Feline HyperTH

Question 1

What is the overall prevalence of hyperthyroidism for cats in europe >9yo?

Answer 1

6% (although may be as high as 10%)

Question 2

What is the main pathophysiology of the disease in cats c.f. humans?

Answer 2

Humans usually IMDz (Graves) whereas cats is due to nodular hyperplasia. Occasionally they may get thyroid carcinomas.

Question 3

What Body systems does thyroid hormones affect?

Answer 3

CNS
CVS
Respiratory
Metabolic/GIT
Urinary

Question 4

What are the effects of thyroid hormone on the CVS?

Answer 4

Increased expression of beta adrenoreceptors:

• tachycardia
• inotropy and cardiac remodelling
• possible BP increase (not proven to be linked)

Question 5

What are the effects of thyroid hormone on general metabolism?

Answer 5

Increased carbohydrate metabolism and lipolysis. Increase amino acid uptake and cellular enzyme synthesis. Overall catabolic.

Question 6

What are the effects of thyroid hormone on the neurological system?

Answer 6

Thyroid hormones needed for normal CNS function. Hyperthyroid states may increase anxiety, activity level and cause behavioural changes

Question 7

What are the effects of thyroid hormone on creatinine levels?

Answer 7

Lowered body mass
Increased tubular secretion
Increased GFR (dilates afferent arteriole)

Question 8

What clfinicopathologic findings are common with hyperTH?

Answer 8

Isosthenuria
Erythrocytocis or anaemia of chronic dz
Eosinopenia/Lymphopenia
Increased ALT (80% cases)
Increase ALP (>50% cases)
Azotaemia (25% cases) - this is associated with poorer prognosis

Question 9

What testing is indicated to confirm a suspicion of hyperTH?

Answer 9

Total T4 is most widely used and useful. Highly specific but less sensitive. FT4 by equilibrium dialysis is useful but is not highly specific.

Thyroid scintigraphy is considered a gold standard of testing.

Question 10

What is the mechanism of action of anti-thyroid medications? What are these called?

Answer 10

Inhibition of thyroid peroxidase
Carbimazole (Pro-drug)
Methimazole/Thiamizole

Question 11

What are the possible side effects of anti-thyroid medications?

Answer 11

Severe:
- Agranulocytosis
- Thrombocytopenia
- Bleeding that is not PLT associated
- Severe hepatopathy
Milder/Transient
- GI upsets
- Facial pruritus

• Leukopenia
• Eosinophilia
• Lymphocytocis

Question 12

What is the aim of thyroid treatment?

Answer 12

Aim to keep TT4 in the middle to lower half of the RI whilst controlling clinical signs

Question 13

What are the risks or radiiodine therapy?

Answer 13

Hypothyroidism

Uncovering renal insufficiency

Question 14

What are the risks or thyroidectomy?

Answer 14

Hypocalcaemia