Thyroid Disease Flashcards Preview

My DEMS 4 > Thyroid Disease > Flashcards

Flashcards in Thyroid Disease Deck (26):
1

T3 ratios

some from gland directly
-some from T4 (Type 1 and 2 deiodinase)
-reverse T3 via Type 3 deiodinase

Things that inhibit Types 1/2 deiodinase, get more rT3
Starvation
Severe illness
Severe stress
Neonatal period
Glucocorticoids
Propranolol
Amiodarone
Radiocontrast dyes

2

Serum total T4

4-12 micrograms/dL

only 0.02% is free and active T4

99.98% is bound and inactive:
TBG, TBPA, albumin

t1/2 of T4: 7 d

3

Serum total T3

-t1/2 1 day
total T3: 80-180 ng/dL

free 0.02%: 1-4 pg/mL
bound: TBG, albumin

4

causes of increased total T4 and total T3

-hyperthyroidism/thyrotoxicosis
-increased binding proteins:
estrogen
-thryoid hormone resistance

5

causes of increased free T4 and free T3

hyperthyroidism/thyrotoxicosis
-thyroid hormone resistance

6

Causes of decreased total or free T4 and T3

Hypothyroidism
Decreased serum protein binding
Euthyroid sick syndrome (nonthyroidal illness)
Drugs
Liver or kidney disease (total T4, total T3)

7

TSH: when is it useful and when is it not reliable?

normal range: 0.4-4
**best test to screen for thyroid dysfunction
-indicates an individual's thyroid hormone "set point"

-Elevated in primary hypothyroidism:
Lack of negative feedback by thyroid hormone

Suppressed in primary hyperthyroidism:
Excess negative feedback by thyroid hormone

When can one not rely on a TSH?
Abnormal pituitary gland
Ex. panhypopituitarism, TSHoma, idiopathic central hypothyroidism

8

TSH action

stimulates iodine uptake into thyroid follicular cells and thyroid hormone production
-binds to receptor, NIS is activated
-ultimately leads to production of T4 and T3

9

Sx of hyperthyroidism

nervous
weight loss
increased appetitie
fatigue
tremor
heat intolerance

10

Dx of hyperthyroidism or thyrotoxicosis

Overt:
low TSH
increased free T4
increased free T3 (not used)

Sublclinical
low TSH
normal T4
normal T3

11

Thyroxtoxicosis

High circulating levels of thryoid hormone
1. no overproduction
-high RELEASE of preformed/stored T4 and T3: no true hyperthyroidism
"thyroiditis"
2. overproduction of T4 and T3 "hyperthyroidism"

-TSH should be low (TSH stimulates thyroid to take up iodine and synthesize T4 and T3.
-if TSH is suppressed, there should be no uptake of iodine
-a normal or elevated iodine uptake in the setting of a low TSH is abnormal and indicates autonomous production of thyroid hormone: true hyperthyroid state
-if uptake is low (approp in the setting of a low TSH), then thyroid hormone excess is due to high release of preformed thyroid hormone

12

Diagnostic eval

**look at slide 21

13

Etiology of hyperthyroidism: high uptake

Thyrotropin receptor antibody:
Graves’ disease
Hashitoxicosis

Thyroid autonomy:
Toxic adenoma
Toxic multinodular goiter (MNG)

HCG:
Hydatidiform mole
Choriocarcinoma

TSH:
TSH-oma (pituitary tumor)
Thyroid hormone resistance

14

Low uptake "hyperthyroidism"

No need to get thyroid scan (dark)

Subacute thyroiditis:
*Granulomatous thyroiditis (viral); de Quervain’s

Chronic lymphocytic thyroiditis (Hashimoto’s):
Postpartum thyroiditis

*Radiation-induced thyroiditis

*Infectious thyroiditis

Drug-induced thyroiditis

Ectopic thyrotoxicosis:
Factitious
Struma ovarii

*pain

15

Grave's dx

-low TSH, high free T3, T4
-can also check for auto-ab against the TSH receptor (Thyroid stimulating immunoglobulin)
-diffuse enlargement and diffuse increased uptake upon scan

16

What else might you see with Grave's disease?

Grave's ophthalmopathy (thyroid eye disease)
-inflammation, mononuclear cell infiltration, collagen and glycosaminoglycans between EOM, edematous changes and fluid behind eyes: protrudes the globes

-Pretibial myxedema

17

Treatment of Grave's Disease

Medications
Antithyroid drugs (methimazole, propylthiouracil), methimazole preferred over PTU in most cases- Inhibit synthesis of thyroid hormone
Beta blockers- Reduce systemic hyperadrenergic symptoms and effects (primarily tremor, palpitations, etc.)

Radioactive Iodine (131I)

Surgery

18

Destructive thyroiditis

ex:
subacute/granulomatous thyroiditis
postpartum thyroiditis

When high T4 phase:
may need Beta blockers
In high TSH phase:
may need LT4 bridge (levothyroxine T4)

19

Dx of hypothyroidism

overt:
high TSH
low free T4

subclinical:
high TSH
normal free T4
(small decrease in free T4 = large increase in TSH)

20

Sx of hypothyroidism

mental slowness
weight gain
decreased appetite
fatigue (in both hyper/hypo)
muscle cramps
cold intolerance

21

Primary hypothyroidism

Chronic autoimmune (Hashimoto’s) thyroiditis

Transient hypothyroidism:
Silent or postpartum thyroiditis
Subacute or granulomatous thyroiditis

Iatrogenic:
Thyroid surgery/thyroidectomy
Radioactive iodine
External neck irradiation

Iodine deficiency or excess

Drugs:
Antithyroid drugs, lithium, amiodarone, tyrosine kinase inhibitors, iron, cholestyramine, phenytoin, carbamazepine

Infiltrative diseases:
Hemochromatosis, sarcoidosis, amyloidosis, fibrous (Reidel’s) thyroiditis, scleroderma

Infections:
M. tuberculosis, P. carinii

Congenital

22

Central Hypothyroidism (secondary or tertiary)

-pituitary tumor
-trauma
-postpartum pituitary necrosis (Sheehan's syndrome)
-hypophysitis
-Craniopharyngiomas
-radiation therapy
-infiltrative disease
-TSH or TRH resistance

23

Hashimoto's thyroiditis

thyroid autoantibodies:
TPO (thryoid peroxidase)
Tg (thyroglobulin)

24

Rate of developing hypothyroidism

-pts with elevated TSH and positive thyroid ab develop hypothyroidism at rate of 5%/yr
-TPO ab alone: 2%/yr

25

When to treat and what is used

-with TSH greater than 10mIU/L (normal 0.4-4)
-Controversial to tx b/t 5-10

Treat w/ Levothyroxine-- synthetic T4
Goal: 1-2.5 mU/L

26

Myxedema coma

-endocrine emergency
-severe/extreme form of hypothyroidism
-Decreased cardiac output, bradycardia, respiratory depression, edema, altered mental status, hypothermia, metabolic derangements
High mortality rate