3/3 Thyroid Hormones - Hypothyroidism COMPLETE***

Question 1

Hypothyroidism: Which species is this more common in?
- Which species is this less common in?

Answer 1

dogs

cats

Question 2

Hypothyroidism: state the 3 types of Hypothyroidism

Answer 2

primary hypothyroidism
secondary hypothyroidism
tertiary hypothyroidism

Question 3

Hypothyroidism: Primary
- Where is this hypothyroidism at the level of?
- what about for secondary?
- What about for tertiary?

Answer 3

the thyroid gland

the pituitary

the hypothalamus

Question 3

Hypothyroidism: Primary Hypothyroidism
- What is wrong with the thyroid gland?
- What 3 types of Primary hypothyroidism are there?

Answer 3

there is a lack of functional thyroid tissue in the gland

acquired
iatrogenic
congenital

Question 4

Hypothyroidism: Primary
- Which type of Primary hypothyroidism is most common?
- What can this be due to? 3

Answer 4

Acquired

lymphocytic thyroiditis
idiopathic follicular atrophy
neoplasia

Question 5

Hypothyroidism: Primary - Acquired
- What is lymphocytic thyroiditis?
- What is idiopathic follicular atrophy?

Answer 5

infiltration of lymphocytes and inflammation of the thyroid gland

follicle tissue starting to atrophy

Question 6

Hypothyroidism: Secondary
- What is happening here?
- What are the 2 possible types of secondary hypothyroidism?

Answer 6

there is impaired secretion of thyroid stimulating hormone from the pituitary gland

acquired
congenital

Question 7

Hypothyroidism: Secondary - Acquired
- What can cause this? 4

Answer 7

neoplasia
pituitary suppression
illness
malnutrition

Question 8

Hypothyroidism: Tertiary
- what happens with tertiary hypothyroidism?

Answer 8

the hypothalamus is releasing insufficient thyroid releasing hormone into the hypothalamic paraventricular nuclei

Question 9

Hypothyroidism: Signalment 2

Answer 9

golden retrievers and cocker spaniels are predisposed
middle aged dogs

Question 10

Hypothyroidism: State the clinical signs 6

Answer 10

dull
lethargic
exercise intolerance
obesity with no polyphagia
cold intolerance
skin changes

Question 11

Hypothyroidism: What effect does Hypothyroidism have on the musculoskeletal system? 2

Answer 11

it reduces muscle tone
it changes fibre types

Question 12

Hypothyroidism: What affect can hypothyroidism have in young animals and why?

Answer 12

growth retardation and short bones because thyroid hormone is needed for normal growth

Question 13

Hypothyroidism: Why do we get obesity?

Answer 13

less thyroid hormone reduces basal metabolic rate so slows carbohydrate and fat metabolism

Question 14

Hypothyroidism: What effect does Hypothyroidism have on the cardiovascular system?
- Why?

Answer 14

bradycardia

it decreases cardiac output and contractility

Question 15

Hypothyroidism: What effect does Hypothyroidism have on the nervous system?

Answer 15

it leads to peripheral neuropathy

Question 16

Hypothyroidism: What effect does hypothyroidism have on the central nervous system?

Answer 16

it causes lethargy

Question 17

Hypothyroidism: What effect does Hypothyroidism have on reproduction? 3

Answer 17

infertility
prolonged anoestrus
testiscular atrophy

Question 18

Hypothyroidism: What effect does Hypothyroidism have on the Gastrointestinal system?
- why? 3

Answer 18

constipation

it reduces appetite
it reduces the secretion of pancreatic enzymes
it reduces gut motility

Question 19

Hypothyroidism: What effect does Hypothyroidism have on integument, specifically hair? 2
- Why? 2

Answer 19

alopecia
failure to regrow hair after clipping

thyroid hormone initiates and maintains anagen phase
so lack of thyroid maintains hair in telogen phase

Question 20

Hypothyroidism: What other skin changes do you see with Hypothyroidism 5

Answer 20

bilateral symmetrical alopecia
lichenification
comedones
hyperpigmentation of alopecic sites
recurrent infections of the skin and ear

Question 21

Hypothyroidism: Diagnosis
- What information gathering tests would you perform before specific hypothyroid tests?

Answer 21

blood biochemistry
complete blood count

Question 22

Hypothyroidism: What would you expect to see on blood biochemistry?
- isn’t this counter intuitive?

Answer 22

increased parameters of lipid metabolism like cholesterol and lipids

yes but you get decreased activity of LDL receptors during hypothyroidism so have less catabolism of lipids

Question 23

Hypothyroidism: What would you expect to see on a complete blood count? 2

Answer 23

normocytic normochromic anaemia
leukocytosis if there is an infection

Question 24

Hypothyroidism: Diagnosis
- What specific hypothyroidism tests can you perform?

Answer 24

total T4 or free T4
baseline TSH

Question 25

Hypothyroidism: Diagnosis
- What does total T4 measure?
- What could a positive result show?
- What type of test is this and why?
- What are the problems with this test? 2

Answer 25

protein bound and free T4

low total T4

a screening test because it has high sensitivity

there are daily fluctuations
non-thyroidal illness may suppress T4

Question 26

Hypothyroidism: Why does Non-thyroidal illness (euthyroid sick) suppress T4? 3
- How can you differentiate between euthyroid sick and hypothyroidism?

Answer 26

less protein binding of T4 and T3
less conversion of T4 to T3
so less TSH release

with hypothyroidism you’d get low total T4 and high TSH

with euthyroid sick syndrome you’d get low total T4 and normal TSH

Question 27

Hypothyroidism: What does Free T4 measure?
- Is this more of less accurate at determining thyroid function than Total T4?

Answer 27

free T4

more accurate

Question 28

Hypothyroidism: Baseline TSH
- Describe the sensitivity and specificity of this test
- For a dog with primary hypothyroidism, what would the result be?
- What would the result be for secondary hypothyroidism?

Answer 28

low sensitivity and high specificity

high thyroid stimulating hormone

low thyroid stimulating hormone

Question 29

Hypothyroidism: Diagnosis Route
- State the steps you would take after obtaining compatible clinical signs and data 3

Answer 29

total T4 or free T4
if there is low or low-normal T4 do baseline TSH
if TSH is more than 0.5 start on therapeutic trial