Hormonal Disorders of Cats

Hormonal Disorders of Cats

Acromegaly

Question: Dear Dr. Mike,

I am a subscriber to Vetinfo Digest.

I would like to know more about acromegaly in cats and how common it is. I have an 8 month old kitten who is very large framed, well muscled and now weighs over 15 lbs. His littermate is smaller, a female at 10 lbs. I am wondering if he could have acromegaly or will prone to it later in life. Although he's extremely healthy and active I've just never known a kitten this huge with a tail that long!

Thank you in advance, Judy

P.S. You've also given me good information about my older diabetic cat who is now doing well on PZI insulin.

Answer: Judy-

Acromegaly is a disorder in which there is overproduction of growth hormone. It usually occurs in adult cats approaching "senior" status, due to pituitary gland tumors (pituitary adenomas) that produce growth hormone. This causes widening of the facial structures which is sometimes easiest to appreciate by looking at the teeth, which move apart as the bone grows, although thickened facial folds, abdominal enlargement, increases in organ size (heart, liver, kidneys) and other growth related symptoms may appear.

This is not likely to be causing the increased size of your male cat compared to his sister. It doesn't sound like he is overweight by your description, either, but you might want to ask your vet on the next visit if he is a good weight for his size.

It sounds like you probably have a normal cat who is just a big boy. Hope so!

Mike Richards, DVM 3/2/2000

Hypothyroidism and Diabetes in cats

Q: Dear Dr. Mike,

I read, with interest, the last VetInfo Digest about drugs and drug interactions especially concerning Levo Thyroxine. I wrote you some weeks ago about my cat, Oliver, who was diagnosed with both hypothyroidism and diabetes. Although you mentioned that Levo Thyroxine increases insulin requirements in dogs, I've found that it also acts the same way in cats. I was unable to regulate Oliver on insulin until my vet contacted the pathologist from the lab which does the blood work and he suggested taking Oliver off the Levo thyroxine completely. Doing so has markedly decreased his insulin requirement.

I am wondering if hypOthyroidism in cats, rare as it is, contributes to diabetes in any way. I 'converse' with others on the Feline Diabetes Message Board and seversl of us own cats who have both these diseases. Do you have any information on this?

Thanks in advance!

Judy

A: Judy-

In cats, hypothyroidism is considered to be very rare. So rare that I have only seen one clinical case report involving more than one cat and it related to congenital hypothyroidism occurring in two kittens who were littermates.

There is a condition known as euthyroid sick syndrome, in which total thyroxine (total T4, TT4) levels fall below normal levels due to other illness but the thyroid gland is actually OK and meeting the body's need for free thyroxine (free T4, fT4), sometimes fTT4). Since free thyroxine is the active form in the body, the cat is actually euthyroid (normal thyroid hormone levels) despite having the low total T4 values. This almost certainly occurs in some cases of diabetes and can occur with any illness that is chronic or severe. Since it is common to run TT4 tests to try to rule out hyperthyroidism in cats who are aged and ill, due to the prevalence of that disease, there are starting to be a lot of reports of low total T4 levels in cats. This happens due to the euthyroid sick syndrome in most cases but it is really tempting to treat these cats with thyroxine when many of the symptoms of hypothyroidism are present.

The best way to differentiate between these conditions for most practitioners is to run a free T4 test. If the serum level for free T4 is also low, there is a better chance that hypothyroidism is present. At that time a clinical trial with levo-thyroxine may be indicated if it is not possible to do TSH response testing (most practices can't get TSH anymore). This has to be done cautiously since cats are susceptible to effects of hyperthyroidism much more commonly than dogs.

I think that it is probably best that you have discontinued l-thyroxine supplementation, as suggested by the specialist. If signs of this problem return it will be possible to do accurate free T4 testing in three or four weeks.

Hope this helps in the understanding of what may be going on.

Mike Richards, DVM 7/27/99