MEDEX Objectives Home: http://faculty.washington.edu/alexbert/MEDEX/

1. Iodine is necessary for the synthesis of thyroid hormone.† Iodine+Tyrosine=T1,†

if 2Iodines+Tyrosine=T2, if you combine T1 + T2= T3. Martini p.610

2. TRH(hypothalamus) -> Ant. Pit. And tells it to release TSH-> TSH goes to the Thyroid and makes T4-> T4 goes to the liver gives up an Iodine and becomes active T3.

Negative Loop- Hypothalmus monitors T3 and T4 levels when there is enough it stops secreting TRH (Thyrotropine releasing hormone) Noble 843 and Patho Made easy.

3.† T4- Thyroxine- Major thyroid hormone.† T4 is the precursor to T3.

††††† T3- Triiodothyronine- Major thyroid hormone.† Is the most active form.

Class notes and CMDT p. 1082

4.† Over 99% of thyroid hormone is bound to a protein, either TBG(thyroid binding globulin) or albumin.† The UNBOUND thyroid hormone is considered active.

T4 is 99.97%† bound to protein (inactive) and T3 is only 99.70% bound to protein.† Therefore T3 is more abundant in the active form. Mosby p. 445-446, Patho made easy.

The Test

Description

T4RIA

Measures TOTAL serum T4.† ^hyperthyroid, ↓ hypothroid

Free T4

Direct measurement of free T4.† Used to check thyroid funx if a pt has a† protein abnormality and monitors replacement and suppressive therapies.

T3 Resin Uptake

Used indirect measure of T4 and thyroid binding proteins.†

^T4=^ T3 resin uptake, ↓ T4= ↓ T3 resin uptake.† So, T3 will want to bind to protein, however if the proteins are saturated with T4 they will take 2nd best by binding to the resin.† And if there is a high T3 resin uptake then the proteins are full and there is a lot of T4.

T3RIA

Measures TOTAL T3 (bound and unbound). Mosby p. 458.† Used to dx hyperthyroid, especially when T4 is ^.† Adjustment using the resin uptake estimates free fraction.

Free Thyroid index

Refects the unbound hormone. Active parts of T3 and T4.†

FTI= T4 X T3Resin Uptake.† Dx hyper or hypo.†

TSH

Dx primary hypothyroidism and or differentiate from 2ndary hypothyroidism.† ^TSH=thyroid dsfunx. ↓ TSH = pituitary, hypothalamus or a TSH secreting tumor.

Antithyroid antibodies

Measures antibodies that can cause thyroid dz. (Hashimotosís, Graves dz and lyphoctic thyroiditis).

Thyroglobulin

Serum level rises in autoimmune dz, thyroid injury/inflammation.† Also used to measure reoccurance of cancer in someone who has had their thyroid removed.

Thyroid radioiodine uptake and scanning

High uptake- thyroxicosis gland overactivity(notes)

Low uptake- thyroiditis or extraglandular hormone.(notes)

-Give then check with gyger counter, most useful in hyper or ^uptake of iodine.† Scanning- differentiates diffuse v. focal overactivity in thyrotoxicosis.† Defines cold warm or hot nodules and the size of the gland including substernal extension. (notes). Useful in neck or substernal mass, thyroid nodule, hyperthyroidism- Graves v. Plummers, metastatic tumors without known primary site, and well differentiated forms of thyroid cancers (Mosby 790-793)

Ultrasound

Useful to determine solid or cyst, guide fine needle aspirations, and surveillance of tumors. (notes, CMDT 1085)

Fine Needle Aspiration

Benign v. malignant (notes, CMDT 1085)

6. US- Autoimmune cause of majority of hypothyroidism. 2nd most common is treatment of†††††††† hyperthyroidism.

††† Worldwide- Lack of Iodine is the major cause. (noble 845)

7. Hashimotoís- Autoimmune thryoiditis that causes hypothyroidism and goiter. In adults.(Noble 845)

8. Cretinism- Congenital condition causing mental retardation and growth delay from lack hypothyroidism. In kids. (notes)

HYPOTHYROIDISM (Noble 848)† When emergent = Myedema

S/S

>50%- Weakness, fatigue, lethargy, Cold intolerance, dry skin or decreased sweating, hair loss, inability to concentrate, memory loss, constipation, weight gain, dyspnea, peripheral paresthesia.† Course skin, cold skin, pallor of skin, course hair, periorbital edema, hoarseness, goiter, non-pitting edema, myedema.† Delayed relaxation of DTRís

 

<50%- Depression, anorexia, muscle cramps, muscular skeletal px, arthralgias, infertility, menorrhagia, anovulation, carpal tunnel syndrome and reduced hearing.† Slow speech, sleep apnea, joint effusions, hypothermia, HTN, hypoventilation, macroglossia, myopathy, cardiomegaly.

TX

Levothyroxine- T4 is the treatment of choice. ***Dose can be ^ q 1-3 wks(Noble)

every 6wks (Dr.Tims notes????) until pt is euthyroid.

Adult- 50-100 ug qd

Pregnant- 100-150 ug qd

Elderly and CV dz- 25-50 ug qd.

MYXEDEMA- is a rare syndrome that represents severe long standing hypothyroidism. Medical emergency.† Clinical Features-Hypothermia, resp. depression, unconsciousness, bradycardia, macroglossia, delayed DRTís and dry rough skin.† ^CPK, ^LDH, acidosis, anemia. LP= ^opening pressure and ^proteins. (noble 848)

NOTES LABS FINDINGS-

Primary-† ^TSH, decreased free T4. Caused by atrophy (autoimmune), post thyroidectomy, RAI tx, lithium, amiodarone.

Secondary- decreased free T4, but may also have a nml or decreased TSH (Pituitary problems sooo also check out the adrenals)

HYPERTHYROIDISM- When emergent = Throid Storm (CMDT 1098-1099)

12. Graves dz is the most common cause of hyperthyroidism and is autoimmune.† Occurs in younger people and can lead to Thyroid Storm. OPTHALOPATHY s/s, pos. thytoid antibodies.

Toxic Adenoma- Plummers Dz is a single nodule NO OPTHALMOPATHY s/s

Multi nodule- NO OPTHAL s/s. usually older pt, NOT autoimmune no antibodies are present. s/s dyphagia, and dyspnea, Afib, decreased TSH and ^ thyroid hormone.†

Subacute Thyroisitis- usually viral, tender thyroid or non-tender= silent thyroiditis.

†hyperthyroid->hypothyroid. RAI uptake is LOW.

TSH Hypersecretion by the pituitary- Tumor

Pregnancy-Mild gestational hyperthyroidism may occur in the first 4 months of pregnancy.

13 S/S- HYPERTHYROIDISM- (Dr. Timís notes, CMDT 1100) nervousness, restless, heat intolerance, diaphoresis, fatigue, weakness, muscle cramps, frequent BMís, wt. change usually loss, palpitations, angina, menstral irregularities.† PE- Tachy, goiter, fine tremor, thyroid bruits, A-fib, lid lag, stare, lid retraction. If not treated may cause osteoporosis.

Graves-most common in females, caused by auto antibodies interacting with the TSH receptor. ^T4, T3RIA, RIA uptake. Scan= diffuse overactivity. EYE s/s= lymphocytic infiltration causes= Opthalmopathy, chemosis, conjunctivitis, proptosis, EOM impairment. Eye involvement severity does not correlate with the severity of the hyperthyroidism.

TREATMENT

PROS

CONS

Propylthiouracil- Blocks conversion of T4 -> T3

NON invasive

Risk hypothyroidism

Methimazole- blocks iodinization of T4 -> T3

Ablates thyroid tissue

hypothyroidism

Radio active iodine RAI-definitive tx, destroys overactive thyroid tissue.† Smoking ^ opthalmopathy flare ups.

Definitive, low chance of reoccurrence of malignancy

Opthalopathy get worse in 15%† and improves in none.

Surgery- thyroidectomy

Preferred for pregnant women

invasive

THYROIDITIS- Viral infection, moderately enlarged tender thyroid.† Silent= non-tender.† RAI is LOW.† Resolves spontaneously.† May tx s/s with propanolol.

THYROID STORM- severe hyperthyroidism, rare, emergent high mortality rate.† S/S marked delirium, severe tachy, vomiting, diarrhea, dehydration, often ^^^^fever.

^T4 + ^T3= ^ epi = ^HR, ^GI, ^temp.

THYROID NODULE-

(CMDT 1087)Labs for TSH and free T4-> US-> fine needle aspiration-> scan.† Check hx of radiation exposure and be suspicious of cancer

(Dr. Tim)

Check TSH and free T4

††††††††††† Normal- aspiration-

††††††††††††††††††††††† Benign

††††††††††††††††††††††† Malignant-papillary

††††††††††††††††††††††† Insufficient

††††††††††††††††††††††† Indeterminant-follicular- Biopsy to determine if cancer or adenoma

††††††††††† High- RAI uptake and scan- then US to check for fluid and size.† US not dx for solids.

Hot- hyperfunctioning and benign.† Cold- Hypofunctioning and Cancer.