Endocrinology - NAVDF 2021 Flashcards
T/F: Most cases of canine hypothryroidism are primary hypothyroidism.
True - a result of dysfunction of the thyroid gland itself
T/F: Lymphocytic thyroiditis is a slowly progressive disease and clinical signs of hypothyroidism will not be present until at least 75% of the function of the thyroid gland is lost.
TRUE
What breeds are at increased risk for hypothyroidism based on their dog leukocyte antigen haplotype?
Doberman pinscher, Giant Schnauzer, Rhodesian ridgeback, English setter
What are possible causes of primary hypothyroidism?
lymphocytic thyroiditis, idiopathic atrophy of the thyroid gland, neoplasia, iodine deficiency, congenital hypothyroidism, radioactive iodine treatment, drugs (potentiated sulfonamides, corticosteroids, phenobarbital, some NSAIDs)
Secondary hypothyroidism results from a dysfunction of what?
pituitary gland (decreased thyrotropin/TSH production) dysfunction leading to secondary follicular thyroid atrophy
What are possible causes of secondary hypothyroidism?
pituitary tumors, congenital pituitary malformations (cystic Rathke’s pouch), pituitary trauma/surgery
Tertiary hypothyroidism results from a dysfunction of what?
hypothalamus dysfunction (decreased thyrotropin-releasing hormone)
What results in decreased TSH secretion (provides negative feedback for TSH secretion)?
thyroid hormones (thyroxine/T4; 3,5,3’-triiodothyronine/T3), somatostatin, dopamine, catecholamine, TNF-alpha, some interleukins
Why do dogs have lower serum total thyroxine/T4 levels than humans?
dogs have weaker protein binding of T4 – lower serum total T4 levels and higher free T4 levels
T/F: Thyroxine must undergo deiodination to T3 to be able to bind to the cell’s nuclear thyroid receptor.
True - although T4 has some intrinsic activity, it is often considered a prohormone as it has to be deiodinated to T3 to exert the metabolic effects of thyroid hormone
What is reverse T3?
metabolically inactive form of T3 - 3,3’,5’-triiodothyronine; this deiodination pathway increases during periods of non-thyroidal illness
Why is alopecia seen in hypothyroidism in areas of wear/tear?
thyroid hormones are very important to the skin and promote the initiation of the anagen phase of the hair follicle cycle
What dogs can have lower T4 concentrations?
older dogs and sight hounds (of any age)
Why is serum T3 not useful in making a diagnosis of primary hypothyroidism?
although T3 is the most important biologically active thyroid hormone at a cellular level, a large portion of it is produced by deiodination in peripheral tissues
T/F: Endogenous canine TSH is consistently increased in canine hypothyroidism.
False - up to 38% of hypothyroid dogs may have a cTSH concentration within the reference range; has a low sensitivity but a good specificity
What is the sensitivity and specificity of free T4 and endogenous TSH serum concentration for diagnosis of primary hypothyroidism?
sensitivity of 74-80%, specificity of 98% (overall accuracy of 86%)
Animals with lymphocytic thyroiditis can have antibodies to what components?
thyroglobulin (59% of hypothyroid dogs), T4, T3
What should be done if a dog has a positive anti-thyroglobulin antibody but normal thyroid function?
monitor for future development of hypothyroidism
What is more common: antibodies to T3 or T4?
anti-T3 antibodies
Why might an animal with true primary hypothyroidism have a normal serum T3 or T4?
anti-T3 and anti-T4 antibodies can interfere with some assays to measure T3 or T4, resulting in an erroneously high value
Glucocorticoids: effect on total T4? Free T4? Endogenous TSH?
decreased or no change; decreased or no change; no change or decreased (all changes are dose and duration-dependent)
Phenobarbital: effect on total T4? Free T4? Endogenous TSH?
decreased or no change; decreased or no change; no change or decreased
Sulfonamides: effect on total T4? Free T4? Endogenous TSH?
decreased; decreased; increased
Potassium bromide: effect on total T4? Free T4? Endogenous TSH?
no change; no change; no change
Clomipramine: effect on total T4? Free T4? Endogenous TSH?
decreased; decreased; no change
Aspirin: effect on total T4? Free T4? Endogenous TSH?
decreased; no change; no change
Ketoprofen: effect on total T4? Free T4? Endogenous TSH?
decreased; no change; no change
Carprofen: effect on total T4? Free T4? Endogenous TSH?
decreased or no change; decreased or no change; decreased or no change
Non-thyroidal illness: effect on total T4? Free T4? Endogenous TSH?
decreased; decreased or no change; no change or increased (slight)
T/F: Thyroid supplementation may cause hair regrowth in an animal with non-thyroidal illness.
True - thyroid hormone therapy is a signal for hair follicles to initiate anagen
How long should thyroid supplementation be decreased before evaluating thyroid function?
6-8 weeks
Why can progesterone-secreting adrenal tumors result in an increase in unbound cortisol?
progesterone is a glucocorticoid agonist and competes with cortisol for binding (increase in progesterone can cause an increase in cortisol)
What part of the adrenal gland makes cortisol?
zona fasciculata
Pituitary tumors may secrete what other hormones besides ACTH?
growth hormone, melanocyte stimulating hormone
What does the hypothalamus produce to regulate cortisol production?
corticotropin-releasing hormone (delivered to the pituitary gland –> stimulates secretion of ACTH)
What stimulates the hypothalamus to secrete corticotropin-releasing hormone?
cytokines (IL-1, IL-6, TNF-alpha) and/or hormones (leptin, dopamine, angiotensin II, antidiuretic hormone)
What are the components of pro-opiomelanocorticin (POMC)?
ACTH, melanocyte-stimulating hormone
What inhibits release of corticotropin-releasing hormone from the hypothalamus?
glucocorticoids and somatostatin
What does the pars intermedia of the pituitary produce?
alpha-MSH and corticotropin-like intermediate peptide; pro-opiomelanocorticin (cleaved to ACTH and beta-LPH)
What does the posterior pituitary produce? (neurohypophysis)
antidiuretic hormone, oxytocin
What stimulates ACTH production from pituitary gland?
corticotropin-releasing hormone; stress & hypoglycemia
What inhibits release of ACTH from the pituitary gland?
cortisol, glucocorticoids
Why can’t the zona glomerulosa produce cortisol or androgens?
lacks 17-alpha-hydroxylase
The enzyme 17-alpha-hydroxylase is required to synthesize what products?
17-hydroxy-pregnenolone and 17-hydroxy-progesterone (precursors to cortisol and androgens)
Why are urinary tract infections common with hypercortisolemia?
immunosuppressive effects of hypercortisolemia and because dilute urine is less bactericidal
Other than the dog, what is the only other species to develop calcinosis cutis with hypercortisolism?
chinchilla
Acquired skin fragility in cats is associated with what conditions?
hyperadrenocorticism, iatrogenic hypercortisolemia, excessive levels of progestational compounds from either adrenal tumors or iatrogenic effect of administered progestational compounds
T/F: Elevated ALP is seen in both the cat and dog secondary to hyperadrenocorticism.
False - the cat does NOT have a steroid-induced isoenzyme of ALP
Why is the ACTH stimulation test the test of choice for identifying iatrogenic hyperglucocorticoidism?
evaluates adrenal cortex reserve – iatrogenic HAC causes adrenocortical atrophy and failure to respond to ACTH stimulation
T/F: Dogs with an adrenal tumor will have lower than normal endogenous ACTH plasma levels.
True - most of the time
What effect does hyper thyroidism have on adrenal gland size in cats?
can increase adrenal glands by as much as 20%
What enzyme does trilostane inhibit?
3-beta-hydroxysteroid dehydrogenase: enzyme needed to convert pregnenolone and 17-alpha-hydroxypregnolone to progesterone and 17-alpha-hydroxyprogesterone (precursors in cortisol synthesis)
T/F: Mitotane is fat-soluble and needs to be administered with a meal.
TRUE
What mineral is present in lesions of calcinsosis cutis?
apatite
What is a proposed pathomechanism for PU/PD seen in hyperadrenocorticism in dogs?
increased GFR due to vascular volume and renal blood flow (mineralocorticoid effects), inhibits responsiveness to ADH in dogs –> decreased renal tubular resorption of H20 –> poyluria and compensatory polydipsia
Which is more effective for treatment of hyperadrenocorticism in cats: mitotane or trilostane?
trilostane – mitotane does NOT control clinical signs
What is the definition of a paraneoplastic syndrome?
disease or clinical signs that develop distant from the site of a tumor, caused by the presence of the tumor or its metastasis, but is not resulting from the local presence of neoplastic cells
Paraneoplastic syndromes are mediated by what?
hormones, cytokines, growth factors released by tumors or by an immune response targeted against the tumor
Mutations in the gene BHD that encodes for folliculin can result in what tumor type in intact female dogs?
uterine leiomyomas
Skin lesions are most commonly associated with what systemic mycosis in dogs? Cats?
Dogs - blastomycosis, Cats - cryptococcus
What viral infections in dogs can cause cutaneous signs?
canine distemper and pseudorabies (and papillomavirus)
What viral infections in cats can cause cutaneous signs?
FeLV, FIV, FHV, feline calicivirus, feline coronavirus (FIP), papillomavirus
Where are the highest concentrations of zinc found?
keratinized tissue of the nasal planum, tongue, and footpad
Zinc Responsive Dermatosis Syndrome II typically occurs in rapidly growing puppies fed poor quality dog food or over-supplemented with what?
calcium – can bind to zinc
Superficial necrolytic dermatitis has been reported in what species?
dog, cat, and black rhinoceros
Clinical signs of superficial necrolytic dermatitis?
footpads develop marked crusting, fissuring, and ulcerations; erythema, crusting, exudation, ulceration and alopecia can also involve the periocular or perioral regions, pressure points on the limbs and scrotum
What are non-immunopathogenic mechanisms that result in vasculitis?
processes that weaken the integrity of the vascular wall - invasion of neoplastic cells or microbial agents, influences of burns, trauma, endotoxin, or hemodynamic factors
What are immunopathogenic mechanisms that result in vasculitis?
deposition of immune complexes, antibodies directed against vascular wall components, anti-neutrophilic antibody-mediated vessel damage, cytotoxic T cells directed against vascular components and cytokine induced mechanisms
What are the histopathologic findings with feline paraneoplastic alopecia?
follicular atrophy with miniaturization of hair follicles; epidermal hyperplasia
How are the nutritional needs of chronic hepatitis and superficial necrolytic dermatitis different?
with chronic hepatitis, you want to restrict protein; with SND, you need to INCREASE protein
What is thought to cause the hypoaminoacidemia in superficial necrolytic dermatitis?
increased hepatic catabolism of amino acids – reason that IV amino acid infusions work is that they bypass the liver
When an erythemic skin lesion blanches on diascopy what does that mean caused the erythema?
increased blood flow to the area (different from non-blanching => vascular compromise)
