Also known as "Hyperadrenocorticism".
Cushing's disease is probably more accurately referred to as hyperadrenocorticism -- the production of too much adrenal hormone, in particular corticosteroids. It can be naturally occurring or due to over administration of corticosteroids such as prednisone (iatrogenic Cushing's). The latter is easy to cure - just cut out the corticosteroid administration slowly to allow the body to return to its normal function. The former is more difficult.
Hyperadrenocorticism occurs for two reasons --- a tumor of the adrenal gland that produces adrenal hormones or stimulation of the normal adrenal glands from the hormones that control it. The primary reason for this occurring is a pituitary gland tumor that produces excessive ACTH, which stimulates the adrenal gland to produce corticosteroids. Adrenal gland tumors account for 15% of the cases of spontaneous hyperadrenocorticism; pituitary tumors accounting for the remaining 85%.
Cushing's disease causes the following symptoms:
Most owners reach a point where the water consumption and urination become bothersome to them.
A blood test can help in the diagnosis of Cushing's Disease. To confirm the diagnosis, a test known as a low dose dexamethasone test is performed. A baseline blood sample is drawn in the morning, an injection of dexamethasone is then given and a follow-up blood test is done 8 hours later. In a normal dog, the dexamethasone should suppress cortisol levels in the blood stream. In Cushing's disease this effect does not occur. Once the disease is diagnosed, it is possible to differentiate between the adrenal tumors and pituitary gland tumors using a second test - a high dose dexamethasone suppression test. Most dogs with pituitary tumors will have cortisol suppression on this test. There are other tests used, including ACTH response tests and urine cortisol/creatinine ratios to help diagnose this disease. X-rays and ultrasonography can help determine if an adrenal gland tumor is present.
If it can be determined that there is an adrenal gland tumor, it can be removed. Many veterinarians prefer to have a specialist attempt this since the surgical risks can be high. Pituitary gland tumors are not usually removed in veterinary medicine. This situation is treated using Lysodren (DDD, which is a relative of DDT) or ketaconazole. Some research with Deprenyl for treatment of this is currently being done. Lysodren selectively kills the outer layer of the adrenal gland that produces corticosteroids. By administering it in proper amounts it is possible to kill just enough of the gland to keep the production of corticosteroids at normal levels. Obviously, close regulation of this using blood testing is necessary since overdoing it can cause severe problems with Addison's disease - hypoadrenocorticism. Adverse reactions to Lysodren can sometimes occur, but it is the standard treatment at this time. Over medication with Lysodren can cause vomiting, diarrhea, lethargy and weakness. If any of these signs occur then your veterinarian should be contacted immediately.
Treatment of Cushing's disease caused by pituitary tumors is symptomatic therapy, as the pituitary tumor cannot be cured. The average lifespan of dogs diagnosed with Cushing's disease, with or without treatment is estimated at approximately two years. At present, treatment should be viewed as a means of providing a better quality of life rather than as a method of extending longevity.
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