Thyroid Disease (Marin) Flashcards
what is the most over diagnosed thing ever in dogs
hypothyroidism
what are the 2 kinds of primary hyppthyroidism?
acquired : lymphocytic thyroiditis, immune mediated destruction. Heritable in beagke and borozi. can also be idiopathic thyroid atrophy
congenital: super rare, associated with cretinism, happens in fox terriers and rat terriers
which breeds tend to get hypothyroidism the most?
golden retrievers, doberman pinschers, beagles, and many many more
hypothyroidism is often in ______ dogs
younger
your friend calls you and says that they think their dog has hypothyroidism. You have neveer actually seen this dog before, so you suggest to your friend to bring it in to you. what clinical signs would you look for to increase your suspicions of hypothyroidism?
dermatologic/skin issues: alopecia, dry dull hair coat, change in coat color, poor hair regrowth, puppy haircoat
could also be: seborrhea, hyperkeratosis, recurrent superficial pyoderma, recurrent otitis externa
others: lethargy, obesity with same or decreased appetite, neurologic signs, myopathies
In an obese dog with subtle dermatologic issues over the last few months that now has facial nerve paralysis and signs of peripheral vestibular disease, what disease are you thinking?
hypothyroidism
corneal lipid deposits are consistent with what disease
hypothyroidism
besides hypothyroidism, what other differentials do you have for peripheral vestibular disease?
otitis media/interna
geriatric idiopathic peripheral vesitbular disease
your friend brings in their dog, Jake, that they think has hypothyroidism and you take a look. He does have some thing hair on his flank, bilateral, and he is very obese. He has also has a catheter shaved spot on his front left leg from a dental procedure he had months ago and the hair hasn’t grown back. If this dog does have hypothyroidism, what would you expect on a CBC chem?
possibly a mild non regenerative anemia
a fasting hypercholesterolemia
hypertriglyceridememia
high ALP and ALT
Jake the dog has high cholesterol, high triglycerides, and a slight non regenerative anemia. What is/are the next test(s) you want to do for him to confirm hypothyroidism? Are there pros and cons for each test?
total T4: this is a good first screening test that is sensitive but not specific (if normal it’s unlikely to be), if this is low, it does not mean they are for sure hypothyroid
free T4: a more complicated test, not affected by antibodies of protein concentrations, a really good single test but VERY EXPENSIVE and takes a few days to come back
TSH: not sensitive on it’s own, would need a total or free T4 test first
why would you want to do an anti-thyroid antibody test?
some dogs like beagles have an immune mediated thyroiditis can have clinical signs of hypothyroidism but normal total T4 because it’s counting the antibodies as T4, so in this case you may want to measure these antibodies
briefly describe sensitivity vs specificity
sensitivity is a big fishing net: you’re wanting to CATCH EVERYTHING! You’re unlikely to miss something but you also might catch some unwanted stuff. total T4 test is like this, it’s useful for ruling OUT
specificity is a harpoon: you go hunting for a specific single fish. You will miss other fish of the same kind but the fish you do catch will for sure be the one you want
what is euthyroid sick syndrome?
when theres a disease or illness not associated with thyroid but affects the thyroid hormone concentrations
true or false: a lot of things affect T4 concentrations daily
true! daily variation, small breed and obese dogs can have higher amounts, greyhounds can have lower, certain meds like steroids can cause low T4, systemic illness elsewhere
You run a total T4 on jake and it’s low. What are your next steps?
run either a TSH or a free T4
if TSH is high: confirmed hypothyroid
if TSH is low: unlikely hypo, but could run a free T4
if FT4 is low: confirmed hypothyroid
if FT4 is normal: unlikely hypo
Jake’s free T4 comes back low, and you diagnose him with hypothyroidism. How will you treat him?
start Jake on Levothyroxine tablets, then re check total t4 4-6 weeks later 4-6 hrs after administration
prognosis is excellent
whats the harm in falsely diagnosing hypothyroid and putting a patient on Levothyroxine?
it can cause high blood pressure and strokes if you over supplement
what actually causes hyperthyroidism in cats?
usually a functional adenomatous hyperplasia or an adenoma, most are bilateral, and we dont know why this happens
which breeds have a decreased risk of getting hyperthyroid?
siamese and himalayans
what clinical exam findings are most common with hyperthyroid cats?
weight loss, polyphagia, hyperactivity, PUPD, tachycardia
palpate the thyroid! 80% will be enlarged on palpation
why can hyperthyroidism in cats cause heart disease?
it makes the heart work too hard (increased demands), causing tahcycardia, gallops, systolic murmurs, can lead to eventual HCM (reversible if treated), and hypertension also possible
why does hyperthyroidism mask CKD?
it makes the kidneys work harder by increasing GFR so it appears like the kidneys are actually fine and working well. the azotemic compounds get flushed
a 12 yo cat named Marsh comes to see you because his owners think he’s skinny. he has a palpable thyroid mass and you suspect hyperthyroidism. What do you expect the CBC/chem and UA results to be?
erythrocytosis/thrombocytosis, a stress leukogram
high liver enzymes: ALT and ALP (hypoxia to liver due to high demands)
hyperphosphatemia: bone turnover and some kidney disease
azotemia: concurrent CKD, dehydration
hypokalemia (flushing), hyperglycemia (stress)
UA: silent UTIs, isosthenuria
Marsh the cat has a high ALT and high ALP, and some azotemia. What is the next step for diagnosis?
total T4: even if it’s slightly high, it’s common to miss some cases with mild disease, so may want to consider retesting in a few weeks if your clinical suscpision is still high
if total T4 is on slightly high normal range, do a free T4 to double check
Marsh’s T4 comes back high and you diagnose hyperthyroidism. what treatment options are there?
Methimazole: inhibits production of T4
can do PO or transdermal
do CBC chem and total T4 3 weeks later
you start Marsh the cat on Methimazole. Before he is given his first pill, what do you need to tell the owner about this drug?
there are adverse effects in the first 1-3 months: vomiting, anorexia, excoriations of the head and neck, eosinophilia, lymphocytosis, leukopenia, thrombocytopenia, severe leukopenia, IMHA, hepatotoxicity
except for _____, you must stop the drug if your patient has adverse effects from Methimazole
GI symptoms
what is I 131 and how does it work?
radioactive iodine, a treatment for hyperthyroidism, given either IV or SQ
it is the safest, simplest, most effective therapy with minimal complications, it is permanent
only adverse effect is sometimes hypothyroidism
it is very expensive
requires a special permit and room and lots of time
if a cat has azotemia before you start them on I 131….
treating the hyperthyroidism way worsen the azotemia and the patient could become very clinical for CKD
what should you do if you see a cat with a heart murmur that has hyperthyroidism?
if you treat the hyperthyroidism, the murmur should dissapear, but can always get an echo to determine if it’s true HCM. Could also consider chest rads
if a cat is experiencing a thyroid storm, what drugs can you give to help treat the tachycardia?
beta blockers like propanolol or atenolol
how does the Hills Y/D diet work for hyperthyroid cats?
it has really low levels of iodine in them and you need iodine to make T4
the cat can only eat this diet
a good option for patients that can’t tolerate methimazole
what other diseases should you screen for if you have a cat that comes to you for weight loss?
GI disease (IBD, neoplasia), secondary GI (CKD, diabetes, liver disease, EPI)
