Chemical pathology 8 - Thyroid

Question 1

What % of T4 is typically bound to TBG?

Answer 1

75%

Question 2

To which proteins can T4 bind?

Answer 2

TBG
TBPA
Albumin

Question 3

Recall the possible aetiologies of primary hypothyroidism

Answer 3

Mnemonic: Hypothyroidism Possible Aetiology 
Main causes are: 
H = Hashimoto's
P = Post-Grave's disease
A = Atrophic 
Other causes (more rare): 
Drugs (eg lithium) 
Thyroid dysgenesis 
Peripheral T3 resistance

Question 4

What is the expected TSH and T4 levels in primary hypothyroidism?

Answer 4

TSH high

T4 low

Question 5

What test should always be done before thyroid-replacement medication is initiated?

Answer 5

ECG - because T4 increases cardiac contractility

Question 6

How does thyroid function change in pregnancy?

Answer 6

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

Question 7

What type of non-thyroid malignancy can cause thyrotoxicosis?

Answer 7

Malignancy that produces hCG

E.g molar pregnancy, struma ovarii

Question 8

What test is used to detect neonatal hypothyroidism?

Answer 8

Guthrie test

Question 9

What does the term ‘sick euthyroid’ refer to?

Answer 9

Any severe illness –> reduced T4, increased TSH and decreased T3
This is normal physiology in sepsis

Question 10

Recall 5 differentials for the cause of hyperthyroidism, and how each would appear on a technetium scan

Answer 10

1. Grave’s (40-60% of cases) - high uptake
2. Toxic multinodular goitre - high uptake
3. Single toxic adenoma - high uptake
4. Subacute thyroiditis - low uptake
5. Postpartum thyroiditis - low uptake

Question 11

What drugs can be used to treat an overactive thyroid? What is their mechanism of action?

Answer 11

Carbimazole and propylthiouracil

Inhibit TPO

Question 12

What is the main risk of carbimazole and propylthiouracil treatment?

Answer 12

Agranulocytosis

Question 13

Over how long should carbimazole and propylthiouracil treatment be titrated ?

Answer 13

18 months

Question 14

How should papillary thyroid Ca be treated?

Answer 14

Removal of thyroid gland
Then radioiodine treatment
Then give supraphysiological thyroxine (so Ca cells not reactivated)

Question 15

Recall 2 tumour markers for medullary thyroid cancer

Answer 15

CEA and calcitonin

Question 16

Which type of thyroid cancer is associated with Men II?

Answer 16

Medullary