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.0.0 RSP Endocrine > [4] Hypothyroidism > Flashcards

[4] Hypothyroidism Flashcards

1
Q

What is hypothyroidism?

A

The clinical effect of a lack of thyroid hormone

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2
Q

What is the prognosis of hypothyroidism?

A

If treated, the prognosis is excellent, however if untreated it can be disastrous

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3
Q

What can hypothyroidism cause if untreated?

A
  • Heart disease
  • Dementia
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4
Q

Why is hypothyroidism not always picked up?

A

Because it is insidious in onset

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5
Q

What is the result of hypothyroidism having an insidious onset?

A

Should be alert to subtle, non-specific symptoms, especially in women over 40 years old

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6
Q

What is the ratio of men to women in hypothyroidism?

A

1:6

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7
Q

What is the importance of thyroid hormone?

A

It is required for normal functioning of numerous tissues in the body

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8
Q

What does the thyroid gland secrete in healthy individuals?

A

Predominantly thyroxine (T4)

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9
Q

What happens to T4 in the body?

A

It is converted to T3 in other organs by selenium-dependant enzymes

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10
Q

What does T3 do?

A
  • T3 binds to thyroid hormone receptor in the nucleus of cells
  • Binds to receptors on cell membrane
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11
Q

What happens when T3 binds to thyroid hormone receptor in the nucleus of cells?

A

It stimulates the turning on of particular genes, and the production of specific proteins

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12
Q

What happens when T3 binds to receptors in the cell membrane?

A

It stimulates processes such as the formation of blood vessels and cell growth

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13
Q

How is thyroid hormone found in the blood?

A

Almost all thyroid hormone is bound to plasma proteins such as thyroxine-binding globulin in the blood

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14
Q

Is all thyroid hormone biologically active?

A

Only in the unbound form

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15
Q

Other than the thyroid gland, what are the other sources of thyroid hormone in the body?

A

None

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16
Q

What does the process of production of thyroid hormone require?

A
  • Iodine
  • The amino acid tyrosine
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17
Q

How is iodine made into thyroid hormone?

A

Iodine in the bloodstream is taken up by the thyroid gland and incorporated into thyroglobulin molecules

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18
Q

What controls the process of thyroid hormone production?

A

TSH

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19
Q

What secretes TSH?

A

Pituitary

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20
Q

What pathway in the body plays a key role in maintaining thyroid hormone levels within normal limits?

A

Hypothalamic-pituitary-thyroid axis (HPT)

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21
Q

How does the HPT axis play a key role in maintaining thyroid hormone levels within normal limits?

A

Production of TSH by the anterior pituitary gland is stimulated by thyrotropin-releasing hormone (TRH), released from the hypothalamus. Production of TSH and TRH is decreased by thyroxine by a negative feedback process.

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22
Q

What changes in thyroid hormone physiology does pregnancy cause?

A
  • Thyroxine gland increases in size by 10%
  • Thyroxine production is increased by 50%
  • Iodine requirements are increased
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23
Q

What are the causes of primary hypothyroidism?

A
  • Primary atrophic hypothyroidism
  • Hashimoto’s thyroiditis
  • Iodine deficiency
  • Drug-induced, including anti-thyroid drugs, lithium, or iodine
  • Subacute thyroiditis
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24
Q

Is primary atrophic hypothyroidism a common condition?

A

Yes

25
Q

What is the ratio of men to women affected by primary atrophic hypothyroidism?

A

1:6

26
Q

What happens in primary atrophic hypothyroidism?

A

There is diffuse lymphocytic infiltration of the thyroid, leading to atrophy

27
Q

Is there a goitre in primary atropic hypothyroidism?

A

No (because there is atrophy)

28
Q

Who is Hashimoto’s thyroiditis more common in?

A

Women aged 60-70

29
Q

Do you get a goitre in Hashimoto’s thyroiditis?

A

Yes

30
Q

Why do you get a goitre in Hashimoto’s thyroiditis?

A

Due to lymphocytic and plasma cell infiltration

31
Q

What kind of thyroid pathology can be caused by Hashimoto’s thyroiditis?

A

Can be hypothyroid or euthyroid. Rarely, there will be an initial period of hyperthyroidism

32
Q

What is an initial period of hyperthyroidism called in Hashimoto’s thyroiditis?

A

Hashitoxicosis

33
Q

What is found on investigation in Hashimoto’s thyroiditis?

A

Autoantibody titres are very high

34
Q

What is secondary hypothyroidism caused by?

A

Hypopituitism, and therefore a lack of TSH

35
Q

Is secondary hypothyroidism common?

A

No, it is very rare

36
Q

What conditions are associated with hypothyroidism?

A
  • Autoimmune hypothyroidism is seen with other autoimmune conditions
  • Turner’s and Down’s syndrome
  • Cystic fibrosis
  • Primary biliary cholangitis
  • Ovarian hyperstimulation
37
Q

What autoimmune conditions are associated with hypothyroidism?

A
  • T1DM
  • Addison’s
  • RA
38
Q

What are the symptoms of hypothyroidism?

A
  • Tiredness
  • Lethargy
  • Cold intolerance
  • Dry skin
  • Hair loss
  • Slowing of intellectual activity, e.g. Poor memory, difficulty concentrating
  • Constipation
  • Decreased appetite with weight gain
  • Deep, hoarse voice
  • Menorrhagia, and later oligomenorrhoea or amenorrhoea
  • Impaired hearing due to fluid in middle ear
  • Reduced libido
39
Q

What are the signs of hypothyroidism?

A
  • Dry coarse skin
  • Hair loss
  • Cold peripheries
  • Myxoedema (puffy face, hands, and feet)
  • Bradycardia
  • Delayed tendon reflex relaxation
  • Carpal tunnel syndrome
40
Q

What signs may be found in autoimmune hypothyroidism?

A

Features of other autoimmuned diseases, e.g. vitiligo, pernicious anaemia, Addison’s disease, diabetes mellitus

41
Q

What may be found on investigation in hypothyroidism?

A
  • Low T4
  • Cholesterol and triglycerides increased
  • Macrocytosis
42
Q

What happens to TSH in hypothyroidism?

A

It is high in primary hypothyroidism, low in secondary hypothyroidism

43
Q

How should hypothyroidism be treated?

A

Levothyroxine

44
Q

What does of levothyroixine should be given to patients with hypothyroidism who are healthy and young?

A

50-100mcg/24hrs

45
Q

How is thyroxine administered?

A

PO

46
Q

When should thyroxine treatment be reviewed after starting in a healthy and young patient?

A

12 weeks

47
Q

How should levothyroxine treatment be adjusted in healthy and young patients?

A

Adjusted 6 weekly based on clinical state, and to normalise but not suppress T4

48
Q

How often should TSH be checked once stabilised in a young and healthy patient?

A

Yearly

49
Q

What dose of levothyroxine should be given to hypothyroidism patients if they are elderly or have IHD?

A

25mcg/24 hours

50
Q

How should the dose of thyroxine be adjusted in patients who are elderly or have IHD?

A

It should be incraeased by 25mcg/4 weeks according to TSH

51
Q

Why should be caution be taken when giving levothyroxine to elderly or IHD patients?

A

Can precipitate angina or MI

52
Q

Why is levothyroxine (T4) preferred over T3 for treatment of hypothyroidism?

A

Because it is better tolerated and has a longer half-life

53
Q

How often is levothyroxine dosed?

A

Once daily

54
Q

How long does it take levothyroxine to reach a steady state?

A

6-8 weeks

55
Q

What is toxicity from levothyroxine directly related to?

A

T4 levels

56
Q

How does levothyroxine toxicity manifest?

A
  • Nervousness
  • Palpitations
  • Tachycardia
  • Heat intolerance
  • Weight loss
57
Q

What drugs can affect the action of levothyroxine?

A

Drugs that induce the cytochrome P450 enzymes, such as phenytoin, rifampicin, and phenobarbital

58
Q

What effect can drugs that induce the cytochrome P450 enzymes have on levothyroxine?

A

They accelerate the metabolism of thyroid hormones, and may decrease the effectiveness

59
Q

What problems can hypothyroidism during pregnancy cause?

A
  • Eclampsia
  • Anaemia
  • Prematurity
  • Low birthweight
  • Stillbirth
  • PPH

.0.0 RSP Endocrine (18 decks)

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