Thyroid Flashcards
What is the most common cause of hypothyroidism?
Hashimoto’s thyroiditis
- iatrogenic - previous ablation, surgery,
amiodarone - 10% of people who take it chronically
What does Amiodarone do to the thyroid?
Hyperthyroidism
type 1 - excess iodine load
type 2 - thyroiditis induced by Amiodarone
Hypothyroidism
What antibodies suggest Hashimoto’s thyroiditis??
Anti-TPO
thyroglobulin antibodies
- in context of clinical picture of hypothyroidism
- high TSH, low T4
What imaging should be performed in hypothyroidism?
USS only if there is a goitre or nodule palpable to exclude malignancy
What is the TFT pattern in sublicinical hypothyroidism and when is treatment indicated?
elevated TSH with normal T4/T3
treat when TSH > 10 (or if symptoms, have a goitre or are pregnant or planning pregnancy or have positive TPO antibodies - more likely to progress to overt hypothyroidism)
What % of thyroid nodules are malignant?
5-15%
What features of a thyroid nodule make it more likely to be malignant?
age 60 male gender FH of thyroid cancer previous head and neck RT presence of cervical lymphadenopathy rapid growth hoarse voice fixed, firm nodule
When are calcitonin levels useful?
In following a patient with medullary thyroid cancer
how is disease activity monitored following resection/ablation of a thyroid cancer?
thyroglobulin level
- this is secreted by functioning thyroid tissue (which should have been removed with treatment)
What initial test should be performed when a thyroid mass is detected and why?
TSH
- if suppressed then the nodule is “hot” and should not be biopsied
What imaging should be performed when a thyroid nodule is detected?
USS thyroid for all radioactive isotope scan if hot nodule - detects MNG - multiple nodules - Graves uniformly increased uptake - single hot nodule - hot nodule with reduced uptake of the rest of the gland
What features make malignancy more likely on USS?
size greater than 3 cm hypoechogenicity shape taller than wide irregular infiltrative margins microcalcifications within the nodule high intranodular vascular flow
When is an FNA indicated to investigate a thyroid nodule?
- any nodule greater than 1 cm in diameter that is solid and hypoechoic on ultrasonography
- any nodule 2 cm or greater that is mixed cystic-solid without worrisome sonographic characteristics
Consideration of biopsy may be appropriate for
- smaller nodules (at least 5 mm in diameter) in patients with risk factors, such as a history of radiation exposure, a family or personal history of thyroid cancer, cervical lymphadenopathy, or suspicious ultrasound characteristics.
FNA biopsy is not routinely recommended for thyroid nodules less than 1 cm in diameter.
When is thyroidectomy indicated for management of a thyroid nodule?
IF FNA indicates malignant
if >4cm nodule with indeterminate FNA - 15-30% are found to be malignant
If an FNA is benign, what should then happen?
Ongoing monitoring with exam and USS every 6-18 months
- repeat FNS if growth > 50% or suspicious changes on USS
if at 18 months there has been no change then can monitor again in 3-5 years
What are the most common types of thyroid cancer?
Papillary - 85%
Follicular - 10%
Medullary - 4%
What condition should be considered in a diagnosis of medullary thyroid cancer?
Medullary thyroid cancer can be a component of MEN2A and can be associated with hyperparathyroidism with hypercalcemia and hypertension due to a pheochromocytoma. Medullary thyroid cancer typically is characterized by plasmacytoid, spindle, round, or polygonal cells on biopsy. All patients with medullary thyroid cancer should have RET proto-oncogene sequencing after other appropriate evaluation, including measurement of plasma free metanephrine and normetanephrine levels to detect or exclude the presence of a pheochromocytoma.
What dose adjustment should be made for women on thyroxine who become pregnant and why?
increase dose by 30-50%
- increased oestrogen in pregnancy causes TBG to increase. This reduces the level of free T4
- normally this would balance through an increase in TSH to raise T4 levels however this is not possible in hypothyroidism so an increased replacement dose is necessary to maintain normal fT4 levels
What normal changes in thyroid hormones are seen in pregnancy and why?
In first trimester TSH levels decrease
This is due to the common alpha subunit of hCG stimulating TSH receptors
It is uncommonly associated with thyrotoxicosis and usually normalises by 16/40
How is a thyroid storm managed?
Propylthiouricil - reduces T4 -> T3 conversion
Propranolol