Hypothyroidism

Question 1

Uses of T3/T4

Answer 1

• activates anagen: hair growth!
• increases metabolic rate
• growth of neurones
• cardiovascular
• haemopoietic
• orthopaedic

Question 2

Synthesis (3)

Answer 2

• thyroglobulin binds to iodine in colloid matrix, moves into follicular cell where it undergoes proteolysis.
• it then passes into cells where it loses the iodine atom and affects the cell
• 99% is protein bound and inactive, only free can pass into cells

Question 3

Control

Answer 3

• Hypothalamus produces TRH
• Pituitary produces TSH
• Thyroid produces T3/T4

all have negative feedback effects

Question 4

Non - thyroidal influences on T3/T4 (7)

Answer 4

• physiological: time of day/year, breed, age, sex
• therapeutic: steroids, potentiated sulphonamides, diuretics
• sick euthyroid syndrome
• obesity/starvation
• surgery/anaesthesia
• neoplasia
• other endocrinopathies

Question 5

Sick euthyroid syndrome

Answer 5

• in illness the body will lower thyroid hormone production to help cope
• DO NOT TREAT

Question 6

Causes of hypothyroidism

Answer 6

primary

• idiopathic
• congenital
• lymphocytic thyroiditis

secondary: TSH failure
tertiary: TRH failure

Question 7

CS of congenital hypothyroidism

Answer 7

• disproportionate dwarfism

- cretinism

Question 8

Lymphocytic thyroiditis

Answer 8

• detected by increase in thyroidglobulin autoantibodies (TGAA)
• only thing increased

Question 9

Progression of hypothyoidism

Answer 9

compensated:
- increase in TGAA and TSH

clinical early:
- increase in TGAA, TSH and decrease in T4

clinical late:
- decrease in TGAA, TSH and T4

Question 10

CS

Answer 10

• lethargy
• obesity
• hypothermia/cold intollerance
• symmetrical allopecia
• pyoderma
• seborrhea
• hyperpigmentation
• myxoedema: increase in proteoglycan matrix between cells
• bradycardia
• pall MM: non regenerative, normochromic anaemia
• neurological abnormalities (LMN disease, peripheral vestibular syndrome, laryngeal paralysis, megaoesophagous)
• decreased fertility

Question 11

Confirming diagnosis

Answer 11

• high cholesterol, TGL, CK, T4/TSH

- low PCV

Question 12

T4 test

Answer 12

0-14 is hypothyroid or sick euthyroid
14-35 is unknown
>35 is normal

Question 13

Thyroid stim tests

Answer 13

TSH stim:
- gold standard

TRH stim:
- less reliable and hard to obtain

Question 14

When is it hypothyroid then???

Answer 14

low T4 and high TSH = NO!

low T4 and high TSH + clinical signs = YES