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Cushing's Disease

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Cushing's Disease, or Hyperadrenocorticism, is the production of an excess of adrenal hormone, or, more particularly, corticosteroids. This disease is present, but rare in humans, and more often found in dogs, than in cats.
One of the most common, and often the only visible symptom of Cushing's Disease is a drastic increase in thirst, which causes excessive water intake. Please remember though, this is ONE symptom, and it is not even a symptom of Cushing's exclusively! This is also a symptom of Addison's disease, which is the direct opposite of Cushing's Disease.
Other outward symptoms may be an increase in appetite, a "pot belly" due to the enlarging of the liver and the abdomen muscles weakening, hair loss (typically in a symmetrical pattern, but no itchiness), and lethargy.

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.
Synacthen® Stimulation:
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 Suppression :
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.
Dexamethasone Suppression will affect a dog three ways. A healthy dog injected with Dexamethasone will show a rapid fall in cortisol levels. A Cushing's affected dog will respond in two ways. Either there will no cortisol level change at all (adrenal tumor), or there is a small decrease (pituitary dependant).

There are three types of Cushing's Disease, and three subsequent treatments available.
Iatrogenic Cushing's:
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.
Adrenal Cortical Tumor:
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.
Treatment for an Adrenal Cortical Tumor is surgical removal of the tumor and it's gland housing, along with supplemental injections of cortical until the remaining gland is producing cortisol at a normal level.
Pituitary-Dependent Hyperadrenocorticism :
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.
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