Hyper/hypo Thyroid

Question 1

What is the active form to thyroid hormone?

Answer 1

T3

Question 2

Which has a stronger effect, T3 or T4?

Answer 2

T3

Question 3

What is the the normal role of thyroid hormone

Answer 3

Maintain metabolic rate and O2 consumption

Question 4

The most common form of hypothyroidism is ???

Answer 4

Primary (95%)

• lymphocytic thyroiditis
• idiopathic atrophy

Question 5

What are other causes of a low T4 that is not hypothyroidism

Answer 5

Iatrogenic
Euthyroid sick syndrome
Drug therapy

Question 6

Thyroidectomy is an example of what type of hypothyroidism

Answer 6

Iatrogenic

Question 7

What drug therapies can cause a low T4?

Answer 7

Glucocorticoids
Carprofen (NSAID)
Furosemide
Phenobarbital /sulfas

Question 8

That is the usual signalment of a primary hypothyroid animal?

Answer 8

Middle age
Medium to large breed dog

Some inherited breeds - OFA registry

Question 9

General appearance of a hypothyroid dog?

Answer 9

Lethargic
Alopecia
Hyperpigmentation

Rat tail
Seborrhea
Hypothyroid myedema

Question 10

What is myxedema?

Answer 10

Facial appearance

Deposition of mucopolysacchharides in the dermis

Question 11

Is myxedema associated with hyperthyroid or hypothyroidism?

Answer 11

HYPOthyroidism

Question 12

You have hypothyroidism on your differential list, what should you do next to confirm?

Answer 12

CBC -> low anemia

Serum biochem -> low levels of T4 (this can also indicated euthyroid sick)

UA

Question 13

Your patient has a history, PE, and lab work with a low T4, you would likely submit what test to confirm hypothyroidism?

Answer 13

TSH

Question 14

Is it appropriate to treat a presumptive diagnosis with low T4 and normal TSH for hypothryoidism, if so, what would you use?

Answer 14

Yes you can treat or retest later

Levothyroxine

Question 15

If there is a low normal T$ and you really think it is hypothyroidism, what do you do? What is there is a high T4?

Answer 15

FT4 by eqd.

FT4 by eqd and measure for anti-T4 autoantibodies

Question 16

In a TSH stimulation test, you see a significant increase in the post-T4 value. How do you interpret ?

Answer 16

Normal

Question 17

In a TSH stimulation, you see no significant increase in post T4 levels. What is your interpretation?

Answer 17

Hypothyroid dog

Due to thyroid gland atrophy or destruction

Question 18

What is the timeline of resolvment of clinical signs for hypothyroid cases?

Answer 18

2wks- improvement in attitude

6wks-improvement in derm signs

3months- hair regrowth

Question 19

What is the etiology of excessive production of T4 and T3

Answer 19

Functional tumor (adenoma is most common)

70% of cats with hyperthyroidism have bilateral tumors

Question 20

What is the signalment for hyperthyroid cases?

Answer 20

Most common endocrinopathy of other cats

Mean age= 12yrs

Question 21

Clinical signs of hyperthyroidism?

Answer 21

Weight loss, unkempt “scraggly” coat

PU/PD -> osmotic diuretics, and renal medullary washout, psychogenic or concurrent RF

Vomiting -> gastric distention/overeating
Diarrhea -> osmotic (increase fat intake), hypermotility

Question 22

What is apathetic hyperthyroidism ??

Answer 22

Weight loss with poor appetite

Decreased activity, lethargy

Question 23

Cat with..
weight loss and scraggly coat
PU/PD
Vomiting

CBC shows stress leukogram with erythrocytosis
Biochem shows increase ALk phos and ALT
UA- isosthenuric
T4- high

Answer 23

Hyperthyroidism

Question 24

What should you do if T4 levels are normal but you still suspect hyperthyroidism?

Answer 24

Repeat T4 in a few days or weeks

OR

Submit a FT4 by eqd if T4 is mid to high normal range

Question 25

Can we just check FT4 to confirm hyperthyroidism in a cat?

Answer 25

Nope FT4 is often high in euthyroid sick syndrome

Question 26

What other tests are possible for tough hyperthyroid cases?

Answer 26

T3 suppression test

Question 27

What additional diagnostic work-up can be done in hyperthyroid cases

Answer 27

BP - fundic exam - UPC/urine culture (protein loss) Cardiac evaluation - ECG - Radiographs - Echocardiography Nuclear scintigraphy -> radioactive iodine

Question 28

What are the 4 treatment options for hyperthyroidism? Which are reversible?

Answer 28

Medical, dietary, surgical, or radioactive iodine Medical and dietary are reversible Surgical and radioactive iodine are not reversible

Question 29

T/F: the best line of treatment for hyperthyroidism is to treat with radioactive iodine first to decrease T4 production

Answer 29

FLASE Hyperthyroidism can often mask renal failure.. in this even you would not want to purpose long term solutions like surgery or radioactive iodine First line should be 30days of methimazole where you check renal function after

Question 30

How does hyperthyroid mask renal disease?

Answer 30

Increase in BP -> increase GFR

Question 31

What are some important considerations to be considered in surgical treatment of hyperthyroid?

Answer 31

Pro- can be a long term solution Con - surgery is close to many major vessels - removal of too much-> iatrogenic hypothryoidism - accidental removal of parathyroid

Question 32

How does I-131 treat hyperthyroidism

Answer 32

Tumor concentrates the radioactive iodine -> emitting beta particles that are locally destructive

Question 33

What is the MOA of methimazole?

Answer 33

Inhibits thyroid hormone synthesis by blocking incorporation of iodine

Question 34

What are some side effects of methimazole?

Answer 34

Vomiting (anorexia) | Liver, marrow, and skin(excoriation) reactions

Question 35

Why would transdermal methimazole be a good choice for hyperthyroid cats?

Answer 35

Some cats difficult to manage with oral meds Give transdermal because of vomiting

Question 36

What is the prognosis for hyperthyroidism?

Answer 36

Good *be sure to monitor renal parameter and T4 with all treatments

Question 37

What is the most common thyroid tumor in dogs?

Answer 37

Malignant (90%) | -usually highly invasive and non-functional

Question 38

Middle aged to older dog PE: Cervical mass on palpation DDX:

Answer 38

Neoplasia. -Thyroid tumor, lymphoid, parathyroid, lipoma, sarcoma Inflammatory -abscess, foreign body, fungal, granuloma Cystic -non-inflammatory lesion of thyroid, parathyroid, salivary mucocele

Question 39

What is your diagnostic plan for a dog with a cervical mass?

Answer 39

Evaluate mass FNA: thyroid tumors are highly vascular -> mostly blood Excisional biopsy Nuclear imaging Labwork Metastasis check

Question 40

What is the treatment for a canine thyroid tumor?

Answer 40

Surgery: palliative, debulk Cobalt irradiation after debulking Chemotherapy Radioactive iodine (only for functional tumors)