Cushing's disease in dogs: Symptoms, diagnosis, and treatment

When hormone levels go awry, dogs can get very sick. A good example is Cushing’s disease, which is almost always caused by too much of the stress hormone cortisol.

Cushing’s disease (also called hyperadrenocorticism, Cushing’s syndrome, and hypercortisolism) is one of the most common hormonal diseases in dogs.

Estimates vary, but around 1-2 dogs out of a thousand will be diagnosed with Cushing’s disease every year.

Knowing what to expect can help you help your dog if they ever develop this serious but treatable condition.

What Causes Cushing's Disease in Dogs?

Most cases of Cushing’s disease in dogs (80-85%) are caused by a benign tumor in the pituitary gland that overstimulates the adrenal glands.

The pituitary gland is located at the base of the brain and makes adrenocorticotropin hormone (ACTH) to control the production and secretion of cortisol from the adrenal glands. Cushing's disease stemming from a tumor in the pituitary gland is often called pituitary-dependent hyperadrenocorticism, or PDH.

The other 15-20% of Cushing's Disease cases are caused by adrenal tumors, with about half of those tumors being benign and the other half being malignant (cancerous).

A dog's adrenal glands lie right on top of its kidneys and are the primary producers of cortisol. Cushing’s disease arising from an adrenal tumor is referred to as adrenal-dependent hyperadrenocorticism, or ADH.

A third type of Cushing’s disease, called iatrogenic Cushing’s disease, can be caused by corticosteroid medications, like prednisone and dexamethasone, that act like cortisol in the body. High doses or long-term corticosteroids given orally, by injection, or even topically can lead to Cushing’s disease in some dogs.

Other types of Cushing’s disease have also been reported but are rare.

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What Types of Dogs May Be Susceptible to Cushing's Disease?

Cushing’s disease is most commonly diagnosed in middle-aged or older and senior dogs.

Smaller dogs (less than 40 pounds or so) more commonly develop PDH, while larger dogs have an equal risk of PDH and ADH.

Breeds that may be predisposed to PDH include:

• Bichon Frise

• Border Terrier

• Miniature Schnauzer

• Lhasa Apso

• Yorkshire Terrier

• West Highland White Terrier

Breeds that may be predisposed to develop ADH include:

• Staffordshire Bull Terriers

• German Shepherds

Life Expectancy for Dogs With Cushing's Disease

Dogs with Cushing's disease who undergo surgery to remove an adrenal gland tend to live for another 1 1/2 to 4 years. Treatment with mitotane or trilostane for PDH generally leads to a survival time of 2–2 1/2 years.

While these numbers may not sound impressive, it's important to realize that the average age at diagnosis for dogs with Cushing's disease is 11 years.

Symptoms of Cushing's Disease in Dogs

Too much cortisol over extended periods leads to problems.

The typical symptoms of Cushing’s disease in dogs are:

• Increased appetite

• Increased thirst and urination

• Coat and skin problems

• Recurrent infections

• Panting

• Muscle weakness

• A pot-bellied appearance

Dogs with large pituitary tumors may also develop neurologic problems like behavioral changes, circling, and seizures.

Talk to your veterinarian if your dog has any of these symptoms. Also, make sure to stay up-to-date with your dog’s regular veterinary check-ups. The earlier health problems are diagnosed, the easier they are to manage!

How to Tell if Your Dog Has Cushing's Disease

Diagnostic testing is the only way to determine whether a dog has Cushing’s disease or if their symptoms are due to another health problem. Unfortunately, there is no single test that will accurately diagnose Cushing’s disease in all dogs. Veterinarians must analyze information gathered from a variety of sources before reaching a definitive diagnosis.

A vet will start with a health history and physical examination, followed by a basic panel of lab work that includes a complete blood count, a blood chemistry panel, and a urinalysis. The results may point towards Cushing’s disease or other health problems that could be to blame for your dog’s symptoms.

Next, the veterinarian may run an inexpensive and simple test called a urine cortisol to creatinine ratio (UCCR). If it is high, your dog might have Cushing’s disease. If it's normal, they probably don’t. If your dog’s UCCR is high, the doctor will probably want to perform either an ACTH stimulation test or a low-dose dexamethasone suppression test to determine if your dog truly does have Cushing’s disease. Both of these tests can be expensive and require that your dog stay in the veterinary hospital for a few hours so multiple blood samples can be taken.

It's also important to determine whether a dog has PDH or ADH. Sometimes a low-dose dexamethasone suppression test can provide this information, but often, veterinarians will need to run more tests. Options include

• a high-dose dexamethasone suppression test

• an endogenous ACTH test

• an ultrasound of the dog’s abdomen

• a CT scan or MRI of the dog’s abdomen or brain

Your veterinarian can determine which combination of tests is most likely to lead to an accurate diagnosis.

Cushing's Disease Treatment Options for Dogs

The right treatment for Cushing’s disease will depend on the type of dog and how severely affected they are.

Dogs with PDH who have only mild symptoms may not need immediate treatment, but they should be closely monitored. Treatment is necessary once the symptoms are bad enough that they’re disrupting the dog’s or your quality of life. Veterinarians typically prescribe oral mitotane or trilostane to lower the amount of cortisol the adrenal glands produce. Removing a pituitary tumor through surgery or radiation therapy may be an option, particularly if the dog is developing neurologic symptoms.

If an adrenal tumor is responsible for a dog’s Cushing’s disease, surgically removing the affected adrenal gland is the treatment of choice. Dogs with benign adrenal tumors can be cured with surgery, but this is usually not the case if the tumor is malignant. Removing an adrenal gland is difficult, so primary care veterinarians will often refer these cases to a board-certified veterinary surgeon. Radiation therapy or medical management with mitotane or trilostane can be considered when surgery is not appropriate.

Dogs with iatrogenic Cushing’s disease need to be slowly tapered off their corticosteroid medications. Oftentimes, the disease that was being treated with steroids will flare up again and need to be managed in another way.

Managing Cushing's Disease in Your Dog

Most dogs with Cushing’s disease require lifelong veterinary care. For example, dogs with PDH have to be closely monitored to ensure they’re getting an appropriate dose of mitotane or trilostane and for potential side effects of the treatment.

Initially, your dog may need to go to the veterinary clinic frequently for testing, but the eventual goal is to try to stretch out re-checks to every three to six months.

If your dog’s condition starts to get worse or you notice any new symptoms, call your veterinarian for advice. It’s not unusual to have to adjust a dog’s treatment as their Cushing’s disease progresses.

How Pet Insurance Can Help

Diagnosing, treating, and managing Cushing’s disease is complicated and can get expensive, but dog insurance may help! Make sure you insure your dog when they’re young so that chronic conditions, like Cushing’s disease, can be covered instead of being considered a pre-existing condition.