What is Cushing's Disease?

Cushing's disease is a disorder in which the adrenal glands overproduce certain hormones, the most common among these is cortisol. The adrenal glands are located near the kidneys and produce several vital substances that regulate a variety of body functions. The medical term for Cushing's disease is hyperadrenocorticism. This disease is most commonly diagnosed in dogs 6 years of age or older but can occur in younger dogs as well. This disease is rare in cats.

What Are the Main Causes of Cushing's Disease?

Pituitary Dependent: This is the most common cause of Cushing's disease being seen in 85-90% of cases. Pituitary-dependent Cushing's disease is caused by a tumor on the pituitary gland, which is located at the base of the brain. These tumors can be benign or malignant and microscopic or large. Either way, they cause the pituitary gland to overproduce a hormone, ACTH, which in turn stimulates the adrenal glands to produce cortisol. Small tumors (<1cm in diameter) are called microadenomas and rarely cause neurologic symptoms. Large tumors (>1 cm in diameter) are called macroadenomas. When tumors become large like this they can put pressure on the surrounding brain tissue causing neurologic symptoms. This type of tumor occurs in approximately 15% of patients and carries a less favorable prognosis.

Adrenal Dependent: This type of Cushing's disease is caused by a tumor on the adrenal gland and is seen in approximately 10-15% of cases. These tumors can also be benign or malignant and cause a direct increase in cortisol production by the adrenal gland.

What Are Symptoms of Cushing's Disease?

The most common symptoms that owners notice at home are an increase in appetite, water consumption, and urination. They may also notice that their pet seems more lethargic, is panting more, and has a poor hair coat or hair loss. Other clinical signs commonly associated with this disease are thin skin, chronic skin infections, dark-colored spots on the skin, skin mineralization, poor skin healing, persistent bladder infections, and a pot-bellied appearance.

How Is Cushing's Disease Diagnosed?

There is not a single test to diagnose Cushing's disease. It is usually suspected based on history, physical exam, blood work, and urinalysis. Once there is a suspicion, there are tests that are more specific for Cushing's disease, the two most common of these are the ACTH stimulation test and the low-dose dexamethasone suppression test. An abdominal ultrasound can also be useful in the diagnosis of this disease because it allows us to evaluate the size of the adrenal glands, however, it is important to remember that tumors on the adrenal glands are only seen in 10-15% of these cases so even if there is not a tumor present, it does not entirely rule-out Cushing's disease, only the adrenal dependent form.

What Are Treatment Options?

There are three treatment options for Cushing's disease; the most common of these is oral medication which can be used for both pituitary and adrenal dependent disease. This medication does not cure the disease but will help to manage the symptoms and is a lifelong medication. The most commonly used drug to manage Cushing's disease is Trilostane which is a once-daily medication. This medication requires follow-up blood work including an ACTH stimulation test to make sure that we are not causing the cortisol to become too low and a chemistry panel with electrolytes to make sure we are not causing an unbalance in the electrolytes. The second treatment option is surgical removal but this is only an option for those with a tumor on the adrenal gland. If the tumor is benign, this can be curative but if it is cancerous there is a chance that it will have already spread to other parts of the body. The third treatment option is radiation therapy and is used for those with a pituitary tumor. This will help to shrink the tumor and is most effective on small tumors.

What Is the Prognosis?

Although medical treatment is not curative, symptoms can be managed for many years if the tumor is small and benign. If the tumor is large and affects the brain, or is malignant the prognosis is guarded to poor.

If your pet is experiencing any of the symptoms related to Cushing's disease or you would like to speak with one of our doctors about any concerns you have, feel free to call or schedule an appointment with us today.