Dear Curious: Cushing’s Disease is common in middle aged to older dogs between 7- to 12-years-old. Your vet may see some of the subtle symptoms of this disease that may appear to be just normal aging to you. Remember when a change occurs slowly and you see the dog every day it may not be apparent. But, then you take her to the vet who hasn’t seen her in a year and the changes are very apparent to him. The symptoms may include drinking more water, weight gain, hair loss, dull coat, increased appetite, pot-bellied appearance and frequent urination. These symptoms can also be for a variety of other conditions so more tests would be needed to try and confirm Cushing’s.

 

Various Causes

The main cause of Cushing’s in dogs is a tumor located on the pituitary gland near the brain. These small tumors produce too much of a hormone called “ACTH.” With excess ACTH the adrenal gland releases a steroid called “cortisol” to reduce the ACTH levels in the dog’s blood. However, with Cushing’s, the pituitary tumor doesn’t recognize the elevated cortisol levels in the blood, which would normally stop the production of ACTH. So, the adrenal glands pump out even more cortisol in response. In effect, too much cortisol is poisoning the dog. Approximately 90 percent of all Cushing’s patients have the pituitary tumor and two enlarged adrenal glands from overproduction.

A less likely cause is a tumor on the adrenal gland itself that would also cause the overproduction of cortisol.

Tests and Treatments

Getting a firm diagnosis for Cushing’s can also be tricky since you are dealing with two possible sources of the tumors. A diagnosis between the adrenal and pituitary gland can help determine treatment options.  

One of the most common tests for diagnosis is called the low-dose dexamethasone suppression (LDDS) test. This test requires a fasting blood sample from the dog as a baseline. This is probably why the vet wants to keep your dog overnight at his clinic. Then, like the test name suggests, a low dosage of a synthetic drug is given and then blood samples are taken at regular intervals to measure cortisol. This test is more than 80 percent effective on determining Cushing’s but still can’t pinpoint if a pituitary gland tumor is the culprit versus the adrenal gland. But in 90 percent of cases it is the pituitary. There are other tests that can help with the adrenal diagnosis.  

 Treatment of the adrenal gland can rely on surgery to remove the offending tumor and the whole gland with a great incidence of recovery. If the Cushing’s is caused by a pituitary tumor, surgery is not an option since the tumors are small and slow growing and located so close to the brain. There are treatment options ranging from radiation therapy to try and shrink the pituitary tumor to various chemotherapy medications.

Quality of Life

Sometimes you are faced with the question, “Will treatment diminish the dog’s quality of life more than the disease?” With older dogs sometimes letting “sleeping dogs lie” is better than evasive surgery or costly radiation treatments. Since most dogs with Cushing’s are over the age of 10, other old-age illnesses or conditions can decrease the dog’s quality of life more so than the Cushing’s. You need to decide if a Cushing’s diagnosis and treatment is right for you and your dog. Discuss the options with your vet.  

Lisa Peterson, a breeder and exhibitor of Norwegian Elkhounds, is a Delegate to the American Kennel Club. Ask Lisa questions at elvemel@aol.com or P.O. Box 197, Newtown, CT 06470.