The disease is caused by a pituitary tumor that triggers excessive levels of the stress hormone cortisol. Left untreated, a pituitary tumor could grow large enough to press on the brain causing neurological symptoms such as difficulty walking or seeing, or other conditions including diabetes or seizures.
Every year, roughly 100,000 dogs are diagnosed with Cushing’s disease in the United States. Most dogs are six years of age or older when diagnosed, but it can occur in younger dogs. The disease is rare in cats.
When functioning normally, the pituitary, a pea-sized gland at the base of the brain, produces adrenocorticotropic hormone, or ACTH, which stimulates the adrenal glands near the kidneys to produce cortisol. A smaller percentage of dogs with Cushing’s disease have a tumor of one of the adrenal glands which may or may not be cancerous. This form of Cushing’s is called adrenal dependent Cushing’s (ADC) and results from a direct increase in cortisol production.
There is no test to diagnose Cushing’s disease. The history, physical exam, and results of initial blood and urine tests often provide a strong suspicion for the presence of the disease. One of the first tests for Cushing’s disease is the urine cortisol/creatinine ratio test. Dog’s with normal cortisol/creatinine ratios likely do not have Cushing’s.
Dog’s with high cortisol/creatinine ratios will require a low-dose dexamethasone suppression test. Dexamethasone is used to suppress cortisol levels. If a dog’s cortisol levels are not suppressed it is likely the dog has Cushing’s disease. Patients with Cushing’s disease may also have an enlarged liver or enlarged adrenal glands. Your veterinarian may take x-rays or use ultrasounds to check the liver or adrenal glands, as well as an ACTH stimulation test to determine if the adrenal glands are functioning properly.
Lifelong oral medication is often prescribed for pituitary dependent Cushing’s disease to help manage the symptoms. The most common drug used to treat Cushing’s disease is Trilostane. For pets with adrenal dependent Cushing’s, Trilostane is not as effective in reducing symptoms. Discuss with your veterinarian which treatment is best for your pet. Radiation may be used to shrink the size of a pituitary tumor. This treatment is most effective on small tumors to help reduce the symptoms of pituitary dependent Cushing’s disease.
Treatment of adrenal dependent Cushing’s disease is by surgical removal of the affected adrenal gland. Adrenal gland tumors, if cancerous, can spread to other parts of the body in which case all the cancer cannot be removed by surgery. Medical treatment may be given to reduce hormone levels before surgery. Surgical removal of the tumor generally eliminates the need for lifelong medication.
The prognosis for pituitary dependent Cushing’s disease with treatment is usually good. Some signs will disappear quickly and others gradually. Appetite and water consumption usually return to normal in a few weeks whereas full return of the fur may take several months. With pituitary surgery, roughly 85 to 95 percent of dogs who have the tumor removed no longer have a hormonal imbalance or neurological symptoms. For dogs with adrenal tumors, surgery can be potentially curative. Treatment of one type of Cushing’s disease, either pituitary or adrenal, does not prevent the development of the other form of the disease.
This information is not meant to be a substitute for veterinary care. Always follow the instructions provided by your veterinarian. Washington State University assumes no liability for injury to you or your pet incurred by following these descriptions or procedures.