Here’s a complication that you’ve been dreading for your beloved diabetic cat: At this point, you can no longer control his glucose levels. Neither diet, nor medicines, nor injections of insulin, work. His diabetes remains out of control. So your veterinarian enlists the diagnostic acumen of a veterinary specialist.
After more tests, the diagnosis is clear: hyperadrenocorticism, aka Cushing’s disease. Your cat’s pituitary — a tiny gland in the brain — is producing too much ACTH (adrenal corticotropin stimulating hormone), which tells your cat’s adrenal glands, near the kidneys, to keep pumping out cortisol. Your cat is producing so much cortisol that it’s either causing the diabetes or making it harder to control. Now that the cause of the problem has been identified, there are treatment options.
The overproduction of cortisol
The reason that the diabetes rages on? Hyperadrenocorticism is causing the cat to overproduce cortisol, which, among many other things, stimulates the production of glucose by the body. Unfortunately, this contributes to an increase in blood sugar. Diets that reduce blood sugar, medicines that improve insulin response and injections of insulin may all fail against the relentless rush of blood sugar.
“The excess of cortisol over long periods of time stimulates the body to produce more and more glucose, which exhausts the insulin supply, so the cat becomes diabetic,” explains Dr. Linda Ross, DVM, MS, DACVIM, associate professor in the Tufts Cummings School of Veterinary Medicine, and an expert in animal kidney diseases. Pouring in more insulin is like adding water to a leaky bucket. “The insulin lowers the blood glucose, but the cortisol raises it, so you’re fighting a losing battle,” says Dr. Ross.
Cushing’s disease is much more common in dogs, but it does occur occasionally in cats, says Dr. Ross. “Most veterinarians might see one or two feline cases in a lifetime of practice.” In all, only about 100 cases have been reported in the veterinary literature, although there have almost certainly been other cases that haven’t been written up. “We see more cats with Cushing’s disease than a private practice, because they are referred to us for evaluation of difficult-to-control diabetes.”
A tumor in the pituitary gland
“About 80 to 85 percent of Cushing’s disease in cats is caused by a tumor in the pituitary gland,” explains Dr. Ross. Less often, there is a tumor in the adrenal glands. While pituitary tumors are generally benign, about half the time adrenal tumors are malignant.
Treatment can be tricky
“Treatment is not always simple,” she says. A new medication, trilostane (Vetoryl), which suppresses production of cortisol in the adrenal gland, “is more effective than treatment used to be,” says Dr. Ross. “The previous drug was relatively toxic for cats.” While trilostane doesn’t do anything about the pituitary tumor, it does suppress cortisol — often bringing the symptoms under control. However, “the tumor can progress,” says Dr. Ross.
Other options include radiation of the pituitary tumor. “It can be beneficial,” she says. “It may or may not work, and it’s expensive, but it’s an option.” In Europe, it’s more common to remove the pituitary gland. “There are some places in the U.S. that do this, too,” she says. “When you do, the cat may need supplementation with other hormones.” For adrenal tumors, the primary choice is surgical removal, she says.
A form caused by treatment
Sometimes, however, a Cushing’s-like syndrome is caused not by a medical condition in your cat but as a result of treatment — specifically, by long-term administration of steroid medications such as cortisone, a form of cortisol. This is called iatrogenic (inadvertently caused by a treatment) hyperadrenocorticism.
Cortisone is often used to treat stubborn allergic conditions, as well as intestinal disease, in cats. Most can handle it without developing a problem. “Cats in general can tolerate high doses of cortisone,” says Dr. Ross. “But we do warn the owners that Cushing’s can be a possible complication.”
If it does happen, the first step is to stop or cut back on the cortisone. “If you take away the cortisone, and it was making diabetes worse, sometimes the diabetes goes into remission,” says Dr. Ross. “However, you need to find another way to treat whatever problem you were treating with cortisone. There are other options, such as different drugs to treat intestinal diseases.” — Bob Barnett
