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3: MED2 Y3 - Endocrinology [5] > [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?

25
What is the ratio of men to women affected by primary atrophic hypothyroidism?
1:6
26
What happens in primary atrophic hypothyroidism?
There is diffuse lymphocytic infiltration of the thyroid, leading to atrophy
27
Is there a goitre in primary atropic hypothyroidism?
No *(because there is atrophy)*
28
Who is Hashimoto's thyroiditis more common in?
Women aged 60-70
29
Do you get a goitre in Hashimoto's thyroiditis?
Yes
30
Why do you get a goitre in Hashimoto's thyroiditis?
Due to lymphocytic and plasma cell infiltration
31
What kind of thyroid pathology can be caused by Hashimoto's thyroiditis?
Can be hypothyroid or euthyroid. Rarely, there will be an initial period of hyperthyroidism
32
What is an initial period of hyperthyroidism called in Hashimoto's thyroiditis?
Hashitoxicosis
33
What is found on investigation in Hashimoto's thyroiditis?
Autoantibody titres are very high
34
What is secondary hypothyroidism caused by?
Hypopituitism, and therefore a lack of TSH
35
Is secondary hypothyroidism common?
No, it is very rare
36
What conditions are associated with hypothyroidism?
* Autoimmune hypothyroidism is seen with other autoimmune conditions * Turner’s and Down’s syndrome * Cystic fibrosis * Primary biliary cholangitis * Ovarian hyperstimulation
37
What autoimmune conditions are associated with hypothyroidism?
* T1DM * Addison's * RA
38
What are the symptoms of hypothyroidism?
* 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
What are the signs of hypothyroidism?
* Dry coarse skin * Hair loss * Cold peripheries * Myxoedema (puffy face, hands, and feet) * Bradycardia * Delayed tendon reflex relaxation * Carpal tunnel syndrome
40
What signs may be found in autoimmune hypothyroidism?
Features of other autoimmuned diseases, e.g. vitiligo, pernicious anaemia, Addison's disease, diabetes mellitus
41
What may be found on investigation in hypothyroidism?
* Low T4 * Cholesterol and triglycerides increased * Macrocytosis
42
What happens to TSH in hypothyroidism?
It is high in primary hypothyroidism, low in secondary hypothyroidism
43
How should hypothyroidism be treated?
Levothyroxine
44
What does of levothyroixine should be given to patients with hypothyroidism who are healthy and young?
50-100mcg/24hrs
45
How is thyroxine administered?
PO
46
When should thyroxine treatment be reviewed after starting in a healthy and young patient?
12 weeks
47
How should levothyroxine treatment be adjusted in healthy and young patients?
Adjusted 6 weekly based on clinical state, and to normalise but not suppress T4
48
How often should TSH be checked once stabilised in a young and healthy patient?
Yearly
49
What dose of levothyroxine should be given to hypothyroidism patients if they are elderly or have IHD?
25mcg/24 hours
50
How should the dose of thyroxine be adjusted in patients who are elderly or have IHD?
It should be incraeased by 25mcg/4 weeks according to TSH
51
Why should be caution be taken when giving levothyroxine to elderly or IHD patients?
Can precipitate angina or MI
52
Why is levothyroxine (T4) preferred over T3 for treatment of hypothyroidism?
Because it is better tolerated and has a longer half-life
53
How often is levothyroxine dosed?
Once daily
54
How long does it take levothyroxine to reach a steady state?
6-8 weeks
55
What is toxicity from levothyroxine directly related to?
T4 levels
56
How does levothyroxine toxicity manifest?
* Nervousness * Palpitations * Tachycardia * Heat intolerance * Weight loss
57
What drugs can affect the action of levothyroxine?
Drugs that induce the cytochrome P450 enzymes, such as phenytoin, rifampicin, and phenobarbital
58
What effect can drugs that induce the cytochrome P450 enzymes have on levothyroxine?
They accelerate the metabolism of thyroid hormones, and may decrease the effectiveness
59
What problems can hypothyroidism during pregnancy cause?
* Eclampsia * Anaemia * Prematurity * Low birthweight * Stillbirth * PPH

3: MED2 Y3 - Endocrinology [5] (18 decks)

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