Hyperthyroid Flashcards
What is the chemical found in fire retardents and plastic softenerd that has been associated with thyroid tumours?
PBDEs
Polybromylatedphenylethers
Are pure breds more or less likely to develop hyperthyroidism? Why?
Less likely. Have colour dilution so use less tyrosine. Tyrosine is a melanin precursor and for thyroid hormone. Less likely to become tyrosine deprived as need less for melanin production (only speculated)
What kind of growth do we get in cats that gives them hyperthyroidism? (mainly)
Adenomatous hyperplasia with autonomous growth capacity
Is it possible for only one side to be affected by adenomatous hyperplasia in the cat?
Nope. May only be palpable on one side but WILL be present in both if present in one
What is a diastolic gallop and why does it happen in hyperthyroid?
Hear lub-a-dub, lub-a-dub, lub-a-dub rather than lub-dub, lub-dub
Occurs due to turbulence of blood being pumped into ventrile when it hasn’t emptied properly or has a reduced diastolic compliance. Reduced diastolic compliance occurs in hyperthyroidism due to thickening of the muscle
May also hear a whoosh murmur due to compromised LVOT
What is the current average age of cats with hyperthyroidism?
Around 10
What are the main clinical signs of hyperthyroidism?
Weight loss with variable appetite
Poydipsia (less than 25%), primary PD
Hyperactive but can be lethargic
Around 85% have cardiovascular abnormality e.g. tachycardia, gallop rhythms, systolic murmur
Thyroid nodule
Roughly what proportion have a palpable thyroid nodule?
around 70%
Hyperthyroidism results in increased ****** sensitivity. Hence tendency to develop ****** and *********
Catecholamine
Tachycardia and tachydysythmias
Can also get diastolic gallop rhythms (impaired ventricular relaxation)
May get tachynpnea and panting
Thyroid hormone ****** systemic vascular resistance
REDUCES
Often reported that hyperthyroidism results in hypertension, not true!!
Why might hyperthyroid cats get tachypnea and panting?
Heart failure and space reduced in thoracic cavity
How do we assess the size of the left ventricle in these cats?
Aorta:LA ration
Is retinal damage common in hyperthyroid cats?
No. Was previously thought a risk as cats seemed to have hypertension but this now thought just to be due to hyperthyroid cats being irritable and therefore getting high BP when you tried to measure them, but not resting
Why do you need to monitor the BP of hyperthyroid cats during and following treatment?
Hyperthyroidism may be MASKING hypertension which might be evident once they are treated
What clinpath findings might you see in hyperthyroidism?
Elevated ALT in most cases
Elevated ALP in about half. Elevated ALP in the cat usually more significant than in the dog as very short half life
Elevated bile acids in about half (hyperthyroid induced hepatopathy-don’t know why, reversible and not clinically significant)
Stress leukogram - lymphopenia, neutrophilia, monocytosis
Catecholamines may stimulate increase in all WBCs
What is the most common way of testing for this problem?
How sensitive/specific is it?
basal total T4, very high specificity, moderate sensitivity
Why is basal free T4 not that helpful?
Costs around 3-4x the price and much as it increases sensitivity a bit it also decreases specificity
Is a cTSH a useful test? what about spes and sens?
Not really, appaling sensitivity but excellent specificity
Is a T3 suppression test useful?
Yes probably
What proportion of hyperthyroid cats have a normal T4?
Around 8-9%
What follow up testing options are there for hyperthyroid cases?
Eloevated free T4 by looking at equilibrium dialysis
Repeat Basal T4 in a month’s time
T3 suppression test (semi expensive to run in the UK)
Does hyperthyroidism increase or decrease GFR?
Increase
Why would you do a T3 suppression test and how would you do it?
If you measured basal T4 and it was normal but you still suspected hyperthyroidism (remember high specificity low sensitivity) you could do a T3 suppression test
Measure basal tT4
30mg of T3 every 12 hours for 7 doses
Last dose over 2 hours before sample
Looking to see whether the animal will suppress its endogenous thyroid hormone production when there’s enough exogenous active T3 available.
If normal T4 should be almost undetectable (<20nmol/L)
May want to measure the T3 as well to make sure it’s been absorbed properly, T3 should be increased
If you’re tableting the cat and it spits it out you will get a false positive if you just measure T4
What is thyroid scintigraphy?
Give technetium and a gamma camera to look at uptake by the thyroid gland
Why does creatinine increase when hyperthyroidism is treated?
Because GFR decreases
Should you avoid treating a cat for hyperthyroidism because you are worried about decreasing its GFR and creating azotaemia?
Probably not.. Hyperthyroidism itself may cause glomerular sclerosis which is more damaging and will decrease GFR eventually too!
In hyperthyroid cats pre-treatment azotaemia **** survival time
shortens
Cats that are not azomtaemic before treatment but become azotaemic after treatment have increased/decreased/same average survival time
same
What is the medical therapy for hyperthyroidism?
Carbimazole
Methimazole
Should you still treat hyperthyroid cats if they are azotaemic before treatment?
Probably yes, they feel crappy when hyperthyroid and hyperthyroidism may be progressing renal disease anyway
What’d the induction protocol for Carbimazole/Methimazole?
Carbimazole: 10-15mg/24h
Methimazole: 2.5-5mg/12h
Induction lasts 2-3 weeks. Consider increasing the frequency or dose if no effect
What should the maintenance dose be for carbimazole/methimazole?
Carbimazole: 10mg/24h
Methimazole: 2.5-5mg/12-24h
What proportion of patients should you expect side effects in with carbimazole/methimazole?
5-20%
Which is the drug and which is the pro-drug? methimazole or carbimazole?
Carbimazole pro-drug. Attractive in that given once a day rather than twice
What sort of side effects might you see with carbimazole/methimazole in the cat?
GIT signs
Depression, lethargy
Haematopetic problems (blabla)openia, anaemia
Facial pruritis
What is the surgical treatment for hyperthyroid?
Unilateral or bilateral thyroidectomy.
Unilateral works ok for about 6 months but the other side will also have adenomatous hyperplasia so will start to express itself and may need to be removed too
Doesn’t solve ectopic thyroid tissue
What happens if you go in to remove the second thyroid gland and damage the parathyroid?
Will have hypoparathyroidism
General recommendation therefore is to implant the parathyroid tissue of the first side into the adjacent cervical musscle hoping to get new blood supply to that parathyroid tissue and won’t get clinically significant hypoparathyroidism when you remove the second one
What is the dose of Radioactive iodine given
Between 110 and 183MBq
What is the efficacy of radioactive iodine treatment?
Over 97%
How long do they tend to stay in hospital after radioactive iodine? Why?
2 weeks,
RPA don’t want radioactive cats running around
How long do they tend to survive with radioactive iodine?
Median over 6.5years
How long do they need to be off medication for before you do the radioactive iodine injection?
at least 2 weeks
Price of RI?
£1900-2100
What is restricted in hyperthyroid diets?
Iodine
What are the reported success rates of hyperthyroid diets?
As high as 80% but contraversial
expensive
How strict do you need to be with hyperthyroid diets?
Very! They mustn’t eat anything other than the diet or the iodine restrction will be insufficient
