Thyroid

Question 1

Does the thyroid produce all T3 and T4?

Answer 1

20% T3

All of T4

Question 2

Are all thyroid hormones active?

Answer 2

Only if unbound

Question 3

Which thyroid hormone is more potent and rapid onset: T3 or T4?

Answer 3

T3

Question 4

99% of cats hyperthyroidism is due to…

Answer 4

Nodular adenomatous hyperplasia

1% malignant tumour

Question 5

Is hyperthyroidism in cats uni or bilateral?

Answer 5

Bilateral

Question 6

How do clinical signs vary between hyperthyroidism and apathetic hyperthyroidism in cats?

Answer 6

Classic hyperthyroidism: hyperactivity, polyphagia

Apathetic: depression, lethargy, anorexia

Question 7

What haematological changes are seen with hyperthyroidism?

Answer 7

Mild-moderate erythrocytosis and macrocytosis
Increased Heinz bodies
Increased platelet size
Leukocytosis
(more and larger everything!)

Question 8

What may be seen on biochemistry with a hyperthyroid cat?

Answer 8

Increased ALP, AST, ALT, LDH
Azotaemia
Hypokalaemia
Hyperphosphataemia
Reduced fructosamine

Question 9

How can hyperthyroidism be diagnose?

Answer 9

Total T4 - detects most

Other tests: free T4, T3 suppression test, scintigraphy

Question 10

How can hyperthyroidism be treated with medication?

Answer 10

Thiamazole, methimazole, carbimazole

Atenolon/propanolol for tachycardia/hypertension

Question 11

Apart from medication, how else can hyperthyroidism be treated?

Answer 11

Thyroidectomy
Radioiodine
Iodine restricted diet

Question 12

Which dogs are predisposed to hypothyroidism?

Answer 12

Middle aged, older

Or younger large/giant breeds

Question 13

What are the two causes of hypothyroidism in dogs? Give examples for each

Answer 13

Congenital - thyroid hypoplasia (dwarfism in Fox/Rat terriers)
Acquired - primary (thyroiditis, atrophy) or secondary (defect in pituitary/hypothalamus)

Question 14

What are the general signs of hypothyroidism?

Answer 14

Weight gain
Lethargy 
Exercise intolerance
Cold intolerance
Diarrhoea
Altered oestrus interval, decreased libido
Facial nerve paralysis

Question 15

What are the dermatological signs of hypothyroidism in dogs?

Answer 15

Alopecia
Hair thinning
Skin hyperpigmentation
Pyoderma
Seborrhea

Question 16

What may be seen on haematology/biochemistry of a dog with hypothyroidism?

Answer 16

Normocytic/normochromic, mild non-regenerative anaemia
Hypercholesterolaemia, hypertriglyceridaemia
Mild elevations in CK, ALP, ALT, fructosamine

Question 17

How is hypothyroidism diagnosed?

Answer 17

Total T4
Free T4
TSH - high levels (loss of -ve feedback)

Question 18

Which breed of dogs should be considered when diagnosing hypothyroidism based on low total T4? Why?

Answer 18

Sighthounds, sled dogs

Low T4 is normal

Question 19

What is the treatment for hypothyroidism?

Answer 19

Levothyroxine