Chemical Pathology - Thyroid Flashcards
how is thyroxine produced?
- iodide goes through membrane from capillary via Na/K ATPase
- iodide to iodine by thyroid peroxidase
- iodine taken up by thyroglobulin
- iodination of tyrosine residues in thyroglobulin = MIT and DIT
- T4 produced and stored in thyroid gland
what happens to T4 in periphery?
converted to T3
to what 3 proteins does T4 bind to?
TBG
TBPA (thyroid binding pre albumin)
Albumin
antibodies in Hashimoto’s/ chronic lymphocytic thyroiditis
anti-TPO
anti-TG
antibodies in Grave’s
anti-TSH
anti-TPO
antibodies in Reidel’s thyroiditis
IgG4 related disease
antibodies in Viral thyroiditis
NO ANTIBODIES
hyperthyroid to hypothyroid
main 3 causes of hypothyroidism?
- Hashimoto’s (AI)
- atrophic thyroiditis
- Post-Grave’s disease (radioactive iodine, surgery, thionamides)
other minor causes of hypothyroidism?
- post-thyroiditis
- thyroid agenesis/dygenesis
- 2nd hypothyroidism (pituitary disease)
- drugs (amiodarone, lithium)
- iodine deficiency
- peripheral thyroid hormone resistance
clinical features of hypothyroidism
- weight gain
- bradycardia
- constipation
- laboured breathing
- oligomenorrhoea
- poor appetite
- hyponatraemia
- cold/dry hands and feet
- normocytic anaemia
Investigations in hypothyroidism
- high TSH
- low T4
- TPO antibodies
- consider presence of other AI conditions
Tx in hypothyroidism
- perform ECG (levothyroxine will exacerbate MI and worsen HF)
- Levothyroxine (titrate to normal TSH)
- Liothyronine
what is subclinical hypothyroidism?
- T4 level is normal, TSH is high
- TPO antibodies are positive, suggests pt may go on to develop thyroid disease
- unlikely to be cause of presenting symptoms
what is hypothyroidism associated with?
hypercholestrolaemia
what is a risk of radioiodine tx?
hypothyroidism
normally occurs within 1 year
how does thyroid function vary in pregnancy?
- hCG has similar structure to TSH
- rise in hCG in 1st trimester = T4 rises (normal)
- TBG levels inc in pregnancy as under control of oestrogen
- later in pregnancy hCG levels fall and T4 drop again
how is neonatal hypothyroidism diagnosed?
Guthrie test at 48-72 hours
what is sick euthyroid syndrome?
alteration in pituitary-thyroid axis in non-thyroidal illness
if v sick, thyroid may shut down to try and reduce basal metabolic rate to conserve energy
NO hypothyroid symptoms
what is the biochemistry in sick euthyroid?
Low T4 and T3
reduced T3 action
normal/high TSH
what are the 3 high uptake causes of hyperthyroidism?
- Grave’s disease
- Toxic multinodular goitre
- single toxic adenoma
what are the 2 main low uptake causes of hyperthyroidism?
- subacute/viral/ de Quervain’s thyroiditis
- postpartum thyroiditis
what are rarer causes of hyperthyroidism?
- TSH-induced
- throphoblastic tumour and struma ovarii (high hCG production)
- thyroid cancer induced
what does a technetium scan do?
used to show which parts of thyroid are producing excessive thyroid hormone
clinical features of hyperthyroidism
- weight loss
- tachycardia
- diarrhoea
- tachypnoea
- osteopaenia and osteoporosis
- irregular periods
