Thyroid Flashcards
Which effects has TSH on the thyroid gland?
It binds to the Thyroid receptor and
- mediates iodine intake into colloid
- meditaes release of already formed T3/T4
Recall the symptoms of Myxoedema
Low basal rate resulting in
- tiredness
- depression
- cold intolerance
- weight gain
- constipation
- bradycardia
–> in severe cases: might lead to myxoedema coma!
What is the cause of myxodema?
Prymary hypothyroidism due to autoimmune response on thyroid
What are the biochemical features of Myxodema?
High TSH
Low T3/T4
How would you treat somone with hypothyroidism?
How are the right dosages adjusted?
Usually T4 replacement (Levothyroxine sodium)
- T4= prohormone that is converted into active T3 by enzymes in body
- In primary hypothyroidism: TSH levels are used to adjust dosage
- In secondary hypothyroidism: free T4 (normally 99.7% bound to Thyroid binding globulin) middle-range levels are aimed
T3 replacement Liothyronine sodium
- less commonly used: normally only used as IV shot when myxodema come –> faster action
What are the advantages and limitations of T3 replacement or a combined replacement instead of T4 replacement in hypothyroidism?
No evidence-based advantages known
- it is more expensive
- As T3 is active form: higher risk of toxicity leading to hyperthyrpoid symptoms like:
- palpitations, tremor, anxiety - often combination treatment suppresses TSH
How are thyroid hormones transported in blood?
Why is this important to consider when supplementing the hormones
It is highly bound to Thyroxine binding globulin (TBG) –> 99.7% T4 is bound, 99.97% T3 bound
BUT: TBG levels can differ:
- plasma binding proteins increase in pregnancy and on prolonged treatment with oestrogens and phenothiazines
- TBG falls with malnutrition, liver disease
- certain co-administered drugs (e.g. phenytoin, salicylates) compete for protein binding sites.
What is the prefered route of administration of thyroid hormones?
What is their half-life?
- active orally –> tablet
- Half-life long
- Levothyroxine (T4) plasma half life of 6 days
- Liothyronine (T3) plasma half life 2.5 days
–> Not the end of the world when somone forgets to take one tablet etc.
What are the three targets of the different Antibodies in Grave’s disease?
Which symptoms do they cause?
- Antibodies binding to TSH receptors
- Hyperthyroidism
- Antibodies binding to GH receptor at back of eye
- Exophtalamos –> starring appearance, can’t close eye
- Antibodies binding to GH receptors at ancles
- Pretibial myxedema –> not pitting-oedema due to growth of soft tissue
What happens to the ß-Receptors in Grave’s disease?
ß-receptors are more sensitive to adrenaline –>increased SNS reaction
How does the thyroid in someone with Graves’ disease feel on examination?
Symmetrical
Smooth
Enlarged (goiture)
Moves when swallowing (indication that it is thyroid)
Not painful on examination
What is Plummers disease?
Benign adenoma that is overactive at making thyroxine
What would a thyroid in someone with Plummer’s disease on examination look/feel like?
Toxic nodular goiture
Asymmetrically enlarged (tumor)
not painful
On scintigram:
- “hot nodule”,
What is lid lag?
When and why does this symptoms occur?
When lowering the eyes:
Normally: there is no white in the eye seen above the iris (because eye lid follows eye movement)
In Lid lag:
- White above the eye can be seen when lowering the eyes because eye lid reaction is delayed
- Because of increased sympathetic reaction of the eyelid (that pulls it back) due to an increased sensitivity of ß receptors due to hyperthyroidism
What is a thyroid storm?
Very rare: but 50% mortality (due to arrythmias and heart failure)
–> Hyperthyroidism
body temperature, heart rate, blood pressures are dangerously high
What are the symptoms of viral thyroiditis?
How would the thyroid feel on examination?
- •Painful dysphagia
- •Hyperthyroidism
- •Pyrexia
- •Raised ESR
Examinaiton
- enlarged, asymetrically
- tender (painful on palpation)
Explain the use and function of a technetium scan
Tyroid takes Technetium (Tc 43) up (instead of iodine) (rather radioactive isotop: Tc-99m)
–> can be seen on scans (radioactive radiation detected)
What are the aniti-thyroid drugs used in hyperthyroidism?
What is their mechanism of action?
I.e. daily treament for Gaves’ and Toxic thyroid nodule/toxic multinodular goitre
- propylthiouracil (PTU)
- carbimazole (CBZ)
–>
- Inhibits production and secretion of T3/T4 (by inhibiting thyroid peroxidase)
- May reduce production of antibodies in Graves’
- And PTU reduces conversion of T4 into T3 in peripheral tissues
Explain the use of Iodine in the treatment of hyperthyroidism
Indications
- Prep for surgery (want less SNS when surgery)
- Thyroid storm
–> need to be taken out afterwards (because expected later high levels of thyroid hormones)
Administraion
- Usually KI
- Orally (maximal effects after 10d of continous administration
- inhibits H2O2 formation and thyroid peroxidase effect and ionidation of tyhoroglobulin
Induced the Wolff-Chaikoff effect:
- presumed autoregulatory effect
- no secretion of thyroid hormone after large dose of iodine –> fast reaction (withing 1-2 days)
Side effects
- allergic reactions
