Thyroid disorders

Question 1

How can we classify thyroid disorders?

Answer 1

Based on symptoms

Based on causes

Question 2

Why is classification of thyroid disorders based on symptoms not useful?

Answer 2

Tells us nothing about the mechanism of the disease

Solely whether it is hyperthyroidism or hypothyroidism

Question 3

What are possible causes of thyroid disorders?

Answer 3

Iodide deficiency

Autoimmunity

Neoplasia - thyroid cancer/ nodule formation

Question 4

What is the most common cause of thyroid disorders?

Answer 4

Iodide deficienct

Affects 2.7% of the population

Easily treated - add dietary salt or supplementation

Most common in underdeveloped areas

Question 5

What is the consequence of iodide deficiency?

Answer 5

Enlarged thyroid gland -> goitre

Question 6

What gland regulates TH synthesis?

Answer 6

Pituitary

Question 7

What hormone regulates TH synthesis?

Answer 7

TSH

Question 8

What happens when TH are larger than required?

Answer 8

Negative feedback loop

TH send negative feedback to the hypothalamus pituitary axis to decrease TSH release

Question 9

What happens to TH synthesis in iodide deficiency?

Answer 9

Low T3 and T4 means negative feedback loop is compromised

Has long-term and short-term effects

1. Short-term effect: TSH release T3 and T4 from gland stores
2. Long-term effects: TSH enhances proliferation of thyroid cells = enlargement of thyroid gland and formation of goitre

Question 10

What is the compensatory mechanism for formation of a goitre?

Answer 10

Ensures the gland absorbs all iodine from the circulation

Question 11

What is a multinodular goitre?

Answer 11

Over time the large thyroid can develop nodules

Question 12

What two autoimmune diseases affect the thyroid?

Answer 12

Grave’s disease

Thyroiditis

Question 13

How do Thyroiditis and Grave’s differ?

Answer 13

Thyroiditis = autoantigens formed against the thyroid - leads to destruction and inflammation of the gland. Decreased TH levels

Grave’s = autoantigens are complementary for TSH receptors on gland. Increased TH levels.

Question 14

Pathogenesis of thyroiditis

Answer 14

Destruction of thyroid gland by inflammatory cells

Antibodies against thyroid gland taget the cells

Infiltration of inflammatory cells - neutrophils and macrophages

Secretion of inflammatory mediators - induce damage to the thyroid cells

Inflammation and destruction of thyroid gland

Question 15

What does Thyroiditis cause?

Answer 15

Hypothyroidism

Question 16

Pathogenesis of Grave’s disease

Answer 16

Formation of autoantibodies targeted against TSH receptor

Agonist to TSH and causes release og T3 and T4

Question 17

What does Grave’s cause?

Answer 17

Hyperthyroidism

Question 18

What are symptoms of Grave’s?

Answer 18

Exophthalmos

Fat tissue in the eyes express TSH receptors

Proliferation of the cells in the orbit upon activation

Question 19

Treatment of Hypothyroidism

Answer 19

Thyroxine structure is simple - easy to synthesise synthetically

Injection of supplements

Question 20

Treatment of Hyperthyroidism

Answer 20

More complicated

1. Inhibition of TH synthesis by inhibition of TPO
2. Ablation - if the patient doesn’t respond to pharmacological inhibition
3. Surgical or radioactive iodine