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Endocrinology > Thyroid > Flashcards

Thyroid Flashcards

1
Q

Explain how T3, and 4 are made?

A

Iodide transported into thyroid follicular cell
Transported into thyroid colloid where it combines wiuth tyurosines (part of teh thyroglubulin molecule, also made in the thyroid follicular cells) to form DIT and MIT (iodinated tyrosines)

The thryoglubulin colloid is endocytosed back into the follicular cell. Lysosome combines with endocytosed part and cleaves of T3 and T4
Rleased into blood stream

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2
Q

WHere does T4 and T3 come from

A

T4 - thyroid gland only
T3 - 80% from peripheral tissues via enzymatic di-iodonisation of T4

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3
Q

How are T3, 4 transported in blood?

A

Mostly protein (thyroid binding glubulin, TBG) bound
- albumin does bind much

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4
Q

3x relevant thyroid abs?
- What are they mainly found in?

Structural test for thyroid
Function thyroid tests?

A

TPO (thyroid peroxidase abs)
- Autoimmune hypothyroid (hashimotos), less so graves disease
TSH receptor
- Graves disease
THyroglobulin

Structural:
- ultrasound

FUnctional:
- THy scintigraph / thy uptakle scan

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5
Q

What is the typical TFT pattern in sick euthyroid?

What is TFT pattern in high dose steroid use?

A

Sick euthyroid
- unwell pts
- Clinically euthyroid
- Low TSH
- T3,4 normal or low

High dose steroid (suppress TSH)
- Low TSH
- Normal T3,4

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6
Q

Pt has adrenal insuificiency and also high TSH. Replace the adrenal or thyroid first?

A

Adrenal
- pts with adrenal insuf can often have high TSH. Replacing the thyroid will solve this

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7
Q

Effect of medications on TSH:
- amiodarone?
- Lithium?
- Preg?

A

Aminodarone - TSH increased, sometimes low
Lithium - TSH high (lithium can cause hypothyroidism)
Preg - TSH low (beta HCG effect)

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8
Q

Common drugs affecting HPA control of thyroid? 4x examples of drug classes

A

Immunotherapy - CTLA 4 mostly (hypophysitis), PD1/L1 less

High dose glucocorticoids
Dopamine agonists
Somatastatin anologues

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9
Q

How does excess iodine affect thyroid function?

A

Excess can inhibit hromone synthesis (wolff-chaikoff effect)
- Lugol iodine used to prepare for thyroidectomy and prevent thyroid storm
Excess iodine can induce thyrotoxicosis (jod-basedow effect)

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10
Q

WHat common drugs can affect thyroid hormone synthesis or release?

A

Amiodarone
- type 1 amiodarone induced thyroiditis (too much iodine, jod basedow mechanism)

Liuthium - hypothyroidism

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11
Q

Drugs / conditions that enhance the autoimmunity against the thyroid?

A

Immunotherapy
Alemtuzumab (CD 52)
Immune reconstitution syndrome (HIV)
post partum thyroiditis

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12
Q

Drugs causing direct thyroid damage?

A

Amiodarone (type 2 amiodarone induced thyroiditis)

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13
Q

Drugs that affect the protein binding of thyroid hormones?

A

Oral estrogen and SERM
- increased TBG binding leading to reduced free hormone

Androgen, glucocorticoids
- increase free hormone by reducing binding

Displacment from TBG
- phenytoin
- carbamazapine
- heparin

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14
Q

Thyroxine should be taken on ? an empty or full stomathc?

A

empty
- Fast for 2 hours post

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15
Q

How does hyperthyroidism affect drug metasbnolism? some examples?

A

Usually increases drug metabolism
- Lower doses of warfarin are required because of accelerated turnover of clotting factors
- increased risk of statin myopathy
- Increased metabolism of antithyroid drugs (hence start very large doses for graves disease then down titrate)

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16
Q

Thyroid scintigtraphy: diffuse uptake bilaterally. Disease?

A

Graves

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17
Q

Thyroid scintigtraphy: nodular uptake with punched out (cold) areas?

A

Toxic MNG, with cold nodules as well

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18
Q

Thyroid scintigtraphy: no uptaske in gland?

A

Thyropiditis

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19
Q

Thyroid scintigtraphy: single hit nodule, nil significant uptake otherwise.

A

Single hot nodule, toxic adenoma

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20
Q

Thyroid scintigtraphy: pregnancy?

A

will have diffuse increased uptake (not as much as graves).
- this is because of the beta HCG affect witch increased thyroid function

In Molar preg where bHCG can be very high, this can result in over hyperthyroidism

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21
Q

Can thy USS distinguish thyroiditis and graves disease?

A

No, will just see increased blood flow throughout in both

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22
Q

Most common 2x causes of hyperthyroidism?

A

Graves disease
hot nodule/Toxic adenoma in MNG

23
Q

What is de quervains thyroiditis?

A

this is p[ainful thyroiditis usually due to a viral infeciton (post viral thyroiditis)

Other form of thyroiditis are non painful
- Hashimotos (autoimmune)

24
Q

What is the characteristic TFT pattern of graves?

A

Elevated T3 is much greater than elevation in T4
Low TSH

25
Q

pathophys of graves?

A

TSH receptor stimulates the thyroid receptor to make thyroid hormone via the normal pathway

26
Q

CLinical features of graves disease specifically?

A

Hyperthyroidism clinically
Graves eye disease
Symetrically enlarge uniform goitre
Graves dermopathy (hard skin, non pitting perippheral oedema)

27
Q

What is pembertons signs? what is it found in?

A

raise arms, become red and flushed appearing
May have difficulty breathing

due to obstruction of thorasic outlet

Due to goitre or thyroid mass (large nodule or cancer)

28
Q

Management of Graves disease hyperthyroidism?

A

beta blockers
- propanolol (also T3 to T4 conversion blockade, this is why this is the prefered BB)
Antithyroid drugs:
- Carbimazole, treat for 12- 18 months
- Trab and T4 fall at same time
radioactive Iodine
- Need hyperthyroid replacement
- Trab rises while T4 fall with RAI
Total thyroidectomy
- Need hyperthyroid replacement
- Trab and T4 fall at same time

29
Q

How is medical therapy for graves disease monitored?

A

Trab
- once Trab not detectible, can consider stopping carbimazole

30
Q

Contraindicaiton for RAI?

A

Pregnancy
Active eye disease (can use in burnt out eye disease)
Nodular graves disease (need to Ix nodules first)

31
Q

What medical therapy for graves in preg?

A

PTU in 1st trimester then carbimazole in 2nd and third

32
Q

Pathophys of graves eye disease?

A

Autoantibodies direceted against IGF-1 receptors or orbital fibroblasts
- leads to autoimmune inflammation of the orbits

33
Q

Severe graves eye disease is distinguished by…?

A

Is vision threatened or not

34
Q

Most common finding in thyroid eye disease?
Most specific finding?

A

Lid retraction
exothamus and proptosis

35
Q

Most common EOM affected in graves?

A

Inferior rectus muscle

36
Q

Treatment of graves eye disease?

A

Initial medical managment to control inflamation, then can consider corective surgery once inflamation settled

Medical therapy:
- Glucocorticoids is mainstay
- More advanced immunotherpies

37
Q

Pt with subclinical hyperthyroidism on initial test. ? what is the typical TFTs seen? what is the intial step?

A

Typical TFTs
- TSH low, T3 and 4 normal range

Initial step
- recheck in 3-6 months (pty may be unwell, have recent iodine exposure etc. Many causes that are not concerning)

38
Q

Subclinical hypothyroidism persistent on repeat TFTs 6 months later. What is next steps in Ix and Rx?

A

Thyroid scintigraphy
- usually due to toxic nodule, therefore this is best test
Thyroid USS to look for cold nodules
Then decide whether and how to treat

Note, If have single toxic nodule treatment with RAI can cure it. Normal thyroid tissue will recover

39
Q

When should you treat subclinical hyperthyroidism? Why do we treat subclinical hyperthyroidism?

A

Age <65
- TSH <0.1 and asymptomatic - consider treatment
- TSH 0.1-0.4 - observe

Age >65
- TSH <0.1 - treat
- TSH 0.1-0.4 - Consider treating

Because the cardiovascular risk associated with it, even if subclinical

40
Q

What drives post partum thyroiditis?

A

Immune reconstitution

41
Q

Most hypothyroidism is self liming over a course of about 4-6 months. Except?

A

Superative thyropiditis (bacterial infection)
this can be life threatening so need to exclude

42
Q

General pattern of T4 level in thyroiditis?

A

Initially will drop causing hypothyroidism, then will recover over a course of 4-6 months

Even tho hashimotos (like most other thyroiditis) usually is self limiting and 4 recovers, there is an increased risk of hypothyroidim later in life hence should have annual TFTs with GP

43
Q

Is scintigraphy helpful in amiodarone induced thyroiditis?

A

No, the high iodine load means there will be no uptake, therefore not helpful

44
Q

Amiodarone can cause hypo and hyperthyroidism via thyroiditis. Explain mechanism of type 1 and 2 amiodarone induced thyroiditis?

A

Type 1 AI thyrotoxicosis
- Jod basedow phenomenon (ie too much iodine = overproduction of thyroid hormone)
- Develops soon (ie 3 months after starting)
- treatment: carbimazole and PTU

Typoe 2 AI thyrotoxicosis
- this is due to destructive thyroiditis causing release of thyroid homrone
- develops later after stating amiodarone (ie 30 moinths down the line)
- Characterised by a rapid rise in thyroid thormone
- treatment is glucocorticoids

45
Q

Pt with subclinical hypothyroidism on initial test? what is the typical TFTs seen? what is the intial step?

A

Elevated TSH, normal FT4
- repeat test 3-6 months to check if resolved (most will)

46
Q

Subclinical hypothyroidism. TSH >10. SHould you treat?

A

Generally yes, this is very high TSH and has high chance of progressing to clinical

47
Q

When are normal TFT derrangments usually worst in preg?

A

1st trimester
- this is when bHCG is highest

48
Q

Initial evaluation of euthyroid and hyperthyroid thyroid nodules?

A

Can be euthyroid or hyperthyroid.

If hyperthyroid
- Antibody testing
- Thyroid uptake scan

If euthyroid
- USS to characterize
- Size and appearance will determine FNAB
-> only nodule >1cm should be evaluated

49
Q

FDG PET positive thyropid nodule = …?
FDG PET positive thyroid gland = … ?

A

higher risk of cancer
Thyroiditis

50
Q

USS features that are concerning for cancer in thyroid nodule?

A

Microcalcification (more so than macrocalcification)
Irregular margins
Hypoechoic changes

51
Q

TIRADS 1 or 5 more concerning?

A

TIRADS 5

52
Q

What are the two types of primary thyroid cell malignancy?

Which is teh most common malignant (ie not benign) thyroid cancer?

A

Tumours of folicular cells:
- Benign: folicular adenoma
- Malignant: Papilliary, folicular, poorly differentiated, anaplastic

Tumours of C cells:
- Medullary carcinoma

Papiliary is the most common

53
Q

Treatment of thyroid cancer?
How is it monitored post resecction?

A

Usually I131 or total thyroidectomy, however there is increasing targeted medical managment option

Thyroglobulin is used to monitor and guide imaging post resection

Endocrinology (4 decks)

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