General Thyroid disorders

Question 1

Describe the basic anatomy of the thyroid gland

Answer 1

It is shield-shaped.
Located in the neck
Highly vascular.
Two lobes (left and right) joined by a narrow band of tissue called the isthmus.
SOME people may have a small pyramidal lobe joining the isthmus.

Question 2

What happens to the thyroid gland when you swallow

Answer 2

It moves up and down

Question 3

What is a risk of surgery on the thyroid gland

Answer 3

Thyroid surgery could sever the recurrent laryngeal nerve resulting in altered speech.
Important

Question 4

Where are the parathyroid glands found

Answer 4

Parathyroid glands are found embedded at the 4 corners of the thyroid and are involved in the control of calcium.
They are functionally distinct to the thyroid gland

Question 5

Describe the embryological development of the thyroid .

Answer 5

The thyroid develops embryologically as a midline outgrowth from the developing floor of the pharynx (base of the tongue) around the fourth week of pregnancy.
This outgrowth forms a duct (thyroglossal duct), as it develops caudally forming two lobes as it comes into contact with the fourth pharyngeal pouch to which it fuses.
The thyroid will be in its final position by week 7.
Normally, the anterior part of the thyroglossal duct is lost but its site of origin can be identified as the foramen caecum, a small dimple medially located on the base of the tongue.
The thyroid gland then develops.

Question 6

What is the origin of the thyroid gland

Answer 6

The base of the tongue

Question 7

Why do some people have a pyramidal lobe

Answer 7

SOME people have a pyramidal lobe which is part of the extension from the back of the tongue from which the thyroid gland originated. The caudal part of this duct becomes the pyramidal lobe.

Question 8

Where is the foramen caecum

Answer 8

Dimple at the back of the tongue (left by the disappearing thyroglossal duct).

Question 9

Describe the dimensions of the thyroid gland

Answer 9

Adult weight = 20 grams

Each lobe = 4 x 2.5 x 2.5 cm

Right lobe larger than left

Question 10

How many lobes does the thyroid gland have

Answer 10

4

Question 11

Why may a baby have a lump in their throat

Answer 11

Enlarged pyramidal lobe.

Question 12

What are the 4 lobes of the thyroid

Answer 12

Right, left, isthmus and pyramidal

Question 13

What can you feel

Answer 13

The thyroid cartilage, in tumours, the cartilage can be moved away.

Question 14

What important nerve runs close to the thyroid gland and what does it supply

Answer 14

The recurrent laryngeal nerve that innervates the larynx, allowing speech.
Its

Question 15

Describe the blood supply of the thyroid

Answer 15

Blood reaches the gland via two main sources. The superior thyroid arteries which branch off the external carotid arteries, terminating in the upper parts of each lobe. The inferior thyroidal arteries which come off the subclavian artery and provide blood for the lower parts of each lobe.
Venous blood form the superior and middle thyroid veins drains into the internal jugular, while venous blood form the inferior veins enter the left brachiocephalic vein.

Question 16

What is meant by agenesis

Answer 16

Complete absence of the thyroid.

Question 17

What is meant by incomplete descent of the thyroid

Answer 17

– Gland does not descend to the correct point in the neck. o Can cause problems during delivery.
o Some people may have a lingual thyroid – Thyroid tissue barely descends and remains close to the back of the tongue which causes problems with breathing. ▪

Question 18

What is a thyroglossal cyst

Answer 18

– Persisting thyroglossal duct can promote cyst formation.

Question 19

Describe the procedure you should take with the thyroglossal cyst

Answer 19

Check they have a fully functioning thyroid gland before removing the cyst. This can be done by ultrasound.
A cyst is a fluid containing round thing which may present later as a lump.

Question 20

Describe the importance of thyroxine in brain development

Answer 20

Neonates with thyroxine deficiency in utero have irreversible brain damage :

CRETIN

Question 21

What is cretinism

Answer 21

An individual with irreversible brain damage caused by a lack of Thyroxine

Question 22

What are the features of cretinism

Answer 22

▪ IQ much lower than normal. ▪ Stunted growth.

Question 23

How can we prevent cretinism

Answer 23

▪ Babies have thyroid function measured using the Heel-Prick Test (measure blood borne TSH). ▪ Test done at the same time as the Guthrie test for phenylketonuria. ▪ Carried out at 5-10 days old - can’t be done immediately as baby may have mother’s thyroxine- thyroxine can cross the placenta.

Question 24

Why is every cell affected by thyroxine

Answer 24

Thyroid follicular cells control thyroxine synthesis which affects basal metabolic rate so every cell is affected by thyroxine. Controls appetite in gastrointestinal tract.

Question 25

Why does the colloid stain pink

Answer 25

Due to the presence of thyroglobulin.

Question 26

What does the presence of white spots indicate

Answer 26

That the follicular cell is active. Proteolytic enzymes are being secreted to break down stored thyroglobulin to release thyroxine into the blood vessels (shown as a pinkish red).

Question 27

What is the function of the thyroid gland

Answer 27

▪ Responsible for the synthesis, storage and secretion of thyroid hormones. ▪ Thyroid hormones regulate growth, development and basal metabolic rate. It is analogous to the clock function on a computer- controls how ‘fast’ all the cells in the body work.

Question 28

Describe the difference between thyroglobulin and thyroxine binding globulin

Answer 28

Thyroglobulin is not thyroxine binding globulin

Thyroxine binding globulin bonds 75% of thyroxine in the circulation whereas thyroglobulin is INSIDE the thyroid gland only.

Question 29

Describe the epidemiology of thyroid disease

Answer 29

Affects 5% of the population

Female : male ratio = 4 : 1
(Much more common in females)

Overactive : underactive = 1 : 1

Question 30

Why are females more likely to suffer from thyroid disease

Answer 30

Thyroid disorders are most commonly caused by autoimmune diseases. In females, who have a more labile immune system, as to prevent rejection of the foetus, are likely to recognise their own cells as foreign.

Question 31

Describe Primary Hypothyroidism(Myxoedema)

Answer 31

When the cause is due to the thyroid gland itself failing, this is known as primary hypothyroidism, It can be caused by autoimmune damage to the thyroid or due to damage to the thyroid during surgery, Circulating levels of thyroxine fall, and in an attempt to compensate for this, TSH levels increase.

Question 32

What does a lack of thyroxine result in

Answer 32

Lack of thyroxine causes HIGH TSH and HIGH TRH. Only TSH is measured because TRH is only present at VERY low concentrations in the blood ( in an attempt to stimulate the production of thyroxine).
The basal metabolic rate of the patient decreases, and the patient slows down, physically and mentally. Utilisation of energy therefore falls, and patients lose their appetite and eat less. However, as BMR falls, patients put on weight despite losing their appetite. As a result patients present with tiredness, lethargy and feeling cold.

Question 33

Describe the differences between TRH and TSH

Answer 33

TRH = thyrotropin releasing hormone

TSH = Thyroid stimulating hormone (thyrotropin)

Question 34

What are the features of primary hypothyroidism

Answer 34

▪ Deepening Voice ( lower rate of vibrations of cartilage) ▪ Depression and fatigue. ▪ Cold intolerance. ▪ Weight gain with reduced appetite. ▪ Constipation (bowl’s metabolic rate reduction). ▪ Bradycardia. ▪ Eventual myxoedema coma (brain stops functioning due to lack of thyroxine). ▪ Amenorrhoea may occur late in the disease. ▪ Heart enlargement (hypertrophy due to malpumping).

Question 35

Explain how it is possible for the thyroid gland to become enlarged in primary hypothyroidism

Answer 35

In primary hypothyroidism it is possible for the thyroid gland to become enlarged (goitre) because the low circulating T3 and T4 exert a reduced negative feedback on the hypothalamo-adenohypophysial axis, with subsequent increase in TSH production by the anterior pituitary. This TSH excessively stimulates the follicular cells which can cause hypertrophy.

Question 36

How do we diagnose primary hypothyroidism

Answer 36

Finding a low level of thyroxine (T4) in the circulation at the same time as a raised level of TSH.

Question 37

Describe myxoedema coma

Answer 37

If the diagnosis of primary hypothyroidism is not considered for several years, the condition worsens until the patient loses consciousness. This is a myxoedema coma, a condition with high mortality if not treated. Common in elderly patients who have no relatives, or in residential homes, the staff may put the patient’s confusion down to dementia.

Question 38

Why is treatment of hypothyroidism essential

Answer 38

The consequences of no treatment include DEATH and a RISE IN CHOLESTEROL (thus an increased risk of death from heart attacks and strokes). The patient will also perform poorly.

Question 39

Why do cholesterol levels increase

Answer 39

Because BMR goes down.

Question 40

How do we treat primary hypothyroidism

Answer 40

Simply replace thyroxine - usually one tablet (100 micrograms on average) daily

Monitor the TSH and adjust dose until TSH is normal

Question 41

Particular for patients who have suffered from a myxoedema coma, why is it important that we don’t give large doses of thyroxine to begin with

Answer 41

A sudden normalisation of the free T3 may cause a sudden tachycardia, which may precipitate cardiac disease and ischaemia. We need to make changes GRADUALLY.

Question 42

What are some of the causes of neonatal hypothyroidism

Answer 42

Absent thyroid
Ectopic thyroid
Biochemical defect- enzyme deficiency in thyroxine synthesis. For example a congenital deficiency in deiodinase, an enzyme important in the recycling of iodine within the follicular cells.
Iodine deficiency- endemic cretinism.

Question 43

What is meant by hyperthyroidism

Answer 43

Excess production of thyroxine, also known as thyrotoxicosis. TSH falls to zero and there is no need to stimulate the production of thyroxine.

Question 44

Describe the features of an overactive thyroid gland

Answer 44

Make too much thyroxine

Raised basal metabolic rate
Raised temperature
Burn up calories and lose weight- due to excessive calorie uptake in metabolism.
Increased heart rate
Every cell in the body speeds up

Question 45

What are the clinical features of hyperthyroidism

Answer 45

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

Question 46

Describe grave’s disease

Answer 46

Graves’ disease, where the whole gland is smoothly enlarged and the whole gland is overactive

Question 47

In Grave’s disease, what will a scan of the thyroid show

Answer 47

Because the whole thyroid gland is active, an uptake scan will show increased uptake of iodine in all areas of the thyroid. The scan is known as a scintgram

Question 48

What is Grave’s disease caused by

Answer 48

Autoimmune
Antibodies bind to and stimulate the TSH receptor in the thyroid
Causing hyperthyroidism.
Another antibody can bind to the same receptor but cause hypertrophy, why patient presents with goitre and hyperthyroidism.

Question 49

Describe the action of other antibodies in hyperthyroidism

Answer 49

Another antibody binds to and stimulates growth receptors behind the eye, which cause muscle hypertrophy. These are responsible for the appearance of exophthalmos (the forward protrusion of the eyeballs), sometimes called proptosis.
Another antibody binds to and stimulates growth factor receptors at the front of the shin, causing pretibial myxoedema,
These antibodies can present in any order, although, commonly, the hyperthyroidism antibodies appear first.

Question 50

How else can we diagnose grave’s disease

Answer 50

Detecting anti-TSH receptor antibodies in the presence of hyperthyroidism.

Question 51

What is pretibial myxoedema

Answer 51

▪ A skin condition where swelling (non-pitting) occurs in the shins of patients. ▪ This is caused by the growth of soft tissue. ▪ This is different to myxoedema (which means hypothyroidism).