Is hypothyroidism related to Cushings Disease in dogs?
My dog was diagnosed with low thyroid. Then we discovered that he has Cushings disease from the steroids used to treat his allergies. He has been off steroids for over 2 months now and is doing very well. Should I have his thyroid rechecked ($130 test) or are these things unrelated?
You definitely ought to have his thyroid function reassessed- if he is truly hypothyroid, he will need to be given synthetic thyroxine (thyroid hormone) for life.
It is a possibility, as Vet Tech said, that the low thyroid function was due to his Cushings- almost any illness can create a condition called Sick Euthyroid Syndrome, which basically means that although the thyroid gland is prefectly normal, less thyroid hormone is being produced as a direct effect of the illness.
As his Cushings was caused by the steroids, rather than by his body producing too much cortisol, the Cushings should resolve over time. You’ve said that he’s doing very well, which I’m taking to mean that the Cushings signs are resolving as expected.
The important thing when you do have him re-tested is to make sure that it is done as a FREE T4 (FT4) test. This is really the only practical and accurate test to diagnose hypothyroidism.
A Total T4 (TT4) test will detect low thyroid hormone, but cannot differentiate between sick euthyroid and true hypothyroidism.
A TSH test is not overly useful either, and I wouldn’t waste your money on it- while it should be higher than normal, up to 40% of hypoT dogs have normal levels, and up to 20% of normal dogs have elevated levels.
I hope that makes sense. Please feel free to email me if anything I’ve said is unclear.
Health & Nutrition : How to Treat Hypothyroidism
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