Hypothyroidism

Question 1

What is hypothyroidism?

Answer 1

Abnormally low activity of the thyroid gland, resulting in retardation of growth and mental development in children and adults.

Question 2

What types of people is hypothyroidism most common in?

Answer 2

Hypothyroidism is more common in women than men.

It is much more common in young women than young men, but as men get older, they start to catch up.

Hypothyroidism is common in Caucasians and Asians.

African-Americans are at lower risk.

Question 3

What hormones does the thyroid gland produce?

Answer 3

The thyroid gland uses iodine from food to make two thyroid hormones: triiodothyronine (T3) and thyroxine (T4).

Levothyroxine is a synthetic version of T4.

Question 4

What are the symptoms of hypothyroidism?

Answer 4

Fatigue.
Increased sensitivity to cold.
Constipation.
Dry skin.
Weight gain.
Puffy face.
Hoarseness.
Muscle weakness.

Question 5

What are the causes of hypothyroidism?

Answer 5

The most common cause of hypothyroidism is an autoimmune disorder known as Hashimoto’s thyroiditis.
Iodine deficiency.
Over-response to hyperthyroidism treatment.
Thyroid surgery.
Radiation therapy.
Medications.

Question 6

How does radioactive iodine cause hypothyroidism?

Answer 6

Intended cause.
Used to treat hyperthyroidism.

The radioactive iodine often kills an excessive amount of thyroid cells, leaving the thyroid unable to produce enough hormones.

Question 7

How does amiodarone cause hypothyroidism?

Answer 7

Unintended cause.

Contains high level of iodine in its molecular structure, this has an inhibitiry effect on T4 synthesis - Wolf-Chaikoff effect.

Regular thyroid function test should be carried out before starting amiodarone and whilst taking.

Question 8

How does lithium cause hypothyroidism?

Answer 8

Inhibits synthesis of T3 and T4.

Inhibits release of T3 and T4 from thyroid gland.

Lithium is concentrated by the thyroid and inhibits thyroidal iodine uptake. It also inhibits iodotyrosine coupling, alters thyroglobulin structure, and inhibits thyroid hormone secretion.

Regular thyroid function test should be carried out before starting lithium and whilst taking.

Question 9

How does thionamides cause hypothyroidism?

Answer 9

Used to treat hyperthyroidism.

Designed to reduce synthesis of T3 and T4.

However, it could cause a hypothyroid state - adjust dose or give levothyroxine.

Question 10

How would you diagnose hypothyroidism?

Answer 10

Carry out thyroid function tests.

T4 test: This is done to measure the blood level of the hormone T4 (thyroxine).

TSH test: A thyroid stimulating hormone (TSH) test can help tell how well the thyroid is working.

T3 total test: The T3 total test measures the other major thyroid hormone in the blood.

TPOAb test: A TPO test detects antibodies against TPO in the blood.

Question 11

What are the aims of treatment​?

Answer 11

Get rid of the symptoms.

Get thyroid function tests to the normal ranges.

Question 12

How would you treat hypothyroidism?

Answer 12

Give levothyroxine or liothyronine.

Levothyroxine is a synthetic version of T4.
Liothyronine is a synthetic version of T3.

Question 13

Which groups of patients need special consideration and why?

Answer 13

Those with cardiovascular diseases.

Thyroxine affects heart rate, if thyroxine levels increase too fast so does heart rate.

Could lead to a heart attack.

Those with diabetes.

Levothyroxine can aslo increase blood-sugar levels.

Question 14

What are cautions when giving levothyroxine?

Answer 14

Elderly​.
Pre existing CV disorders​.
Diabetes mellitus​.

Question 15

What are some adverse drug reactions of levothyroxine?

Answer 15

Diarrhoea​.
Angina, palpitations, tachycardia. ​
Weight loss​.

Question 16

What are the drug interactions of levothyroxine?

Answer 16

Ferrous sulphate affect T4 levels: affects absorption of T4 from the GI tract. T4 level decreases and TSH level increases. This can be managed by spacing doses at least 2 hours apart.

​Phenytoin affect T4 levels​: phenytion is an enzyme inducer, it lowers the level of T4. It does this by increasing the metabolism of T4 in the liver. T4 level decreases and TSH level increases. This can be managed by increasing the dose of T4.

Question 17

How do thyroid hormones affect warfarin?

Answer 17

Enhance anticoagulant effect of warfarin.
Levothyroxine increases metabolism of clotting factors. There is less clotting, higher risk of bleeding.
This can be managed by reducing the dose of warfarin.

Question 18

What are the prescribing aspects of levothyroxine​?

Answer 18

Should be taken in the morning on an empty stomach. Wait for an hour after taking and then have breakfast.

If taken with food - erratic absoption of levothyroxine unsteady blood level.

Takes a few weeks for symptoms to go away.

Blood tests should be carried out every 6 weeks.