Cushing's Disease in Senior Dogs

Named after noted American neurosurgeon, Harvey Cushing, Cushing's disease occurs when your dog’s body makes too much of a natural steroid hormone called cortisol. This hormone helps him respond to stress, control his weight, fight infections and keep his blood sugar levels in check. 

Harvey Cushing

There are two major types of the disease. Pituitary dependent is the most common, affecting about 80% to 90% of those with Cushing’s, and is caused by a benign tumor in the pituitary gland, a pea-sized gland at the base of the brain. Adrenal dependent affects about 15% to 20% of dogs and is caused by a benign or malignant tumor in one of the adrenal glands that lie on top of the kidneys.

While the disease’s warning signs may be harder to spot at the beginning, symptoms include: increased thirst, hunger, panting and urination, a pot-bellied abdomen, fat pads on the neck and shoulders, loss of hair, thinning or darkening skin, lack of energy, muscle weakness, insomnia and recurrent infections.

To diagnose the disease, your veterinarian will first take a comprehensive health history of your dog and conduct a thorough physical exam, followed by a blood chemistry profile, complete blood cell count, fecal examination and urinalysis. 

The most common test is the low-dose dexamethasone suppression test (LDDS). A blood sample is taken to measure your dog’s baseline cortisol level and a small amount of dexamethasone is administered by injection. Blood cortisol levels are measured four and eight hours after the dexamethasone is given. In a dog with Cushing’s, cortisol is NOT suppressed.

Since no one diagnostic test is definitive in every case, your vet may also run an ACTH stimulation test, a high-dose dexamethasone suppression test, and perform an abdominal ultrasound to determine whether or not your dog has Cushing’s, and if so, whether the pituitary or adrenal glands are to blame.

Treatment of an adrenal tumor requires major abdominal surgery. If successful  -- the entire tumor is removed and it’s not malignant – there’s a good chance that your dog’s health will return to normal. But if surgery’s not an option or the tumor has spread to other parts of his body, his condition may be managed – for as long as possible -- with medications.

If your dog has pituitary-dependent Cushing’s (a tumor on the pituitary gland), your vet will likely prescribe one of two drugs -- mitotane (Lysodren) or trilostane (Vetoryl) -- for him. Other medications such as ketoconazole, selegiline or cabergoline may also be used under certain circumstances. 

Because your dog must remain on this treatment for life, you must take care to administer the right doses to him at the right times and monitor his behavior and symptoms carefully. You must also be on the alert for any adverse reactions to the drugs. Typical signs of an adverse reaction are lack of appetite, lack of energy, weakness, vomiting, diarrhea and sometimes difficulty walking. Should any of these side effects occur, discontinue the medication and contact your vet immediately. 

Otherwise, your vet will schedule regular follow-up visits to examine your dog and run blood tests to ensure the treatment is working and that he’s receiving the correct dose of medication. While schedules vary, be prepared to see your vet several times a year once the maintenance phase of your dog’s therapy has been reached.

Sadly, the average survival time for a dog with Cushing’s disease is approximately two years, with only 10 percent of dogs living past the four-year mark.

Written by Nomi Berger