Thyroid Gland

Question 1

What do thyroid C (parafollicular) cells do?

Answer 1

secrete calcitonin in response to increased blood Ca (hypercalcemia)

Question 2

What do thyroid follicular cells do?

Answer 2

Thyroglobulin –> monoiodotyrosine (MIT) and diiodotyrosine (DIT) –> biologically active hormones T3 and T4

under the influence of TSH and TRH

negative feedback on hypothalamus and adenohypophysis

regulate growth rate of metabolism and growth

Question 3

what disorder of the C cells do we have to know?

Answer 3

C-cell (parafollicular cell) tumors

Question 4

what disorders involving hypo function of the thyroid gland do we have to know?

Answer 4

hypothyroidism
congenital hypothyroidism (goitre, CHDS of foals)

Question 5

what disorders involving hyper function of the thyroid gland do we have to know?

Answer 5

hyperthyroidism
nodular hyperplasia, follicular tumors

Question 6

Hypothyroidism results in what pathophys thing?

Answer 6

decreased concentrations of thyroid hormones T3 and T4

Question 7

what is one of the most common endocrinopathies of dogs? which breeds most affected?

Answer 7

hypothyroidism
beagles, daschunds

Question 8

what are the causes of hypothyroidism

Answer 8

primary thyroid disease (idiopathic follicular collapse, lymphocytes thyroiditis)

rarely pituitary or hypothalamic lesion resulting in lowered TSH or TRH

Question 9

what’s the lesion?

Answer 9

thyroid gland atrophy

thyroid atrophy makes the parathyroid glands more prominent (arrow)

Question 10

what are the extra-thyroidal lesions of hypothyroidism?

Answer 10

reduction in BMR –> weight gain)
cutaneous
reproductive
hypercholesterolemia –> atherosclerosis

Question 11

what are some examples of cutaneous lesions present in hypothyroidism?

Answer 11

bilaterally symmetrical alopecia
hyperkeratosis
hyperpigmentation
myxedema

Question 12

what is goiter?

Answer 12

clinical term used to describe a non-neoplastic enlargement of the thyroid glands

Question 13

what are some causes of goiter?

Answer 13

multiple cases, but have a shared pathogenesis
ex. iodine deficient diest, goitrogenic compounds, excess dietary iodine, genetic enzyme defects (Dyshormonogenetic goiter)

Question 14

what is the pathogenesis of goiter, no matter the cause?

Answer 14

1. inciting cause
2. inadequate thyroid hormone synthesis
3. decreased blood levels of T3 and T4
4. increased TRH
5. increased TSH
6. hypertrophy/hyperplasia of follicular cells
7. goiter

Question 15

what’s the lesion?

Answer 15

goiter

Question 16

thyroid gland. what’s the lesion?

Answer 16

goiter

Question 17

what are the gross lesions of a thyroid gland with goiter?

Answer 17

bilaterally enlarged, dark purple thyroid glands

Question 18

What does CHDS stand for?

Answer 18

Congenital Hypothyroidism-Dysmaturity Syndrome (in foals)

Question 19

True or false: CHDS is common in western Canada

Answer 19

true

Question 20

CHDS is characterized by ____ ____ and _____ _____.

Answer 20

Perinatal death, MSK malformations

Question 21

with CHDS, there’s _____ gestation but foals appear _____.

Answer 21

prolonged
dysmature

Question 22

what are the MSK abnormalities that come with CHDS?

Answer 22

contracted or ruptured tendons
mandibular prognathia
immature carpal and tarsal bones on radiographs

Question 23

This goat has this lesion, plus contracted tendons and immature carpal and tarsal bones. what might this foal have?

Answer 23

congenital hypothyroidism-dysmaturity syndrome

Question 24

with CHDS cases, why must you ALWAYS take the thyroid for histo?

Answer 24

grossly, the thyroid may look normal, but microscopic lesions are present

Question 25

true or false: the etiology of CHDS is unknown

Answer 25

true

Question 26

hyperthyroidism results in what pathophys thing?

Answer 26

elevated circulating levels of thyroid hormones (T3 or T4)

Question 27

dogs commonly get ____ and cats commonly get _____

Answer 27

hypothyroidism hyperthyroidism

Question 28

true or false: hyperthyroidism is common in dogs

Answer 28

false! rare in dogs

Question 29

what is one of the most common endocrine diseases of cats?

Answer 29

hyperthyroidism

Question 30

what is the typical signalment for a cat with hyperthyroidism?

Answer 30

geriatric

Question 31

why is hyperthyroidism rare in dogs?

Answer 31

they have more efficient enterohepatic excretion of thyroid hormones

Question 32

if dogs get hyperthyroidism, how do they get it?

Answer 32

thyroid follicular tumors (Carcinoma > adenoma)

Question 33

Hyperthyroidism results in what 2 important things clinically?

Answer 33

increased BMR cardiac manifestations

Question 34

hyperthyroidism causes increased BMR. what are the results of this?

Answer 34

weight loss despite ravenous appetite!! PU/PD, nervous or hyper excitability, heat intolerance

Question 35

hyperthyroidism causes cardiac manifestations. What are two clinical signs of this? what gross lesion can you see?

Answer 35

tachycardia, dysrhythmias concentric hypertrophy of the heart (DON'T MISTAKE THIS FOR PRIMARY HYPERTROPHIC CARDIOMYOPATHY!)

Question 36

Tell me which lesions are most common with hyperthyroidism

Answer 36

multifocal nodular hyperplasia and thyroid follicular adenomas > thyroid follicular carcinoma

Question 37

Hyperthyroidism: Cats most commonly get what lesions? Dogs most commonly get what lesions?

Answer 37

Cats: multifocal nodular hyperplasia, thyroid follicular cell adenoma Dogs: thyroid follicular carcinoma

Question 38

What species/signalments do multifocal nodular hyperplasias occur in most commonly?

Answer 38

old horses, *cats*, dogs

Question 39

what do multifocal nodular hyperplasias that cause hyperthyroidism look like grossly?

Answer 39

multiple, tan to brown, nonencapsulated nodules

Question 40

this is from a cat with hyperthyroidism. what's the lesion/cause?

Answer 40

multifocal nodular hyperplasia

Question 41

what species do thyroid follicular cell adenomas occur in most commonly ?

Answer 41

cats

Question 42

malignant thyroid tumors are more common in _____, benign thyroid tumors are more common in ____.

Answer 42

dogs, cats

Question 43

what do thyroid follicular cell adenomas that cause hyperthyroidism look like grossly?

Answer 43

single, white to tan, well-defined and encapsulated mass

Question 44

tell me the differences between multifocal nodular hyperplasia and thyroid follicular cell adenomas in terms of gross appearance?

Answer 44

Adenoma: single, encapsulated, white to tan Hyperplasia: multiple, tan to brown, non encapsulated

Question 45

thyroid follicular carcinomas: 1) can develop where? 2) invasive/non-invasive? 3) metastasize ____(early/late) to where?

Answer 45

1) ectopic thyroid tissue 2) non-invasive 3) early, lungs

Question 46

what is the typical signalment of an animal with a thyroid c-cell tumor?

Answer 46

old bull

Question 47

what is the cause of thyroid c-cell tumors?

Answer 47

unknown, but might be linked to high calcium diets

Question 48

a bull with a thyroid c-cell tumor will have concurrent... what?

Answer 48

pheochromocytoma and pituitary tumors

Question 49

true or false: thyroid c-cell tumors are only adenomas

Answer 49

false! both adenomas and carcinomas