Why Your Diabetic Cat Should Be Tested for Growth Hormone

Blood tests may reveal acromegaly — which may sound alarming but presents a surgical treatment option that stops many cats from being diabetic altogether.

Cats may drink to much water to combat symptoms. By: Dave Dugdale
Cats may drink water excessively in order to combat diabetes symptoms. By: Dave Dugdale

As a veterinarian, I find diabetes to be both a rewarding and a frustrating condition to treat. Sugar diabetes (diabetes mellitus) is common in cats, and the reward comes from making a real difference to the cat’s health. However, not all cases respond as they should.

But why is this?

Before we jump ahead to talk about complications, let’s remind ourselves what diabetes is. A diabetic cat has poor control of his blood sugar levels, which runs too high. This is because the hormone that regulates sugar levels, insulin, is either lacking or the body tissues can’t respond to it.

High blood sugar levels are toxic, and sugar is expelled in urine. However, this means the body also loses water. The patient drinks excessively to replace it.

Insulin Resistance

Some cases need almost unimaginably high doses of insulin, and yet the cats’ blood glucose still refuses to come down.

Think of insulin as the key to unlock the body’s cells and allow sugar in. When insulin doesn’t work (known as insulin resistance), this is equivalent to having the locks changed so the key no longer fits.

We now know that health problems can lead to insulin resistance. Conditions such as gum disease, overactive thyroid glands or even cystitis can “change the lock” so insulin can’t open the cells, which results in poor glucose control.

Acromegaly

However, this article is about a relatively new condition, acromegaly, which is thought to adversely affect 1 in 3 diabetic cats.

Acromegaly is caused by too much growth hormone in the bloodstream. Growth hormone tells tissue to grow, but it also causes insulin resistance.

The typical acromegalic cat has a big, chunky face and enormous paws. However, blood tests now reveal that many normal-looking cats have acromegaly — 1 in 3 diabetics — so physical appearance is not a reliable guide.

Causes of Acromegaly

Growth hormone is produced by an area of the brain called the pituitary gland. I don’t wish to alarm anyone, but the reason for hormone overproduction is because of a tumor within this gland.

Yes, strictly speaking, the cat has brain cancer. But it is of a very low grade, which the cat can live with for many years without it causing problems (other than acromegaly).

The pituitary tumor rarely spreads to other parts of the body (it is not an aggressive cancer), and the majority of cats do not die because of the cancer but from unrelated causes.

How Does Acromegaly Affect Diabetic Cats?

Growth hormones create insulin resistance. Some affected cats need huge doses of insulin — which produces a new problem:

  • The tumor produces growth hormone erratically, and blood levels may wax and wane.
  • Therefore, there is a risk — if hormone levels suddenly drop to normal — of the cat receiving a dangerously high dose of insulin and falling into a coma.

However, when the acromegaly is corrected, a large percentage of unstable diabetics improve dramatically. You can go further and say that many stop being diabetic and go back to having normal blood glucose levels. In other words, they become non-diabetic.

Treatment

Now for the dramatic part: The treatment is brain surgery.

However, what’s convenient about the pituitary gland is that it sits in a small, bony chamber that is accessible through the roof of the mouth. Obviously, this is specialist surgery, but in the right hands it’s perfectly achievable. Cats who have had this surgery are usually up on their paws and tucking into food within an hour or so of their operation.

A cat at my clinic has been through this procedure, and I’m convinced it saved his life. Before surgery, he had several life-threateningly dangerous hypos (low blood sugar events), which means a day of hospitalization to get him well again. After surgery, he’s no longer diabetic.

If one of my own cats was diagnosed with diabetes tomorrow, I’d run the blood test for growth hormone. Not only will it help me predict if the cat will stabilize properly, but it gives me a treatment option that can be close to a “cure.”

References

  • Neissen, S.J. (2010). Feline acromegaly, an essential differential diagnosis for the difficult diabetic. J Feline Med Surg, 12.
  • Neissen, S.J. & Petrie, G., Gaudiano, M., et al. (2007). Feline acromegaly: An underdiagnosed endocrinopathy? JVIM 21: 889.
  • Elliot, D.A., Feldman, E.C., Koblik, P.D., Samii, V.F., & Nelson, R.W. (2000). Prevalence of pituitary tumors among diabetic cats with insulin resistance. JAVMA 216: 1765–1768.

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This pet health content was written by a veterinarian, Dr. Pippa Elliott, BVMS, MRCVS. It was last reviewed March 27, 2015.

Dr. Pippa Elliott, BVMS, MRCVS

View posts by Dr. Pippa Elliott, BVMS, MRCVS
Dr. Pippa Elliott, BVMS, MRCVS, is a veterinarian with nearly 30 years of experience in companion animal practice. Dr. Elliott earned her Bachelor of Veterinary Medicine and Surgery from the University of Glasgow. She was also designated a Member of the Royal College of Veterinary Surgeons. Married with 2 grown-up kids, Dr. Elliott has a naughty puggle called Poggle, 3 cats, and a bearded dragon.

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