What Causes Cushing’s Disease?

Cushing’s disease, or hyperadrenocorticism, is caused by an excess of stress hormone (cortisol) from the adrenal glands. This excess can be caused by overproduction of cortisol by the adrenal glands, abnormal signaling from brain to the adrenal glands or long-term steroid usage (such as prednisone, prednisolone, Temaril P, or dexamethasone). This extra stress hormone can cause several symptoms, leading to trouble regulating blood sugar, immune-mediated problems, weak bones and cartilage, liver problems, and problems with metabolism of essential nutrients. Permanent damage to organs may occur if the disease is left untreated.

What Age & Breeds Are Typically Affected?

Although Cushing’s disease can occur in any breed, poodle breeds, dachshunds, terriers, German shepherds, beagles, and Labrador retrievers are most commonly affected. Dogs with Cushing’s disease are typically older than six, with an average age of 10 years old.

How Will I Know if My Dog Is Showing Signs?

Signs of Cushing’s disease can be non-specific, and are often confused with normal aging, making this disease tricky to recognize.

Common Signs:

-increased drinking
-frequent urination or accidents in the house
-“pot-bellied” or enlarged abdomen
-hair loss
-muscle wasting or loss of muscle tone

Other Signs:

-recurrent skin infections
-urinary tract infections
-hypertension / high blood pressure
-diabetes (especially those that are hard to regulate)
-bilateral cranial cruciate disease

How Can We Test My Dog for Cushing’s Disease?

Cushing’s disease can be very tricky to diagnose. Diagnosis starts with a thorough history of your dog’s health and general physical examination. Often, there are changes on basic bloodwork, such as elevated liver enzymes, that indicate possible Cushing’s disease. A complete urine exam may also be performed as Cushing’s disease often causes recurrent urinary tract infections. Abdominal x-rays or ultrasound may be needed to evaluate the health and structure of your dog’s liver and rule out other disease.

If results of these basic tests raise suspicion, we will recommend additional testing to specifically identify Cushing’s disease. Each test for Cushing’s disease has advantages and disadvantages.

Urine Cortisol / Creatinine Ratio: This test is convenient because you collect the pet’s urine at home and deliver it to the clinic for processing. The first morning urine should be collected each morning for three days in a row. The samples may be combined into one container and must be refrigerated until delivery to the clinic. Sample collection should be delayed at least six days after a visit to the veterinarian or groomer. Negative results from this test indicate that the Cushing’s disease is very unlikely. However, positive results must be confirmed with a specific blood test.

Low-Dose Dexamethasone Test: This test requires the patient to be fasted (held off of food) and stay at the clinic for the day. Three blood samples are drawn throughout the day over an eight-hour period. This test is the most sensitive test available to diagnose Cushing’s disease.

ACTH Stimulation Test: This test must be used when a patient has been receiving steroids for treatment of other disease. It is also used for monitoring treatment levels in pets currently receiving treatment for Cushing’s disease. This test requires the patient to remain at the clinic for a half day for two to three blood samples over several hours. Patients should be fasted for this test. When using this test for monitoring of treatment, Vetoryl® (trilostane) should be administered 4-6 hours prior to testing.

Unfortunately, there is no perfect test for Cushing’s disease and all of these diagnostic tests can have confusing results. For this reason, many testing trials may be required to reach a conclusion or confirm a diagnosis. This can be frustrating, but it is important to remain persistent and patient as we work through this diagnosis.

How Is Cushing’s Disease Treated?

Medical and surgical methods are used to treat Cushing’s disease. Surgical treatment involves removal of the adrenal glands and may “cure” disease but is risky to perform. Medical treatment is usually preferred and will alleviate your pet’s symptoms. Medical treatment for Cushing’s disease is lifelong. Supportive care for liver disease is often recommended.

Vetoryl® (trilostane): Trilostane is the only FDA-approved medication for treatment of all types of Cushing’s in dogs. This medication may be given once or twice daily depending on the individual. An ACTH Stimulation test will be conducted two weeks after starting this medication or two weeks after any dose change. Side effects: weakness, collapse, lethargy, decreased appetite, diarrhea and vomiting. Should any of these side effects occur, please notify our office as soon as possible.

Lysodren® (mitotane): Mitotane may be used as an alternative treatment and should be discussed on a case-by-case basis.

Liver Supplements: Supplements such as S-Adenosyl-L-Methionine (SAMe) and adenosine may be recommended to support general liver health.

My Dog Has Been Diagnosed With Cushing’s! What Now?

Although lifespan is generally shortened by 2.5-5 years, dogs with Cushing’s disease may live for many years with appropriate treatment. Lifespan is also affected by concurrent disease, age at the time of diagnosis and treatment compliance.

ACTH Stimulation Tests: Monitoring of appropriate medication levels is important as serious side effects and even death may occur. An ACTH stimulation test should be conducted every six to twelve months. Some patients may require testing every three months to ensure appropriate control of the disease.

Blood Pressure: Blood pressure should be checked during regular examinations to detect hypertension.

Keep a Journal: Note changes in your dog’s habits, particularly urination and weight gain or loss. In addition, note any recurrence of clinical signs and the appearance of possible side effects.

Veterinary Visits: Semi-annual physical examinations are important to detect other problems such as skin infections, ear infections and urinary tract infections.