General thyroid notes and other information

Question 1

Where in the thyroid is thyroid hormone made?

Answer 1

In the follicles which are filled with colloid (the reservoir from which thyroid hormone is made)

Question 2

What does the columnar epithelium produce in the thyroid?

Answer 2

The thyroid follicular cells make thyroglobulin

Question 3

What do C-cells make?

Answer 3

Calcitonin

Question 4

Tyrosine combines with iodine to form what?

Answer 4

T4

T3 - the more potent

Question 5

How does the pituitary-thyroid hormone axis work?

Answer 5

Negative feedback of T4/T3 on pituitary TSH and hypothalamic TRH

• LOW T4 -> increased TSH
• HIGH T4 -> suppressed TSH

Overactive thyroid: high T4 and T3, LOW TSH
Under-active thyroid: LOW T4 and HIGH TSH

Question 6

What is looked at in thyroid function tests?

Answer 6

Free T4 - only free hormone: 10-25 picomol/l
Total T3 and free T3

TSH - done as an assay
Antibodies:
- TPO Abs (thyroid peroxidase antibodies)
- TSH-R Abs (thyroid stimulating hormone receptor antibodies)

Question 7

What does goitre mean?

Answer 7

Enlarged thyroid

Question 8

What must be assessed on a goitre?

Answer 8

Must assess thyroid status - e.g thyrotoxic, hypothyroidism

Are there compression symptoms? - is it pressing on oesophagus or trachea

Diffuse vs Multinodular - distinguished by palpation

Question 9

What are causes of diffuse goitres?

Answer 9

Graves’ disease
Hypothyroidism (Hashimoto’s)
Colloid goitre (euthryoid)
Iodine deficiency, drugs (e.g. lithium)

Question 10

What are solitary lumps?

Answer 10

Common and increase with age
30-60% of normal thyroids have nodules at autopsy 
May be part of multinodular disease
Palpation: 5-20% (>1cm)
Ultrasound scan: 15-50% (>2mm)
Thyroid cancer - this is rare

Question 11

How are thyroid nodules evaluated?

Answer 11

Ultrasound

Fine needle aspiration (FNA)

Question 12

What diagnostic approach is used for goitres?

Answer 12

Non-diagnostic: Thy1 - inadequate cellularity 5-20%
Benign: Thy2 - 70%, usually colloid nodules
Indeterminate: Thy3
- 10-20% ‘follicular lesion’
- Could be adenoma or carcinoma
Suspicious of malignancy: Thy4 - about 30% will be malignant
Diagnostic of malignancy: Thy5
- Clear features of papillary, follicular, medullary or other carcinoma; lymphoma, metastasis