Thyroid Gland

Question 1

What are the 3 forms of thyroid hormones and which is the most active?

Answer 1

T3, T4 and Reverse T3

T4 is less biologically active but more abundant

Question 2

At the target cell T_ is converted to T_ and ___

Answer 2

4

T3 and rT3

Question 3

What are conditions associated with decreased tT4?

Answer 3

Primary hypothyroidism

Euthyroid sick syndrome

Question 4

What is a condition associated with increased tT4?

Answer 4

Hyperthyroidism; Feline thyroid adenoma

Question 5

What condition is associated with decreased fT4?

Answer 5

Primary hypothyroidism

ESS: rarely see decreased fT4

Question 6

What condition is associated with increased fT4?

Answer 6

Hyperthyroidism; feline thyroid adenoma

Question 7

T/F tT3 and fT3 can be used and have good diagnostic utility

Answer 7

FALSE

Question 8

Endogenous TSH comes from _____

Answer 8

pituitary gland

Question 9

A _____ in tT4 and an _____ in TSH is supportive of hypothyroidism

Answer 9

Increase in tT4

Decrease in TSH

Question 10

TSH stimulation tests looks at what?

Answer 10

Thyroid gland’s ability to respond to TSH to produce T4

Question 11

A TSH stim test would get what result in a hypothyroid dog? What about normal dog?

Answer 11

Hypothyroid: No response

Normal/ESS: Increase tT4 post TSH stimulation

Question 12

TRH stimulation test looks at what?

Answer 12

Pituitary’s response to TRH to produce TSH

Question 13

What results would you see with a TRH stimulation test?

Answer 13

Hypothyroid: No increase in tT4

Normal/ESS: increase in tT4 following stim

Question 14

T3 suppression test is useful for what disease?

Answer 14

Feline hyperthyroidism

Question 15

What response would you see in a hyperthyroid cat to a T3 suppression test?

Answer 15

No decrease in tT4 after the T3 administration

Question 16

What is the most common form of canine hypothyroidism?

Answer 16

Primary (At the level of the thyroid)

Question 17

What are some common lab abnormalaties seen with canine hypothyroidism?

Answer 17

Hyperlipidemia
Increased ALP, GGT, and AST
Mild anemia

Question 18

Euthyroid sick syndrome is what?

Answer 18

Non-thyroidal disease that suppresses plasma T4

Question 19

Total T4 test would be helpful to rule ___ hypothyroidism

Answer 19

OUT; most hypothyroid dogs have decreased total T4

Question 20

T/F Euthyroid sick syndrome dogs will have decreased total T4

Answer 20

TRUE

Question 21

T/F Most Euthyroid sick syndrome dogs have decreased free T4

Answer 21

FALSE; most of these have normal fT4

Question 22

Hypothyroidism dogs will have ____ fT4

Answer 22

Decreased

Question 23

What is the best one-measurement test for diagnosing canine hypothyroidism?

Answer 23

Free T4 by equilibrium dialysis

Question 24

What other test could you use to test a hypothyroid dog to DDx from EES?

Answer 24

Endogenous TSH
Hypo: Increased TSH w/ decreased tT4
EES: normal TSH

Question 25

What is the gold standard test to diagnose primary hypothyroidism?

Answer 25

TSH stimulation test

Normal/EES dogs will see increase in tT4 after stimulation

Question 26

What’s a reason to not run the TSH stimulation test?

Answer 26

Cost

Question 27

What is the most common subset of feline hyperthyroidism?

Answer 27

Primary hyperthyroidism: at the level of the thyroid

Question 28

What are the most common causes of T4 secretion?

Answer 28

Thyroid adenoma

Question 29

What are some signs/lab abnormalaties of Primary hyperthyroidism?

Answer 29

Signs: vomiting, thyroid slip, low muscle mass, weight loss

Lab: Stress leukogram, azotemia, increased ALT/AST/ALP, increased PO4

Question 30

T/F 100% of hyperthyroid cats will have increased tT4

Answer 30

FALSE; 5-10% of hyperthyroid cats will have high normal tT4

Question 31

In hyperthyroid cats you would expect fT4 to be ____

Answer 31

Increased

Question 32

What is the gold standard test to diagnose feline hyperthyroidism?

Answer 32

T3 suppression test

Question 33

A cat that is suffering from hyperthyroidism will see what in response to T3 suppression test?

Answer 33

No suppression; this would confirm diagnosis!