you will
Who is at increased risk for hypothyroidism (and therefor should likely be screened)
Goiter Hx AI disease Hx radioactive iodine therapy Hx head/neck radiation FHx thyroid disease Meds that impair thyroid fxn (lithium, amiodarone)
Once hypothyroidism has been diagnosed, how do you treat it
Synthetic thyroxine (T4) replacement to achieve and maintain euthyroid state; 80% absorption, 1 week half life
Brand: Levothyroxine
Generic: levothyroid, levoxyl, synthyroid
Is brand better than genetic?
Endocrinologists think so bc with brand you get the same formulation every time so you better achieve and maintain euthyroid
With generic you get different formulations making it harder to maintain
How do you dose Levothyroxine
average dose: 1.6 mcg/kg/day
Elderly: 25-50 mcg/day, titrate up
Hx CHD: MAX 25 mcg/day, titrate up
Goals of hypothyroid Tx are
Symptom relief
Normalize TSH secretion
Decrease goiter (if applicable)
How do you manage hypothyroid therapy
Monitor labs q6 weeks until TSH is normal
avoid OVER replacement and sending into hyperthyroid
Weird hypothyroid drug combos are
T3/T4 combo (cytomel): T3 absorption is highly variable and has a short half life to it is hard to get consistent levels in the system
Dessicated thyroid extract (Armour thyroid): extracted form pigs, for patients who want “natural” drug. has T3 and T4. Endocrinologists hate it
Do meds interact with levothyroxine
Yes, many!
Ferrous sulfate, PPI
just take them at a different time during the day
What is subclinical hypothyroid
Associated with CVD, NAFLD, Neuropsych, and reproductive d/o
1/2 progress to primary hypothyroidism
How do you treat subclinical hypothyroidism
If TSH >10: Give supplemental T4
If TSH 5-10: only treat if symptomatic! what is their clinical presentation?
