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ENDOCRINOLOGY > THYROID AND THYROID DISEASE > Flashcards

THYROID AND THYROID DISEASE Flashcards

1
Q

What are the arteries which supply the thyroid gland and where do they branch from?

A

Superior thyroid artery is a branch of the external carotid

Inferior thyroid artery is a branch of the thyrocervical trunk

Thyroid ima artery is small and not always present. Either a branch of the aorta or the brachiocephalic trunk.

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2
Q

In the thyroid, what substance fills the follicles?

A

Colloid

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3
Q

What is the role of the c-cells (the parafollicular cells) of the thyroid gland?

A

To make calcitonin

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4
Q

On histological examination, what would the thyroid follicles of someone with underactive thyroid disease look like?

A

Flattened follicular epithelial cells with increased colloid

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5
Q

On histological examination, what would the thyroid follicles of someone with overeractive thyroid disease look like?

A

Tall columnar epithelial cells with reduced colloid

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6
Q

What is congenital hypothyroidism?

A

Failure of the gland to develop as a result of a genetic mutation such as PAX8.

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7
Q

What is a thyroglossal cyst?

A

Failure of thyroglossal duct to atrophy after the thyroid has migrated.

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8
Q

What are the functions of thyroid hormone?

A

Increase basal metabolic rate
Regulate long bone growth (with GH)
Neural maturation
Cardiovascular - positively chronotropic and inotropic
Increase body’s sensitivity to catecholamines (eg adrenaline)
CNS - regulates alertness

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9
Q

What are the two forms of thyroid hormone that are made by the thyroid follicles?

A

Thyroxine (T4) and Tri-iodothyronine (T3)

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10
Q

Which form of thyroid hormone is most abundant in the blood?

A

T4 - 60-150 nmol/L
T3 - 1.2-2.9 nmol/L

But most of this is bound to proteins

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11
Q

What is the normal range of TSH in the blood?

A

0.3-4.5 mU/L

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12
Q

When we measure levels of thyroid hormone in the blood what are we actually measuring?

A

The amount of free T4 (9-22 pmol/L)

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13
Q

Which form of thyroid hormone is the most bioactive?

A

T3

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14
Q

What effect does thyroid hormone have on insulin?

A

It is antagnostic

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15
Q

How does thyroid hormone affect growth hormone releasing hormone?

A

It decreases the secretion of GHRH

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16
Q

What hormones do thyroid hormones have an effect on?

A

Insulin
Growth hormone releasing hormone
Adrenaline
Thyroid releasing hormone

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17
Q

In which part of the cell does thyroid hormone have its affect?

A

DNA - binds to TR response elements

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18
Q

Over which tracheal cartilages is the thyroid gland found?

A

Second and third

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19
Q

What attaches the thyroid gland to the trachea?

A

Pretracheal fascia

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20
Q

Does the thyroid gland move with the trachea and larynx during swallowing?

A

Yes, unless the tongue is protruded.

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21
Q

What are the veins that drain the thyroid gland?

A

Superior thyroid vein
Middle thyroid vein
Inferior thyroid vein

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22
Q

What are the four groups of nodes that drain the lymphatics from the thyroid gland?

A

Prelaryngeal
Pretracheal
Paratracheal
Deep cervical

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23
Q

How many days worth of thyroid hormone is normally stored in the thyroid gland?

A

100 days - this means it takes a long time for an acquired hypothyroidism to manifest as symptomatic.

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24
Q

What is the amino acid used to make thyroid hormone?

A

Tyrosine

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25
Q

What is the catalytic enzyme involved in the oxidation of iodide into iodine in the thyroid?

A

Thyroid peroxidase (TPO)

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26
Q

What is the catalytic enzyme involved in the binding of iodine to tyrosine in the thyroid?

A

Thyroid peroxidase (TPO)

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27
Q

Where is T4 converted into T3? What stimulates this conversion?

A

In the liver and kidney

Stimulated by TSH

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28
Q

Other than T3, what form can T4 be converted into?

A

Reverse T3 (rT3)

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29
Q

Is rT3 more or less biologically active than T4?

A

Less. rT3 has little or no biological activity.

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30
Q

How much iodine is need per day in the diet?

A

150 mg although only a fraction can actually be absorbed

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31
Q

Where is iodine excreted?

A

Kidney

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32
Q

What is the catalytic enzyme that is inhibited by thiacarbamide drugs (such as carbimazole)?

A

Thyroid peroxidase (TPO)

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33
Q

How is thyroid activity regulated?

A

Hypothalamus and anterior pituitary glands

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34
Q

What is the hormone released by the hypothalamus in the regulation of thyroid gland activity?

A

Thyrotrophin releasing hormone (TRH)

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35
Q

What is the role of TRH, release from the hypothalamus into the hypophyseal portal blood?

A

Stimulate the anterior pituitary to release TSH

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36
Q

What are the factors that might increase TRH (thyrotrophin relseasing hormone) release?

A

Low thyroid hormone levels
Cold
Pregnancy (oestrogens acting on anterior pituitary)

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37
Q

What acts directly on the thyroid gland to increase release of thyroid hormone?

A

TSH

Adrenaline

38
Q

What will inhibit the release of TSH?

A 
Raised serum thyroid hormones
Somatostatin
Glucocorticoids
Chronic illness
Heat
High levels of iodine in serum
39
Q

What are the half lives of T3 and T4?

A

T3 - 1 day

T4 - 7 days

40
Q

What is the role of rT3 (reverse T3)?

A

To conserve energy by blocking the binding site of T3. This happens in periods of illness or when energy stores are low.

41
Q

What is the prevalence of hyperthyroidism in women?

A

1 in 50

42
Q

What is the prevalence of hyperthyroidism in men?

A

1 in 500

43
Q

What are the classic symptoms associated with general hyperthyroidism (as opposed to Graves’)? (Name at least 7)

A 
Weight loss (although paradoxical weight gain in 10-30%)
Poor toleration of warm weather
Sweating
Anxiety
Restlessness
Fatigue
Hair loss
Reduced libido

Goitre

Palpitations

Diarrhoea

Tremor

Infertility
Menorrhagia

Osteoporosis

44
Q

What do we call an acute exacerbation of symptoms associated with thyrotoxicosis?

A

Thyrotoxic storm

45
Q

On examination, what are the signs that might be seen in a patient with hyperthyroidism?

A 
Restlessness
Tachycardia
Atrial fibrillation
Tremor
Hypereflxia
Sweating
46
Q

What are the signs and symptoms specifically associated with Graves’ disease?

A 
Exophthalmos
Excess lid retraction
Lid lag
Pretibial myxoedema
Bruit in the goitre
47
Q

What are the main causes of hyperthyroidism?

A

Graves’ disease - most common
Toxic multinodular goitre
Toxic adenoma

48
Q

What are the precipitating factors of a thyrotoxic storm?

A

Recent thyroid surgery
Infection
MI
Resistance to therapy

49
Q

What are the clinical features and complications of a thyrotoxic crisis?

A 
High fever (often above 40˚)
Sweating
Confusion
Tachycardia
AF
Vomiting
Diarrhoea
Agitation
Heart failure
MI
50
Q

How should someone suffering a thyrotoxic storm be managed?

A 
Beta blockers
Anti-thyroid agents - thionamide, propylthiouracil, methimazole
Potassium iodide
Fluids
Oxygen
Paracetamol
51
Q

How is a diagnosis of a thyrotoxic storm confirmed?

A

Technetium scan

52
Q

What investigations would you order for someone with suspected hyperthyroidism?

A

Blood tests - TSH, T3 and T4
ECG
Autoantibody screen - ELISA (enzyme-linked immunosorbent assay)
Radioisotope scanning

53
Q

Why might radioisotope scanning be useful in someone with suspected hyperthyroidism?

A

To show the size of the thyroid and to look for any abnormal ‘hot’ areas such as a toxic adenoma.

54
Q

What is the medical management of hyperthyroidism?

A

Beta-blocker

Carbimazole - inhibits TPO, sometimes used in conjunction with thyroxine to prevent iatrogenic hypothyroidism.

55
Q

What are the non-medical management options for someone with hyperthyroidism?

A

Radioiodine - slow response, may require adjunct carbimazole

Partial thyroidectomy

56
Q

What are the antibodies that might be detected on an autoantibody screen in someone with Graves’ disease?

A

Present in Graves’ and Hashimoto’s:
Thyroglobulin antibody (TgAb)
Thyroid peroxidase antibody (TPOAb)

Specific to Graves’:
Thyroid receptor antibody (TRAb)
Thyroid-stimulating hormone receptor antibody (TSH-RAb)

57
Q

How is Graves’ disease treated?

A

Same as other causes of hyperthyroidism, although eye disease will only respond to non-medical management.

58
Q

What is thyroid hormone resistance syndrome?

A

Rare condition which occurs as a result of mutation of thyroid receptor genes. Normally compensated for by raised T3 and T4 but can present as congenital hypothyroidism.

59
Q

What is the term used to describe symptomatic hypothyroidism?

A

Myxoedema

60
Q

What is the prevalence of myxoedema in men and women?

A

Men 1 in 500

Women 1 in 100

61
Q

What are the main features of hypothyroidism?

A 
Coarse and thin hair
Mental slowing
Tiredness
Pale puffy face
Weight gain/obesity
Intolerance to cold
Goitre
62
Q

What are the less common features of hypothyroidism?

A 
Loss of outer third of eyebrow
Psychosis
Deafness
Hoarse voice
Bradycardia
Muscle weakness
Constipation
Carpel tunnel syndrome
Cold peripheries
Chronic oedema
Slow relaxing reflexes
63
Q

What stage of life is hypothyroidism most damaging? Why?

A

From birth to puberty thyroid hormones are essential for normal development of the CNS. Deficiency can cause cretinism (irreversible mental retardation).

64
Q

What screens are done to avoid the development of cretinism?

A

TSH levels are checked in all newborns. Levels will be raised in those with a dysfunctioning thyroid gland.

65
Q

If the blood tests of a patient with signs and symptoms of hypothyroidism show low levels of T3, T4 and TSH, where is the likely source of the myxoedema?

A

Lesion in the pituitary gland or hypothalamus.

66
Q

What is Hashimoto’s thyroiditis?

A

Hashimoto’s thyroiditis is an autoimmune disease in which the thyroid gland is attacked by a variety of cell- and antibody-mediated immune processes, causing primary hypothyroidism. It was the first disease to be recognized as an autoimmune disease.

67
Q

What is the gene most strongly implicated in Hashimoto’s disease?

A

HLA-DR5

68
Q

How is hypothyroidism treated?

A

Levothyroxine

69
Q

What do we monitor in someone with hypothyroidism currently on Levothyroxine?

A

TSH levels

70
Q

What are the causes of hypothyroidism?

A 
Congenital hypothyroidism
Over treatment of hyperthyroidism
Hashimoto's thyroiditis
Primary atrophic hypothyroidism
De Quervain's (subacute) thyroiditis
Iodine deficiency
Dyshormogenesis
71
Q

What are the autoantibodies associated with Hashimoto’s thyroiditis?

A

Present in Graves’ and Hashimoto’s:
Thyroglobulin antibody (TgAb)
Thyroid peroxidase antibody (TPOAb)

Present in Hashimoto’s:
Antibodies against rough endoplasmic reticulum (microsomal antibodies)

72
Q

What might be seen in early Hashimoto’s thyroiditis?

A

A hyperthyroid picture as early destruction of the thyroid gland leads to release of thyroglobulin colloid.

73
Q

What is De Quervain’s thyroiditis?

A

Inflammation of the thyroid gland caused by a virus (often Coxsackie virus, mumps or adenoviruses). More common in young or middle-aged women. Immune reaction against thyroglobulin release causes formation of granulomas.

74
Q

Why do hyperthyroid patients get a goitre?

A

Excessive TSH stimulation leads to hypertrophy.

75
Q

How would you describe a goitre associated with iodine deficiency hypothyroidism?

A

Diffusely enlarged and smooth

76
Q

How would you describe a goitre associated with Graves’ disease?

A

Diffusely enlarged and smooth. Very vascular to the extent that a bruit can be heard with a stethoscope.

77
Q

What might a multinodular central neck goitre be indicative of?

A

Hyperplasia

78
Q

What proportion of women are found to have a thyroid lump?

A

5%

79
Q

What proportion of thyroid lumps are benign?

A

80%

80
Q

What investigations would you order for someone who presents with a thyroid lump?

A

Fine needle aspirate

Thyroid function tests

81
Q

Will fine needle aspirate be enough to distinguish between a thyroid follicular adenoma and a thyroid follicular carcinoma?

A

No. You need to do thyroid function tests. A low TSH indicates adenoma as it is producing thyroid hormone. Carcinomas do not tend to produce active hormone.

82
Q

What are the causes of a thyroid lump?

A

Thyroid cyst
Nodule of multinodular goitre
Follicular adenoma
Malignancy

83
Q

What are the five types of malignancy that can arise in the thyroid gland? Which cells does each type affect?

A 
Papillary - Follicle cells
Follicular - Follicle cells
Medullary - Parafollicular cells
Malignant lymphoma - lymphatics
Anaplastic - Follicle cells
84
Q

What hormones do malignancies of the parafollicular cells tend to secrete?

A

Calcitonin
ACTH - Cushings
5-Hydroxytryptamine (5HT/serotonin) - Carcinoid

85
Q

What is the mutation associated with papillary thyroid cancer as well as medullary thyroid carcinoma?

A

RET proto-oncogene - transmembrane receptor with tyrosine kinase

86
Q

What is the mutation most commonly associated with follicular thyroid cancer?

A

RAS proto-oncogene

87
Q

What is the mainstay of treatment for thyroid cancer?

A

Surgery

Radioactive-iodine

88
Q

Which thyroid cancer is most associated with p53 mutation?

A

Anaplastic thyroid cancer

89
Q

What are the two medical emergencies associated with thyroid gland?

A

Thyrotoxic storm

Myxoedema coma

90
Q

What are the precipitates of myxoedema coma?

A

Infection
Stroke
MI
Trauma

91
Q

What are the signs and symptoms of a myxoedema coma?

A 
Hypothermia
Hyporeflexia
Hypoglycaemia
Bradycardia
Coma
Seizures

ENDOCRINOLOGY (8 decks)

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