Cushing’s Syndrome is the resulting set of symptoms observed when the body is exposed to excess cortisone (or related hormones) over a long period of time. Cortisone, or more correctly
“Cortisol,” is a hormone produced by the adrenal glands which are located atop the kidneys. Cortisol is stored in the adrenal gland and released in times of stress where it helps our bodies prepare for a
“fight or flight” situation. It adjusts the metabolism to expect physical exertion by mobilizing fat and sugar stores and retaining sodium and water. It puts us in a state of “break down” so that our
stored resources can be used quickly. If the body is exposed to this hormone most of the time instead of during short stressful periods, the state of break down becomes debilitating.
There are several mechanisms which can lead to Cushing’s syndrome and, as they are treated differently, it is important to determine which one is at work in a given animal.
In the normal body, the pituitary gland, located at the base of the brain, can detect when cortisol levels in the blood are declining. In response, the pituitary secretes a stimulating substance
which causes the adrenal gland to release more cortisol. When the pituitary gland detects that cortisol levels are again appropriate, it stops its stimulatory message.
You can think of the pituitary gland as a sort of a thermostat for cortisol. This raising and lowering of cortisol blood level is regulated throughout the day and occurs rapidly.
PITUITARY-DEPENDENT CUSHING'S SYNDROME
This accounts for 85% of dogs with Cushing's syndrome.
Basically, the pituitary gland grows a tumor, generally microscopic and generally benign. This tumor, however, over-produces its stimulatory message thus leading to enlargement of both adrenal glands and an over-production of cortisone. Occasionally (10% of pituitary-dependent Cushing's dogs), these benign pituitary tumors are large enough to compress the brain. In these cases, neurological signs may be observed; these cases are unusual but very hard to treat.
ADRENAL-DEPENDENT CUSHING'S SYNDROME
In 15% of dogs with Cushing's syndrome, an adrenal tumor is directly over-producing cortisone. The tumor is often large enough to see with radiographs or ultrasound and may be malignant.
OVERUSE OF CORTISONE-TYPE HORMONES
Cortisone derivatives may well be the most over-used drugs in veterinary medicine. Their anti-inflammatory actions soothes such common maladies as allergic skin disease (especially flea allergic
dermatitis) and degenerative arthritis. Relief is usually rapid and and many owners find themselves requesting "cortisone" shots or pills over and over again.
In time, Cushing's syndrome results, not from any inherent disease in the pet's system but from the effects of the hormones given.
The pituitary gland perceives the high steroid levels yielded by the medication and does not send a stimulation to the adrenal glands. In time, the adrenal glands atrophy and are not able to
release cortisone for a period of three months after the medication is discontinued. To allow the adrenal to gradually recover, cortisone pills are usually prescribed in a decreasing dose and an owner should
never discontinue the pills suddenly.
