Recently, two of my patients needed testing for a possible diagnosis of Cushing’s disease, a.k.a. hyperadrenocorticism. Named after Harvey Cushing, the famous neurosurgeon who first described the disease in humans, Cushing’s disease results from excess production of steroids by the body. In dogs, we recognize two major forms of this endocrine disease: a pituitary form in which the pituitary gland in the brain sends a signal to the adrenal glands near the kidneys to make excessive levels of steroids. The second form is the adrenal form where the adrenal gland becomes autonomous and pumps out excessive amounts of steroids, causing abnormalities recognized by pet families and veterinarians. A third type of Cushing’s disease can be seen when dogs receive steroids like prednisone as treatment for a disease like allergies or immune mediated hemolytic anemia. This form is called iatrogenic Cushing’s disease.

Lengthy List of Clinical Signs

Cushing’s disease results in a wide range of clinical signs. One of my patients was panting and had elevated liver tests; the other spent most of her day at the water bowl drinking excessive amounts of water. In addition to panting, increased drinking and elevated liver tests, we also see the following with Cushing’s disease:

• panting
• increased water drinking
• increased liver tests
• increased appetite
• weight gain
• skin infections
• hair loss
• skin calcification
• urinary tract infections
• easy bruising

Lengthy List of Cushing’s Tests

Diagnosing Cushing’s disease can be a challenge, since not all available tests will give a positive result even if the dog has Cushing’s disease. Some tests measure excessive steroids in a urine sample, others stimulate adrenal production of steroids via administration of a synthetic pituitary hormone, and others suppress adrenal production of steroids. Sometimes measurement of a hormone that comes from the pituitary gland in the brain is used to identify the pituitary form of the disease. Ultrasound and MRI may be useful to identify adrenal gland tumors or pituitary tumors which are the cause Cushing’s disease in some cases.

Lengthy List of Treatments

If an adrenal tumor is identified as the cause of Cushing’s disease, then surgery may be the treatment of choice to remove the tumor and the source of excessive steroids. Pituitary tumors which cause Cushing’s disease are treated in Europe with surgical removal of the gland, but in the United States, veterinarians use oral medications when adrenal surgery is not possible or for Cushing’s disease stemming from the pituitary gland.  Until recently, the drug of choice (mitotane, Lysodren®) induced atrophy of the layers of the adrenal gland responsible for producing steroids. Currently, the drug used most commonly (trilostane, Vetoryl®) blocks production of steroids responsible for the clinical signs of Cushing’s disease.

Back to My Patients

Of the two dogs I tested for Cushing’s disease, only one has the disorder. To make the diagnosis in her, we did three different Cushing’s tests over several months:  the urine steroid level was normal, the adrenal suppression test and measurement of the pituitary hormone both indicated her pituitary gland was over active. Treatment with trilostane has been a success and the excessive water drinking has resolved. The other dog did not have Cushing’s disease and the cause of her panting remains a mystery. If your dog has signs of Cushing’s disease, be patient as the diagnosis can sometimes be elusive and your veterinarian will need to work through a series of tests to find the right diagnosis for your dog.