Thyroid disease

Question 1

What enzyme converts T4 to T3?

Answer 1

Type 1 or 2 Deiodinase

Question 2

Type 3 deiodinase

Answer 2

Removes iodine from T3 and makes reverse T3 (inactive)

Question 3

What types of things can inhibit Type 1 or 2 Deiodinase?

Answer 3

T4 cannot be converted to T3

1. Starvation
2. Severe illness
3. Severe stress
4. Neonatal period

Question 4

Half life of T4 and T3

Answer 4

T4: 7 days
T3: 1 day

Question 5

Causes of increase total T3 and T4

Answer 5

1. Hyperthyroidism/Thyrotoxicosis
2. Increased binding proteins
   - Estrogen: acts on liver and stim TBG and albumin production - binds more T3 and T4
3. Thyroid H resistance

Question 6

Causes of decreased total T4 and T3

Answer 6

1. Hypothyroidism
2. Decreased serum protein binding
3. Euthyroid sick syndrome
4. Drugs
5. Liver or kidney disease

Question 7

TSH nl range

Answer 7

0.4-4.0

Question 8

Thyroid hormone axis

Answer 8

D2, T4–>T3, at hypothalamus secretes TRH –>
Ant pit secretes TSH –>
Thyroid releases T3 + T4

Question 9

TSH significance

• when is it elevated?
• when is it suppressed?

Answer 9

1. Single best test to screen for thyroid dysfxn
2. Indicates indiv. TH “set points”
3. TSH stimulates Iodine uptake into thyroid follicular cells and TH production

Elevated: in primary HYPOthyroidism
Suppressed: in primary HYPERthyroidism

Question 10

Sx of hyperthyroidism

Answer 10

1. Nervousness
2. Weight loss
3. Increased appetite
4. Fatigue
5. Tremor
6. Heat intolerance

other:
- Palpitations, hyperdefecation, trouble sleeping, diaphoresis

Question 11

Which should you not order? TSH, Free T4, Free T3

Answer 11

Free T3

Question 12

Thyrotoxicosis

• What
• TSH, free T4 + T3 levels
• Two causes

Answer 12

High circulating lvls of TH (various causes)
Serum TSH is low
Free T4 and total T3 are elevated

Overproduction of T4+T3: suggestive of hyperthyroidism

High release of PREFORMED T4 and T3:
no true hyperthyroidism

Question 13

If TSH is suppressed, should the thyroid gland take up Radioactive iodine?

Answer 13

no - if it does, it indicates HYPER thyroidism

TSH is low: no stimulus to take up iodine

Question 14

TSH fxn

Answer 14

stimulates the thyroid to take up iodine

and

synthesize T4 and T3

Question 15

In thyrotoxicosis, should TSH be high or low?

Answer 15

Low: the hypothalamus and pit “sense” elevated T4 and T4 and secretion of TRH and TSH is suppressed

• if TSH is suppressed, there should be no uptake of iodine

Question 16

A nl or elevated Iodine uptake in the setting of a LOW TSH indicates:

Answer 16

indicates autonomous production of thyroid hormone

- true hyperthyroid state

Question 17

If the uptake of iodine is low in the setting of a low TSH (appropriately so), what could TH excess be due to?

Answer 17

High release of preformed TH

Question 18

Low uptake Hyperthyroidism

Answer 18

1. Subacute thyroiditis
   - granulomatous thyroiditis (viral)
2. Chronic lymphocytic thyroiditis
3. Radiation-induced thyroiditis
4. Infectious thyroiditis
5. Drug induced thyroiditis
6. Ectopic thyrotoxicosis

Question 19

High uptake hyperthyroidism

Answer 19

1. Thyrotropin receptor antibody
   - Graves
2. Thyroid autonomy
   - toxic adenoma
   - toxic multinodular goiter (MNG)
3. HCG
4. TSH

Question 20

Graves disease has ______ autoantibodies against the TSH receptor

Answer 20

Thyroid stimulating Immunoglobulin

–> causes high uptake Hyperthyroiditis

Question 21

Common locations for Graves disease findings

Answer 21

Due to deposition of glycosaminoglycan behind eyes and in dermis over shins

1. Opthalmopathy
2. Pretibial Myxedema

Question 22

Treatment for Graves disease

Answer 22

1. drugs:
   - Antithyroid H drugs: methimazole, propylthiouracil
   - Beta blockers: reduce systemic hyperadrenergic symptoms and effects
2. Radioactive Iodine
3. Surgery

Question 23

How do you determine the cause of thyrotoxicosis if there is no true TH production?

Answer 23

If pt has thyroid autoimmune damage –> release a ton of preformed TH –>
Body senses and drops TSH levels –>
Body reaches thyrotoxic phase
- antithyroid drugs done work since it inhibits TH SYNTHESIS, (not the case here)

Eventually T4 levels fall –>
Body senses and increases TSH –>
Body cant make more T4 –> Hypothyroid phase

Question 24

Symp of hypothyroidism

Answer 24

1. mental slowness
2. weight gain
3. decreased appetite
4. Fatigue a (non specific)
5. muscle cramp
6. cold intolerance

Question 25

Etiology of hypothyroidism

Answer 25

1. Chronic autoimmune (Hasimoto's) thyroiditis 2. Transient hypothyroidism 3. Iatrogenic 4. Pituitary tumor (secondary)

Question 26

Hashimoto's Thyroiditis : thyroid autoantibodies

Answer 26

1. TPO (thyroid peroxidase) | 2. Tg (thyroglobulin)

Question 27

How to treat a pt with a TSH >10 mIU/L?

Answer 27

Nl TSH is 0.4-4.0 So treat with levothyroxine (synthetic T4) --> body (-) feedbacks and reduces TSH