Cushing's Disease - November 2019
This month I am writing about Hyperadrenocorticism, also known as Cushing’s disease. This is a relatively common problem in dogs and rare in cats. It is a syndrome that caused by the overproduction of natural steroids in the body, which are regulated by the pituitary gland in the brain and produced by the adrenal glands, which are located next to the kidneys in the abdomen. This syndrome can range from simple to multi-faceted in presentation and can be associated with other diseases, making it a complex disease process.
The signs of this syndrome are varied and can be numerous. In most cases, dogs are seen to be drinking excessively and urinating more often. Also, thinning hair or fur loss can present as well. The skin may become thin and easily tented when pulled. Dogs may look pot-bellied in appearance, and muscle may atrophy. Panting is seen commonly, due to effects of the excess steroids. Pets may gain weight and have lethargy as well. All of these signs may present in an animal or only one or two may be seen. The most common is the increased drinking and urination, a very common symptom seen with numerous other diseases as well.
You may be asking: Why does an overproduction of the body’s steroids cause these signs? Steroids have a powerful effect on many organs and regulatory processes within the body. If there is an excess of these chemicals in the body then the organs and processes will become abnormal over time, and disease will result. Cushing’s disease may take a long time to develop within the body, and animals can live relatively well for a while without treatment, but the disease processes lead to other associated problems. Disorders that are associated with hyperadrenocorticism are bladder infections, bladder stones, hypertension, diabetes, retinal degeneration, pancreatitis, and the list goes on.
There are three forms of this syndrome that can arise in a dog. The simplest form is associated with an animal being medicated long-term with steroids for an ailment. The steroids add on to the natural steroids and cause signs of disease to present. This is called the iatrogenic form, and it can be easily remedied by stopping the steroid medication. Another type is called the pituitary-dependent hyperadrenocorticism (PDH); it is the most common case of Cushing’s seen. It is caused when a tumor (almost always benign) forms on the pituitary gland, and causes an over secretion of the regulatory hormone that controls the production of steroids produced by the adrenal glands. The excess of the hormone causes the adrenals to grow larger, and they produce more cortisol that is distributed throughout the body. An alternative form is called adrenal tumor hyperadrenocorticism (ATH), caused by a tumor growing on one or both adrenal glands. The tumors, due to their excessive growth, cause the adrenal glands to produce extra steroids, leading to the disease process. Unfortunately, these adrenal masses can be malignant, and have spread to other parts of the body by the time of diagnosis.
How is the disease diagnosed? It involves the combination of history, lab work, and possibly abdominal ultrasound to find out the answer that question. If an owner reports that their dog is drinking and peeing a lot, a physical exam will be performed to see if any other signs of the disease are seen. If Cushing’s is suspected, a general lab work panel is performed first. The general panel helps in a few ways, one is to rule out other diseases that may cause excessive drinking and urination, and there are general changes in lab work that can be seen that can further help lead to the diagnosis. Hyperadrenocorticism does require an advanced blood test to be diagnosed as well, there are two commonly run tests that can be used to identify the disease. Abdominal ultrasound may be used to confirm an adrenal tumor or excess growth of the adrenal gland itself.
The only good thing about Cushing’s disease is that is can be treated successfully. There are several medications for this syndrome but the standard treatment is called Trilostane, with the brand name of Vetoryl. The dog is usually treated with this medication once daily, and for the life of the patient. The protocol can vary if the certain complications arise with medication, or if other diseases are present as well. Blood tests are used to monitor the drug’s effects on the body, at certain intervals. Alternative treatments are available but are less commonly used. When a malignant adrenal tumor is found, it may be surgically removed, barring no signs of metastasis. The average prognosis with most medical therapies is about a 2-year survival time, which can be dependent on which form of Cushing’s is involved, and if other disorders are present at the time of diagnosis. Survival time can be much longer if the patient is younger, has the PDH form, and no other disease develops along with the hyperadrenocorticism.
The main drawback to treatment is overall cost. The medication can be expensive, and is for the life of the dog. The monitoring tests can be costly as well, and may have to be performed many times over the course of the therapy.
Cushing’s disease is a complex syndrome that can present in many ways. The signs can be easily recognized, but may take a while to develop. Once the disease develops, it is a life-long management when treated. Early diagnosis is always better! So, if you have suspected your dog has this disease, or have any questions about it, please give us a call or ask at your next visit. Have an excellent fall and a joyous Thanksgiving!
Dr. Jaime Kozelka
St. Francis Hospital for Animals