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Path - Chempath > Thyroid > Flashcards

Thyroid Flashcards

1
Q

What hormone controls uptake of iodide into the thyroid?

A

TSH

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2
Q

What occurs once iodide enters the thyroid?

A

It is converted from iodide to iodine by thyroid peroxidase

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3
Q

Explain T4 status possibilities once secreted by the thyroid gland into circulation’

A

75% is Thyroxine Binding Globulin Bound
20% is TBPA bound
5% is albumin bound
0.03% is FREE T4

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4
Q

Explain the hypothalamus-pituitary-thyroid axis

A

Hypothalamus produces TRH
TRH stimulates the pituitary to produce TSH
TSH stimulates the thyroid to produce T4
T4 is converted to T3 in the peripheries
Excess T4 negatively feedbacks to the hypothalamus to prevent it from producing too much TRH and the pituitary to produce too much TSH

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5
Q

What occurs to TSH and TRH if you have low T4?

A

TSH and TRH increase

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6
Q

What are the three main causes of hypothyroidism?

A

Hashimotos (Autoimmune)
Atrophic thyroid (congenital, with age)
Post-Graves disease (due to radioactive iodine, surgery, thionamines)

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7
Q

What are other causes of hypothyroidism?

A 
Post-thyroiditis
Drugs (amiodarone, lithium) 
Thyroid agenesis/disgenesis 
Iodine deficiency 
Secondary hypothyroidism
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8
Q

What are clinical features of hypothyroidism?

A 
Slow metabolic rate - tiredness, weight gain, poor appetite
Cardiovascular - bradycardia
GI - constipation 
Respiratory - laboured, slow breathing 
Reproductive - oligomenorrhoea
Cold hands and feet
Hyponatraemia 
Normocytic anaemia 
Myxoedema, goitre
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9
Q

How does hypothyroidism cause hyponatraemia’

A

Low thyroxine causes low cardiac output
Low CO increases ADH production
ADH increases water reabsorption (not salt)
Hence hyponatraemia occurs

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10
Q

What investigations should you perform + findings to confirm hypothyroidism?

A

High TSH + low fT4 in primary hypothyroidism

Thyroid peroxidase antibodies (autoimmune)

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11
Q

What antibodies confirm Hashimoto thyroiditis?

A

TPO (thyroid peroxidase) autoantibodies

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12
Q

What investigation is fundamental before starting a patient on thyroxine treatment?

A

Do an ECG

If patient has CV disease, giving them thyroxine will increase cardiac contractility, causing ischaemia

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13
Q

What medication can you give for primary hypothyroidism?

A

Levothyroxine (T4)

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14
Q

What are risks of excess levothyroxine?

A

Osteopoenia

AF

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15
Q

When should you prescribe T3?

A

Never

Because there is no evidence that it is beneficial over T4

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16
Q

What does the blood test look life for subclinical hypothyroidism?

A

T4 levels are NORMAL
TSH levels are HIGH

essentially COMPENSATED hypothyroidism

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17
Q

What is the benefit of treating subclinical hypothyroidism?

A

That SH associated with hypercholesterolaemia, treating it will also treat the hypercholesterolaemia

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18
Q

What is an important sequela of radioactive treatment?

A

HYPOTHYROIDISM (usually occurs within 1 year)

19
Q

Explain how thyroid function changes in pregnancy

A

hCG rises in first trimester
hCG acts similarly to TSH: it stimulates the thyroid gland to produce thyroxine > rise in T4

Oestrogen triggers increase of TGB

20
Q

How is neonatal hypothyroidism diagnosed?

A

Gunthie test

Measures TSH >48 h after birth (if before that, will measure mothers TSH not baby’s)

21
Q

What occurs to thyroxine levels in a very sick patient?

A

They are SICK EUTHYROID
Normal / high TSH with low T4
This is because the thyroid sits down to reduce metabolioc rate

22
Q

How do you treat sick euthyroid patients?

A

You don’t

They do not have hypothyroid symptoms

23
Q

What is the typical blood results of someone with primary hyperthyroidism?

A

High T4

Low TSH

24
Q

What are 3 common causes of primary hyperthyroidism?

A

Graves disease
Toxic multi nodular goitre
Single toxic adenoma

25
Q

Explain the pathophysiology of Graves

A

Autoimmune
TSH receptor antibodies stimulate TSH R on the thyroid
This causes excess T4 production

26
Q

What test allows to see a single toxic adenoma?

A

A techtenium scan

27
Q

What are other less common causes of hyperthyroidism?

A

Viral thyroiditis

Post partum thyroiditis

28
Q

What causes Post partum thyroiditis ?

A

Pregnancy

The body produces antibodies that stimulate the thyroid to release excess amounts of thyroxine

29
Q

What is the technetium scan like for patients with viral /post partum thyroiditis?

A

LOW uptake on technetium scan

30
Q

What are clinical features of hyperthyroidism’

A 
Increased metabolic rate 
CV: tachycardia, palpitations 
GI: diarrhoea
Respiratory: tachypnoea
Skeletal: osteopenia 
Reproductive: irregular periods
31
Q

How do you investigate primary hyperthyroidism?

A

Low TSH
High T4
Technetium scan (high/low uptake)
Thyroid antibodies (Graves)

32
Q

What tests are required once hyperthyroidism is confirmed?

A 
ECG (check for AF) 
DEXA scan (osteopoenia)
33
Q

How do you manage hyperthyroidism?

A

Beta blocker - if pulse >100bpm

Radioactive iodine (taken up by thyroid, releases radiation, destroys thyroid gland)

Thionamides e.g. carbimazole, propylthiouracil

34
Q

How do thionamides work?

A

They block Thyroid Peroxidase

Thereby they inhibit the conversion of iodide to iodine

35
Q

What is a dangerous side effect of thionamides?

A

AGRANULOCYTOSIS

36
Q

What are indications for perchlorate

A

Prior to thyroid surgery in hyperthyroidism

37
Q

What is the MOA of perchlorate?

A

It blocks the uptake of iodide by the thyroid cells

38
Q

What are the types of thyroid carcinoma?

A

Papillary / follicular thyroid cancer

39
Q

What is the aggressiveness of thyroid carcinoma?

A

Indolent (patients survive 40-50 years)

40
Q

What is the treatment for thyroid carcinoma?

A

Total thyroidectomy
Then radioactive tx to remove any remaining cells
Then give thyroxine in high doses (this lowers TSH levels, so TSH does not stimulate any remaining thyroid cell cancers)

41
Q

What is a tumour marker to see if thyroid carcinoma has returned?

A

Thyroglobulin

42
Q

What cells are affected by medullary carcinoma of the thyroid?

A

C cells (which produce calcitonin)

43
Q

What are tumour markers for medullary carcinoma of the thyroid?

A

Calcitonin

CEA

Path - Chempath (23 decks)

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