Cushing's Disease is diagnosed by both a full physical exam, and a series of blood panels done by a veterinarian. Once Cushing's is confirmed, or rather highly suspected, there are two tests that should be completed before undertaking expensive drug therapy.
The dog is injected with Synacthen®, a synthetic hormone which should cause the adrenal glands to react and produce more cortisol. The rise in cortisol is detected with a blood screen after a couple of hours.
Dexamethasone is a synthetic steroid that affects the adrenal gland, telling it to stop producing cortisol.
A healthy dog will inhibit the release of Adrenocorticotropic hormone (ACTH) from the pituitary gland as the cortisol levels in his blood rise. In turn, this prevents the further release of cortisol. With Cushing's Disease, this process no longer works well, and cortisol levels continue to increase.
There are three types of Cushing's Disease, and three subsequent treatments available.
Iatrogenic Cushing's Disease is caused by the frequent use of cortisol. The excess amount of cortisol tells the adrenal glands that they can halt production of cortisol in the body, which causes them to decrease in size.
The treatment for Iatrogenic Cushing's Disease is a slow withdrawal of cortisol. A dramatic decrease in cortisol before the adrenal glands have recovered can result in severe consequences, like vomiting, diarrhea, or vascular collapse, even death.
A tumor of the cortisol producing cells will cause an increase of cortisol production. Although there are two adrenal glands, the tumor is typically in one gland only, resulting in a large gland, and a small gland, both of abnormal sizes. This leads to one gland over-producing cortisol, and the other gland (without the tumor) under-producing cortisol.
Caused by microtumors inside the pituitary gland, Pituitary-Dependent Hyperadrenocorticism that cause the gland to produce excessive hormones, which in turn cause the adrenal glands to produce too much cortisol. In cases of Pituitary-Dependent Hyperadrenocorticism both adrenal glands are abnormally enlarged.
There is no cure-all for Pituitary-Dependent Hyperadrenocorticism. Treatment of the symptoms is all that is currently available. There are FDA drugs that are manufactured for this, Anipryl® being one of them.