3 - Thyroid

Question 1

What’s the difference between T3 and T4?

Answer 1

T3 has three iodine atoms and is much more potent

T4 has four

Question 2

Levothyroxine is T___

Answer 2

T4

Question 3

Thyroid hormones have three principal actions:

Answer 3

1. Stimulation of energy use
2. stimulation of the heart
3. promotion of growth and development

Question 4

What is the purpose of T4 and T3?

Answer 4

T3 exerts practically all of the effects of thyroid hormone

T4 only serves as a source of T3 in the tissues

Question 5

How does T3 exert its effects?

Answer 5

Penetrates the nuclear membrane and binds with nuclear receptors, which in turn bind to specific DNA sequences

Results in increased production of the proteins associated with thyroid activation

Question 6

Why does iodine deficiency cause goiters?

Answer 6

The drop in thyroid hormone production promotes release of TSH, which hypertrophies the thyroid in an attempt to increase secretion

Question 7

What is the most sensitive method of detecting hypothyroidism?

Answer 7

TSH levels

The anterior pituitary is EXQUISITELY sensitive to changes in thyroid levels

Question 8

In primary hypothyroidism, TSH should be ______

In secondary hypothyroidism, TSH should be ______

Answer 8

Primary (thyroid problem): High

Secondary (AP problem): Low

Question 9

What is myxedema?

Answer 9

A severe level of hypothyroidism

Question 10

SKIN

HYPO AND HYPER

Answer 10

Hypo: Cold and Dry, har is brittle with hair loss

Hyper: Warm and Moist, with heat intolerance

Question 11

CARDIAC

HYPER AND HYPO

Answer 11

Hypo: Bradycardia, Hypotension

Hyper: Tachycardia, Hypertension

Question 12

In countries where iodine deficiency is rare, what is the primary cause of hypothyroidism?

Answer 12

Hashimoto Thyroiditis - an autoimmune disease

Question 13

What are the primary deficits a neonate of a mother with hypothyroidism will most likely develop?

Answer 13

Thyroid hormones are primarily responsible for neurological and skeletal mm development

Children will have neuropsychological issues and stunted growth

Question 14

When women taking thyroid supplements get pregnant, what should happen to their synthroid dose?

Answer 14

It should be increased, often by as much as 50%

Question 15

When are the effects of maternal hypothyroidism on the fetus the highest?

Answer 15

During the first trimester

Once the baby’s thyroid is developed, it can make its own thyroid hormone

Question 16

With untreated congenital hypothyroidism, how will a child appear?

Answer 16

Large and protruding tongue

potbelly

dwarfish stature

Question 17

In children who have hypothyroidism, how long do they require treatment?

Answer 17

After three years, we stop replacement therapy for four weeks and see what happens

If thyroid levels drop, it’s permanent and they’ll require lifelong treatment

Question 18

There are two major forms of hyperthyroidism:

Answer 18

Grave’s Disease

Plummer Disease

Question 19

What is plummer disease?

Answer 19

toxic nodular goiter (much less common than Grave’s disease)

It’s caused by a thyroid adenoma

Question 20

What are some physical characteristics that can help determine whether hyperthyroidism is caused by Plummer disease or Graves Disease?

Answer 20

Exophthalmos that’s seen in Grave’s disease is due to an immune reaction, not to thyroid hormone levels

A patient with Plummer disease will not have exophthalmos

Question 21

What symptoms are associated with Graves Disease?

Answer 21

Thyrotoxicosis

Exophthalmos

Question 22

What are the symptoms of thyrotoxicosis?

Answer 22

Increased appetite with weight loss (increased BMR)

nervousness, insomnia, rapid thoughts, rapid speech

Skeletal mm may weaken and atrophy

Question 23

Thyroid stimulation in Graves Disease is caused by:

Answer 23

Thyroid Stimulating Immunoglobulins (TSIs), which mimic the effects of TSH

by stimulating receptors for TSH on the thyroid gland

Question 24

What is the preferred treatment for adult hyperthyroidism?

Pediatric hyperthyroidism?

Answer 24

Adult: Radiation

Pediatric: Antithyroid drugs

Question 25

In hyperthyroidism, which two types of drugs may be used as adjunct to main therapy?

Answer 25

Beta blockers (suppress cardiac effects)

Nonradioactive iodine (inhibits the synthesis and release of thyroid hormones)

Question 26

Describe the manifestations of a Thyrotoxic Crisis (Thyroid Storm)

Answer 26

Profound Hyperthermia (105 degrees)

Severe tachycardia

Restlessness/Agitation/Tremor

Unconsciousness

Question 27

What three medications are given during a thyrotoxic crisis?

Answer 27

1. Potassium iodide (suppresses thyroid release)
2. Methimazole (suppresses thyroid synthesis)
3. Beta blocker (prevents imminent death)
4. Will also need cooling, steroids, and IV fluids

Question 28

Should synthroid be taken with food?

Answer 28

No. Decreases absorption.

Question 29

Why do we give T4 instead of T3?

Answer 29

It gets converted to T3 in the tissues anyway, and the preparation works a lot better

Question 30

How long does it take for Levothyroxine to start working?

Answer 30

Since it has a half life of a week, it takes about a month to reach a steady state

Question 31

Levothyroxine has a _____ therapeutic index

Answer 31

Narrow

Question 32

How does ¹³¹I work?

Answer 32

It’s a radioactive isotope that emits beta particles and gamma rays

The iodine travels to the thyroid and the beta particles destroy thyroid tissue, but they really don’t travel anywhere else in the body so no other tissues are harmed

Question 33

What is the biggest complication of using ¹³¹I?

Answer 33

Delayed hypothyroidism due to excessive damage

Occurs in up to 90% of patients within the first year

Question 34

When is ¹³¹I absolutely contrainidicated?

Answer 34

Pregnancy and Lactation

Can damage the developing thyroid in the fetus

Question 35

What is Lugol solution?

Answer 35

“Strong Iodine”

5% elemental iodine and 10% potassium Iodide

Question 36

Why does a strong iodine solution reduce thyroid function?

Answer 36

When present in high concentrations, iodide has a paradoxical suppressive effect on the thyroid

The iodide competes with iodine and slows release of thyroid hormone

It really only works short term, because the body gets wise, so it’s only used in emergency situation

Question 37

There are two times with Lugol solution is used:

Answer 37

Thyrotoxic Crisis

Before thyroidectomy, to prevent massive release of thyroid during the operation