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46 Cards in this Set

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Describe the sequence of the HPT (hypothalamus, pituitary, thyroid) axis
hypothalamus secretes TRH --> TRH stims pituitary to secrete TSH --> TSH stims thyroid to secrete T3 & T4 --> T3 & T4 have negative feedback on pituitary
What percentage of the thyroid must be destroyed before you see c/s in primary hypothyroidism?
75%
What percentage of primary HOT (HypOThyroidism) is caused by lymphocytic thyroiditis?

what does lymphocytic thyroiditis cause?
~50% of cases

leakage of thyroglobulin, fibrosis and inflammation
What percentage of primary HOT is caused by idiopathic thyroid atrophy?

What type of tissue is it?
~50%

adipose tissue
Thyroid adenocarcinoma is often productive or nonproductive?

How does it cause hypothyroidism?
nonproductive

if it destroys enough tissue --> hypothyroidism
Secondary HOT is usually due to what?
pituitary malformation/neoplasia
1 HOT is due to the dysfunction of what?

2 HOT is due to the dysfunction of what?

3 is due to the dysfunction of what?
1. thyroid

2. pituitary

3. hypothalamus
Cretinism can be caused by what 3 things?
congenital hypothyroidism
Iodine deficiency (rare)
thyroid dysgenesis/dyshormonogenesis (most common)
Hypothyroidism is inherited by which 3 dog breeds?
beagle, borzoi, old english sheepdogs
What age, sex, and breed do you think of when thinking about HOT?
middle aged, female, goldens
What are some c/s seen with HOT?
**weight gain
lethargy/mental dullness
dermatological signs (rat tail, deborrhea, etc)
**heat seeking/cold intolerance
bradycardia
constipation
muscle weakness/atrophy
edema
**Tragic expression
infertility
some opthalmologic signs (KCS, ulcers, glaucoma)
neuro signs (peripheral neuropathies, vestiburlar dz)
myxedema (rare)
What is myxedema?

What does it feel/look like?
hyaluronic acid deposition in eyelids, cheeks, and forehead

skin feels funky, slides, slimy-feeling
What are some c/s of cretinism?
mental retardation
stunted/disproportionate growth (delayed skeletal maturation, epiphyseal dysgenesis)
large broad heads
macroglossia
hypothermia
delated dental eruption
ataxia
abdominal distention
dermatologic signs
Which breed is predisposed to cretinism?
Giant Schnauzers
What would you see on a CBC/Chemistry with HOT?
mild non-regen anemia
fasting hypercholesterolemia (in 75% of patients)
hypertryglyceridemia
Screening test(s) for HOT
total T4
Diagnostic test(s) for HOT
Free T4
TSH
What is the test of choice for dx of HOT?

In what order would you do the screening/diagnostic tests for HOT?
fT4

tT4 is low, do a fT4
What is a thyroglobulin autoantibody and what type of HOT is it seen in?
antibody against the thyroglobulin seen in lymphocytic thyroiditis (Abs attack the thyroid itself
What does it mean when a tT4 comes back in a elevated in a dog?
The dog could have anti-T4 antibodies and is most likely hypothyroid
What is euthyroid sick syndrome and what can cause it?
where thyroid levels are decreased without an actual thyroid problem

systemic illness can decr T4
60% of dogs w/severe illness of any kind have low T4
What do you do for a sick dog that comes back with a decr tT4?
test fT4 (could be HOT or euthyroid sick syndrome)
What meds do you use to treat HOT?
L-thyroxine (normalized T3 and T4 and risk for hyperthyroidism is low)
When using L-thyroxine, what types of improvement should you see when?
1-2 weeks: improvement in activity
4-6 weeks: improvement in coat (neuro, cardio, hyperpigmentation may take months)
When do you recheck treated HOT patients?
recheck in 1 month if no abnormal signs beforehand, then recheck every 6 months
What is the most common endocrine disorder in cats?
hyperthyroidism (HET)
is HET more often unilateral or bilateral?
bilateral (70%)
What causes HET?
adenomatous hyperplasia/adenoma (most are benign)
What is a common cause of feline HOT? In what breeds is it congenital?
treatment of HET often causes HOT in cats

congenital in DSH and Abyssinians
How does HET contribute to chronic kidney disease?
it causes hypertension and increases GFR, sclerosis
What are come c/s and physical exam findings you could see with HET?
weight loss
PU/PD/polyphagia
v/d
hyperactivity, aggressive
weakness
dyspnea/panting (thyrotoxic cardiomyopathy)
blindness/retinal hemorrhage
palpable thyroid/thyroid slip
systolic murmur, tachycardia, gallop rhythm
unkempt appearance
What would you see on a CBC/Chemistry in a cat w/HET?
erythrocytosis
incr MCV
leukocytosis
lymphopenia
eosinopenia
elevated: ALT, ALP, LDH, AST, glucose, azotemia, Phos, Bili (almost always have elevated liver enzymes)
If you find azotemia w/incr phosphorus, what two diseases in a cat would you think of?
kidney disease or hyperthyroidism
Why would you find an incr R wave and ventricular arrythmias on an ECG of a cat w/HET?
bc HET causes thyrotoxic cardiomyopathy which looks the same as hypertrophic cardiomyopathy, and both cause a thickened/large left ventricle, which corresponds to the R wave in an ECG
What test will diagnose HET in cats, but not HOT in dogs?
tT4
What is found on a normal pertechnetate scan? What can it be used for?
normal: thyroid gland is 1:1 with salivary gland

can be used to find distant metastasis
What 2 treatments are there for HET in cats? What can be used to treat the side effects (specifically cardiomyopathy)?
anti-thyroid meds (methimazole, tapazole)
I-131 therapy
B-Blockers for cardiomyopathy
How does methimazole work? is it reversible?
blocks hormone synthesis and replease by preventing I incorporation and inhibiting coupling of DIT and MIT

reversible in 24-72 hrs
What is the treatment of choice for HET?
methimazole
What is the one problem with transdermal methimazole?

when using methimazole, which is more important to test: CREA or USG?
the effect changes over time - slows the cat's metabolism --> decr absorption of drug --> loses effect

USG bc it's the first to go
Reversible side effects of methimazole

what do you do if these effects occur?
anorexia, vomiting, lethargy

stop tx for a few days, then restart at a lower dose
Irreversible side effects of methimazole
facial excoriations, bleeding diathesis, hepatopathy, MG, cold agglutinin-like disease (blood clots @ lower temps, ear margins)
What side effect could you find in cats on methimazole that you also find in lupus?
+ANA (antinuclear antibodies)
What would you hope to find during a methimazole trial and why?
tT4 in the lower 1/2 of the range and a normal USG (does not guarantee absence of kidney disease)
Obligate anaerobes:
Can't Breathe Air
Clostridium
Bacteroides
Actinomyces
(lack catalase and/or superoxide dismutase; therefore, susceptible to oxidative damage)

Note: generally foul smelling (short-chain FAs), difficult to culture, and produce gas in tissue (CO2 and H2)
What would you expect to see i the history and PE in a dog with thyroid neoplasia?
**mass that bleeds w/FNA
dyspnea
dysphonia
dysphagia

(all bc there's a MASS in the throat region)