Chemical pathology 8 - Thyroid Flashcards
(36 cards)
Outline the steps in thyroid metabolism
- Iodide through membrane via Na+/K+ ATPase
- Iodide → iodine (thyroid peroxidase)
- iodine taken up by thyroglobulin → thyroxine
- iodination of tyrosine residues in thyroglobulin → monoiodotyrosine (MIT) and diiodotyrosine
- thyroxine (T4) produced + stored within thyroid gland → secreted → lumen when required
- T4 → T3 in peripheries
What % of T4 is typically bound to TBG?
75%
To which proteins can T4 bind?
TBG - 75%
TBPA - 20%
Albumin - 5%
Where is T4 converted to T3?
Peripheries
Recall the possible aetiologies of primary hypothyroidism
Mnemonic: Hypothyroidism Possible Aetiology
Main causes are:
H = Hashimoto’s
P = Post-Grave’s disease
A = Atrophic
Other causes (more rare):
Iodine def (commonest worldwide)
Drugs
Thyroid dysgenesis
Peripheral T3 resistance
What autoAbs are present in Hashimoto’s ?
(TPO/TG), Hurthir cells
What conditions are associated with atrophic thyroid?
a/w pernicious anaemia/vitiligo/endocrinopathies
Which drugs are associated with hypothyroidism?
amiodarone, lithium
What is Riedel’s thyroiditis?
IgG4-related disease
dense fibrosis → painless stony hard
How would you treat hypothyroidism?
Levothyroxine (T4), 50-125-200 mcg/day
Liothyronine (T3)
titrate to normal
What is subclinical hypothyroidism?
↑ TSH normal T4
pit gland sense T4 → thinks there isn’t enough → ↑ TSH
TPO +ve → may develop thyroid disease
unlike cause of sx → only treat to reduce hypercholesterolaemia
s/s of hypothyroidism
weight gain
bradycardia
constipation
laboured breathing
oligomenorrhoea
poor appetite
cold/dry hands and feet
normocytic anaemia (unless pernicious)
myxoedema, goitre
What is the expected TSH and T4 levels in primary hypothyroidism?
TSH high
T4 low
What test should always be done before thyroid-replacement medication is initiated?
ECG - because T4 increases cardiac contractility
How does thyroid function change in pregnancy?
hCG similar structure to TSH
hCG has the same configuration as TSH -> ↑hCG → ↑T4
↑ TBG (oestrogen)
later → ↓hCG → ↓T4
However, this is normal in pregnancy, so the woman doesn’t become clinically hyperthyroid
What may excess thyroxine lead to?
AF, osteropoenia
What type of non-thyroid malignancy can cause thyrotoxicosis?
Malignancy that produces hCG
What test is used to detect neonatal hypothyroidism?
Guthrie test on day 2/3 of life
too early → erroneously high because of maternal TSH in blood
What does the term ‘sick euthyroid’ refer to?
Any severe illness –> reduced T3/4, increased TSH
with any severe illness/sepsis → thyroid shut down to conserve energy
no hypothyroid symptoms
Causes of high uptake hyperthyroidism
- Grave’s - AI (40-60% of cases)
- Toxic multinodular goitre/Plummers
- Single toxic adenoma
Which Abs are present in Graves disease?
anti TSH
Features of Grave’s disease
ophthalmopathy (TSHR on eye muscles)
IMPORTANT: RI treatment can make Graves’ eye disease worse
Thyroid-associated dermopathy (pretibial myxoedema)
Thyroid acropachy
Painless diffuse goitre
Feaures of toxic multinodular goitre/Plummer’s
high uptake, hot nodules, painless, enlarged follicular cells distended with colloid/flattened epithelium
Causes of low uptake hyperthyroidism
Sub-acute/ viral /de Quervain’s thyroiditis
postpartum thyroiditis
