Endo 4 - Hypothyroidism

Question 1

In the thyroid, where is thyroxine and thyroglobulin stored?

Answer 1

Colloid

Question 2

What are some symptoms associated with primary hypothyroidism?

Answer 2

1. Deepening voice
2. Depression/tiredness
3. Cold intolerance
4. Weight gain w reduced appetite
5. Constipation
6. Bradycardia
7. Eventual myxoedema coma

Question 3

Thyroxine is T4. How is it converted to T3?

Answer 3

Via a deiodinase enzyme

Question 4

Where does T3 bind?

Answer 4

TRE (Thyroid response element) - alters gene expression

Question 5

What drugs are given as part of thyroid hormone replacement therapy?

Answer 5

1. Levothyroxine sodium (T4 - more common)

2. Liothyronine sodium (T3 - less common)

Question 6

When do you administer levothyroxine sodium for primary hypothyroidism?

Answer 6

If patient has primary hypothyroidism

Orally administered - TSH should come down and reference range used for dosage

Question 7

How is levothyroxine sodium used for patients with secondary hypothyroidism?

Answer 7

Orally administered.

TSH low due to APG failure

Aim for fT4 in middle of reference range

Question 8

When is liothyronine (T3) used clinically?

Answer 8

If patient has myxoedema coma (very rare complication)

Given IV, faster onset than T4.

T4 Orally given afterwards when possible

Question 9

What is difficult about combined T4/T3 therapy?

Answer 9

T3 tablets expensive, and hard to get dosage right.

Therefore, may get symptoms of toxicity e.g. palpitations etc

Question 10

What is the half life of T4 and T3?

Answer 10

Levothyroxine = 6 days

Liothyronine = 2.5 days

Question 11

T4 and T3 are bound to what protein in the blood?

Answer 11

Thyroxine Binding Globulin (TBG)

Question 12

When can TBG levels vary?

Answer 12

TBG levels increase in pregnancy and when treated with oestrogen/phenothiazines

TBG levels decrease with malnutrition and liver disease

Question 13

Graves disease is a form of hyperthyroidism. Explain how it causes hyperthyroidism

Answer 13

Autoimmune disease whereby antibodies stimulate TSH receptor in thyroid - causing goitre and hyperthyroidism

Question 14

How can Graves disease cause exophthalmos?

Answer 14

Different antibodies bind to muscles behind eye and causes them to grow, pushing the eye outwards

Question 15

3 signs of Graves disease

Answer 15

1. Goitre (enlarged thyroid gland)
2. Exophthalmos
3. Pretibial myxoedema

Question 16

What is pretibial myxoedema

Answer 16

Non pitting swelling that occurs on shins, growth of soft tissue

Question 17

MYXOEDEMA = HYPOTHYROIDISM BUT PRETIBIAL MYXOEDEMA = HYPERTHYROIDISM

Answer 17

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