Hypothyroidism

Question 1

What are some causes of hypothyroidism?

Answer 1

Hashimoto’s Thyroiditis
Iodine Deficiency 
Secondary to Hyperthyroidism treatment
Medications
Secondary Hypothyroidism

Question 2

What is Hashimoto’s Thyroiditis?

Answer 2

This is the most common causes of hypothyroidism in the developed world. It is caused by autoimmune inflammation of the thyroid gland. It is associated with antithyroid peroxidase (anti-TPO) antibodies and antithyroglobulin antibodies. Initially it causes a goitre after which there is atrophy of the thyroid gland.

Question 3

What antibodies are associated with Hashimoto’s Thyroiditis?

Answer 3

antithyroid peroxidase (anti-TPO) antibodies

Question 4

Where is Iodine Deficiency the most common cause of hypothyroidism?

Answer 4

the developing world (where iodine is not added to salt, cereal etc)

Question 5

What hyperthyroidism treatments cause hypothyroidism?

Answer 5

Carbimazole
Prophylthiouracil
Radioactive iodine
Thyroid surgery

Question 6

What medications can cause hypothyroidism (not hyperthyroid medications)?

Answer 6

Lithium inhibits the production of thyroid hormones in the thyroid gland and can cause a goitre and hypothyroidism.

Amiodarone interferes with thyroid hormone production and metabolism, usually causing hypothyroidism but it can also cause thyrotoxicosis.

Question 7

What is Secondary Hypothyroidism?

Answer 7

This is where the pituitary gland is failing to produce enough TSH. This is often associated with a lack of other pituitary hormones such as ACTH. This is called hypopituitarism

Question 8

What are causes of Secondary Hypothyroidism?

Answer 8

Tumours
Infection
Vascular (e.g. Sheehan Syndrome pituitary insufficiency following birth)
Radiation

Question 9

How does hypothyroidism present?

Answer 9

Weight gain
Fatigue
Dry skin
Coarse hair and hair loss
Fluid retention (oedema, pleural effusions, ascites)
Amenorrhoea
Constipation
Proximal myopathy

Question 10

What is Primary Hypothyroidism?

Answer 10

Thyroid gland insufficiency.

Question 11

How does primary hypothyroidism present hormonally?

Answer 11

Thyroid hormones (i.e. free T3 and T4) will be low. TSH will be high because there is no negative feedback to the brain, so the pituitary produces lots of TSH to try and get the thyroid working.

Question 12

What is Secondary Hypothyroidism?

Answer 12

Secondary Hypothyroidism is caused by pituitary pathology that results in low production of TSH.

Question 13

How does secondary hypothyroidism present hormonally?

Answer 13

Thyroid hormones will be low due to the low TSH.

Question 14

How to manage hypothyroidism?

Answer 14

Replacement of thyroid hormone with oral levothyroxine is the treatment of hypothyroidism.

Levothyroxine is synthetic T4, and metabolises to T3 in the body. The dose is titrated until TSH levels are normal. When starting levothyroxine, initially measure TSH levels monthly until stable, then once stable it can be checked less frequently unless they become symptomatic.

If the TSH level is high, the dose is too low and needs to be increased. If the TSH is low, the dose is too high and needs to be reduced.