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Baz Y2 Semester 1 > Week 9 Endocrinology Thyroid Disorders > Flashcards

Week 9 Endocrinology Thyroid Disorders Flashcards

1
Q

Which is more active T4 or T3

A

T3

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2
Q

What does the thyroid produce more of T3 or T4?

A

T4:T3 14:1

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3
Q

What is the chemical difference between T4 and T3?

A

An Iodine molecule

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4
Q

What is Tri-iodothyronine?

A

T3

Hint - tri - 3

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5
Q

What is the chemical name for T4?

A

Thyroxine

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6
Q

Which of these blood plasma proteins binds the most thyroxine?

Transthyretin
Albumin
Thyroxine Binding Globulin (TBG)

A

Thyroxine Binding Globulin (TBG) 70%

Transthyretin 20%

Albumin 10%

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7
Q

How much of blood plasma thyroxine is free?

A
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8
Q

How much T3 is made in the thyroid and how much is synthesised in the peripheries?

A

20% T3 produced from thyroid gland

80% T3 produced from peripheral conversion of T4 in liver, kidney and muscle

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9
Q

What is the enzyme that converts T4 into T3?

A

T4 converted to T3 by deiodinase enzymes

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10
Q

What parts of the body convert T4 to T3?

A

liver, kidney
and muscle

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11
Q

Which two things mean the body can access active T3 when it needs?

A

The fact that most T4 is bound to protiens in the plasma where it is inactive mean there is this huge reserviour which can be freed and accessed and easily converted into T3

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12
Q

What is Grave’s disease?

A

Most common cause of hyperthroidism at 75%

Auto immune

Anti-bodies attack thyroid making it overactive

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13
Q

In the context of thyroid disorders what does eye disease imply?

A

Grave’s disease

Eye disease associated with 1/4 cases of Grave’s

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14
Q

What is Toxic Multinodular Goitre (MNG)

A
  • Multiple lumps (nodules) on enlarged thyroid (goitre)
  • Often one or more lumps will be overactive
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15
Q

How does MNG change with progression?

A

As T4 begins to get elevated more nodules appear and you begint o get a tracheal compression/ elevation

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16
Q

What is an overactive thyroid lump celled if there is just one?

A

Single toxic nodule

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17
Q

What is Thyroiditis?

A

Temporary overactivity of thyroid

Can be followed by period of underactivity

Triggered by pregnancy, infection or some drugs (eg amiodarone)

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18
Q

4 causes of hyperthyroidism

A

Gaves ~ 75%
Multinodular goites ~ 15%
Single toxic nodule
Thyroiditis (temp from pregnancy, drugs or infection)

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19
Q

What are these symptoms a history of?

  • Weight loss despite good appetite (often very hungry)
  • Tiredness
  • Tremor
  • Hot, sweaty
  • Palpitations
  • Diarrhoea
  • Light/absent menses
  • Mood: irritable, anxiety
  • Eyes (change in appearance, red, gritty, painful, double vision)
  • Muscle weakness

Family history: Autoimmune diseases

A

Primary hyperthyroidism

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20
Q

What is a goitre?

A

A swelling int he neck caused by an elarged thyroid

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21
Q

Eyes

When it comes to hyperthyroidism what is the difference between these two sets of eye symptoms?

Set 1:
* Lid retraction
* Lid lag

Set 2:
* Redness
* Gritty sensation
* Dry or watery eyes
* Pain on eye movement
* Swelling around the eyes
* Proptosis (pushed forward appearance of eyes)
* Double vision
* Loss of colour vision

A

First is Associated with any cause of thyrotoxicosis
Caused by activation of sympathetic nervous system

Second group is eye conditions only assciated with Graves

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22
Q

Why do most of the eye related symptoms such as swelling and proptosis occur in Grave but not other forms of primary hyperthyridism?

A

Main takeway: It isn’t high T4/T3 that causing the swelling in the eyes but it is the antibodies responsible for Graves themselves

Don’t need to remeber these details but basically the same antibodies that bind to TSH receptors and cause hyperthyroidism bind to receptors in the orbital connective tissue causing imflammtory swelling, build up of adipose tissue and fibrosis.

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23
Q

What is TPO?

A

Thyroid Peroxidase

The enzyme responsible for thyroxine synthesis

24
Q

What is TRAbs and what does it have ot do with Graves?

A

TRAbs (TSH Receptor Antibodies) significantly positive
indicates Graves

25
Q

What can you give to help with the symptoms of hyperthyroidism?

A

Beta blockers to help with the heart palpitations

26
Q

What is going on here?

34 y/o female

Hx of neck discomfort

Prodromal flu symptoms; No FHx of thyroid dysfunction

On examination: HR 98 bpm, no goitre, eyes- normal

TSH <0.05mU/L, f T4 54 pmol/l, TT3-2.7 nmol/l, TRAB<0.9 iU/L

A

It is hyperthyroidism due to symptoms such as flu like and high BPM plus high TSH and T4/T3.

However without family history, eye symptoms and low TRAb we can rule out Graves. And without any goitre we cna rule out nodules.

This leaves tempory thyroiditis.

27
Q

What is initial treatment for thyroiditis 0-2 months?

What is the later treatment for thyroiditis 3-5 months?

A

We don’t want to give anti thyroid drugs as the thyroid is not overactive it is just releasing hormones due to damage.

Initially give beta blockers to help with the cardiac symptoms.

Later as the thyroid has released all it’s hormones you get a bounce back into hypothyroidism requiring levothyroxine.

28
Q

What is initial treatment for hyperthyroidism due to graves or nodules?

A

Antithyroid drugs (ATDs) :

Carbimazole and propylthiouracil (PTU)

Both decrease production of thyroid hormone (block TPO enzyme)

Propranolol good for tremor and elevated HR

29
Q

What are the two antithyroid hormone drugs?

A

Carbimazole (symptom of hyperthyroidism is high metabolism therefore eating lots but losing weight, “carb ma”)

Propylthiouracil (PTU) (remember because it has thyroid sounding like name)

30
Q

What is indicated first carbmazole or propythiouracil?

A

Carbmazole is always given first as has less side effects.

And propythiouracil if not responsing to carbazole particularly before thyroid surgery to bring symptoms under control.

31
Q

What is the form of thyroxine we give people to raise T4 levels?

A

Levothyroxine

32
Q

What is a very dangerous side effect of carbmazole and propythiouracil?

A

Rare side effect of agranulocytosis ( less than 1/500).

Low WBCs and immune failure. Patients need to be monitered for this.

33
Q

What is the long term treatment for hyperthyroidism due to graves or MNG?

What is the long term effect of this?

A

Radioactive Iodine to burn out the thyroid gland.

Surgery.

Both leave patients with perminant hypothyroidism.

Graves might respond to a treatment of ATDs. However MNG will always require radioactive iodine or surgery.

34
Q

What is the risk of radioactive iodine over surgery?

A

You can’t have close contact with others during treatment. Therefore it is not suitable for poeple with younge children who won’t inderstand this.

35
Q

Treatment of graves eye disease

A

Smoking cessation (smoking makes eye disease 9x more likely)

Topical lubricants

Selenium 200mcg daily (antioxidant)

Steroids

Consider other forms of immunosupression.

For long term damage might need decompression or surgery to repair.

36
Q

Symptoms of primary hypothyroidism

A
  • Tired
  • Weight gain, puffy eyes and skin
  • Feeling cold
  • Slow heart rate
  • Constipation
  • Dry hair and skin
  • Heavy periods (menorrhagia)
  • Hyperlipidaemia
  • (Enlarged thyroid = goitre)
37
Q

Common causes of primary hypothyroidism

A
  • Hashimoto’s thyroiditis:

Antibodies attack thyroid and make it underactive
Permanent
Tendency can run in families

  • Iatrogenic (post surgery or radioactive iodine)
  • Spontaneous atrophic

Iodine deficiency, however this is not common in the UK

38
Q

Why do you get an enlarged thyroid in iodine deficiency?

A

Cannot manufacture enough
thyroid hormone without
iodine
TSH rises in response to fall
in T4
High TSH stimulates
hypertrophy (growth) of the
thyroid gland

39
Q

What is the common dose of levothyroxine?

A

100mcg daily before breakfast.

This is normally enough to reach stable and normal levels of T4

40
Q

Medications that counter levothyroxine absorption?

A
  • Proton Pump Inhibitors eg omeprazole/lansoprazole
  • H2 antagonists eg ranitidine
  • Iron, calcium, aluminium, bile acid sequestrants
41
Q

What is a TFT?

A

Thyroid function test

42
Q

How does the blood test differ for subclinical hypothyroidism and primary hypothyroidism?

A
43
Q

What is a non-thyroidal illness? How does a non thyroidal illness present? How can you tell it apart from a thyroid disorder?

A

When very sick circulating cytokines can surpress TSH release resulting in low TSH.

Hormone uptake by the liver is also reduced resulting in less T4 getting converted into T3.

The result is low TSH and high circultating free T4 mimiking hyperthyroidism. Except the syptoms will be that of hypothyroidism. Plus the other givaway will be low T3.

44
Q

Why is hypothyroidism particularly bad during pregnancy?

A

T4 is essential for foetal neuro development.

T4 requirement in the mother can increase by 50%.

Results in premature births and nurological impairment.

Mothers should be given levothyoxine and TFTs should be done every trimester.

45
Q

What investigation can confirm the nature of a toxic nodule?

A

Scintigraphy - usually use technetium

46
Q

What is a carbimazole side effect?

A

Can cause agranulocytosis (low white blood cell count)

Symptoms include fever, sweats, chills, weakness, sore throat

47
Q

You perform a technetium scan to distinguish between what is causing the hyperthyroidism and the result is diffusely increased uptake.

What is this indicative of?

A

Grave’s

48
Q

How would the uptake of technecium vary between the different types of hyperthyroidism?

A
49
Q

How can the combined contracepetive pill have an effect on total thyroid hormone levels?

What does this mean for thyroid hormone testing?

A

Oestrogen increases synthesis of TBG
Increased TBG - more bound, total T4/T3 seems normal but available free T3/T4 low therefore leading to hypothyroidism.

Thyroid hormone testing in someone who is on the combined contraceptive pill should always be free T4/T3. And in pregnancy.

50
Q

What is the difference betweena toxic and cold nodule in the thyroid?

A

Cold - not productive
Toxic - productive

51
Q

How do you distinguish between mallignant thyroid nodules?

A
  • Follicular & papillary most common. Generally good prognosis
  • Medullary carcinoma (C cells, calcitonin present in fine needle aspiration) less common
  • Anaplastic carcinomas and lymphoma present as
    rapidly enlarging thyroid mass.
52
Q

Telltale sign of a thyroid medullary carcinoma?

A

Cells found ot be expressing calcitonin

53
Q

Telltale sign of a thyroid nodule which is an anaplastic carcinoma or lymphoma

A

Anaplastic carcinomas and lymphoma present as rapidly enlarging thyroid mass

54
Q

What does the term euthyroid mean?

A

Normal thyroid function.

E.g. Patient present with a lump in the thyroid, they are clincally euthyroid therefore the nodule isn’t toxic.

55
Q

When would you expect to find high levels anti-TPO antibodies?

A

In Hashimoto’s

Can also appear in Grave’s however less significantly as the main antibody in grave’s is TRAbs

56
Q

What is the result of extreme hypothyroidism

A

Myxedema

This is hypothyroidism with extreme swelling and scalely skin

57
Q

What is the relationship between hyperthyroidism and hypocortisolism?

A

High levels of T4/T3 can lead to a faster metabolism which breaks down cortisol faster thus leading to hypocortisolism

Baz Y2 Semester 1 (17 decks)

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