Chem Path 9 - Thyroid Flashcards

1
Q

What controls the uptake of iodine by thyroid follicular cells?

A

TSH

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2
Q

Which channel is important for the transport of iodide across the cell membrane?

A

Na+/K+ ATPase

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3
Q

Which enzyme converts iodide to iodine?

A

Thyroid peroxidase

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4
Q

How is thyroxine produced?

A

Iodination of tyrosine residues in thyroglobulin generates MIT and DIT which leads to the formation of T3 and T4

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5
Q

What percentage of thyroxine is free active T4?

A

0.03%

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6
Q

What does thyroxine bind to in the blood?

A

Thyroxine binding globulin (TBG)

Thyroxine-binding prealbumin (TBPA)

Albumin

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7
Q

Outline the hypothalamo-pituitary-thyroid axis.

A

The hypothalamus produces TRH which stimulates the release of TSH from the anterior pituitary

TSH stimulates T3/T4 production

T4 feeds back to the hypothalamus and pituitary

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8
Q

List some causes of hypothyroidism.

A

Hashimoto’s thyroiditis (autoimmune)

Atrophic thyroid gland

Post-Graves’ disease (after treatment)

Post-thyroiditis

Drugs (e.g. amiodarone, lithium)

Iodine deficiency

Pituitary disease

Peripheral thyroid hormone resistance

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9
Q

Outline the investigation findings that may be seen in hypothyroidism.

A

High TSH

Low T4

Thyroid peroxidase antibodies

Look out for other autoimmune conditions

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10
Q

Why is it important to do an ECG in patients with suspected hypothyroidism?

A

If someone with hypothyroidism has underlying cardiovascular disease, giving them thyroxine may induce ischaemia

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11
Q

How is hypothyroidism treated?

A

Thyroxine (50-125-200 µg/day titrated to a normal TSH)

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12
Q

What are some risks of overtreatment with thyroxine?

A

Osteopaenia

Atrial fibrillation

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13
Q

What is subclinical hypothyroidism?

A

Normal T4 with high TSH

Sometimes referred to as compensated hypothyroidism

NOTE: if TPO antibodies are positive, the patient may go on to develop hypothyroidism

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14
Q

Why might there be some benefit to treating subclinical hypothyroidism?

A

Hypothyroidism is associated with hypercholesterolaemia

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15
Q

Outline how thyroid function changes in pregnancy.

A

hCG has a similar structure to TSH so high hCG levels can cause hyperthyroidism

Free T4 levels rise slightly

TBG level increase dramatically

NOTE: hCG level drops later on in pregnancy

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16
Q

How is neonatal hypothyroidism diagnosed?

A

Guthrie test

17
Q

Why is the timing of this test important?

A

It needs to be done at least 48-72 hours after birth to make sure maternal TSH is no longer in the baby

18
Q

What is sick euthyroid?

A

Alteration in the pituitary thyroid axis in non-thyroidal illness

In other words, when you are very sick, your thyroid will shut down to try and reduce your basal metabolic rate

19
Q

What are the TFT findings in sick euthyroid?

A

Low T4 and T3

Normal/high TSH

NOTE: these patients do not have symptoms of hypothyroidism

20
Q

What are the three main causes of hyperthyroidism?

A

Graves’ disease

Toxic multinodular goitre

Single toxic adenoma

Others: subacute thyroiditis, post-partum thyroiditis

21
Q

What is post-partum thyroiditis?

A

During pregnancy, the body may produce antibodies that stimulate the thyroid gland

22
Q

What is struma ovarii?

A

A rare form of ovarian tumour (usually a teratoma) that contains mostly thyroid tissue and produces thyroxine

23
Q

List some investigation findings of hyperthyroidism.

A

Low TSH

High T4 and T3

Technetium scan

Thyroid antibodies (thyroid microsomal)

24
Q

Outline the management of hyperthyroidism.

A

Beta-blocker

ECG

Bone mineral density

Radioiodine

Thionamides

25
Q

What is a major risk of radioiodine treatment for hyperthyroidism?

A

Can precipitate thyroid storm

Can result in hypothyroidism

26
Q

List some features of Graves’ disease.

A

Diffuse goitre

Thyroid-associated ophthalmopathy

Pretibial myxoedema

Thyroid acropachy

NOTE: radioiodine can make Graves’ eye disease worse

27
Q

What is the mechanism of action of thionamides?

A

Prevents the conversion of iodide to iodine by thyroid peroxidase

28
Q

What is a rare but important side-effect of thionamides?

A

Agranulocytosis

NOTE: patients should be advised to stop treatment if they develop a sore throat or fever

29
Q

What kind of dosing regimes can be used for thionamides?

A

Can be titrated to achieve normal T4 levels

Block and replace – high dose is given to block the thyroid gland and then given thyroxine replacement

30
Q

Which drug can be given to hyperthyroid patients prior to surgery to block uptake of iodide?

A

Potassium perchlorate

31
Q

What is the long-term treatment of thyroiditis?

A

Thyroid hormone replacement

32
Q

What are the two most common forms of thyroid cancer?

A

Papillary thyroid cancer

Follicular thyroid cancer

33
Q

How is thyroid cancer treated?

A

Total thyroidectomy

34
Q

Which cells do medullary thyroid cancer arise from?

A

Calcitonin-producing C cells

NOTE: it is part of MEN2

35
Q

Name two tumour markers used for medullary thyroid cancer?

A

Calcitonin

CEA