MEH - Thyroid Dysfunction

Question 1

Where does the word ‘thyroid’ come from?

Answer 1

Greek “oval shield”

Question 2

Should a normal thyroid be felt on examination?

Answer 2

Nope

Question 3

What is the pre-tracheal fascia?

Answer 3

This attaches the thyroid gland to the trachea and larynx, meaning that the thyroid moves upwards on swallowing

Question 4

Describe briefly the embryology of the thyroid gland

Answer 4

It forms initially under the tongue, and is connected to the skin by the thyroglossal duct. It then moves down past the hyoid bone to in front of the larynx, and the thyroglossal duct closes up

Question 5

What is a thyroglossal duct cyst?

Answer 5

The thyroglossal duct usually disappears, but it may remain and form a cyst. It will always be in the anterior part of the midline of the neck. When tongue poked out, it will be drawn in

Question 6

Why can TSH levels be used as an effective screening test for hyper/hypothyroidism?

Answer 6

Very rare for pituitary adenoma to produce TSH and cause thyrotoxicosis, so 98% of metabolic thyroid disease is due to primary abnormality of thyroid gland itself.

Question 7

What does it suggest about thyroid function if TSH is raised?

Answer 7

Thyroid gland is underfunctioning (hypothyroidism)

Question 8

What does it suggest about thyroid function if free T4 is increased?

Answer 8

It is over-functioning (hyperthyroidism)

Question 9

Why is there a wide range of acceptable values for TRH, TSH and T4?

Answer 9

They are constantly responding to the environment

Question 10

Are autoimmune endocrine diseases more common in women or men?

Answer 10

Women - we don’t know why

Question 11

What are the three goitre structures?

Answer 11

• diffuse
• multinodular
• single nodule

Question 12

Give three points in a woman’s life at which physiological goitre may occur

Answer 12

• menarche
• pregnancy
• menopause

Question 13

How does iodine deficiency cause goitre?

Answer 13

Reduced thyroxine levels lead to increased TSH, which causes generalised thyroid enlargement, usually nodular

Question 14

What is multinodular goitre?

Answer 14

Condition of unknown cause which affects 5% of western populations. Normal thyroid function at first, although after many years some may develop hyperthyroidism

Question 15

What would be the symptoms in a child with iodine deficiency?

Answer 15

• intellectual disability
• abnormal gait
• deaf-mutism
• short stature
• goitre
• hypothyroidism

Question 16

What is a retrosternal multinodular goitre?

Answer 16

A multinodular goitre may enlarge inferiorly into the superior mediastinum to form a retrosternal goitre. This can cause tracheal compression

Question 17

What is myxoedema?

Answer 17

Non-pitting oedema due to deposition of mucopolysaccharides around eyes, hands and feet.

Question 18

What can cause hypothyroidism?

Answer 18

• autoimmune destruction of the thyroid (Hashimoto’s disease)
• severe iodine deficiency
• post-surgical removal of the thyroid

Question 19

How is hypothyroidism treated?

Answer 19

Oral thyroxine

Question 20

Give some clinical signs of thyrotoxicosis

Answer 20

• weight loss
• warm, sweaty hands
• fine hand tremor
• tachycardia/atrial fibrillation
• bounding pulse
• proximal myopathy
• lid lag
• staring eyes

Question 21

Why do staring eyes occur in thyrotoxicosis?

Answer 21

The levator palpebrae superioris muscle is 90% skeletal muscle and 10% smooth muscle - this smooth muscle is supplied by the sympathetic nervous system. Over stimulation of this leads to staring eyes and lid lag

Question 22

Give some causes of thyrotoxicosis due to hyperthyroidism

Answer 22

• Graves’ disease
• toxic multinodular goitre
• toxic adenoma

Question 23

What is Graves’ disease?

Answer 23

An autoimmune condition affecting the thyroid. Thyroid stimulating immunoglobulin (TSI) attaches to and stimulates the TSH receptor. This causes symptoms of thyrotoxicosis with additional symptoms of exophthalmos and pre-tibial myxoedema

Question 24

How is thyrotoxicosis treated?

Answer 24

• carbimazole, which prevents thyroid peroxidase coupling and iodinating the tyrosine residues on thyroglobulin, reducing production of T4
• surgical excision of thyroid
• ablative dose of radioactive iodine

Question 25

How do thyroid cancer present?

Answer 25

As a thyroid nodule - they do not cause either hyper- or hypothyroidism

Question 26

Which conditions can cause goitre but no metabolic dysfunction?

Answer 26

• multinodular goitre
• iodine deficiency
• thyroid cancer

Question 27

Which conditions can cause metabolic dysfunction without goitre?

Answer 27

Hashimoto’s disease in some cases