7. Hypothyroidism

Question 1

Who is most likely to develop hypothyroidism?

Answer 1

Elderly women.

• Women more likely to men
• More likely as you get older

Question 2

What is the definition of hypothyroidism?

Answer 2

The inadequate output of thyroid hormones by the thyroid gland

Question 3

What are the causes of hypothyroidism?

Answer 3

• Hashimoto’s Thyroiditis
• Iodine Deficiency
• Secondary to treatment of hyperthyroidism
• Medications
• Congenital
• Central causes (eg. sheehans)
• Subclinical hypothyroidism

Question 4

What is the most common cause of hypothyroidism in the developed world?

Answer 4

Hashimotos Thyroiditis

Question 5

What is the most common cause of hypothyroidism in the developing world?

Answer 5

Iodine Deficiency

Question 6

What is Hashimotos thyroiditis?

Answer 6

It is an autoimmune condition, where there are antithyroid peroxidase and antithyroglubin antibodies.

Question 7

Who does hashimoto’s thyroiditis commonly affect?

Answer 7

It affects 10x as many women as it does men, commonly in those 40+ years of age

Question 8

How is iodine deficiency prevented?

Answer 8

It is added to foods such as table salt

Question 9

What hyperthroid treatment can lead to hypothryroidism?

Answer 9

• Carbimazole
• Prophylthiouracil
• Radioactive iodine
• Thyroid surgery

Question 10

Which medications (not used for hyperthyroidism) can cause hypothyroidism?

Answer 10

• Lithium
• Amiodarone

both of these inhibit/interfere with the production of thyroid hormones.

Question 11

What is dysgenesis of the thyroid gland?

Answer 11

This is where there is an underdeveloped thyroid gland

Question 12

What is dyshormonogenesis of the thyroid gland?

Answer 12

This is where the thyroid gland is fully developed, but not producing enough hormone

Question 13

How is congential hypothyroidism typically identified?

Answer 13

Newborns are screened for it on the newborn blood spot screening test

Question 14

What is central hypothyroidism?

Answer 14

This is when there is an issue with the anterior pituitary or hypothalmus, and it results in too little TSH being produced.

Question 15

What are the causes of central hypothyroidism?

Answer 15

• Tumours
• Infection
• Vascular
• Radiation

Question 16

Give an example of a vascular cause of central hypothyroidism?

Answer 16

Sheemans syndrome

Question 17

What is Sheemans syndrome?

Answer 17

It is a condition that affects women who lose a life-threatening amount of blood in childbirth or who have severe low blood pressure during or after childbirth, which can deprive the body of oxygen. This lack of oxygen that causes damage to the pituitary gland is known as Sheehan’s syndrome.

Question 18

How does hypothyroidism present? (ie. signs and symptoms)

Answer 18

• Weight gain
• Fluid retention (oedema, pleural effusions, ascites)
• Fatigue
• Muscle cramps
• Depression
• Memory problems and poor concentration
• Dry skin
• Coarse hair and hair loss
• Brittle nails
• A slow heart rate
• Feeling cold
• Heavy or irregular periods
• Periods of infertility (rare)
• Constipation
• Goitre (depending on the cause)

Question 19

What would a TFT appear as in someone with primary hypothyroidism?

Answer 19

TSH - High
T3 - Low
T4 - Low

Site of pathology - Thyroid gland

Question 20

What would a TFT appear as in someone with secondary hypothyroidism?

Answer 20

TSH - Low
T3 - Low
T4 - Low

Site of pathology - Pituitary gland / hypothalamus

Question 21

Is T3 or T4 the most useful in a TFT?

Answer 21

T3 is not as helpful as T4, as it is often maintained at a low-normal level

Question 22

How is hypothyroidism treated?

Answer 22

Replacement of thyroid hormone with oral levothyroxine, which is synthetic T4.

Question 23

When starting someone on levothyroxine, what do you need to do?

Answer 23

The dosage of levothyroxine given is 1.6 micrograms/kg/day orally. The dose is titrated until TSH levels are normal. It is then adjusted in increments of 12.5-25 micrograms until the TSH is normalised.

TFTs are measured monthly until stable, then it can be checked less frequently unless they become symptomatic.

Question 24

If someones TSH level is too high after starting levothyroxine, what do you need to do?

Answer 24

Increase the dose of levothyroxine

Question 25

If someones TSH level is too low after starting levothyroxine, what do you need to do?

Answer 25

You need to reduce the dosage of levothyroxine

Question 26

In which patients do you need to take extra-precautions with when starting them on levothyroxine? Why? How do we do it?

Answer 26

Elderly patients and those with known IHD or severe hypertension. This is because higher doses of thyroxine may worsen angina or precipitate myocardial infarction.

They should start on the lowest dose (25mcg daily), then increase by 25mcg every 4 weeks until it produces the desired effect.