Cushing’s disease, or hyperadrenocorticism, occurs when the adrenal glands produce excessive amounts of cortisol/endogenous steroid. The most common cause is a functional, but benign, tumor of the pituitary gland in the brain. This gland secretes a hormone (ACTH) that stimulates the adrenals to produce and secrete cortisol. When a functional tumor is present, the pituitary secretes ACTH in excess and over-stimulates the adrenals. These pituitary tumors typically do not metastasize/spread. A primary problem with one or both adrenal glands, such as a tumor, can also be a cause of Cushing’s, but pituitary dependent disease is more common. Generally, pituitary tumors are small and do not cause local issues in the brain, but occasionally they can be large and cause compression of surrounding brain tissue, resulting in neurologic signs.
This disease is relatively common in dogs and uncommon in cats. Middle-aged to older dogs are usually affected. Both sexes are equally affected. Many breeds (large and small) can develop Cushing’s disease, but Poodles, Dachshunds, most terriers, German Shepherds, Beagles and Labrador Retrievers may be at an increased risk. The most common clinical signs include:
- increased drinking and urination;
- increased appetite; panting;
- apparent abdominal distension;
- hair loss, especially over the back.
Several complications that may arise from uncontrolled Cushing’s disease exist. The most common are high blood pressure, diabetes mellitus, lung/respiratory disease (pulmonary thromboembolism/PTE), chronic skin or urinary tract infections, pancreatitis and protein loss from the kidneys. Animals with one or more of these complications are more likely to require treatment. Thus, patients that have been diagnosed with or are suspected of having Cushing’s should have routine medical check-ups.
Routine blood work can raise clinical suspicion of Cushing’s disease, such as elevated cholesterol and alkaline phosphatase/ALKP; however, a definitive diagnosis requires more specific blood testing. The two blood tests of choice are the ACTH stimulation test and the low-dose dexamethasone suppression (LDDS) test. A LDDS test is often useful to differentiate pituitary from adrenal based Cushing’s. A LDDS test also has a higher sensitivity of detecting the disease than the ACTH stimulation test. Adrenal based disease may also be detectable on abdominal ultrasound, if the adrenal tumor is large enough for visualization. In some instances, a CT scan or MRI will be ordered to assess the pituitary gland for a larger tumor.
Treatment of Cushing’s disease relies on reducing the body’s production of steroid hormones to a range where signs are no longer apparent. The typical treatment for pituitary dependent Cushing’s disease is medication (although there is a surgical option with limited availability in the United States). The typical treatment for adrenal dependent Cushing’s is surgical removal of the abnormal adrenal gland. If surgery is not pursued, medical therapy can also help reduce clinical signs.
There are two options for medication – Lysodren and Trilostane (Vetoryl). Lysodren is a drug that destroys the cells of the adrenal gland. Trilostane is an enzyme inhibitor that helps stop synthesis of steroid hormones. With both medications, there is a risk, although small, that we could lead to the opposite condition of Cushing’s – Addison’s disease, in which the body cannot produce enough steroids.
It is common to be asked if treatment is 100% necessary. Untreated dogs may be weak, have ongoing problems with increased thirst and appetite, and develop complications as listed above. If the owner does not see any abnormalities in their particular dog and believes that their pet is doing well with good quality of life, treatment is not always recommended. We treat dogs based on their physical exam findings, clinical signs, and quality of life. We also treat dogs that we feel are at high risk for developing complications from untreated disease.