Cushing's disease affects a dog's adrenal glands, which are part of the endocrine system. It deteriorates the skin, hair, and kidneys, making a dog feel tired and unwell. Female dogs and a few specific breeds are more likely to develop Cushing's disease. If left untreated, this disease can be life-threatening, so dog owners need to recognize the signs and understand treatment options.
What Is Cushing's Disease?
Cushing's disease, also known as hyperadrenocorticism, is an endocrine condition that affects the adrenal glands (small glands located near the kidneys). It causes the adrenals to overproduce cortisol, the body's main stress-regulating hormone. Cortisol plays a role in regulating blood sugar, reducing inflammation, and controlling blood pressure. If too much cortisol is produced, multiple systems in a dog's body are unable to work properly. Addison's disease is the opposite of Cushing's disease, in which too little cortisol is produced.
Symptoms of Cushing's Disease in Dogs
Excessive cortisol levels can cause visible changes in a dog's appearance and behavior that are characteristic of Cushing's disease.
Dogs with Cushing's disease often have distended abdomens (a pot-bellied appearance) due to fluid retention, and their coats are thin and coarse. Because the kidneys aren't regulating fluid balance well, these dogs also experience an increase in thirst and urination. Frequently emptied water bowls and urinary accidents in the house are indications of these problems that owners may recognize.
Some dogs with Cushing's also have increased appetites but low energy, and they may pant excessively. Recurrent skin infections are another noticeable sign of Cushing's disease.
Causes of Cushing's Disease
There are three causes of Cushing's disease in dogs:
- Pituitary Gland Tumor: The pituitary gland, located in the brain, stimulates the adrenal glands to produce cortisol. A tumor on the pituitary may cause the adrenals to make too much of this natural steroid. This is called pituitary-dependent Cushing's disease and is the most common type of the disease.
- Adrenal Gland Tumor: If a tumor develops on one or both adrenal glands, it may produce too much cortisol, causing adrenal-dependent Cushing's disease.
- Prolonged Steroid Use: If steroids are taken regularly for a long time to manage allergies or inflammation, they can impact the adrenal glands, causing iatrogenic Cushing's disease.
While any dog can be affected by Cushing's disease, female dogs develop adrenal tumors more often than males, and certain breeds are more susceptible to adrenal malfunction, including poodles, dachshunds, and Boston terriers.
Diagnosing Cushing's Disease in Dogs
Your veterinarian will perform a full physical examination and obtain a medical history of your dog. If Cushing's disease is suspected, then blood work is the first step to a diagnosis. Specific blood tests called ACTH stimulation and low-dose dexamethasone suppression (LDDS) tests are performed to check for Cushing's disease. A complete blood count (CBC) and chemistry profile will indicate organ function as well.
A high-dose dexamethasone suppression (HDDS) test, a urine cortisol-to-creatinine ratio test, or a 17-hydroxyprogesterone response to ACTH administration test may also help determine if your dog has adrenal-dependent or pituitary-dependent Cushing's disease.
Finally, an abdominal ultrasound may be recommended to check for tumors on your dog's adrenal glands.
If your dog's Cushing's disease is diagnosed as pituitary-dependent, then lifelong oral medications will need to be given. Trilostane and mitotane are two drugs that are commonly used to treat pituitary-dependent Cushing's disease in dogs.
Adrenal-dependent Cushing's disease may require surgery to remove a tumor. If the tumor is not removable, some dogs may be managed with medications.
Iatrogenic Cushing's disease may require discontinuation of steroids, which can cause the original condition to flare. If continued steroid use is deemed necessary, then concurrent medication for Cushing's disease may also be required, but this is not a long-term solution and may only be suitable for very old or ill dogs who need quality of life management for the time they have left.
Prognosis for Dogs with Cushing's Disease
Dogs with adrenal or pituitary tumors can recover completely if the tumors are successfully removed during surgery. These dogs rarely need medication to manage their condition. Dogs that are not candidates for surgery can take medications that help manage the symptoms of Cushing's disease and improve their quality of life.
In the case of long-term steroid use, owners and veterinarians must consider the risk-to-benefit ratio of the steroids versus Cushing's symptoms. Ceasing the steroids may cause life-threatening rebound symptoms to occur, but it may be possible for Cushing's medication to be administered with the lowest effective steroid dose to preserve a dog's quality of life for a limited time.
Untreated, Cushing's will progress and eventually result in death.
How to Prevent Cushing's Disease
Most Cushing's disease cases are caused by tumors on the pituitary or adrenal glands, and there is no way to prevent them from occurring. Iatrogenic Cushing's disease, caused by steroid use, can be prevented by using medications other than steroids to manage your dog's inflammatory condition.