WHAT IS CUSHING'S DISEASE
Cushing’s Syndrome (AKA Cushing's Disease) is the resulting set of symptoms observed when the body is exposed to excess cortisone (or related hormones) over a long period of time. There are many cortisone-type hormones, both natural and synthetic. Cortisol (called "hydrocortisone" when used as a medication) is a hormone produced by the adrenal glands which are located atop the kidneys. Cortisol is stored in the adrenal glands and is released in times of stress where it helps our bodies prepare for a “fight or flight” situation. It adjusts the body's 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 just during short stressful periods, the state of break down goes on and on. Obviously, this has repercussions with muscle strength, hair growth, the immune system and more.
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.
CORTISOL REGULATION IN A HEALTHY BODY
In the normal body, the pituitary gland, located at the base of the brain, can detect when cortisol levels in the blood are getting low. In response, the pituitary secretes a stimulating substance, called "ACTH," 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, though the pituitary gland regulates many other hormones as well. This raising and lowering of cortisol blood level is regulated throughout the day via ACTH secretion and occurs rapidly.
This may seem like too much science information for a regular pet owner but, if your pet has Cushing's disease, you are going to hear the name "ACTH" a lot. You can expect numerous "ACTH Stimulation tests" during treatment and possibly even ACTH blood level during testing so it is helpful to have some idea what this term means and why it is being measured.
PITUITARY-DEPENDENT CUSHING'S SYNDROME
This form of Cushing's disease accounts for 85% of dogs with Cushing's syndrome. Basically, the pituitary gland grows a small tumor. The tumor is generally too small to cause any trouble due to its size and is generally a benign tumor. This tumor, however, over-produces ACTH thus leading to over-stimulation and enlargment of both adrenal glands and an over-production of cortisol. 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 (see section on "macrotumors.")
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. There is very little or no production of ACTH from the pituitary gland and as a result the opposite adrenal gland is usually atrophied/small.
Page last updated: 2/16/2022