Disorders of the Thyroid Gland Flashcards
Dr. Swan
Briefly look at the physiology of the hypothalamic-pituitary-thyroid axis
The majority of T3 and T4 are _____
protein-bound
What are the effects of T3 and T4 in circulation?
have a positive effect of development, growth, and metabolism on organs and tissues throughout the body
What 2 cell types are the thyroid gland composed of?
- thyroid follicular epithelial cells
- thyroid C-cells
What are the functions of thyroid follicular epithelial cells?
- produce colloid (thryoglobulin) storage form
- convert thyroglobulin by iodinating to form T3/T4 to release into circulation
What is circulating T3 and T4 called? Small or large amount?
fT3 and fT4 (free)
small
What is the function of thyroid c-cells?
produce calcitonin
What is canine hypothyroidism characterized by?
decreased circulating T4
What is often normal in dogs with hypothyroidism?
T3
What are 3 primary hypothyroidism causes?
immune-mediated destruction of thyroid follicular epithelial cells (lymphocytic thyroiditis)
severe thyroid follicular atrophy - probably end-stage immune-mediated thyroiditis
neoplastic destruction
What are the T4 levels in a dog with hypothyroidism? TSH?
total T4 (tT4): decreased
free T4 (fT4): decreased
TSH: increased
What is canine secondary hypothyroidism?
decreased TSH
pituitary-related malformation
compression, destruction, or atrophy of thyrotrophs from pituitary adenomas
What is canine tertiary hypothyroidism?
decreased TRH (from hypothalamus)
very rare
What are clinical signs of canine hypothyroidism?
- weight gain
- heat-seeking behavior or cold intolerance
- lethargy
- dermatopathy (alopecia surrounding base of tail)
- persistent or reoccurring infections
- vestibular
What are CBC findings of canine hypothyroidism?
normocytic normochromic non-regenerative anemia
What are chemistry findings of canine hypothyroidism?
hypercholesterolemia
hypertriglyceridemia
What is the screening assay for canine hypothyroidism?
total T4 (tT4)
Regarding canine hypothyroidism, a minimum panel of what should be performed?
tT4, fT4, TSH
What assay can be used to diagnose 50% of canine hypothyroidism cases?
thyroglobulin autoantibodies (TgAA)
lymphocytic thyroiditis - 50% of cases
What is total t4?
measurement of both bound and free T4 hormone within circulation
If tT4 is in the upper half of the reference interval, is hypothyroidism unlikely or likely?
unlikely