EXAM #1: HYPOTHYROID Flashcards
What are the major steps of thyroid hormone synthesis?
1) Trapping of iodide (NIS)
2) Organification (add I to thyroglobulin)
3) Coupling (MIT and DIT)
4) Storage (Colloid)
5) Secretion
What is the Jod Basedow effect?
Increased T4 formation with Iodide concentration
What is the Wolff-Chalikoff effect?
Decreased T4 formation with increased iodide, after initial increase
What is the escape effect?
Increased T4 formation AFTER wolff-chalikoff effect
What subunit of TSH gives the hormone its specificity?
Beta
Aside from TSH, what else can be increased by TRH?
Prolactin
What factors increases TGB?
1) Estrogen (pregnancy, BCP)
2) Congenital
What factors decreases TGB?
1) Systemic illness
2) Glucocorticoids
What is the best test of thyroid function?
TSH
*Note that this will be inversely proportional to thyroid function
What are the expected values of TSH and free T4 in hypothyroidism?
- High TSH
- Low FT4
*Note that the TSH will be above the reference range before FT4; thus, more sensitive
What are the expected values of TSH and free T4 in hyperthyroidism?
- Low TSH
- High FT4
*Note that the TSH will be below the reference range before FT4; thus, more sensitive
What is the utility of radionuclide scans in evaluating the thyroid?
This is used to determine thyroid function
What does “subclincal” refer to in regards to interpreting the results of FT4 and TSH levels?
Changes in TSH with normal FT4
What labs are associated with primary hypothyroidism?
- High TSH
- Low T3/4
What are the possible etiologies of primary hypothyroidism?
1) Thyroiditis
2) Iodine deficiency
3) Radiation
4) Surgery
5) Infiltrative
6) Drugs
What are the possible etiologies of secondary hypothyroidism?
1) Surgical
2) Infiltrative/ metastatic
3) Radiation therapy
4) Apoplexy
What will the TSH and T4 be in secondary hypothyroidism?
- LOW TSH
- Low T4
What is a delayed relaxation phase?
Testing DTR, takes a long time for muscles to relax
*Associated with hypothyroidism
What is the most common cause of hypothyroidism in iodine-sufficient areas?
Hashimoto’s Thyroiditis
What is Hashimoto’s Thyroiditis?
Auto-immune destruction of the thyroid
What are the major clinical features of Hashimoto’s Thyroiditis?
1) Goiter
2) Bossillated feel
What antibody is usually elevated in Hashimoto’s Thyroiditis?
TPO antibodies
*Note that these are NOT required for diagnosis
What is the hallmark US finding in Hashimoto’s Thyroiditis?
Heterogenous appearance
What causes goiter in iodine-related hypothyroidism?
- Deficiency= gland has to work harder
- Increased TSH= increases size of thyroid gland
What is the name of the effect that can cause iodine to lead to hypothyroidism?
Wolff-Chaikoff phenomenon
How is hypothyroid treated?
Levothyroxine (T4)
Roughly 1.5 mcg/kg/day
When is treatment indicated for hypothyroidism?
TSH greater than 10
If the TSH is below 10 but the patient is symptomatic, what should you do?
Give a levothyroxine trial
When treating hypothyroid, how long should you wait to check a TSH after a dose change?
4-6 weeks
*UNLESSS, patient switches brands of medication, starts birth control, or is pregnant
What is Liothyronine?
T3
*Note that this is not usually recommended as therapy
What is contained in “natural” thyroid sources, such as Armour Thyroid?
Both T3 and T4
How do the thyroid hormone needs change in pregnancy?
Needs for thyroid hormone increase
Clinically, what do you need to do with pregnant patients regarding thyroid?
1) Check TSH at diagnosis of pregnancy
2) Monitor TSH 4-6 weeks
3) Doses redcuced post delivery
What is myxedema coma?
Acute medical emergency w/
1) Mental status change
2) Hypothermia
3) Hypoglycemia
4) Resp. failure
5) Hypotension
6) Bradycardia
*More common in women, precipitated by infection, CVA, or MI
What is the treatment for myxedema coma?
1) Supportive measures/ tx of underlying cause
2) IV thyroxine replacement
3) Hydrocotisone
What should you use to guide dose adjustments in secondary hypothyroidism?
Free T4
What should T4 NOT be used for?
1) Shrinking nodules
2) Weight loss
3) Treating depression
4) Lowering cholesterol
