Critter Talk: Diagnosis and Treatment of Cushing’s Disease in Dogs

Last week, I was asked for my take on Cushing’s disease, or hyperadrenocorticism as it is also called. I am happy to oblige as diagnosing Cushing’s disease is not always easy. First of all, the symptoms can be somewhat nebulous and are seen with other diseases as well. The classic signs of Cushing’s disease are:

Increased appetite
Increased thirst and urination
Poor coat quality
Skin problems
Recurrent infections
Panting
Muscle weakness
A pot-bellied appearance
Neurologic changes in advanced pituitary-dependent hyperadrenocorticism

Keep in mind that every Cushingoid dog does not necessarily have all of these symptoms.

The underlying cause of Cushing’s is overproduction of the hormone cortisol or overuse of corticosteroid drugs like prednisone. Most cortisol in the body is made by the adrenal glands. If an adrenal tumor is present, it can over-secrete the hormone. Adrenal tumors are responsible for about 20 percent of Cushing’s cases in dogs, usually in larger breeds. A tumor in the pituitary gland, located within the brain, can also stimulate the adrenal glands to produce more cortisol than normal. Pituitary tumors are responsible for around 80 percent of naturally occurring Cushing’s disease cases.

I handle diagnosing Cushing’s disease when I have a patient that exhibits suspicious signs like this:

1. Run a blood chemistry panel, complete blood cell count, a urinalysis, and any other lab work (e.g., heartworm test or fecal exam) that might be called for based on a dog’s physical exam and history. The results should either point toward (e.g., elevated alkaline phosphatase levels and a stress leukogram) or away from Cushing’s.

2. I save a sample of urine for a cortisol:creatinine ratio test. If the results are normal, Cushing’s disease is extremely unlikely. If they are elevated, Cushing’s disease is possible, but not definitively diagnosed, as other disease can produce the same result.

3. Identifying most (but not all) cases of Cushing’s disease and determining whether the pituitary or adrenal form of the disease is present (which is important for picking the right form of treatment) is possible with some combination of an ACTH stimulation test, low dose dexamethasone suppression test, high dose dexamethasone suppression test, and/or abdominal ultrasound. Which tests I run in which order is based on a dog’s presentation and whether an owner wants a quick and complete diagnosis or would rather take a step-wise approach and potentially avoid the expense of an unnecessary test.

We have options when it comes to the treatment of Cushing’s disease. If a dog’s symptoms are not too serious, (e.g., he or she is panting more but is otherwise normal), treatment may not be warranted unless the problems worsen over time. The pituitary form of the disease is usually treated with either mitotane or trilostane, both of which suppress cortisol production. The drug selegeline can also be used to control symptoms associated with Cushing’s but is not as effective as mitotane or trilostane. Non-invasive adrenal tumors are best dealt with surgically. If surgery is not an option, the aforementioned medications are of some benefit for the adrenal form of the disease.

Close monitoring of dogs undergoing treatment for Cushing’s is essential. Our goal is to suppress cortisol production enough to keep pets healthy, but not so much that we create the opposite problem — hypoadrenocorticism, or Addison’s disease.

Dogs with Cushing’s disease can be expected to live three years, or even longer, after diagnosis with appropriate treatment and a little bit of luck, but it must be remembered that while this is a condition that can often be successfully managed, it is only rarely cured.

Dr. Jennifer Coates writing for PetMD

Edited by MJS.

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