Thyroid Dysfunction

Question 1

Which deiodinase deactivates T4?

Answer 1

Type 3 deiodinase (which creates reverse T3)

Question 2

What can promote a shift to type 3 deiodinase?

Answer 2

Starvation
Severe illness
Neonatal period
Stress
Glucocorticoids
Propranolol
Amiodarone
Radiocontrast dyes

Question 3

What percent of T4 is free?

Answer 3

0.02%

Question 4

Decreased thyroid binding proteins can cause ___________.

Answer 4

hypothyroidism

Question 5

The normal range of TSH is _____________.

Answer 5

0.4 - 4.0 (treat if greater than 10)

Question 6

What is the best test for thyroid dysfunction?

Answer 6

TSH (provided the pituitary does not show other signs of dysfunction)

Question 7

_______________ leads to an increased expression of NIS.

Answer 7

TSH (NIS is Na-Iodide Symporter)

Question 8

Thyrotoxicosis presents with _________________.

Answer 8

low TSH and high T3/T4

Question 9

If TSH is low but the thyroid is still taking up iodide, then this is ________________.

Answer 9

true hyperthyroidism, characterized by the autonomous production of thyroid hormone

Question 10

Deposition of hyaluronic acid in the anterior calves leads is called ____________ and is pathognomonic for Graves’ disease.

Answer 10

pretibial myxedema

Question 11

The activating deiodinases are _________.

Answer 11

types I and II

Question 12

What lab pattern is suggestive of subclinical hyperthyroidism?

Answer 12

Low TSH
Normal T4
Normal T3

(Similarly, subclinical hypothyroidism presents with elevated TSH but normal T4 and T3.)

Question 13

Which cell type mediates the damage in Hashimoto’s?

Answer 13

Lymphocytes

Question 14

Iodine uptake will be low in which types of hyperthyroidism?

Answer 14

• Factitious
• Struma ovarii
• All the disorders that damage the thyroid (viral, onset of Hashimoto’s, autoimmune)