Chap 300 : Feline Hypothyroidism

Question 1

Etiology ?

Answer 1

Iatrogenic
Congenital
Spontaneous adult onset rare

Question 2

Incidence of iatrogenic hT4?

Answer 2

5 - 83%
More common when bilateral HT4

Question 3

Congenital hT4?

Answer 3

Dyshormonogenesis : defective thyroid peroxydase activity
Dysmorphogenesis : autosomal inheritence

Hypothalamic deficiency not reported in cats

Question 4

Clinical signs indicative of congenital hT4?

Answer 4

Goiter, disproportionnate dwarfism (often seen around 2 months), delayed growth plate closure,

Question 5

Transcient iatrogenic hT4?

Answer 5

TT4 return to normal within 3-6 months

Question 6

Treatment of iatrogenic hT4?

Answer 6

If azotemic
L-thyroxine enhance GFR, improve renal function, reduce severity of azotemia

Question 7

Diagnosis ?

Answer 7

1/ TT4 and cTSH
2/ scintigraphy, rhTSH stim test

Question 8

Free T4 ?

Answer 8

Unclear benefit
decrease value also present with non thyroidal illness

Question 9

Treatment

Answer 9

75 mcg BID

Reevaluation after 4 to 8 weeks