Hypothyroidism

Question 1

Define hypothyroidism.

Answer 1

Underproduction of T3 and T4.

Question 2

What are the main 2 causes of hypothyroidism?

Answer 2

95% of cases are due to primary hypothyroidism - a failure of the thyroid gland to produce thyroid hormones.

5% of cases are due to secondary hypothyroidism - underproduction of TSH by the pituitary gland.

Question 3

What is the epidemiology of hypothyroidism?

Answer 3

· More common in women.
· More prevalent in white people.
· Prevalence increases with age.

Question 4

What is the pathophysiology of hypothyroidism?

Answer 4

· T4 is the main hormone produced by the thyroid gland.

· It’s converted to T3 in target tissues.

· T3 mediates the main actions of TSH.

· Failure of the thyroid to produce T4 and T3 stimulates the pituitary to increase production of TSH.

· Autoimmune thyroiditis:

• Thyroid is diffusely infiltrated with lymphocytes.
• Majority of patients have antithyroid peroxidase (95%) or anti-thyroglobulin (60%) antibodies.

· Affected individuals have an increased risk of other autoimmune disorders such as vitiligo and Sjogren’s syndrome.

Question 5

What are the 5 main aetiologies of hypothyroidism?

Answer 5

1. Autoimmune thyroiditis (Hashimoto’s disease).
2. Damage/destruction of the thyroid gland from.
3. Infiltrative diseases.
4. Drugs.
5. Pituitary disorders.

Question 6

Who does Hashimoto’s disease affect?

Answer 6

· Affects women 8-9 times more often as men.

· Peak incidence between ages of 30-50.

Question 7

What is the most common aetiology of primary hypothyroidism?

Answer 7

Autoimmune thyroiditis (Hashimoto’s disease).

Question 8

What happens in Hashimoto’s disease?

Answer 8

Body considers thethyroidantigens as foreign&raquo_space;> lymphocytic infiltration and destruction of thyroid tissue.

Question 9

What can cause damage/destruction of the thyroid gland?

Answer 9

· Thyroidectomy.
· Radioactive iodine therapy for Graves’ disease or nodular goitre.
· Radiotherapy for head and neck cancer.

Question 10

What infiltrative diseases can cause hypothyroidism?

Answer 10

· Sarcoidosis.

· Haemochromotosis.

Question 11

What drugs can cause hypothyroidism?

Answer 11

· Lithium - interferes with thyroid hormone secretion.
· Amiodarone - contains iodine.
· Interferon alpha.
· Tyrosine kinase inhibitors.

Question 12

List the potential risk factors of hypothyroidism.

Answer 12

· Iodine deficiency - particularly in the developing world. 
· Female. 
· Middle age. 
· FHx of autoimmune thyroiditis. 
· Autoimmune disorders. 
· Graves' disease. 
· Radiotherapy.

Question 13

What are the typical presenting signs and symptoms?

Answer 13

· Non-specific weakness. 
· Lethargy/Tiredness. 
· Cold sensitivity. 
· Constipation.
· Weight gain.
· Depression. 
· Constipation. 

· Menstrual irregularity - heavier period. 
· Myalgia. 
· Dry skin. 
· Eyelid oedema. 
· Thick tongue. 
· Facial oedema. 
· Bradycardia. 
· Delayed relaxation of tendon reflexes.

Question 14

What investigations would help you to diagnose hypothyroidism?

Answer 14

· Serum TSH - Elevated.
· Free serum T4 - Low.
· Antithyroid peroxidase antibodies.

Question 15

Suggest some differentials.

Answer 15

· Central or secondary hypothyroidism.

· Depression.

Question 16

What is the treatment for confirmed primary hypothyroidism?

Answer 16

· Healthy aged <60 years - Levothyroxine.

· Pre-existing CAD or aged >60 years - Low-dose levothyroxine.

Question 17

What is the treatment for sub-clinical hypothyroidism with TSH >1?

Answer 17

Low-dose levothyroxine.

Question 18

What complications may arise?

Answer 18

· Angina. Can occur with high initial dose of levothyroxine in patients with CAD.
· AF. Can occur with over-treatment.
· Osteoporosis. Can occur with over-treatment.
· Myxoedema come - rare, severe form of hypothyroidism with multi-organ failure.
· Complications in pregnancy.