7. Thyroid disease

Question 1

How do TSH and free T4/T3 levels relate to thyroid activity?

Answer 1

Hypothyroidism

• increseased TSH
• decreased free T4/T3

Hyperthyroidism

• decreased TSH
• increased free T4/T3

Question 2

What is a goitre and what are the 3 types?

Answer 2

Swelling of the thyroid gland:

1. diffuse
2. multinodular
3. single nodule

Question 3

What is the prevalence of goitre in UK?

Answer 3

1% males

7% females - oestrogen/progesterone ratio affects thyroid function

Question 4

At which stages in life can physiological goitre (normal thyroid function) occur at?

Answer 4

• menarche
• pregnancy
• menopause

Question 5

What is the most common cause of goitre globally?

Answer 5

Iodine deficiency: reduced thyroxine levels… increased TSH… generalised thyroid enlargement (usually nodular).

Severe cases can become hypothyroid.

Question 6

What is the most common cause of goitre in the UK?

Answer 6

Multinodular goitre

• affects 5% of Western pops.
• 7x more common in women
• aetiology unknown

Question 7

What is the thyroid function in multinodular goitre?

Answer 7

normal, though very small no. may develop hyperthyroidism after many years (toxic multinodular goitre).

Question 8

Why is iodine deficiency a particular concern during pregnancy?

Answer 8

If mother is iodine deficient and hypothyroid then the foetus is also iodine deficient.
Leads to cretinism:
- mental retardation
- abnormal gait
- deaf-mutism
- short stature
- goitre
- hypothyroidism

Question 9

Name a possible complication of multinodular goitres.

Answer 9

may enlarge inferiorly into superior mediastinum to form a retrosternal goitre - may cause tracheal compression and respiratory problems (inspiration stridor)

Question 10

Name a 3rd possible cause for goitre (without metabolic dysfunction). How does this present and what is the prognosis?

Answer 10

thyroid cancer (<1% of all cancers in UK)

• don’t cause metabolic disturbance
• present as thyroid nodule
• prognosis is excellent - 97% cure rate

Question 11

Name some hypothyroidism symptoms.

Answer 11

1- lethargy
2- weight gain
3- intolerance to cold
4- bradychardia
5- constipation
6- dry skin
7- hair loss (alopecia), esp. outer 1/3 of eyebrows
8- myoedema (puffy eyes, face, hands and feet) and associated carpal tunnel syndrome symptoms
9- hoarse voice
10- memory problems, depression, psychosis (myxoedema medness)
11- menorrhagia

Question 12

Name some signs of hypothyroidism.

Answer 12

1. weight gain
2. dry skin, coarse brittle hair, loss of outer 1/3 of eyebrows
3. pallor - ‘peaches and cream’ face
4. coarse facial features and periorbital puffiness
5. bradycardia
6. hyporeflexia with delayed relaxation
7. non-pitting oedema - myxoedema - around eyes, hands and feet
8. ascites or pericardial effusion (both uncommon)

Question 13

Why does myxoedema occur in hypothyroidism?

Answer 13

deposition of mucopolysaccharides

Question 14

What is the main cause of hypothyroidism?

Answer 14

Hashimoto’s disease (autoimmune destruction of thyroid follicles) - antibodies to thyroglobulin and thyroid peroxidase are present in blood

10x more frequent in women

Question 15

Is Hashimoto’s disease associated with goitre?

Answer 15

may be associated in early stages with a small diffuse goitre (due to inflammation)

Question 16

Apart from autoimmunity, name possible causes for hypothyroidism.

Answer 16

1. severe iodine deficiency
2. post-surgical removal of thyroid with inadequate thyroxine replacement
3. TRH or TSH deficiency

Question 17

What is the treatment for hypothyroidism?

Answer 17

Oral thyroxine (longer 1/2 life) - adjust dose to normalise serum TSH

Question 18

What is the difference between hyperthyroidism and thyrotoxicosis?

Answer 18

Hyperthyroidism = thyrotoxicosis due to over production of thyroxine by thyroid gland

Question 19

What are the symptoms of thyrotoxicosis?

Answer 19

1. weight loss in spite of increased appetite and increased bowel movement/diarrhoea
2. irritability, anxiety, insomnia
3. heat intolerance, sweating warm vasodilated hands
4. tachycardia and palpitations
5. fatigue, weakness esp. of proximal muscles (buttocks and thighs)
6. amenorrhea

Question 20

Name some signs of thyrotoxicosis.

Answer 20

1. weight loss
2. warm sweaty hands
3. fine hand tremor
4. tachycardia, atrial fibrillation
5. bounding pulse - wide pulse pressure
6. proximal myopathy
7. lid lag and staring eyes

Question 21

Why are lid lag and staring eyes signs of thyrotoxicosis?

Answer 21

Lids controlled by levator palpebrae superioris muscle (90% skeletal muscle and 10% smooth muscle) - SM portion supplied by sympathetic nervous system.
Overstimulation of sympathetic portion causes signs.

Question 22

Suggests possible causes for hyperthyroidism. Which is the most common?

Answer 22

1. Graves’ disease (most common)
2. Toxic multinodular goitre
3. Toxic adenoma (benign tumour causing overactivation)
4. Ectopic thyroid tissue

Question 23

What is Graves’ disease?

Answer 23

Autoimmune disease resulting in hyperthyroidism. Caused by production of thyroid stimulating immunoglobulin (TSI) which continually stimulates TSH receptor and thyroid hormone secretion outside normal negative feedback control.

Question 24

Which features are unique to Graves’ disease in addition to the symptoms of thyrotoxicosis?

Answer 24

1. exopthalmos - bulging of eyes anteriorly out of orbit

2. pre-tibial myxoedema (5% of Ps)

Question 25

What are the treatment options for thyrotoxicosis?

Answer 25

1. carbimazole - pro-drug converted to methimazole in body - prevents thyroid peroxidase from coupling and iodinating the tyrosine residues on thyroglobulin, thereby reducing T4 production 2. thyroidectomy - surgical excision of thyroid 3. ablative dose of radioactive iodine

Question 26

Which drug can affect thyroid function? Explain why.

Answer 26

Anti-arrhythmic drug AMIODARONE - similar structure to thyroxine so can affect thyroid function (can cause hypo- or hyperthyroidism)