Thyroid Disorders

Question 1

true or false: most t4 & t3 is protein bound

Answer 1

True! and only unbound thyroid hormone is biologically active

Question 2

is T3 or T4 more biologically active?

Answer 2

T3 is more active than T4

Question 3

2 mechanisms of hypothyroidism

Answer 3

congenital - RARE
acquired - lymphocytic thyroiditis [auto-immune] (50%) or idiopathic thyroid atrophy (50%)

Question 4

what happens in lymphocytic thyroiditis

Answer 4

the thyroid tissue gets destroyed so there is no tissue to produce T3/T4
TRH and TSH are extremely high, but no thyroid to respond

Question 5

signalment of hypothyroidism

Answer 5

middle aged dogs (mean = 7 years) but purebreds may develop signs younger
sterilized dogs are the highest risk

Question 6

what is the prevalence of hypothyroidism

Answer 6

0.2-0.8% of dog population (probably towards the lower end)

Question 7

breeds at risk of hypothyroidism

Answer 7

any dog can develop, but tends to be more common in purebreds
golden retriever!!!! Doberman pinscher, beagle, daschund, minature schnauzer, Great Dane, mini poodle, etc

Question 8

hypothyroidism clinical signs

Answer 8

falls into metabolic or dermatologic
metabolic: lethargy, weight gain, cold and exercise intolerance
dermatologic (80-93%): alopecia and poor hair coat CLASSIC, hyperkeratosis and hyperpigmentation, infections: pyoderma/demodicosis/otitis externa (can present like allergies)

Question 9

clinical signs of hypothyroidism that aren’t metabolic or dermatologic (less common)

Answer 9

neurological: probably - peripheral polyneuropathy, central vestibular disease and maybe laryngeal paralysis, facial nerve paralysis, megaesophagus

muscular: myopathy

ocular: corneal lipid deposits

cardiac: may reduce systolic function - but probably not a big deal

Question 10

what is myxedema coma

Answer 10

even more rare - life threatening complication of hypothyroidism usually associated with precipitating factors (surgery, cardiac disease, sepsis, etc)

Question 11

myxedema coma hallmark

Answer 11

non-pitting edema formation - mucopolysaccharide accumulation under skin via reduced inhibition of GAG formation and reduced clearance

Question 12

patients with myxedema coma present with

Answer 12

hypothermia (no shivering), bradycardia, weak/anorectic, and collapsed

Question 13

how does congenital hypothyroidism present?

Answer 13

any of the other clinical signs
significantly stunted growth and MSK abnormalities (wide skulls, short limbs, macroglossia)
delayed dental development
+/- goiter