How to Treat Cushing's Disease in Dogs

Cushing's disease is a condition of the endocrine system that affects dogs, humans, and some other animals. Left untreated, this disease can affect a dog's quality of life and overall health.

What is Cushing's Disease?

Cushing's disease, or hyperadrenocorticism, is a condition in dogs that occurs when the body produces too much cortisol. Cortisol is a hormone and natural steroid that helps regulate essential bodily functions, including metabolism, blood sugar, blood pressure, and immune responses. It also has an important role in helping the body respond to stress.

There are three forms of Cushing's disease seen in dogs. 

1. Pituitary-dependent (most common form): The pituitary gland in the brain overstimulates the adrenal glands, causing them to produce too much cortisol. 
2. Adrenal-dependent: the adrenal glands cause cortisol overproduction
3. Iatrogenic hyperadrenocorticism: this may occur if a dog has been treated with steroids at high doses or for a prolonged period of time.

Cushing's disease is relatively common in dogs and somewhat common in horses. Cushing's can occur in cats and humans, though less commonly so.

Signs of Cushing's Disease in Dogs

Dogs with Cushing's disease often develop thinning hair and a potbelly accompanied by extreme hunger and thirst. Excess cortisol disrupts water resorption by the kidneys, leading to frequent urination. The skin may become fragile and develop infections or other problems. Many dogs with hyperadrenocorticism pant excessively and seem weak or lethargic.

Causes of Cushing's Disease

• Pituitary Gland Tumor (most common cause): The pituitary gland stimulates the adrenal glands to produce cortisol. If there is a tumor present, the pituitary may tell the adrenal glands to make too much cortisol. These tumors are typically benign.
• Adrenal Gland Tumor: A tumor on one or both adrenal glands may result in excess cortisol production. About half of these tumors are malignant.
• Prolonged Steroid Use: Long-term treatment with steroids may impact the adrenal glands and lead to iatrogenic hyperadrenocorticism. Long courses of steroids are sometimes used to treat allergies and immune-mediated diseases.

The cause of pituitary and adrenal tumor development in dogs is unknown, and these tumors may be malignant or benign.

Some dog breeds are predisposed to Cushing's disease, such as Boston Terriers, Dachshunds, and Miniature Poodles. Most dogs that develop Cushing's disease are middle-aged or older.

Diagnosis

Your veterinarian will discuss your dog's history and perform a thorough physical examination on your dog. If Cushing's disease or another problem is suspected, your vet will most likely recommend lab work.

The signs of Cushing's disease may be similar to the signs of other health problems, so it's important to see your veterinarian if your dog seems sick.

First, most vets run blood chemistry, complete blood count, and urinalysis. Abnormalities in these tests such as increased liver enzymes, increased cholesterol, and dilute urine may suggest Cushing's disease, and your vet will need to perform additional lab tests and diagnostic imaging.

Urine Cortisol: Creatinine Ratio (UCCr): This urine test is typically used as a screening tool. Urine cortisol is high/abnormal in dogs with Cushing's disease. If seen, further diagnostic testing is necessary in order to confirm Cushing’s disease.

Adrenocorticotropic hormone stimulation test (ACTH stim): A blood sample is drawn, then a hormone injection is given. Another blood sample is drawn one to two hours later to measure the body's response. An exaggerated response is considered consistent with Cushing's disease.

Low-dose dexamethasone suppression test (LDDST) OR High-dose dexamethasone suppression test (HDDST): These eight-hour tests involve a blood sample, an injection of a steroid, then additional blood samples at timed intervals to measure the body's response. These tests may help your vet determine where the problem is in the pet’s body (pituitary vs. adrenal).

Abdominal ultrasound or CT scan: An abdominal ultrasound allows the vet to see the adrenal glands and look for abnormalities. A CT scan will enable vets to see abnormalities of the pituitary gland (located at the base of the brain). These tests may help your vet learn if your dog has pituitary-dependent or adrenal-dependent hyperadrenocorticism.

Treatment

Pituitary-dependent hyperadrenocorticism requires treatment if the symptoms affect the dog's quality of life. A drug called trilostane (Vetoryl) is most commonly prescribed. Trilostane inhibits an enzyme that is involved in the body's production of cortisol. Inhibiting this enzyme inhibits the production of cortisol. Other less commonly used medications include mitotane (Lysodren), ketoconazole, and l-Deprenyl (Anipryl).

Adrenal-dependent hyperadrenocorticism may also be effectively treated with trilostane or mitotane. Some cases may achieve resolution with exploratory surgery during which the affected adrenal gland is removed. 

Iatrogenic hyperadrenocorticism is treated by slowly weaning the dog off steroids and monitoring the results.

Dogs being treated for Cushing's disease will need to visit the vet regularly to have recheck examinations and follow-up lab work. If your dog has been diagnosed with Cushing's disease, talk to your veterinarian about the pros and cons of the various treatment options.

How to Prevent Cushing's Disease in Dogs

Cushing's disease cannot be prevented, but early detection is key to effective treatment. Contact your veterinarian if your dog exhibits signs of Cushing's disease or other signs of illness.