Chemical pathology 8 - Thyroid Flashcards
What % of T4 is typically bound to TBG?
75%
To which proteins can T4 bind?
TBG- thyroid binding globulin
TBPA- thyroxine binding prealbumin
Albumin
**TBG production depends on albumin itself**
- essenially very little of it is free
Recall the possible aetiologies of primary hypothyroidism
Mnemonic: Hypothyroidism Possible Aetiology
Main causes are:
H = Hashimoto’s - this is the most common
P = Post-Grave’s disease - the treatment is radio-iodine which can cause hypothyroid
A = Atrophic
Other causes (more rare):
Drugs (eg lithium and amiodarone)
Thyroid dysgenesis
Peripheral T3 resistance
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?
In 1st trimester, there is a huse rise in hCG
hCG has the same configuration as TSH - this then stimulates the thyroid gland to produce supra-physiological amounts of thyroxine
However, this is normal in pregnancy, so the woman doesn’t become clinically hyperthyroid
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
What does the term ‘sick euthyroid’ refer to?
Any severe illness –> reduced T4, increased TSH and decreased T3
This is normal physiology in sepsis
Recall 5 differentials for the cause of hyperthyroidism, and how each would appear on a technetium scan
-
Grave’s (40-60% of cases) - high uptake
2. Toxic multinodular goitre - high uptake
3. Single toxic adenoma - high uptake - Subacute thyroiditis/viral (INITIAL PHASE where thyorid hormone is released from the gland) - low uptake
- Postpartum thyroiditis (INITIAL PHASE where thyroid hormone is released from the gland) - low uptake
HIGH T4/T3
LOW TSH
__-
Other rarer differentials:
1) factitious- intake of thyroiine (high T4, normal TSH)
2) pituitary problem - TSHoma (high T4/T3 and High TSH)
3) thyorid cancer induced
4) trophoblastic tumour (hcg mimics TSH) or struma ovarii (high T4, normal TSH)
Treatment of hyperthyoridism
in order
What is the main risk of carbimazole and propylthiouracil treatment?
Agranulocytosis
Over how long should carbimazole and propylthiouracil treatment be titrated ?
18 months
How should papillary thyroid Ca be treated?
Removal of thyroid gland
Then radioiodine treatment
Then give supraphysiological thyroxine (so Ca cells not reactivated)
Recall 2 tumour markers for medullary thyroid cancer
CEA and calcitonin
Which type of thyroid cancer is associated with Men II?
Medullary
WHat is the most common cause of hypothyoridism?
most causes are primary i.e. a problem with the thyroid gland itself rather than a problem with the pituitary
worldwide- iodine deficiency
uk - hashimotos (autoimmune)
Clinical features of hypothyoridism
- Low metabolic rate- e.g. tiredness, lethargy
- Cardiovascular- e.g. bradycardic
- GI- e.g. constipation
- Respiratory- e.g. breathing is more laboured
- Reproductive- e.g. oligomenorrhoea, infertility
- Weight gain (reduced resting energy expenditure) and poor appetite
- Cold and dry hands, feels cold
- Hyponatraemia: rmb it causes euvolaemic hyponatraemia
- Normocytic anaemia:unless they have pernicious anaemia
- Lack of intrinsic factor → poor vitamin B12 absorption
- would be macrocytic anaemia- another autoimmune condition similar to thyroid disease
- Myxoedema madness
- goitre
- Subtle in elderly
- Secondary hypothyroidism → pituitary tumour leads to the development of visual problems
What does high TSH and normal T4 indicate?
Either treated hypothyroidism or subclinical hypothyoridism
subclinical hypothyoridism- measure anti-TPO antibodies; if positvie then they have a chance of developing hypothyoridism later on in life.
only benefit of treating subclinical hypothyroidism is if they have hypercholesteramiea
What do you see in sick euthyroid disease and what is it?
In any severe illness, the thyroid gland shuts down to preserve metabolic rate
Low T3/T4–> high TSH (later comes back to normal)
Clinical features of hyperthyoridism
Raised metabolic rate (weight loss)
Cardiovascular (tachycardia, AF, palpitations)
GI (e.g. diarrhoea)
Respiratory (e.g. tachypnoea)
Skeletal (e.g. osteopaenia/ osteoporosis)
Reproductive (e.g. irregular periods, infertility)
Features of graves disease
- Diffuse smooth goitre
- Exophthalmos
- Thyroid associated dermopathy (pretibial myxoedema)
- Thyroid acropachy (bones and fingers)
- Other autoimmune disease (or family history)
anti TSH receptor antibody positive
Summary of the main causes of hypo and hyperthyoridism and how to distinguish between them
Antiboduyes in ahshimotors
anti TPO or anti thyroglobulin
Papillary thyroid cancer - tumour marker
thyroglobulin
Follicular thyorid cancer- tumour marker
thyroglobulin
3 multiple endocrine neoplasias
MEN1 (3Ps): Pituitary, Pancreatic (e.g. insulinoma), Parathyroid (hyperparathyroidism)
MEN2a (2Ps, 1M): Parathyroid, Phaeochromocytoma, Medullary thyroid
MEN2b (1P, 2Ms): Phaeochromocytoma, Medullary thyroid, Mucocutaneous neuromas (& Marfanoid)
Thyroid neoplasias
