Endocrinopathy (NAVDF 2021 Outerbridge) Flashcards
Thyroid hormone pathway
Hypothalamus -> TRH -> Pituitary -> TSH -> Thyroid gland -> T3, T4
How is most T4 found in the blood
Most is bound to transport proteins.
Only 0.1% is fT4
How is most T3 made in the body
Peripheral tissue deiodinization of T4 (from I4 to I3)
How does T4 enter the cell
1) Passive diffusion
2) Active receptor-mediated transport
Which thyroid hormone binds the nuclear receptor
T3
What is primary hypothyroidism
At level of the thyroid
1) Lymphocytic thyroiditis (AA)
2) Idiopathic atrophy (degenerative)
—
3) Neoplastic
4) Congenital, iodine deficiency, I131, Drug (like TMS)
How much thyroid function must be destroyed prior to seeing clinical signs
75%
Which type of hypothyroidism is most common (primary, secondary, tertiary)
Primary
What is secondary hypothyroidism
At the level of the pituitary gland
Lack of TSH
1) Tumors, congenital, trauma, surgery
What is tertiary hypothyroidism
At the level of the hypothalamus
Lack of TRH
What clinical signs would you expect to see in a congenital hypothyroidism case
Poor growth and development
Signalment of hypothyroidism
Middle-aged (4-10yr)
Medium-large breed dogs
Dog leukocyte antigen (DLA) haplotypes associated with hypothyroidism
1) Doberman pinscher
2) Giant Schnauzer
3) Rhodesian Ridgeback
4) English Setter
Non-skin clinical signs of hypothyroidism
- Muscle weakness
-Myopathy
-Peripheral neuropathy
-Laryngeal paralysis
-Megaesophagus - CNS signs with myxedema
- Ocular: corneal lipid deposits
- Reproductive
-Prolonged anestrus
-Prolonger parturition, higher puppy mortality
What causes myxedema coma in hypothyroid patients
Increase in myxedema in the brain itself!
Fatal!
Microscopic findings of hypothyroidism
*Sebaceous gland and follicular gland atrophy
*Failure to initiate anagen
*Disturbances to cornification
What causes facial myxedema in hypothyroid dogs
Increase in glycosaminoglycans in the dermis
Labwork findings in hypothyroidism
*Hypercholesterolemia
*Normocytic, normochromic, nonregenerative anemia
+/-
*ALP elevation
*CK elevation
What is the best test for hypothyroid diagnosis
fT4 + TSH
TSH increases the specificity of fT4
Which breed experiences “tiger striping” with hypothyroidism
Rhodesian ridgebacks
What is the value of a TT4 test
Screening tool
Why may a TT4 be low without true hypothyroidism
1) Old dog
2) Sight hound
3) Drugs
4) Concurrent illness
Why is TT3 not a good gauge for thyroid function
Most T3 is actually made by deiodination in the peripheral tissues, NOT by the thyroid
Clinical sign seen in 6/7 cats with spontaneous hypothyroidism
Bilateral goiter
Not all had skin lesions (but if they do, looks similar to dogs)
Which thyroid hormone has the most influence on TSH
fT4