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Y3 - Endocrine and metabolic > Hypothyroidism > Flashcards

Hypothyroidism Flashcards

1
Q

What is hypothyroidism?

A

Insufficient production of thyroid hormones, T3 and T4

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2
Q

What is primary hypothyroidism?

A

where the thyroid gland itself produces inadequate thyroid hormones and without negative feedback there is increased production of TSH from the pituitary

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3
Q

Are the TSH levels high or low in primary hypothyroidism?

A

high

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4
Q

What is secondary hypothyroidism?

A

where the pituitary gland produces inadequate TSH, resulting in under stimulation of the thyroid gland and insufficient T3 and T4

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5
Q

What is the prevalence of hypothyroidism in the UK?

A

Prevalence in the UK is about 1% in women, but only 0.1% in men.
Lifetime risk is actually higher – about 9% for women and 1% for men.
The mean age of diagnosis is about 60.

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6
Q

What is the normal thyroid physiology?

A
  1. The hypothalamus first releases thyrotropin releasing hormone
  2. The pituitary produces thyroid stimulating hormone (TSH) in response to this, and in response to feedback loops from T4 and T3

3.TSH acts upon the thyroid gland to stimulate it to produce thyroid hormones
T4
T3 – only about 25% of the circulating T3 is produced by the thyroid gland. The rest is produced in the tissues by converting T4 to T3
This is why when we replace thyroid hormone we only need to give T4 – as T3 is subsequently produced by the metabolism of T4 to T3

  1. These thyroid hormones circulate in the blood, and act on the peripheral tissue to cause a wide variety of effects – mainly related to metabolism
  2. They also act as a feedback loop to the hypothalamus – which can then adjust the amount of TSH that is produced in response to this
    Under normal control, the thyroid gland responds to the ‘signal’ of the TSH, to alter its production of T3 and T4 relative to the bodies needs
    In thyroid disease, the production of T3 and T4 becomes “uncoupled” from the production of TSH
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7
Q

What are the causes of primary hypothyroidism?

A
  1. Autoimmune diseases eg Autoimmune lymphocytic thyroiditis
  2. Congenital
  3. Defects in hormone synthesis
  4. Infective
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8
Q

What are 3 causes of secondary hypothyroidism?

A
  1. Hypopituitarism (Produces isolated TSH deficiency)
  2. Post Surgery - Post irritation (eg radiotherapy iodine therapy, external neck irradiation)
  3. Peripheral resistance to thyroid hormone
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9
Q

What is the most common form of primary hypothyroidism in the Western world?

A

Hashimoto’s thyroiditis

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10
Q

What is Hashimoto’s thyroiditis?

A

autoimmune destruction of the thyroid gland

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11
Q

What happens in Hashimoto’s disease?

A

Anti-thyroid peroxidase antibodies (anti-TPO) attack the thyroid gland, impairing the gland’s ability to produce thyroid hormones.

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12
Q

Who is Hashimoto’s disease most popular in?

A

It is most common in women aged 30 to 50 and is four to ten times more common in women than men

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13
Q

Who is more likely to develop autoimmune thyroiditis?

A

Individuals with other autoimmune conditions, such as diabetes and rheumatoid arthritis

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14
Q

Name two antibodies associated with Hashimoto’s thyroiditis:

A

1) anti-thyroid peroxidase (anti-TPO)
2) anti-thyroglobulin (anti-Tg)

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15
Q

What is the most common cause of primary hypothyroidism in the developing world?

A

iodine deficiency

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16
Q

In which type of food is iodine found abundantly?

A

Diary

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17
Q

Give 4 causes of primary hyperthyroidism:

A

1) Hashimoto’s thyroiditis
2) iodine deficiency
3) treatment of hyperthyroidism
4) medications

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18
Q

How does treatment of hyperthyroidism cause hypothyroidism?

A

Treatment of hyperthyroidism or thyroid cancer can cause hypothyroidism because radioactive iodine or medications used in treatment interfere with the body’s ability to make thyroid hormones. Surgical removal of the thyroid gland leads to a lack of thyroid hormone production.

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19
Q

What is atrophic hypothyroidism?

A

It is the result of T-cell mediated auto-reactive cytotoxicity against follicular cells
it is thought that the antibodies may block TSH receptors and that this results in the hypothyroidism.

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20
Q

What is the main difference between atrophic hypothyroidism and Hashimoto’s disease?

A

The main difference between this and atrophic hypothyroidism, is that atrophic hypothyroidism does not cause goitre, but that Hashimoto’s can do.

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21
Q

How can hypothyroidism cause Goitre>

A

The condition causes an enlarged thyroid (goitre). The enlargement is due to infiltration of the thyroid with lymphocytes, and resultant fibrosis.

The thyroid usually becomes firm and rubbery but this is not always the case – it can be anywhere from soft to hard.

There will be massive lymphocytic infiltrate into the thyroid, and there will be varying destruction of tissue. Often there will be no colloid. The remaining cells will have an increased concentration of mitochondria. There will be varying degrees of fibrosis. With thyroxine replacement, the goitre will usually disappear

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22
Q

How can a goitre be cause by a lack of iodine?

A

The goitre is caused by a continuing underlying iodine deficiency, that will ultimately stimulate TSH production, and thus result in thyroid enlargement to compensate for the low levels of iodine.

23
Q

What is congenital hypothyroidism due to?

A

60% of cases are due to thyroid aplasia or hypoplasia
30% of cases are due to ectopic tissue
10% of cases are due to dyshormonogenesis

24
Q

What is dyshormonogenesis?

A

Thyroid dyshormonogenesis is a rare condition due to genetic defects in the synthesis of thyroid hormones.

It is due to either deficiency of thyroid enzymes, inability to concentrate, or ineffective binding.

25
Q

Give 2 hyperthyroid medications that can cause hypothyroidism:

A

1) carbimazole
2) propylthiouracil

26
Q

Give two hyperthyroid interventions that can cause hypothyroidism:

A

1) radioactive iodine
2) thyroid surgery

27
Q

Name two drugs that cause hypothyroidism:

A

1) lithium (bipolar)
2) amiodarone (anti-arrhythmic)

28
Q

True or false: amiodarone can cause both hypothyroidism and thyrotoxicosis

A

true

29
Q

Give 5 causes of secondary hypothyroidism:

A

1) tumours (pituitary adenomas)
2) surgery to the pituitary
3) radiotherapy of the brain
4) trauma
5) Sheehan’s syndrome

30
Q

What is Sheehan’s syndrome?

A

where a major post-partum haemorrhage causes avascular necrosis of the pituitary gland

31
Q

Give 7 clinical presentations associated with hypothyroidism:

A

1) weight gain
2) fatigue
3) dry skin
4) coarse hair and hair loss
5) fluid retention (oedema, ascites, pleural effusion)
6) heavy and irregular periods
7) constipation

32
Q

What examination sign is associated with iodine deficiency?

A

goitre

33
Q

What examination sign is associated with Hashimoto’s thyroiditis?

A

initially a goitre followed by atrophy of the thyroid gland

34
Q

How is the nervous system affected in hypothyroidism?

A

Headache
Sluggish reflexes
Parasethesia
Cerebellar ataxia
Carpal tunnel syndrome

35
Q

How is the cognitive system affected in hypothyroidism?

A

Poor memory / mental slowness
Depression
Reduced attention span

36
Q

How is the cardiovascular system affected by hypothyroidism?

A

Bradycardia – slow heart beat (<60bpm)
Peripheral oedema
Decreased exercise tolerance
Hypertension

37
Q

How is the GI system affected by hypothyroidism?

A

Poor appetite – especially when in combination with weight gain
Constipation

38
Q

How is the reproductive system affected by hypothyroidism?

A

Poor libido
Menorrhagia or oligomenorrhoea
Infertility

39
Q

What is the main diagnostic test for hypothyroidism?

A

Thyroid stimulating hormone (TSH) is the main diagnostic test. A high TSH suggests hypothyroidism – the diagnosis is then usually confirmed with a T4 level. Together, TSH and T4 are often referred to as Thyroid function tests (TFTs).

40
Q

What results would indicate hypothyroidism in a TSH test?

A

TSH raised >10 on two separate occasions = overt hypothyroidism
TSH >2.5 AND T4 low = overt hypothyroidism
TSH 2.5 – 10 with normal T4 – subclinical hypothyroidism

41
Q

What are the risk factors for hypothyroidism?

A

A family history of hypothyroidism
Pregnancy in the last six months
Autoimmune diseases such as type 1 or 2 diabetes, coeliac disease and rheumatoid arthritis
Previous thyroid surgery or treatment with radioactive iodine
Radiation treatment to the head, neck or thorax

42
Q

What are important areas to include in the history for hypothyroidism?

A

Obstetric history: current or recent pregnancy
Drug history: to identify any drugs which may cause hypothyroidism (e.g. lithium)
Past medical history: history of other autoimmune conditions (e.g. rheumatoid arthritis)
Family history: thyroid or autoimmune disease

43
Q

Name 5 typical clinical findings of hypothyroidism upon examination.

A

Dry skin
Bradycardia
Cold peripheries
Stiff muscles
Hair loss

44
Q

What is Hertoghe’s sign?

A

Hertoghe’s sign (also called Queen Anne’s sign), the loss of the outer third of the eyebrow, is a rare sign of hypothyroidism

45
Q

What would a TFT test show in a hypothyroid patient?

A

hyroid function blood tests, including TSH, free T3 and free T4, should be performed when investigating potential thyroid conditions. In hypothyroidism, these tests will show a low free T3 and low free T4.

In primary hypothyroidism, the HPT axis will attempt to correct the deficiency, resulting in a raised TSH. However, in secondary causes, this will be low or normal due to reduced pituitary production of TSH

46
Q

What anti-body can be tested for to aid the identification of autoimmune thyroid conditions?

A

anti-thyroid peroxidase (anti-TPO)

TPO antibodies are found in 90% of people with Hashimoto’s thyroiditis. However, they may also be present in Grave’s thyrotoxicosis.

47
Q

What imaging can be used to investigate hypothyroidism?

A

Doppler ultrasound can visualise the thyroid gland to assess for nodules and/or infiltrative disease.

48
Q

What is the first line management for hypothyroidism?

A

oral levothyroxine (synthetic version of T4 that is metabolised into T3 in the body)

49
Q

High TSH while taking levothyroxine indicates what change to the dosage?

A

increase dose

50
Q

Low TSH while taking levothyroxine indicates what change to the dosage?

A

decrease dose

51
Q

What medication can be given to those who cannot tolerate levothyroxine? (rarely used)

A

liothyronine sodium (synthetic version of T3)

52
Q

What are the side effects of treatment for hypothyroidism?

A

Palpitations and atrial fibrillation
Diarrhoea
Increase appetite
Anxiety
Insomnia
Tremors

There is an association with other autoimmune diseases, particularly:
Pernicious anaemia
Addison’s disease

53
Q

What is myoxedema?

A

Myxedema coma is a life-threatening complication in which breathing slows, seizures occur, and blood flow to the brain decreases. Myxedema coma can be triggered in a person with hypothyroidism by physical stresses, such as exposure to the cold, as well as by an infection, injury, surgery, and medications such as sedatives that depress brain function.

If untreated, hypothyroidism can eventually cause anemia, a low body temperature, and heart failure. This situation may progress to confusion, stupor, or coma (myxedema coma).

Y3 - Endocrine and metabolic (20 decks)

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