Hypothyroidism Flashcards
___ is released from the _____ pituitary, which acts on the thyroid and stimulates thyroid hormone release
TSH, anterior pituitary
Which hormone released from the hypothalamus stimulates TSH release from the anterior pituitary? A) T4 B) TRH C) T3 D) thyroxine
B - thyroid releasing hormone
Which element is vital for thyroid hormone production? A) iron B) zinc C) iodine D) molybdenum
C - iodine
T/F: there is more T3 in the body than T4
False, T4 80%, T33 20%
A primary thyroid disease involves disease in the: A) blood B) pituitary C) thyroid D) hypothalamus
thyroid
Disease of the pituitary is _______ and of the hypothalamus is ______.
secondary and tertiary
Most common type of hypothyroidism (95% of cases)
primary hypothyroidism
Breakdown of hypothyroidism
95% primary - most due to lymphocytic thyroiditis, rest idiopathic
other 5% - secondary congenital/acquired or primary congenital
3 other major causes of low T4
iatrogenic (I131, antithyroid drugs, thyroidectomy)
Euthyroid sick syndrome (decreased protein binding, fT4 –> rT3)
Drug therapy (glucocorticoids, carprofen, furosemide, phenobarbital/sulfas)
Factors affecting T4 levels
age, breed, pregnancy, exercise, fasting, anesthesia
Signalment of hypothyroid dogs
middle aged
medium to large breed dogs
can be inherited
Clinical signs of hypothyroidism
lethargy, alopecia, hyper pigmentation, rat tail, seborrhoea, myexdema
What causes myxedema?
deposition of mucopolysaccharides in the dermis
reproductive signs of hypothyroidism
failure to cycle, weak pups
ocular signs of hypothyroidism
lipid in cornea, anterior chamber
T/F: normal T4 rules out hypothyroidism
True
T/F: it is easy to diagnose hypothyroidism in a sick dog
False, it is difficult because low levels may indicate hypothyroidism or euthyroid sick syndrome
Serum T4 levels reflect:
bound and free T4
You have a patient with low T4 and you suspect hypothyroidism. You submit for TSH and it comes back high. What is your next step? A) Measure T3 levels B) euthanize, it doesnt stand a chance C) Leave it, it will resolve on its own D) Treat with levothyroxine
D - treat with levothyroxine
Is it possible to have low T4 with normal TSH levels?
Yes, you can either treat, retest later, or perform further testing
A patient comes in with seborrhoea, myxoedema, alopecia and is lethargic. You decide to take a blood sample to assess the T4 status. The T4 value is within the normal range but is at the low end of normal. You suspect hypothyroidism. What can you do?
fT4 by equilibrium dialysis
You conduct a TSH stimulation test and collect T4 levels 8 hours after TSH administration. You notice there is a significant increase in T4 levels compared to before the TSH was given. What is your conclusion?
This dog is normal! A hypothyroid dog would have no increase in post-T4 (due to gland atrophy/destruction)
Treatment for hypothyroidism
Synthetic T4
Soloxine 0.02mg/kg/BID or Leventa 0.02mg/kg/SID
Time line of therapy monitoring for hypothyroidism?
1-2w - improvement in attitude
4-6w - improvement in term signs
2-3m - hair regrowth
An owner is concerned about the appearance of her hypothyroid dog. She is getting married in 4 months and wants her dog to be in all of her wedding photos. You have just started the dog’s treatment. Will her dog’s hair be grown in by her wedding?
Yes, hair regrowth at 2-3m
T/F: treatment of hypothyroidism can be stopped once T4 levels are normal
false, treatment is lifelong
You want to assess the treatment plan you have been using for a hypothyroid dog, Sparky. Sparky has been receiving 0.02mg/kg Soloxine BID for the past month. When should you take a blood sample?
A) It doesn’t matter when as long as it’s one month after tx plan began
B) As soon as you finish giving the first dose of the day
C) 4-6h after the first does was given
D) Right before bed
C - if you are giving the doses BID, you want to make sure you are not taking a sample during a peak or trough time. 4-6h is roughly halfway between doses
if SID, would test ~8h after dose
Signs of drug treatment overdose in hypothyroid dogs
PU/PD/PP, nervousness, aggression, panting, excess weight loss, fever
