Thyroid Flashcards

1
Q

What is the most common cause of hypothyroidism?

A

Hashimoto’s thyroiditis

  1. iatrogenic - previous ablation, surgery,
    amiodarone - 10% of people who take it chronically
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What does Amiodarone do to the thyroid?

A

Hyperthyroidism
type 1 - excess iodine load
type 2 - thyroiditis induced by Amiodarone

Hypothyroidism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What antibodies suggest Hashimoto’s thyroiditis??

A

Anti-TPO
thyroglobulin antibodies
- in context of clinical picture of hypothyroidism
- high TSH, low T4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What imaging should be performed in hypothyroidism?

A

USS only if there is a goitre or nodule palpable to exclude malignancy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is the TFT pattern in sublicinical hypothyroidism and when is treatment indicated?

A

elevated TSH with normal T4/T3
treat when TSH > 10 (or if symptoms, have a goitre or are pregnant or planning pregnancy or have positive TPO antibodies - more likely to progress to overt hypothyroidism)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What % of thyroid nodules are malignant?

A

5-15%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What features of a thyroid nodule make it more likely to be malignant?

A
age  60
male gender
FH of thyroid cancer
previous head and neck RT
presence of cervical lymphadenopathy
rapid growth
hoarse voice
fixed, firm nodule
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

When are calcitonin levels useful?

A

In following a patient with medullary thyroid cancer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

how is disease activity monitored following resection/ablation of a thyroid cancer?

A

thyroglobulin level

- this is secreted by functioning thyroid tissue (which should have been removed with treatment)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What initial test should be performed when a thyroid mass is detected and why?

A

TSH

- if suppressed then the nodule is “hot” and should not be biopsied

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What imaging should be performed when a thyroid nodule is detected?

A
USS thyroid for all
radioactive isotope scan if hot nodule
- detects MNG - multiple nodules
- Graves uniformly increased uptake
- single hot nodule - hot nodule with reduced uptake of the rest of the gland
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What features make malignancy more likely on USS?

A
size greater than 3 cm
hypoechogenicity
shape taller than wide
irregular infiltrative margins
microcalcifications within the nodule
high intranodular vascular flow
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

When is an FNA indicated to investigate a thyroid nodule?

A
  • any nodule greater than 1 cm in diameter that is solid and hypoechoic on ultrasonography
  • any nodule 2 cm or greater that is mixed cystic-solid without worrisome sonographic characteristics

Consideration of biopsy may be appropriate for
- smaller nodules (at least 5 mm in diameter) in patients with risk factors, such as a history of radiation exposure, a family or personal history of thyroid cancer, cervical lymphadenopathy, or suspicious ultrasound characteristics.

FNA biopsy is not routinely recommended for thyroid nodules less than 1 cm in diameter.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

When is thyroidectomy indicated for management of a thyroid nodule?

A

IF FNA indicates malignant

if >4cm nodule with indeterminate FNA - 15-30% are found to be malignant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

If an FNA is benign, what should then happen?

A

Ongoing monitoring with exam and USS every 6-18 months
- repeat FNS if growth > 50% or suspicious changes on USS
if at 18 months there has been no change then can monitor again in 3-5 years

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the most common types of thyroid cancer?

A

Papillary - 85%
Follicular - 10%
Medullary - 4%

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What condition should be considered in a diagnosis of medullary thyroid cancer?

A

Medullary thyroid cancer can be a component of MEN2A and can be associated with hyperparathyroidism with hypercalcemia and hypertension due to a pheochromocytoma. Medullary thyroid cancer typically is characterized by plasmacytoid, spindle, round, or polygonal cells on biopsy. All patients with medullary thyroid cancer should have RET proto-oncogene sequencing after other appropriate evaluation, including measurement of plasma free metanephrine and normetanephrine levels to detect or exclude the presence of a pheochromocytoma.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What dose adjustment should be made for women on thyroxine who become pregnant and why?

A

increase dose by 30-50%

  • increased oestrogen in pregnancy causes TBG to increase. This reduces the level of free T4
  • normally this would balance through an increase in TSH to raise T4 levels however this is not possible in hypothyroidism so an increased replacement dose is necessary to maintain normal fT4 levels
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What normal changes in thyroid hormones are seen in pregnancy and why?

A

In first trimester TSH levels decrease
This is due to the common alpha subunit of hCG stimulating TSH receptors
It is uncommonly associated with thyrotoxicosis and usually normalises by 16/40

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How is a thyroid storm managed?

A

Propylthiouricil - reduces T4 -> T3 conversion

Propranolol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What treatment changes should be made for a pregnant woman with hyperthyroidism on anti-thyroid drugs?

A

Change Carbimazole to PTU in 1st trimester

Grave’s often improves in pregnancy

22
Q

What is an important consideration in treating myxoedema coma?

A

Check cortisol levels - give hydrocortisone until adequate adrenal function is confirmed

23
Q

What is the treatment for Grave’s?

A

Anti-thyroid drugs - Carbimazole/ PTU
- can consider stopping after 18months
Radioactive iodine (not if eye disease)
Thyroidectomy

24
Q

What is the target TSH in pregnant patients with hypothyroidism?

A
  1. 1 and 2.5 microunits/mL

- associated with fewer adverse outcomes for mother and fetus

25
Q

What is the treatment for stage III thyroid cancer?

A

surgery
thyroxine
radioactive iodine therapy

26
Q

What is the management of follicular neoplasia detected on FNA?

A

Thyroidectomy

  • unable to distinguish benign adenoma from malignancy on FNA
  • 15-30% are malignant so remove gland and histology gives the answer
27
Q

Steps in thyroid hormone synthesis

A

Iodine transported into cell by Na/I synporter on basolateral membrane
Iodine transported to apical membrane and oxidised to TPO (thyroid peroxidase)
Oxidised iodine added to tyrosyl residues within thyroglobulin
Coupling of iodotyrosines catalysed by TPO
Thyroglobulin taken into cells
Enzymes cleave thyroglobulin to form T4 and T3 which are then released

28
Q

Where does T3 form

A

7% is secreted from thyroid along with T4

In peripheral tissues deiodinase enzymes convert T4 to T3

29
Q

Findings on Tc99 scan (or radioiodine scan)

A

Graves - enlarged gland, homogenous diffuse uptake
Toxic adenoma - focal area of increased uptake, rest of gland suppressed
Multinodular goitre - enlarged gland with multiple areas of high and low uptake
Subacute thyroiditis - low uptake due to follicular damage
Thyrotoxicosis factitia or iodine containing substances - low uptake due to blockage by iodine

30
Q

Cause of pretibial myxoedema

A

Infiltrative dermopathy due to lymphoid invasion of skin
Increased glycosaminoglycans trap water in skin
Seen in 3% of Graves

31
Q

Risk factors for Graves opthalmopathy

A

Smoking
Iatrogenic hyperthyroidism
Radioactive iodine

32
Q

Features of Graves opthalmopathy

A

Not related to severity/activity of hyperthyroidism
Inflammation of extra-ocular muscles, orbital fat and connective tissues
Exopthalmos, impairment of eye movements, periorbital and conjunctival oedema

33
Q

Features of hyperthyroidism

A

Skin - warm, sweaty, thinning of hair, hyperpigmentation
Eyes - stare, lid lag, opthalmopathy
CVS - tachycardia, AF, hypertension
Metabolic - hyperglycaemia, low cholesterol
GI - diarrhoea, increased appetite
Thymic enlargement (in graves)
Anaemia, ITP, pernicious anaemia
Osteoporosis
CNS - anxiety, muscle weakness, depression, tremor

34
Q

Tests in diagnosis of Graves

A

Suppressed TSH
Increased T3 more than T4
TSH receptor antibodies
Diffuse uptake on scan

35
Q

Actions and ADRs of Carbimazole

A

Inhibits function of TPO

ADRs - cholestasis, rash, fever, pANCA vasculitis, agranulocytosis

36
Q

Actions and ADRs of Propylthiouracil

A

Inhibits function of TPO and blocks deionodinase in peripheries (decreased conversion from T4 to T3)
ADRs - hepatitis, agranulocytosis, rash, pANCA vasculitis

37
Q

What is Wolff-Chaikoff effect?

A

Excess iodine transiently inhibits thyroid iodide organification so decreased thyroid hormones are produced
Effect can last approx 10 days but then will have upregulating effect and produce lots of thyroid hormone

Used pre-op before removal of gland

38
Q

What is Jod-Basedow phenomenon?

A

Iodine administration to a person who is iodine deficient will put gland into overdrive and get lots of hormone secretion

39
Q

Features of type 1 amiodarone induced thyrotoxicosis

A

More common in context of pre-existing multi nodular goitre or activation of latent graves with iodine load

Difficult to distinguish on radioiodine scan
USS will show increased vascularity
Treat with thionamides - need high dose

40
Q

Features of type 2 amiodarone induced thyrotoxicosis

A

Destructive thyroiditis with excess relase of preformed T4 and T3
Occurs in patients without existing disease
Hyperthyroid then hypothyroid then recovery
Treat with steroids and thionamides

41
Q

When to treat subclinical hyperthyroidism

A
TSH less than 0.1
Multinodular goitre
Elderly
Osteoporosis
Heart disease, AF
42
Q

Features of thyroiditis

A

Release of preformed hormone due to inflammation of thyroid follicles
No uptake on radioiodine scan
Typically have period of hyperthyroidism lasting 2 weeks, then transient hypothyroidism then recovery

43
Q

Type of thyroiditis

A

Subacute thyroiditis
Lymphocytic and post partum thyroiditis
Riedels thyroiditis
Other - drug induced, radiation, infiltration, trauma

44
Q

Features of subacute thyroiditis

A

Painful swollen thyroid
Associated with HLA B35 in 75%
Implicated cause is post viral
Treat with NSAIDs, prednisone, b blocker for symptoms

45
Q

Antibodies in autoimmune hashimotos thyroiditis

A

90% have antibodies to TPO, thyroglobulin or Na-I transporter - but these arent’t specific
70% have TSH-R antibodies - but these block receptor instead of stimulating it

46
Q

Causes of hypothyroidism

A

Autoimmune hashimotos thyroiditis
Iodine deficiency - most common cause worldwide
Iatrogenic - post thyroidectomy, irradiation, radioiodine
Drugs - thionamides, lithium, amiodarone
Infiltrative disease
Transient - ie post thyroiditis
Hepatitis C - increased autoantibodies and interferon related

47
Q

Features of hypothyroidism

A

Skin - dry, coarse, pale, thin hair, oedema of face
Consititional - weakness, lethargy, weight gain
CVS - diastolic HTN, bradycardia, effusions
GI - constipation, thick tongue
CNS - slow relaxation of reflexes, memory loss, cognitive decline, depression
Hyponatraemia, anaemia, raised CK, raised LDL
Menorrhagia

48
Q

When to treat subclinical hypothyroidism

A

Pregnany
TSH greater than 10

2-3% progress per year

49
Q

Features of myxoedema coma

A
Impaired cognition
Seizures
Hypothermia
Hyponatraemia
Hypoglycaemia
Hypotensive
Hypoventilation
Rhabdomyolysis
Acute kidney injury
50
Q

Treatment of myxoedema coma

A

Ensure not hypocortisolism - need to replace cortisol first
Load with T4 or give T3 IV
Passive rewarming
Treat precipitating illness

Mortality 20-50%

51
Q

Features of sick euthyroid

A

can have variety of abnormalities - usually low T3, normal/low T4, normal/low TSH
Increased conversion of T4 to reverse T3
Impairment of peripheral deiodoniation

52
Q

Treatment of hypothyroidism

A

Aim to achieve TSH of 1.0
Long half life - don’t adjust doses too quickly (2/52)
Start low in elderly or heart disease
High TSH despite high dose indicates non compliance