By Lynn McCarron, DVM
Cushing’s Disease is a disease in which the adrenal glands make too much cortisone (cortisol). The most common clinical signs include a tremendous increase in appetite, water consumption, and urination. Lethargy, panting excessively, a poor coat, muscle weakness and recurrent urinary infections are also common. Some pets will have many of the symptoms, while other pets may not have obvious symptoms at all.
If your veterinarian performs basic blood tests, they may become suspicious that your dog has Cushing’s disease if certain abnormalities are present, such as abnormalities in liver tests. However, the diagnosis is not always an easy one to make, and may require repeated blood tests. These basic tests will help the veterinarian evaluate your pet’s overall health and may identify problems that could have similar signs. These blood tests are not specific for Cushing’s syndrome but will often help indicate whether further testing is needed. Further tests that may be recommended include a dexamethasone suppression test or an ACTH stimulation test, both of which evaluate the function of the adrenal glands.
There are two mechanisms by which this disease can occur.
Pituitary gland tumor. The most common cause of Cushing’s Disease (85% of all cases) is a tumor of the pituitary gland. The majority of these tumors are benign, but a small percentage may be malignant. The tumor causes the pituitary to overproduce a hormone, which stimulates the adrenal glands. Excessive cortisone secretion results. The tumor may be either microscopic or quite large. Depending on the size of the tumor, the presence of signs other than Cushing’s will be variable. Generally, if the activity of the adrenal gland can be controlled, many dogs with this form of Cushing’s Disease can live normal lives for many years as long as they take their medication and stay under close medical supervision. Growth of the pituitary tumor would give the patient a less favorable prognosis.
Adrenal gland tumor. Cushing’s Disease may be the result of a benign or malignant tumor of the adrenal gland. If benign, surgical removal may cure the disease. If malignant, surgery may help for a while, but the prognosis is less favorable than for a benign tumor.
What are the treatment options?
Adrenal Tumor. Cure of an adrenal tumor requires major surgery. Although this surgery can be risky to the dog, if it is successful and the tumor is not malignant, there is a good chance that the dog will regain normal health. If surgery is not an option, some of these can be managed with the medication for some time.
Pituitary Tumor: Two medications are available for the treatment of Cushing’s Disease. Both are effective, but each has different advantages and disadvantages. Both medications work by reducing cortisone levels produced by the adrenal glands. Both are safe and effective, but require diligent monitoring and client education and attentiveness. The goal of medical management is to reduce cortisone levels from the abnormally high levels produced during disease back down to a normal physiological level. As some cortisone is needed for daily life, a fine balance is necessary to reduce the levels to a healthy level but not too low. If the dog’s level falls to low, then weakness, vomiting, and even life-threatening complications can occur.
What is the prognosis for Cushing’s Disease?
The long term survival depends on the cause of the disease. Adrenal tumors usually mean a worse prognosis, and pituitary tumors can be successfully managed for many years. Close monitoring and care by the owner improves survival times.