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YEAR 5: Chemical Pathology JK > ChemPath: Thyroid > Flashcards

ChemPath: 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 iodine 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 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 hypothryoidism?

A

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

NOTE: so you would start on a low dose of thyroxine and then escalate

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11
Q

How is hypothyroidism treated?

A

Thyroxine (50-150-200 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 a 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 the Guthrie 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 stimulat 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 thionamdes?

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

NOTE: radioiodine treatment may also be given

NOTE: high dose thyroxine may be given to suppress TSH levels to prevent TSH from stimulating any remaining cells

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

Clacitonin

CEA

YEAR 5: Chemical Pathology JK (26 decks)

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