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CEP > Thyroid > Flashcards

Thyroid Flashcards

1
Q

Where is thyroid gland located?

A

Located in neck
Wraps around trachea

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2
Q

Description of thyroid gland

A

25-30g
Brownish red
Thin fibrous capsule of connective tissue
Left and right lobes united by a narrow isthmus

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3
Q

Cell types in thyroid gland

A

Parafollicular cells
Follicle cells

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4
Q

Description of follicle cells

A

Produce hormones
Simple cuboidal epithelial lining
Colloid - contains mature thyroid hormones

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5
Q

What is the role of thyroid hormones?

A
  • Control of metabolism
    Energy generation and use
  • Regulation of growth
  • Multiple roles in development
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6
Q

Where are thyroid hormone receptors in the body

A

Every organ of the body

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7
Q

Control of thyroid hormone secretion:

A

Hypothalamus - secreted TRH
Anterior PG - secretes TSH
Thyroid gland - secretes T3 and T4
T3 Targets tissue
T3 negatively feeds back and decreases TRH and TSH secretion

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8
Q

Main target tissues of T3

A

Cardiovascular
Digestive
Neurological

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9
Q

What produces thyroid hormones?

A

Follicular thyroid cells

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10
Q

What precursor are thyroid hormones synthesised from?

A

Thyroglobulin

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11
Q

What is absorbed from the bloodstream and concentrated in follicles

A

Iodine

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12
Q

The function of thyroperoxidase (TPO)?

A

Enzyme
That binds iodine to tyrosine residues in thyroglobulin molecules to form MIT and DIT

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13
Q

MIT + DIT forms

A

T3

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14
Q

DIT + DIT forms

A

T4

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15
Q

What are MIT and DIT?

A

Thyroid hormone precursors

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16
Q

The mechanism of production of T3/ T4 in follicular cells?

A
  1. TSH binds to TSHR (receptors on follicles)
  2. Iodine uptake by NIS (Na/I symporter)
  3. Iodisation of thyroglobulin tyrosyl residues by TPO
  4. Coupling of iodotyrosyl residues by TPO
  5. Export of mature thyroglobulin into colloid
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17
Q

Which thyroid hormone is biologically active

A

T3

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18
Q

HOW IS T3 PRODUCED FROM T4

A

By mono deionisation of T4
3 types of deiodinase enzymes (D1, D2, D3) present in peripheral tissues

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19
Q

What hormone does thyroid gland majorly produce?

A

80% T4 which then gets deiodinised
20% originally T3

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20
Q

What protein carriers to T4 and T3 bind to?

A

TBG
Albumin
Transthyretin

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21
Q

What is the percentage of free t4

A

0.03%

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22
Q

What is the percentage of free T3

A

0.3%

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23
Q

3 main test for thyroid function

A
  1. Serum TSH (best)
  2. Serum T4
  3. Serum T3
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24
Q

What would be the test results for hyperthyroidism?

A

Low serum TSH
High serum free T4
High serum free T3

Due to negative feedback

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25
Q

The test results for primary hypothyroidism?

A

High serum TSH
Low serum free T3 and T4

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26
Q

Prevalence and incidence of hyperthyroidism

A
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27
Q

What thyroid disease has the largest prevalence?

A

Goitre
24.4%

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28
Q

Is prevalence of hyperthyroidism bigger in females or males

A

Females

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29
Q

Main Aetiology (causes) of hyperthyroidism:

A
  1. Graves hyperthyroidism
  2. Toxic nodular goitre (single or multinodular)
  3. Thyroiditis - inflammation following a viral infection
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30
Q

What are the other causes of hyperthyroidism?

A
  • Exogenous iodine
  • Factitious (taking excessive thyroid hormone)
  • TSH secreting pituitary adenoma (benign)
  • Neonatal (newborn) hyperthyroidism
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31
Q

Percentage of cases of hyperthyroidism that are Graves’ disease?

A

60-80%
Most prevalent autoimmune disorder in UK and US

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32
Q

What are the environmental factors causing Graves’ disease?

A

Interplay between genetic (80%) and environmental factors (20%)
Gender - more common in females
Stress
Infection
Pregnancy
Drugs

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33
Q

How does Graves’ disease cause hyperthyroidism?

A

Autoimmune disease that cause IMS to target thyroid gland and make it overactive - unregulated overproduction of thyroid hormones
Pathogenic antibodies bind to TSH receptor on thyroid follicular cells
Antibodies are “long acting thyroid stimulators”

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34
Q

Cardiovascular symptoms and signs of hyperthyroidism:

A
  • Tachycardia (rapid heart rate)
  • Atrial fibrillation
  • Shortness of breath
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35
Q

Atrial fibrillation?

A

Irregular and abnormally fast heart beat
That can lead to blood clotts in the heart

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36
Q

Neurological signs and symptoms of hyperthyroidism?

A
  • Tremor
  • Myopathy (muscle weakness)
  • Anxiety
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37
Q

Gastrointestinal symptoms and signs of hyperthyroidism?

A
  • Weight loss
  • Diarrhoea
  • Increased appetite
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38
Q

Signs and symptoms of eyes/skin with hyperthyroidism?

A
  • Sore gritty eyes
  • Staring eyes
  • Pruritus (itching)
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39
Q

If a patient has family history of Graves’ disease what is likely to happen

A

Patient will present at a younger age
Inverse relationship between age an diagnosis

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40
Q

How are Extrathyroidal manifestations caused in Graves’ disease

A

Long acting antibodies that attach to TSH receptors on follicular cells can also attach to skin and soft tissues in the eyes

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41
Q

Extrathyroidal manifestations in the eyes in Graves’ disease:

A
  • Lid lag/ retraction
  • Conjunctival oedema (swelling)
  • Proptosis/ unilateral proptosis (bulging)
  • Ophthalmoplegia (weakness of eye muscles)
42
Q

Extrathyroidal manifestations on the skin in Graves’ disease:

A

Pretibial myxoedema - waxy, discolored induration of the skin
Acropachy - soft-tissue swelling of the hands and clubbing of the fingers

43
Q

How does neonatal hyperthyroidism occur?

A

If mother has Graves’ disease, TSH-R antibodies cross the placenta
Treatment: control hyperthyroidism in mother during pregnancy
May cause fatal death

44
Q

How is hyperthyroidism diagnosed?

A
  • Clinical features of graves
  • Consider iodine uptake scan
  • Consider isotope imaging
  • TPO absence in 75% of graves
  • measure TSH receptor antibodies
45
Q

Treatment of hyperthyroidism

A
  • Anti thyroid drugs to block hormone synthesis
  • Surgical removal of thyroid
  • radioiodine therapy
46
Q

Examples of anti thyroid drugs

A
  1. Carbimazole
  2. Propylthiouracil
47
Q

How do anti thyroid drugs (thionamides) work?

A

Block iodine incorporation and organification through inhibition of thyroperoxidase TPO

48
Q

What is the role of TPO?

A

Assists the chemical reaction that adds iodine to thyroglobulin

49
Q

Thionamide therapy side effects

A

Rash
Joint pain
Sickness
Agranulocytosis: no WBC infection risk
Liver disease with propylthiouracil
Pancreatitis with carbimazole

50
Q

What is the cure rate of thionamide drugs?

A

30-40%

51
Q

Is surgery for hyperthyroidism used frequently?

A

No

52
Q

What is the pre treatment of surgery for hyperthyroidism?

A

Antithyroid drugs

53
Q

Indications that surgery are needed for hyperthyroidism:

A
  • Large goitre (co-existing thyroid cancer)
  • Pregnancy (thionamide drugs have serious side effects)
  • Pronounced opthalmopathy
  • patient preference
54
Q

What is radioiodine treatment? Adv and Dis

A

Iodine-131
Capsule (fixed dose)
Usually pre treatment with drugs
Adv:
Highly effective (85% cure)
Dis:
May worsen eye disease (steroidS)

55
Q

Risks of using radioiodine therapy to treat hyperthyroidism?

A
  • Hypothyroidism (60%)
  • Cancer due to radioactive
  • Infertility
  • Teratogenesis (congenital malformations produced in an embryo/ fetus)
56
Q

What are the treatment aim of treating thyroid diseases?

A
  • To relieve symptoms
  • To restore T4 and T3 values within an normal range
  • To obtain long-term normal thyroid function
57
Q

Prognosis of thyroid disease treatments

A
  • 30% of patients with Graves’ disease have normal thyroid function long term following drugs
  • 131-I and surgery associated with >50% risk of long term hypothyroidism
58
Q

Prevalence of hypothyroidism in females:

A

40/1000

59
Q

Aetiology of hypothyroidism:

A
  1. Autoimmune - Hashimoto thyroiditis (TPO and Tg antibodies - genetic predisposition
  2. After treatment of hyperthyroidism
  3. Subacute/ silent thyroiditis
  4. Iodine deficiency
  5. Congenital (having it since birth)
60
Q

What is the indication of high Tg antibodies?

A

Antithyroglobulin antibodies can be a sign of thyroid gland damage via the immune system
Autoimmune disease like Hashimotos/ Graves’ disease

61
Q

What is subacute/ silent thyroiditis?

A

Most common in women in postpartum period
Symptoms starts with hyperthyroidism, then hypothyroidism, then the recovery period to euthyroid period

62
Q

What is the congenital cause of hypothyroidism?

A

Born with thyroid deficiency

Thyroid agenesis:
Missing the thyroid
Severely reduced in size
Located ectopically

63
Q

Ectopically?

A

Placed abnormally

64
Q

The effects of Tg antibodies in Hashimotos thyroiditis?

A

Inflammation
Goitre
Swelling
Fibrosis and shrinkage - unable to produce sufficient thyroid hormones

65
Q

What is the major cause of hypothyroidism world wide and UK?

A

WORLD WIDE: iodine deficiency
UK: Hashimoto’s disease

66
Q

What country doesn’t suffer from iodine deficiency?

A

Japan

67
Q

How is iodine deficiency combatted?

A

Supplementation programs
E.g. salt and flour is iodinated

68
Q

Where are the main sources of iodine?

A

Milk
Diary

69
Q

Cause of congenital hypothyroidism (cretinism) ?

A

Lack of iodine in mother - Affects fetus
Random mutation

70
Q

Cardiovascular symptoms and signs of hypothyroidism?

A
  • Bradycardia (slow heart rate)
  • Heart failure
  • Pericardial effusion
71
Q

Pericardial effusion?

A

Excessive fluid build up in the sac like structure that covers the heart, the pericardium

72
Q

Gastrointestinal symptoms and signs of hypothyroidism?

A
  • Weight gain
  • Constipation
73
Q

Skin symptoms and signs of hypothyroidism?

A
  • Myxoedema
  • Rash on legs
  • Vitiligo
74
Q

Neurological symptoms and signs of hypothyroidism?

A
  • Depression
  • Psychosis
  • Carpal tunnel syndrome
75
Q

Treatment of hypothyroidism?drug names

A

Levothyroxine - 3rd most prescribed med in UK
Goal: restore patients to euthyroid state and to normalise serum T4 and TSH conc

76
Q

Is hypothyroidism the most common endocrine condition?

A

Yes

77
Q

What are thyroid nodules and goitres?

A

Goitre is an enlargement of the thyroid can be uniform and smooth
Nodular goitre is multiple enlargements at thyroid

78
Q

Epidemiology

A

Incidence
Detriments
Distribution
Possible control of disease
In a certain population

79
Q

How may nodules be discovered?

A

Palpating
Imaging
Incidentally

80
Q

What gender and age is thyroid nodules more common in?

A

Most common in women 4:1
Older population

81
Q

Common cause of thyroid nodules:

A

Increased in areas of low iodine uptake

82
Q

What would thyroid nodules cause?

A

Cause Thyroid dysfunction
Cause Compression

83
Q

Prevalence of malignancy in goitre:

A

4-6.5%

84
Q

What is a pet scan?

A

3D image produced
Scans for specific diseases
Cancer, heart disease and brain disorder

85
Q

Percentage risk of PET positive thyroid nodule?

A

27%

86
Q

Does risk of cancer depend on nodule size?

A

No

87
Q

Prevalence (percentage) of nodules in the population?

A

50%

88
Q

How are nodules found incidentally?

A

Found when patients are undergoing imaging (CT, MRI, carotid Doppler)

89
Q

Clinical features associated with increased risk of malignancy? LIST

A
  • Age <20 or >60
  • Firmness of nodule on palpating
  • Rapid growth
  • Fixation to adjacent structure
  • Vocal cord paralysis
  • History of neck irritation
  • Family history of thyroid cancer
90
Q

To investigate thyroid nodules:

A
  1. Assessment of thyroid function
  2. Assessment of thyroid size
  3. Assessment of thyroid pathology
91
Q

What are the assessment of thyroid function in investigation of thyroid nodule?

A

Serum TSH
Serum free T4 and T3
Thyroid antibodies

92
Q

What are the assessments of thyroid size in the investigation of thyroid nodules?

A

Symptoms
X ray thoracic inlet
CT or MRI of neck
Respiratory flow loop

93
Q

Assessment of thyroid pathology in investigation of thyroid nodules? (Is this cancer?)

A

Radionuclide scanning
Ultrasound scanning
Fine needle aspiration cytology

94
Q

What is the criteria for malignancy of thyroid nodules?

A

Irregular margin
Calcifications
Solidity
Increased blood flow

95
Q

What does ultrasound allow differentiation of when investigating a thyroid nodule?

A

Differentiation of a solid from a cystic nodule
Differentiation of single from multiple nodules (can be superior to palpation - hidden nodules)

96
Q

What does ultrasound provide guidance for?

A

Fine needle aspiration

97
Q

Main type of thyroid cancer (72-85%)

A

Epithelial cell malignancy showing differentiation in follicular cells

98
Q

What is the cause of medullary carcinoma (1.7-3%)

A

Malignant differentiation of C cells in medulla of thyroid gland

99
Q

Causes of thyroid cancer:

A
  • External irradiation e.g. Chernobyl accident
  • Iodine deficiency
  • Oncogene expression
  • Genetic factors
100
Q

Treatments for thyroid cancer:

A
  1. Surgery - doesnt always remove all thyroid
  2. Radioiodine
  3. Drugs

CEP (12 decks)

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