HYPERADRENOCORTICISM
"CUSHING'S DISEASE"
Cushing's Disease was named after Harvey Cushing, the physician who first described the disease in people at the turn of the century. The technical name of Cushing's Disease, hyperadrenocorticism, is easier to understand if it is broken down into its component parts. The adrenal glands are located on each side of the body just in front of each kidney. The outer layer of these small glands, called the cortex, produces hormones called corticosteroids - the body's own cortisone-like chemicals. The corticosteroid that we measure with blood testing is called cortisol.
The inner layer of the adrenal glands, called the medulla, produces a set of hormones called mineralocorticoids, which regulate sodium and potassium levels in the body.
In hyperadrenocorticism, the adrenal glands produce excessive amounts of adrenal hormones. The excess hormones in the body lead to the symptoms of the disease - excessive urination and water drinking, thin skin and haircoat, liver swelling, muscle weakness often leading to a pot-bellied appearance, panting, obesity and a tendency toward urinary tract or skin infections.
These symptoms may not all occur at once. Many times in the early stages Cushing's Disease resembles many other disease problems. The diagnosis may be suggested by changes in blood chemistry tests, which also help diagnose other diseases which can cause similar symptoms.
There are two causes of the disease. The first is a tumor of an adrenal gland. This tumor consists of excess glandular tissue which simply produces too much of its normal hormone. Adrenal tumors can be benign or malignant (cancerous).
More commonly (80-85% of the time) the tumor causing the problem is in the pituitary gland at the base of the brain. The pituitary responds to changes in the body such as stress, day length exposure, disease and other factors, and releases a hormone called adrenocorticotropic hormone, or ACTH, into the bloodstream. ACTH stimulates the adrenal glands to produce cortisol. In a normal dog or person, the pituitary sends an appropriate amount of ACTH into the system to produce the proper amount of cortisol to maintain health. A pituitary tumor produces too much ACTH, which stimulates the adrenal gland to produce too much cortisol.
Pituitary tumors can also be benign or malignant. Benign ones tend to grow very slowly, causing no problems for years other than the effects on the adrenal glands. Malignant tumors may cause trouble much sooner. If the tumor becomes large enough it will eventually damage other tissues in the brain and neurological symptoms will start to occur - seizures, blindness or behavior changes.
There are several specific test protocols that are used to diagnose Cushing's Disease and to determine which type of disease, pituitary dependant or adrenal, a dog has. They all involve testing cortisol levels before and after the administration of other hormones, to see if the adrenal and pituitary glands respond appropriately. An ultrasound scan of the abdomen can also be done to look for adrenal tumors.
Adrenal tumors can be surgically removed. If only a single gland is involved, the other one will take over cortisol production after surgery and the symptoms of Cushing's Disease will go away. Sometimes the opposite adrenal gland will eventually develop a tumor as well. This is especially common in ferrets.
Pituitary tumors are located such that they are very difficult to remove. Therefore, the treatment for the 85% of patients who have this form of the disease is usually medical. There are two types of medication that can be used. The first of these destroys adrenal tissue so that there is less adrenal gland left to produce cortisol. Even though the pituitary is still producing too much ACTH, there isn't enough adrenal tissue left to respond.
The hard part is getting the right dosage of the medication, called Lysodren, to destroy just enough adrenal tissue but not too much. The medication is given twice daily until
1) Water consumption drops below 1 oz./lb. of body weight.
2) Appetite decreases.
3) The dog becomes lethargic, develops vomiting or has diarrhea.
The time until this occurs can be anywhere from 2 to 35 days, though the average is 5-16 days. One or two doses too many can destroy so much adrenal tissue that mineralocortecoid production is affected. When this happens the sodium and potassium balance is disrupted. Vomiting, heart rhythm disturbances, collapse and death can result. Emergency IV saline treatment is necessary if sodium levels become too low.
Often oral supplements of the mineralocortecoids are needed after treatment with Lysodren - sometimes temporarily, sometimes for life. Often supplements of cortico-steroid hormones are needed as well, at least for the first few days after the initial Lysodren therapy.
If all goes well, the dog receives Lysodren twice daily until adrenal production drops. As soon as production starts to resume, a weekly dosage of Lysodren is initiated to maintain control. Periodic testing for adrenal function assures good control of the disease. Unless the tumor causing the disease can be removed, treatment is lifelong.
The second, newer medication, called Anipryl, is much safer, but it is not effective in every case. Anipryl, or selegiline hydrochloride, takes effect slowly and only works for the pituitary form of Cushing’s Disease but has fewer problems and side effects. This medication would need to be administered every day for life.
The cost of treating Cushing’s Disease varies greatly depending on the dog. Diagnosis alone can cost well over $400 in some cases. Both medications are expensive. There is no way we can predict whether your pet will need Lysodren for 3 days or for the rest of a pet’s life. If emergency treatment is needed for electrolyte disturbances, that may be several hundred dollars. Even if all goes well, if your pet is on Lysodren regular routine recheck blood tests will be needed. Usually these are done 3-4 times a year.
Before you decide to have your dog treated for hyperadrenocorticism we want you to be well aware that this is a complicated and difficult disease. You will be making a large financial and emotional investment to treat it, especially for the first few months. The good news is that IF your dog makes it through the first 1-2 months of treatment without serious complications, the long term prognosis is fairly good. The average lifespan after diagnosis is about two and one half years, but many patients do well on their medication for more than 5 years. Hyperadrenocorticism IS considered a life-shortening disease, and some dogs will do much better than others. Since the disease usually occurs in middle to aged or older animals, there may also be complications due to other organ dysfunction.
