Hyperadrenocorticism (Cushing’s Syndrome) in Dogs

Overview of Canine Hyperadrenocorticism

Hyperadrenocorticism, commonly referred to as Cushing’s disease or Cushing’s syndrome, refers to a disease state in which an overactive adrenal tissue produces excessive amounts of cortisone. Cortisone and related substances are essential hormones of the body, but when produced in excessive amounts these substances may cause systemic illness.

A small tumor in the pituitary gland (located at the base of the brain) is the cause of Cushing’s syndrome in 80 to 85 percent of dogs with hyperadrenocorticism. The tumor produces a hormone called adrenocorticotropic hormone or ACTH that stimulates the adrenal glands to grow larger (become hyperplastic) and produce excessive amounts of cortisone. This type of Cushing’s syndrome is called pituitary-dependent hyperadrenocorticism because it originates from the pituitary gland.

In the remaining 15 to 20 percent of dogs with Cushing’s syndrome, the cause is a tumor of the adrenal gland. This form is called adrenal-dependent hyperadrenocorticism because it originates from the adrenal gland itself.

Occasionally, a dog might have a diagnosis of iatrogenic Cushing’s disease. This is not an adrenal disorder, but rather it is caused by the administration of steroids (given to treat other diseases) to a dog. Long-term administration of steroids can cause a dog to exhibit all the classic signs of Cushing’s disease. In this case, the excessive steroids are not being produced in the body, they are being provided as a form of medication to your pet.

Canine Cushing’s syndrome usually occurs in middle-aged to older dogs with most affected dogs being over 9 years of age at presentation. The syndrome does not have a strong gender bias, but it may occur slightly more often in female dogs than in males. Dogs of any breed can develop Cushing’s syndrome, but it is most common in poodles, dachshunds, miniature schnauzers, and German shepherds. Boxers and Boston terriers are prone to development of Cushing’s syndrome caused by pituitary tumors.

Hyperadrenocorticism can be difficult to recognize due to its variable clinical symptoms and very gradual onset. For example, many owners mistakenly assume that the changes they see in their dog are simply a result of the aging process.

What to Watch For with Cushing’s Syndrome in Dogs

Abnormal high blood concentration of cortisone results in the clinical symptoms of Cushing’s syndrome. These include:

Diagnosis of Hyperadrenocorticism in Dogs

No single laboratory test definitively identifies Cushing’s syndrome, and the disorder should not be diagnosed solely on the basis of laboratory tests. Your veterinarian should also consider the medical history and physical examination findings when establishing a diagnosis and determining the appropriate laboratory tests to perform. Several of the following diagnostic tests may be required for the diagnosis of Cushing’s syndrome:

Treatment of Hyperadrenocorticism (Cushing’s Syndrome) in Dogs

Pituitary-dependent Hyperadrenocorticism in Dogs

Adrenal-dependent Hyperadrenocorticism in Dogs

Home Care

Follow your veterinarian’s instructions very closely when administrating medications, especially in the induction phase when using mitotane. Observe your dog for weakness, vomiting, diarrhea, loss of appetite or change in attitude. You should also observe your dog for improvement or worsening of clinical signs.

Follow-up with your veterinarian for routine re-evaluation of blood tests so as to maximize the chance for successful treatment.

Preventative Care

There is no known way to prevent Cushing’s syndrome. However, some preventative measures may lead to earlier diagnosis and potentially more effective treatment:

In-Depth Information on Canine Hyperadrenocorticism

The adrenal glands are small endocrine organs located near the kidneys. They are comprised of two major parts:

Diseases that Can Produce Similar Signs of Cushing’s Disease

Several other diseases may produce symptoms similar to those of Cushing’s syndrome. Such disorders include:

In-depth Diagnosis of Hyperadrenocorticism in Dogs

The diagnosis of Cushing’s syndrome involves two steps.

Diagnostic Tests may include:

Tests used to differentiate pituitary- and adrenal-dependent hyperadrenocorticism include:

Treatment of Pituitary-dependent Hyperadrenocorticism in Dogs

Treatment of Adrenal-dependent Hyperadrenocorticism in Dogs

Optimal treatment for your dog requires a combination of home and professional veterinary care. Follow up can be crucial, especially if your dog does not improve. Administer as directed all medications prescribed by your veterinarian. Alert your veterinarian promptly if you are experiencing problems treating your dog.

Monitor for any recurrence of clinical signs, especially increased thirst, increased urination and increased appetite. If your dog suddenly deteriorates, especially during treatment with mitotane, contact your veterinarian immediately. He or she may prescribe prednisone to be given in the event of an emergency.

Routine blood testing (especially ACTH stimulation tests) will be needed at least twice a year.

Dogs on mitotane therapy generally require progressively higher maintenance dosages of the drug over time due to increasing blood cortisol concentrations.

Follow-up after surgical removal of an adrenal tumor includes monitoring the dog for recurrence by means of abdominal ultrasound examination.

Follow-up Care of Dogs with Cushing’s Disease

Optimal care for the dog with Cushing’s syndrome requires a good understanding of the disease and its symptoms, a significant financial and time commitment by the owner, and excellent communication between the veterinarian and the owner.