Hyperthyroidism Flashcards
What should you do if you think there is an early hyperthyroid case that isn’t showing high T4?
Early cases can fluctuate so at some times will be wnl, but will always be high normal
Can repeat at another time (e.g. 1m)
Can repeat with free T4 as this is more likely to be high
Must do fT4 and TT4 together if so as some non thyroid illnesses can make ft4 go very high. If FT4 is high and TT4 is very middle range then this is the case
What should you do if there is possibly non thyroidal illness causing a falsely lowered TT4?
Tx the other disease then retest
Or test canine TSH. If cTSH not detectable and TT4 normal then the cat is not hyperthyroid and unlikely to become so in the next 6m
How common is bilateral disease?
70%, normally a functional adenoma, 3% carcinoma
How can renal values help guide prognosis
If azotaemic before therapy, worse prognosis. If become azotaemic once euthyroid, no worse prognosis than if no azotaemia
How long can it take for renal values to change after becoming euthyroid?
Up to 6months
How does iatrogenic hypothyroidism affect renal values?
Can cause increases - need to avoid hypothyroidism!
What should you do if you have a cat with suggestive signs of hyperthyroidism but a t4 wnl?
Repeat t4 and ft4 2-4 weeks post initial bloods
If the T4 and fT4ed areboth within the referenceinterval the cat should be evaluated for non-thyroidaldisease
If no concurrent illness is found and FHT is still suspected, further testing is warranted, including triiodothyronine (T3) suppression testing,serum TSH concentration in conjunction with T4 and fT4, or thyroid scintigraphy.
What should you do with a cat that has a goitre but no raised t4
Monitor clinical signs in these cats and repeat aserum T4 assay in 6 months.
What are some common co-morbidities with hyperthyroidism?
Thyrotoxic heart disease
How frequently should cats treated with sx or I be assessed with crea, t4, and tsh post tx?
30, 60, 90 and 180 days
How should you assess cats with concurrent HCM and hyperthyroidism?
N-terminal probrain natriuretic peptide (NT-proBNP) values increase in cats with FHT and in cats with hypertrophic cardiomyopathy (HCM), but typically decrease within 3 months of achieving a euthyroid state.54 If NT-proBNP remains elevated after 3 months, further evaluate the cat for HCM.
What are the advantages of radioactive iodine treatment?
The potential to eliminate benign thyroid tumors or hyperplastic thyroid tissue with a single treatment.
Treatment of functional extrathyroidal tissue, which may occur in 10–20% of cases.21,58
No general anesthesia.
Minimal side effects.
What is a thyroid storm?
rare, but life-threatening,complication of FHT.
results from a rapid increase in serum thyroid hormone. Causes include damage to the thyroid gland during 131I therapy or vigorous thyroid gland palpation,abrupt withdrawal of antithyroid medication, anesthesia, exacerbation of NTD or a stressful event.
If you anticipate the occurrence of a possible event, using a beta-adrenergic antagonist, such as atenolol at 6.25mg/cat q24h, as a prophylactic treatment at least 24 h prior to the event will effectively prevent clinical signs.
How do adenomas change with time?
20% change to carcinomas by year 4 of medical tx
How may diet affect risk of hyperthyroidism?
Poss risk associated with canned food isoflaones (only if combined with low iodine or other goitrogen) dietary restriction of iodine Bisphenol A (in plastic sheets)
How may soy isoflavones increase the risk of hyperthyroidism?
inhibit the activity of thyroid peroxidase,
a key enzyme in the synthesis of thyroid hormones, which liberates iodine for addition
onto thyroglobulin for production of T4 and T3
They also inhibit 5’-deiodinase activity, the enzyme that converts total T4 into the biologically active T3
By blocking the production of thyroid hormones,
pituitary TSH secretion would be increased,
leading to thyroid hyperplasia and possibly
goiter
How can hyper t4 affect the heart?
Incr HR and SV
Flow murmur
LV hypertrophy
What can cause a poor response to tx?
Inadequate dosage as the adenoma is v large or active, or it is a carcinoma - can go off label to v high doses
Rapid metabolism so lots of fluctuation throughout the day
Poor compliance
How should you respond to a patient that is not responding to tx as expected?
Incr dose or frequency
scintigraphy
Cytology/ histo (pref)
What is the tx aim
20-30mmol
When should you given thyroxine
If t4 still low after a month
Whta re possible s/e of t4 medical tx?
GI upset hetapic necrosis or cholestasis Dermatological Blood dyscrasias Myasthaenia Lymphadenopathy
Lots of the are immune mediated
How do you limit s/e?
Go low with dose to start
Give with food
Decrease dose or temp withdrawl if v+
Switch to transdermal gel
Why may food not be the best tx?
V low in protein so hard to get good weight gain - can get weight loss
