Cushing’s disease, also known as pituitary dependent hypercortisolism, is caused by a non-cancerous 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 and cause neurological symptoms such as difficulty walking or seeing, or other conditions, including diabetes or seizures.
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 that may or may not be cancerous in one of the adrenal glands. This form of Cushing’s is called adrenal dependent Cushing’s (ADC) and results from a direct increase in cortisol production.
How common is Cushing’s disease?
Every year, roughly 100,000 dogs are diagnosed with Cushing’s disease in the United States. Most dogs are 6 years of age or older when diagnosed, but it can occur in younger dogs. The disease is rare in cats.
What are the common symptoms of Cushing’s disease?
- Hair loss
- Pot-bellied appearance
- Increased appetite
- Increased drinking and urination
- Thin skin
- Lack of energy
- Bladder infection
- Difficultly walking
- Vision issues
How is Cushing’s disease diagnosed?
There is no single test to diagnose Cushing’s disease. A patient’s 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. Dogs with normal cortisol/creatinine ratios likely do not have Cushing’s.
Dogs 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.
How is Cushing’s disease treated?
Lifelong oral medication is often prescribed for pituitary dependent Cushing’s disease to help manage the symptoms. The most common drugs used to treat Cushing’s disease are Trilostane and o,p’-DDD (also called Mitotane or Lysodren). For pets with adrenal dependent Cushing’s, these drugs are not as effective in reducing symptoms.
Radiation may also 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.
Adrenal dependent Cushing’s disease is treated by surgical removal of the affected adrenal gland. Adrenal gland tumors, if cancerous, can spread to other parts of the body if the cancer is not removed by surgery. Surgical removal of the tumor generally eliminates the need for lifelong medication.
What is the prognosis for an animal diagnosed with Cushing’s disease?
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, but full return of fur lost 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.
What should I do if my dog is showing signs of Cushing’s disease?
If you are concerned your animal has Cushing’s disease, consult with your veterinarian or schedule an appointment with one of our veterinarians by calling 509-335-0711.
WSU is one of only a handful of veterinary hospitals in the country performing transsphenoidal hypophysectomy, a pituitary surgery used to treat Cushing’s disease in dogs.
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.