7- General Thyroid Disorders

Question 1

Describe the thyroid

Answer 1

• It is located in the neck and is shield shaped
• It has a left lobe, right lobe and an ISTHMUS in the middle
• Some people have a PYRAMIDAL LOBE which is part of the extension from the
back of the tongue from which the thyroid originated
• The thyroid moves up and down when you swallow
• PARATHYROID GLANDS are found embedded at the four corners of the thyroid
• The parathyroid glands are involved in the control of calcium

Question 2

How does the thyroid develop

Answer 2

Origin: midline outpouching of the floor of the pharynx (base of the tongue is the origin)
• Outpouching forms a duct which elongates down - THYROGLOSSAL DUCT
• It migrates down the neck and divides into TWO LOBES
• The thyroid will be in its final position by WEEK 7
• Usually the thyroglossal duct disappears leaving only a dimple at the back of
the tongue called the foramen caecum
• The thyroid gland then develops

Question 3

What are 3 problems in thyroid development

Answer 3

AGENESIS
Complete absence of the thyroid
• INCOMPLETE DESCENT
It may not descend to the correct point in the neck
This can cause problems with delivery
• THYROGLOSSAL CYST
The thyroglossal duct may persist
Cysts may form - presenting as a lump years later

Question 4

What is cretinism

Answer 4

IQ is much lower than normal
• Stunted growth
Due to lack of thyroxine

Question 5

How is cretinism prevented

Answer 5

All babies have a HEEL-PRICK TEST to acquire blood to test thyroid function
(measuring TSH)
• This is done at the same time as the Guthrie Test for Phenylketonuria
• Carried out at 5-10 days
• The test isn’t done immediately after birth because the neonate may have the
mother’s thyroxine
• Thyroxine is given immediately if TSH is found to be abnormally HIGH

Question 6

Describe primary thyroid failure (myxoedema)

Answer 6

Autoimmune damage to the thyroid is the most common cause of myxoedema
• Thyroidectomy can also cause myxoedema (obviously) because thyroid tissue is
removed
• Thyroxine levels decline
• TSH level rise - to try and stimulate the production of more thyroxine
• Eventually TSH levels will fall as it becomes exhausted

Question 7

Describe the Hypothalamo-pituitary-thyroidal axis

Answer 7

• Thyroxine will have a direct negative feedback effect on the pituitary to inhibit production of more TSH
• It will also have an effect on the hypothalamus where it’ll inhibit the production of TRH
• These negative feedback loops make sure that blood thyroxine concentration hardly changes

Question 8

Describe features of primary hypothyroidism

Answer 8

EVERYTHING SLOWS DOWN
• Deepening voice
• Depression and tiredness
• Cold intolerance
• Weight gain with reduced
appetite
• Constipation (bowels slow
down)
• Bradycardia
• Eventual myxoedema coma
(brain stops functioning due to lack of thyroxine)
• Amenorrhoea may occur in late disease
• Heart enlargement - as it isn't pumping properly

Question 9

How is hypothyroidism treated

Answer 9

Otherwise death
• Rise in cholesterol - increased risk of death from heart attacks and strokes
• Treatment involves giving thyroxine daily
• Monitor TSH and adjust dose of thyroxine until TSH is normal

Question 10

Describe hyperthyroidism

Answer 10

Make too much thyroxine
• TSH falls to zero - because there is no need to stimulate the production of
thyroxine
• Can be referred to as thyrotoxicosis or hyperthyroidism
• Features of hyperthyroidism:
Make too much thyroxine Raised basal metabolic rate Raised temperature
Burn up calories and lose weight Increased heart rate
EVERYTHING SPEEDS UP

Question 11

Describe the clinical features of hyperthyroidism

Answer 11

Myopathy
• Mood swings
• Feeling hot in all weather
• Diarrhoea
• Increased appetite but weight loss
• Tremor of hands
• Palpitations
• Sore eyes, goitre

Question 12

Describe Graves’ disease

Answer 12

GRAVES’ DISEASE - the whole gland is smoothly enlarged and the whole gland is overactive
• Graves’ disease triggers hyperthyroidism because the immune system produces an antibody which pretends to be TSH
• The antibody binds to the TSH receptor and the thyroid gland becomes overactive
• This can lead to enlargement of the thyroid forming a goitre
• Other antibodies bind to muscles behind the eye which pushes the eye
forwards and causes EXOPHTHALMOS (also known as proptosis)
• Other antibodies stimulate the growth of soft tissue on the shin and causes
PRETIBIAL MYXOEDEMA (hypertrophy)