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Endocrinology > Thyroid > Flashcards

Thyroid Flashcards

1
Q

Thyroid:

Order of endogenous production?

A

Hypothalamus - Thyrotropin Releasing Hormone (TRH)

Anterior Pituitary - Thyroid Stimulating Hormone (TSH)

Thyroid gland - combines iodine with tyrosine with
peroxidase enzyme - T4 and T3 (Biologically active)

Peripheral tissue - T3 (converted from T4)

During illness the thyroid increases the production of rT3 (inactivated T3) and reduces T4 levels.
-Profound medical illness will result in abnormal thyroid test
-transient low T3 in acute illness
-low T4 in severe/chronic illness

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2
Q

Thyroid:

Hypothyroidism?

A

Symptoms to trigger testing

  • lethargy
  • weight gain
  • hyperlipidaemia
  • constipation
  • hairloss
  • low mood
  • cold intolerant

1) TSH - if high repeat test in 4 - 6 weeks with the following

2) FT4 and Thyroid Peroxidase Antibodies (TPOAb)
- LOW = hypothyroidism = treat

  • normal = subclinical hypothyroidism
    a) TSH 4.5 - 10 = monitor

b) TSH >10 AND
-TPOAb positive = Hashimotos thyroiditis (Chronic lymphocytic thyroiditis)
->70yo
-CVD
-symptomatic
Then treat

Treatment considerations:

  • aim for 1.6microg/kg
  • if >60yo or CVD start at 25microg per day increasing weekly as tolerated
  • otherwise start 50microg daily
  • Eltroxin and Levoxine do not require refrigeration (oroxine and eutroxsig do)
  • Eltroxin may be slightly less potent (10%) so be mindful if changing agents

Risks of over suppressed TSH:
-cardiac arrhythmia
-bone loss
*mainly in the elderly

-Amiodarone contains iodine so can lead to induced hypothyroidism
-Lithium inhibits thyroid hormone syntheses and can result in hypothyroidism
-Immune checkpoint inhibitors can cause hypothyroidism

-initiation of T4 may take months for the TSH to respond accordingly so the T4 level should be used to reach target

testing must be done PRE-DOSE (trough levels)

  • retest after 6 weeks
  • T4 half life is 7 days
  • T3 half life is 24hours (need regular dosing)
  • TSH for monitoring
  • T4 should be high normal, T3 will be low normal because depending on how much residual thyroid production there is the body is missing out on the natural proportion of T3 produced rather than peripherally synthesised).

*Replacement with low T3 is not going to change measured T4 levels, TSH should be the marker to monitor.

*T3 dosage 20 – 40mcg per day in a divided dose (only trial if persistent symptoms on T4 and TSH is stable at 1 -2 mIU/L)
*Decrease T4 dosage if adding T3 to prevent over-treatment

  • *Warfarin dosage is impacted by thyroid levels
  • elevated T4 = reduce warfarin dose
  • low T4 = increase warfarin dose
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3
Q

Thyroid:

Goitre/cancer disease?

A

Goitre is an overgrowth of thyroid tissue due to reduced thyroxine synthesis.

a) Non toxic goitre
Iodine deficiency
-bread and salt in Australia is iodine reinforced to prevent this
-smoking is goitrogenic particularly if combined with iodine deficiency

b) Toxic goitre
1) Graves
2) Hashimotos thyroiditis
3) Nodules
- very common is asymptomatic population (30 - 50% on USS)
- benign or malignant

Approach

  • TSH low = need Technetium 99 scan (Tc99m)
  • TSH high = USS and FNA if indicated
  • Any cold nodule on Tc99 scan requires USS and FNA
  • Any benign nodule should have repeat USS in 6 - 18months
  • repeat FNA IF increases by >20% in 2 dimensions by 2mm

USS features with highest specificity for cancer

  • microcalcifications
  • irregular margins
  • anterior posterior greater than transverse diameter (when scanning recumbent patient)

Thyroid cancer

  • most common endocrinology malignancy
  • risk of 7 - 15% for nodules
  • higher risk if Multiple Endocrine Neoplasia type 2 (MEN2)
  • types; anaplastic, follicular, medullary, papillary, lymphoma, metastasis
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4
Q

Thyroid:

Hyperthyroidism?

A

Symptoms to trigger testing:

  • anxiety
  • increased metabolism
  • palpitations
  • sweating
  • weight loss
  • amenorrhoea
  • tremor
  • atrial fibrillation
  • proptosis
  • goitre

1) TSH low repeat with

2) FT4 and FT3
a) Normal without any of the following:
->65yo
-CVD risk factors
-post menopausal osteoporosis
-TSH <0.1
= repeat TFTs in 3 months then annually

b) Normal with any of above met OR elevated FT4 then add

3) TSH Receptor Antibodies (TRAb)
a) TRAb Positive (95% - 100%) = Graves disease

b) TRAb Negative

4) Tc99m scan
a) low or no uptake = thyroiditis
b) focal uptake = toxic adenoma
c) patchy uptake = toxic multinodular goitre
d) diffuse uptake = Graves disease

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5
Q

Thyroid:

Thyrotoxicosis?

A

THYROIDITIS

1) Painless Post Partum Thyroiditis (PPPT)
- occurs 1 - 6 months post partum
- more common in DMT1
- *can become hypothyroid transiently/permanently 6 - 12 months post partum
- symptomatic management beta blockers/T4 if required

2) Painless Thyroiditis
- F > M 2:1
- 30 - 40yo
- *can become hypothyroid transiently/permanently

3) Painful Subacute Thyroiditis
- F > M 5:1
- 20 - 60yo
- occurs post URTI
- *can become hypothyroid transiently/permanently
- symptomatic management beta blockers/NSAIDs for pain/possibly prednisolone

TOXIC ADENOMA

  • F > M 10:1
  • 30 - 50yo
  • treated with radioactive iodine (RAI)

TOXIC MULTINODULAR GOITRE

  • F > M 10:1
  • > 50yo
  • treated with radioactive iodine (RAI)

AMIODARONE INDUCED THYROIDITIS

  • type 1 = underlying thyroid condition
  • type 2 - no underlying thyroid disease (Destructive thyroiditis)
  • can take ≤1 year post amiodarone cessation to develop
  • treated with thyroid blocking agents and symptomatic medications

GRAVES DISEASE

  • F > M
  • 40 - 60yo
  • ophthalmopathy (exophthalmous/proptosis - lid lag, periorbital oedema), Dermopathy (myxoedema), Aropachy (nail cuticle clubbing)
Management:
1)
a) Symptomatic relief
-beta blockers
-verapamil or Diltiazem if beta blockers contraindicated

b) thyroxine blockade
FIRST LINE (unless 1st trimester pregnancy)
Carbimazole
-start 10 - 30mg daily
-reducing to 2.5 - 10mg daily for 12 - 18months
-side effects: agranulocytosis (usually within the first 3 months - cease if getting mouth ulcers), GIT disturbance, rash, teratogenic, liver dysfunction

SECOND LINE (unless 1st trimester pregnancy)

  • Propylthiouracil
  • 100 - 200mg BD
  • preferred in thyroid storm as reduces peripheral conversion to T3 so acts quicker than carbimazole
  • side effects: same as carbimazole and 0.1% liver injury risk (10% of these develop liver failure which may require lead to transplant or death)

*monitor using FT4/FT3 as TSH can remain suppressed for months

2) RAI
- 67 - 81% cure rate at 12 months
- 10% will get radiation thyroiditis
- avoid pregnancy for 6 months post RAI
- men to avoid conception until >4 months post for sperm normalisation
- for 1 -2 weeks post treatment avoid children contact due to risk of radiation exposure
- *not for moderate to severe ophthalmopathy as it can worsen it

3) Thyroidectomy

Ophthalmopathy management

  • smoking cessation (smoking worsens condition)
  • steroids
  • EOM radiotherapy
  • surgery

Thyroid storm

  • Fever from thermodysregulation
  • tachycardia/oedema
  • jaundice/diarrhoea
  • agitation/confusion
  • seizures/coma

Hospital management often required with thyroidectomy the last resort if it cannot be treated effectively.

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6
Q

Thyroid:

Thyroid disease and pregnancy?

A
  • Maternal T3 cannot cross placenta
  • foetus is reliant conversion of maternal T4
  • T3 essential for neurological development
  • bhCG acts like TSH so TSH level will fall while bhCG is elevated (pregnancy reference ranges are required)
  • T4 production increases by 30 - 50% (so if on replacement requires dose escalation)
    -meet this by doubling the dose 2 days in a week (of the patient’s normal dosage)
    -in non diagnosed women if TSH above 2.5mIU/L consider T4 supplementation
    -TPO Ab should be assessed if TSH greater than 4 mIU/L (if not yet pregnant; otherwise use pregnancy ranges)
  • increase production requires iodine availability
  • WHO recommends 250microg/day (iodine excess can cause foetal hypothyroidism)

Overt hypothyroidism
-can lead to lower IQ of child, miscarriage, stillbirth, preterm birth, low birth weight

Subclinic hypothyroidism
-minimal complications

Euthyroid TPO Ab positive

  • if recurrent miscarriages treat with low dose T4
  • check TPO Ab in all women with recurrent miscarriage

Hyperthyroidism

  • 1st trimester = propylthiouracil
  • 2nd and 3rd trimester convert to carbimazole
  • the transition is challenging and needs close monitoring

Graves disease

  • check TRAb at 28 - 32 weeks
  • often can have thyrotoxic flares post partum
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Endocrinology (12 decks)

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