Cushing’s Disease in Cats

You might have heard of Cushing’s disease in dogs, and even in people, but can cats get Cushing’s disease? Even though it’s rare in cats, it is possible for cats to get Cushing’s. The first case of Cushing’s in cats was described in 1976 (1) and is still rarely diagnosed today. It’s thought that only a few hundred cats have ever been diagnosed with Cushing’s, although it’s becoming more common now that vets and pet parents alike know what to look for. 

We’ll go over Cushing’s disease in cats so you can keep an eye out for this rare condition.

What Is Cushing’s Disease?

Cushing’s disease is properly called hyperadrenocorticism. Let’s break that down: hyper (too much), adreno (adrenal gland), and corticism (cortisol hormone). In other words, Cushing’s disease in cats occurs when the adrenal glands are producing too much cortisol, a naturally-occurring steroid. This steroid is essential for life, and having an under-production is extremely serious. But having an overproduction causes the symptoms of Cushing’s disease.

While Cushing’s disease is rare in felines, there are some trends appearing that help us to identify affected cats. It’s more common in older cats, averaging 10 years old at diagnosis (2). In addition, 80 percent of cats with Cushing’s will also have diabetes (3), which complicates diagnosis and treatment. It’s also thought that females are more likely to develop Cushing’s syndrome than males (4). There is no breed association with Cushing’s in cats.

What Causes Cushing’s Disease in Cats?

So why does Cushing’s disease happen? The adrenal glands—two small glands near the kidneys—are responsible for producing cortisol. Usually, the amount of cortisol in the body is carefully controlled by the pituitary gland, a small gland at the base of the brain. If there’s too much, the pituitary gland signals the adrenals to stop producing cortisol. If there’s too little, the glands get the message to produce more. This messaging is done with a hormone called adrenocorticotropic hormone, or ACTH. When a cat has Cushing’s, this feedback mechanism breaks down.

There are three categories of Cushing’s with different causes:

Pituitary-dependent: In most cats, Cushing’s is caused by a small (benign) tumor on the pituitary gland, which secretes ACTH, stimulating the adrenals to produce cortisol. This tumor doesn’t recognize that there is too much cortisol and therefore doesn’t send feedback to the adrenals to stop production. 

Adrenal-dependent: Around a quarter of cats will have a tumor on their adrenal gland instead. The tumor is made of cells that produce cortisol. Again, the tumor doesn’t listen to feedback from the body—no matter the feedback it’s receiving, the tumor cells continue to produce cortisol.

Iatrogenic: There is one more cause of Cushing’s you might come across. It is called Iatrogenic Cushing’s and it happens when an animal is given too much steroid drug for too long. When we give steroids for a long time—especially if they are high doses—the pituitary gland and adrenals will be responding as best they can, but we continue to overdose the body on cortisol.

Regardless of which category your cat falls into, the result is too much cortisol in the body. This hormone is known as the chronic stress hormone, and too much of it is bad for health, causing a range of symptoms.

Cat Cushing’s Disease Symptoms

The symptoms of Cushing’s disease in cats are all related to having too much cortisol in the body. In over 75 percent of cases (1), the symptoms will be thirst, hunger, and urinating more often. The problem is that these symptoms are also symptoms for two much more common diseases in cats—diabetes mellitus and hyperthyroidism—both of which also affect older cats. This is further complicated by the fact that the majority of cats with Cushing’s also have diabetes, which is usually diagnosed first. It’s only when the cat isn’t responding to insulin treatment that Cushing’s is considered.

Unlike dogs, cats with Cushing’s get extremely fragile skin. They may have severe wounds or get wounds during routine investigations that heal poorly. Hair loss and skin infections are also common in Cushingoid cats.

Other symptoms of Cushing’s in cats include:

• Excessive thirst
• Excessive urination
• Excessive hunger
• Enlarged abdomen (pot belly)
• Muscle wasting
• Weakness and lethargy
• Fragile, thin skin
• Hair loss or poor coat
• Skin and urine infections

All of these symptoms can be caused by other diseases, so it can be difficult to diagnose Cushing’s in cats, especially given how rare it is.

Diagnosing Cushing’s Disease in Cats

Diagnosing Cushing’s disease in cats can be difficult, and there’s no perfect test that gives a clear answer.  First, your veterinarian will do a clinical exam. This will need to be thorough, as they will want to see if there are any other explanations for your cat’s symptoms. 

Next, your vet will conduct screening tests. If evidence points to Cushing’s, they will then perform diagnostic tests.  

Screening Tests for Cushing’s Disease

Routine screening blood test. A routine screening blood test (biochemistry and hematology) will allow your vet to look for evidence of diabetes (which is much more common in cats and causes similar symptoms), liver disease, kidney disease, and other complicating conditions. Unlike dogs, however, cats don’t have many clues on this minimum database test—it’s more about ruling out other, more common, causes of problems.

Urine screen. A urine screen will often also be undertaken. Not only can this help diagnose or rule out diabetes, but urine infections are a common complication of Cushing’s in cats, so testing for a UTI is sensible. Cortisol in the urine may also be measured, but isn’t a perfect test. Although it increases suspicion of Cushing’s in cats if it’s high, it’s not a definite answer. However, a low result does rule Cushing’s out, so it’s a non-invasive way to rule out Cushing’s in some diabetic cats.

If at this point your vet has diagnosed diabetes, they’ll usually start treatment for diabetes, only returning to the possible Cushing’s diagnosis if the diabetes becomes difficult to manage. Although 80 percent of Cushing’s cats have diabetes, very few diabetic cats will have Cushing’s (as it’s so rare), so it makes sense to treat your cat for diabetes first. 

Diagnostic Tests for Cushing’s Disease

If your vet still strongly suspects Cushing’s as a cause, they’ll likely undertake one of the following tests:

Dexamethasone suppression test. This involves taking blood then injecting a large amount of dexamethasone, a steroid. A second blood sample is then taken. The cortisol levels in the samples are compared to see whether the feedback loop is working. If the body’s cortisol level drops once the body recognizes the dexamethasone, the feedback loop is working and Cushing’s is unlikely. On the other hand, if the cortisol stays the same, your cat’s body is producing cortisol regardless of the feedback loop—which makes it likely your cat has Cushing’s. 

ACTH stimulation test. Another common test is called the ACTH stimulation test, but it’s less accurate than the dexamethasone suppression test in cats (3). This test also requires two blood samples, but ACTH is injected instead of dexamethasone. If your cat’s cortisol is high before the ACTH and extremely high after the ACTH, it suggests Cushing’s.

Differentiating Tests

Lastly, your cat might need imaging, usually ultrasound, to diagnose whether it’s the adrenal glands or the pituitary glands that are involved. Although this is rarely done, it can help with treatment options.

Cushing’s Disease in Cats Treatment

Cushing’s disease in cats is so rare, we’re still working out the best treatment. No drugs are currently licensed for Cushing’s in cats, so all medication is used off-label. A medication called trilostane, which is usually used in dogs with Cushing’s, is most often used. This drug needs to be given once or twice daily, for life. Regular blood tests will be needed to make sure the dose is correct, as overdosing is dangerous. Once the dose is stable, it can still take a long time for symptoms of Cushing’s disease in cats to reduce, especially the thin skin.

Surgery is sometimes indicated for cats with a one-sided adrenal tumor, as the other gland should respond normally to feedback and continue to function. Even if surgery is an option for your cat, they will still need medication first to get their cortisol levels down to normal, as cats with Cushing’s have poor wound healing, making surgery a bad idea.

Cushing’s Disease in Cats Life Expectancy

Cushing’s disease in cats is serious. It’s harder to diagnose than Cushing’s in dogs, meaning cats are often extremely ill when diagnosed. The thin skin can make handling a problem, and cats are often humanely euthanized for wounds before treatment has a chance to work. Since most cats with Cushing’s also have diabetes, this makes euthanasia even more likely. 

However, if cats respond to the recommended treatment, and don’t have any major wounds that refuse to heal, then they can theoretically live a relatively normal life for several years. 

For the minority of cats who have a malignant tumor, the prognosis is unfortunately guarded. 

Cost to Treat Cushing’s Disease in Cats

Cushing’s disease in cats is expensive to treat. The trilostane itself is moderately pricey, but the regular check-ups and blood tests to ensure a safe and effective dose can make treatment costly. Since most cats will also have diabetes, owners should factor in the cost of insulin for their diabetic cat, as well as further monitoring and testing for the diabetes. Wound complications and urine infections will also add to the cost. Although surgery (for those cats who are eligible) may be expensive, it does provide a cure, and may be more affordable in the long run.

How to Prevent Cushing’s Disease in Cats

Unfortunately, there are no known ways to prevent Cushing’s disease in cats. Early diagnosis makes it more likely that your cat will survive, so keeping an eye on your cat’s water intake and talking to your vet early if you suspect a problem is the best measure you can take to protect your cat from Cushing’s.

Related Conditions

• Diabetes mellitus

References

1. Hoenig M. Feline hyperadrenocorticism–where are we now?. J Feline Med Surg. 2002;4(3):171-174. doi:10.1053/jfms.2002.0178
2. Boland LA, Barrs VR. Peculiarities of feline hyperadrenocorticism: Update on diagnosis and treatment [published correction appears in J Feline Med Surg. 2018 Aug;20(8):NP5]. J Feline Med Surg. 2017;19(9):933-947. doi:10.1177/1098612X17723245
3. Delventhal, V. Feline Cushing’s Syndrome – clinical case and review. Kleintierpraxis. 2019;64(2):75-89.
4. Wooten, S. DVM 360. The feline facets of Cushing’s disease. March 2018. Retrieved from https://www.dvm360.com/view/feline-facets-cushings-disease.